Archive for the ‘Plastering’ Category

Metal In Straw Bale Wall Assemblies

Welded Wire MeshI know that the topic of metal in straw bale wall assemblies is a contentious one, and that is precisely why I want to bring it up and talk about it with you all. I have been saying for years that the use of welded wire mesh and plaster lath is essential to a quality bale house, and that sentiment has not changed. I want to quickly share my thoughts about using metal mesh and lath, and then hear from those of you who either agree or disagree with the practice. My preference is that you only write in if you actually have experience with using (or not using) metal mesh and lath and that the conversation be held to those with something to share from the experience, not from assumptions or beliefs. Of course, that’s my want and I have learned over the years that I don’t always get what I want. :)


The Impact of Design Details

off grid

Wind Prairie Architecture. Photo credit Lois Shelden.

There is always a balance that needs to be struck between the desire to have an architecturally pleasing house and the impact of design details on the cost and difficulty of actually building that house. For most home owners, the desire to have something other than a rectangle as their forever home comes into play early in the design process followed swiftly by the reality check of finances. There is no question that the more elaborate your design, the more expensive it will be to build; however, there are ways to find that sought after balance that will please both your senses and your finances.


The Benefits of Using a Commercial Plaster Sprayer

Most of us don’t have a commercial plaster spraying machine lying around, so we can’t just run out to the garage and turn it on. That said, the benefits of using a commercial plaster sprayer are well worth investigating the availability of one in your area either to rent or to hire out (the entire job). If you have access to a commercial sprayer, it’s an incredible machine that will speed your process up dramatically. You have seen me post in the past about sprayers that we as consumers can use with great effectivity. I am still a big fan of these sprayers and highly recommend them; however, the commercial sprayer shown here, and others like it, is a big step up in power and production.

These machines have the mortar mixer built right in so you can literally mix the material and dump it straight into the pumper. The pump then drives the material down the hose and provides a constant stream of plaster. Because we have to mix the scratch and brown coats of natural hydraulic lime plaster for a minimum of 20 minutes, it’s best to have a secondary mixer on site as well so that you can work between the two to keep the flow going.

I have included some video footage of the sprayer in action on the Flathead Lake, Montana straw bale workshop from this past year. Rather than tell you about the benefits, I figured I would just show you. If you have ever plastered, you will see the advantage right away. If you have never plastered, let me tell you that the main advantage is the speed and ease of application. It still takes several people to do the work, but less than a hand applied crew.

The first video is of the scratch coat application on the interior of an exposed timber frame. The ability to quickly “cut in” around the timbers and ceiling line is immediately apparent.

The second video shows plastering on the tall gable ends. If nothing else, not having to transport the mud to the top of the scaffolding makes this machine well worth having on site. Keep in mind that even with the other sprayer I use, one would still have to transport the mud to the point of application.

The final video is of the finish coat application. Note that there are two trowel finishers in addition to the two men running the sprayer. It is also necessary to have someone making the mud. That means you are looking at at least 5 people for the crew. That’s better than the 15 people I used to have on my plaster crew that did everything by hand application.


Plastering Overhead

Dining Room HutchThere is no question that plastered window wells look beautiful; however, the skill it takes to get them to that point may seem out of reach to a novice plasterer. The good news is, it’s not. With a little practice and a good serving of patience, anyone can learn to plaster their window wells to look magnificent.

Perhaps the hardest part of the entire process is getting the plaster to stay put. Gravity has a large say in this process and whenever a novice plasterer tries to apply mud to the top of a window well, often called “the lid” in the industry, gravity usually wins. Below are some tips to beat gravity and create your own beautiful window well.


Step By Step Guide To Creating Niches

Finished Niche

One of the most artistic expressions of a straw bale wall are the niches that are carved into it. There are about as many options of what a niche can be as there are ideas, so describing how to create each one would take just shy of forever. For that reason, I have decided to lay out a step-by-step process for the most common niche I see in straw bale homes: the arch top.

  • Golden RatioDecide on the location for your niche. As much as it’s a good idea to lay out potential locations on your construction drawings, I always recommend that people walk the house once the bales are all in place as new locations that you had not considered before may reveal themselves.
  • Pay attention to scale. Once you know where the niche will go, be sure to properly size it for the space. I suggest you use “the Golden Ratio” to determine your height to width. No matter which way you orient the niche, the ratio would be 1 to 1.618. This ratio appears all over in nature; the most commonly known example is the chambers of the nautilus shell.
  • Back CameraCalculate the space in and around the niche. Keep in mind that the plaster will reduce the width of the niche so be sure to add in enough “extra width” for that. Look at perpendicular walls or window and door openings and estimate where the finish walls will land so that you can properly center (or not) your niche.
  • Use a cardboard template to test your niche out on the wall. Hang it with landscape pins or nails in the desired location and then take a step back to see if it is what you had hoped for.
  • Once you are happy with the size and location, mark the outside of the template with spray paint to transfer the shape onto the wall.
  • Niche ChainsawUse a chainsaw to cut out the niche to the desired depth. I prefer to stay around 6″ – 8″ deep in a two-string bale wall and 12″ – 14″ for a three string bale wall. I mark the bar of my chainsaw with spray paint so that I know when I have plunged the blade in far enough. Be aware that you WILL cut the strings of the bales at this depth. As soon as you feel one pop, stop the chainsaw and remove the string from the area. If you don’t, it will wrap itself around the chainsaw sprocket and you will spend a lot of time unravelling it.
  • Install the wire mesh on the wall (both sides) as if the niche were not there. Just go right over the top of it for now. If you try to cut the niche out before the mesh is attached top and bottom, it will weaken the mesh and you won’t be able to get it as tight as you need.
  • Use wire cutters to cut the mesh out of the niche. It’s best to cut the mesh a little bigger than the opening so that your plaster lath installation is not hindered by the mesh.
  • Niche 6Place the section of mesh that you cut away in the back of the niche and sew it to the mesh on the opposite side of the wall with baling twine. This tightens the mesh on the opposite side of the wall and it provides extra plaster reinforcement in the niche.
  • Cut a strip of plaster lath so that it fits tightly in the bottom of the niche from side to side. Cut it at least 6″ wider than the niche is deep so that you can fold the excess lath down over the face of the wall. This provides extra strength for the plaster as it turns from inside the niche to the face of the bale wall.
  • Fold the lath over and secure to the mesh with tie wire, cable ties, or landscape pins (into the bales).
  • Niche 7Cut another strip of plaster lath (also at least 6″ wider than the niche is deep) long enough to measure from the bottom of the niche on one side to the bottom of the niche on the other side in one continuous piece. This piece will shape the arch and, once folded over on to the face of the wall, reinforce the plaster for the rest of the niche to wall transition.
  • Cut the lath in small sections as necessary to conform to the shape you have created. Use stuffing behind the lath to fine tune the shape.
  • Fold the lath over and secure to the mesh with tie wire, cable ties, or landscape pins (into the bales).
  • Niche 8You may need to use some landscape pins on the interior surface of the niche to hold the lath in place. If you cut the lath big enough, you will be able to jamb it tightly into the wall and avoid the pins. Do whatever it takes to make the lath tight and sturdy. You don’t want it bouncing around when you plaster.
  • Eat a lot of yogurt. Okay, that’s not entirely necessary, but the yogurt lids make the perfect plastering tool for the soft edges and tight corners of the niche. Cut the rigid part of the top off and use the pliable plastic as a curved trowel. You will proceed with the plastering the same way you would on the rest of the wall and at the same time. Just be careful when working in the niche as it is a small and delicate space that can be difficult to plaster well.
  • Niche 9Decorate as you will…Now you get to turn the show piece (the niche) into a vessel for other items you wish to showcase.

Even if you don’t choose an arch top niche for your straw bale home, you can transfer the steps of this tutorial to just about any style you choose. You may have to tweak a step here or there, but the overall process is the same. Happy Baling, and create something beautiful!


Delicious, Aged Lime Putty Still Available

Lime Putty BucketsNot long ago, I received an email from Curtis in Kansas who had literally 10,000 gallons of lime putty he was selling. The putty was all slaked with water and mixed in a 300 gallon stainless steel mixer and then placed in 55 gallon drums or 5 gallon buckets to age. He claimed that the lime has great plasticity and consistency, is high in calcium, and is sourced from the Mississippi Lime Company in St. Genevieve, Missouri. I wrote a blog post about this (in fact, much of what you just read was from that original blog post) and helped him sell almost half of the lime. Pretty cool when people with a product meet people with a need for that product!

Lime Plastering PartyOne such person was Bev, the host of the Taos, New Mexico straw bale workshop this past July. I got to use the lime putty first hand and I must say that it was truly delicious. The consistency, workability, and ease of use was perfect. I can certainly recommend this lime for anyone who is looking to use a quality lime putty. I’m sure that you all know that I am a huge fan of quality Natural Hydraulic Lime (NHL) plaster for straw bale structures and that’s still the case. I think it is the best plaster to use. That said, I know that some of you cannot afford NHL and others choose to use lime putty for other reasons. For those of you, I suggest you check out Curtis’ material.

The putty is all shrink wrapped and on pallets for easy transportation. They have a forklift and can assist with loading at their facility; however, all shipping arrangements are up to the buyers and all orders must be picked up from the seller’s facility in the Wichita, Kansas area. The putty has been stored in a temperature controlled warehouse and has never been subjected to freezing temperatures. They are currently selling the putty at $2 per gallon which is a very good price for such yummy lime putty.

Keep in mind that if you plan to use lime putty in the US, you will have to make it yourself by slaking quick lime (see the video, but don’t try this without learning a lot more about the process first!!!). This is a slow, laborious and often dangerous process so you are much better off purchasing the lime pre-slaked. Unfortunately, there are not many companies that offer pre-slaked lime in the US. That makes this deal even better. What’s more, the longer the slake, the better the putty, and three years is a very good time line for quality lime putty. Obviously shipping will come into play in regards to price, but I think it is still worth the effort and a good value. If you know others in your area in need of lime, perhaps you can share the trucking costs. You can reach Curtis to find out more or to place an order at this email address.

Properly Wet Your Plaster

IMG_6520I work almost exclusively with lime plaster. My favorite is Natural Hydraulic Lime from St. Astier ( I teach people all the time about proper plastering techniques and one detail that often comes as a surprise is the amount of water that is needed to complete a good plastering job. The obvious water is that which is used in the mix; however, that is only a minor slice of the pie when it comes to the necessary water, especially if you live in a hot/dry climate.

Follow these steps to make sure you have the best plaster job available. Be sure to protect your walls from wind, rain, and direct sun by hanging tarps. There’s more to that, but the scope of this blog post is about water, so let’s address that directly.


Too Many Plaster Failures

delaminating plasterOver the years I have spoken many times about the importance of a quality plastering job. That importance has not waned, and I am unfortunately hearing more and more stories about failed plaster jobs around the world. A large percentage of the consulting work I do is helping clients deal with these plastering issues. There are two common themes, or dare I say causes for the failures. If you avoid these two approaches to plastering your home, your plaster should provide you with a very long life.

Failure #1: Mixing earthen and lime plasters on a wall surface. This is perhaps the most common mistake that I see over and over again. People choosing to use earthen plaster for the scratch and brown coats and a final, “durability coat” of lime. The problem here is that what you have is stronger plaster over weaker plaster when in reality, you want it the other way around: weaker plaster over stronger plaster.

If you consider all plaster work over the last say…thousand years, one thing holds true no matter what material you use. The second coat has more sand in it than the first coat and the third has more than the second. That makes the coats “weaker” as they move away from the wall. This is important because plaster moves, as do homes. If the weaker plaster beneath a strong lime finish coat can move more than the finish coat, you will ultimately get delamination between the two coats which will lead to eventual plaster failure. By laying weaker plaster over a stronger finish coat, it will always be able to move at least as much as the coat beneath it. This keeps the plasters well bonded and eliminates the high risks seen in the opposite application. (more…)

Three Year Old Slaked Lime Putty For Sale

Plastering with LimeI recently received an email from a gentleman named Curtis in Kansas who has literally 10,000 gallons of lime putty he is looking to sell. He used the lime to make custom plasters in his company for the last few years; however, the slow economy has forced him to close his doors. Once whipped up with a paddle, the lime putty reaches a beautiful, creamy consistency as shown in the photo. The putty was all slaked with water and mixed in a 300 gallon stainless steel mixer and then placed in 55 gallon drums or 5 gallon buckets to age. The lime  has great plasticity and consistency, is high in calcium, and is sourced from the Mississippi Lime Company in St. Genevieve, Missouri. It actually looks a bit like tofu before it gets whipped up…delicious!

Lime PuttyThe putty is all shrink wrapped and on pallets for easy transportation. They have a forklift and can assist with loading at their facility; however, all shipping arrangements are up to the buyers and all orders must be picked up from the seller’s facility in the Wichita, Kansas area. The putty has been stored in a temperature controlled warehouse and has never been subjected to freezing temperatures. They are currently selling the putty at $2 per gallon which is a very good price for such yummy lime putty.

Keep in mind that if you plan to use lime putty in the US, you will have to make it yourself by slaking hydrated lime. This is a slow, laborious and often dangerous process so you are much better off purchasing the lime pre-slaked. Unfortunately, there are not many companies that offer pre-slaked lime in the US. THat makes this deal even better. What’s more, the longer the slake, the better the putty, and three years is a very good time line for quality lime putty. Obviously shipping will come into play in regards to price, but I think it is still worth the effort and a good value. If you know others in your area in need of lime, perhaps you can share the trucking costs. You can reach Curtis to find out more or to place an order at this email address.

Tips to Making Your Plaster Beautiful and Durable

Plastering is perhaps the hardest part of the entire process when building a straw bale house. Think about it, your framing, although difficult, is hidden within the walls nine times out of ten. As long as it is structurally sound, you will be fine. Furthermore, it is inspected (in many cases) so you end up with a “free” set of helpful eyes to make sure you are doing the work properly. The same is true for the other major systems of the house: plumbing, electrical, mechanical, and so on. As long as the systems are built properly and they meet or exceed codes, you are all set. What those systems actually look like is mostly irrelevant.

The same cannot be said about plaster. That’s a system that not only has to be structurally sound and function in a way that protects the bales, and ultimately your entire house, but it also has to look good. After all, when have you ever heard someone say “Wow, you really did a great job with the rough plumbing in this house. It sure is beautiful.”? Probably never. How about someone commenting on plaster? Now that’s one that you have likely heard or even uttered yourself. “Man, that plaster looks amazing!”


Announcing a Natural Hydraulic Lime Plaster Workshop

TransMineral USA is hosting a plastering workshop this fall, October 11 and 12, 2012. This is a great opportunity to learn the material from some of the best. Keep in mind that TransMineral USA is the sole US importer of Natural Hydraulic Lime, so they know their stuff. I don’t know exactly who will be leading the workshop, but I imagine he or she will be top notch and I expect Michel, the owner of TransMineral USA will be there as well. I highly recommend you attend this workshop if you can make it.

Here’s what they have to say in their workshop announcement:


Natural Hydraulic Lime For Sale 50% Off

This message is from the host of the Junction City, CA workshop. She has just finished plastering her scratch and brown coats and has some extra bags for sale at a great price (50% Off!). See below…
I have 18 bags of 3.5 NHL. They have been stored in the house the entire time and are dry.

I paid $50.00 a bag for them and they are 55 pounds each.

I will sell all 18 for 450.00 ($25/bag) if some one wants to come get them in Junction City, CA.

Please contact me at My name is Jan.


Failures of Lime Plaster Over a Clay Base

I wanted to share a (relatively long) conversation with you all about lime plaster over an earthen plaster (clay) base that is happening now on a straw bale list serve. This conversation sums up what I have been seeing and hearing about quite a lot in recent years: failures of lime over clay plasters. I hope everyone considering this option reads this conversatrion and changes their mind. Here’s the letter from Chris, the man whose plaster has failed. My response is below. (more…)

Spraying Plaster or Hand Application: Which is Better?

In regards to plastering by hand or by spray application, there are several schools of thought. Some people believe that plastering by hand is better because the force of the application is higher when arm power is used to press the plaster into the bales, giving it a high level of “key” or adhesion. Others believe that the force applied by the spraying is actually better because it shoots the plaster deep into the webbing of the straw. I have discussed this question at length with several master plasterers over the years and have learned a lot about both processes. The fact of the matter is that both systems are absolutely acceptable as long as certain details are maintained.

The most important aspect of plastering, whether it be by hand or sprayer, is the mixing ratio. Just like many aspects of construction, there are many different recipes used by different builders; however, the most common mixing ratios are as follows. Scratch coat (first coat) 2:1 (sand:lime). The brown coat (second coat) would be 2.5:1 (sand:lime) and the third coat would be either 3:1 (sand:lime) or a ratio matching the scratch or brown coat ONLY if the lime used is a weaker lime. For example, a scratch coat of NHL 5 could be applied 2:1 followed by a brown coat of NHL 5 applied 2.5:1 and finished with a coat of NHL 3.5 at 2:1. This is because the 3.5 is a weaker lime than the 5. Plaster should ALWAYS get weaker as it “comes off the wall.” In other words, the coats further from the straw should be weaker than those beneath them. This is an industry standard.

I’ll discuss hand application first. Muscle is perhaps the most important part of hand application. If the plaster is not properly worked into the substrate (straw in this case) it will not anchor properly or achieve the right key/tooth. If the plaster is not properly anchored, then even if it hardens perfectly, it is hardening AWAY from the wall surface and thus is prone to full delimitation (where it peels away from the wall). Delamination can also be caused by the walls not being properly prepped. For example, if loose straw remains on the wall and no meshing system is in place, that loose straw can peel away from the wall with the plaster attached to it: thus delaminating. I should mention that this is true for both hand and spray applications.

The next important detail is often referred to as “put it on the wall and leave it alone.” What that means is that if the plaster is overworked with the trowel, it will start to separate. The creamier aspects of the mix, the lime, will be pulled from the aggregate, the sand, and left at the surface. When the plaster dries/cures, this material will dust off of the wall and the remaining sand will be weak because the binder (the lime) has dusted off, leaving the sand to bind itself, something it cannot do. The best hand application is one that is done with minimal “extra” working of the mud once it is placed on the wall.

Spraying plaster, as mentioned above, is just as viable an option as hand application. The biggest mistake that people make when spraying plaster is they water it down under the assumption that it needs to be “lighter” in order to be sprayed. This is 100% incorrect and when done, has a very negative affect on the plaster. The more water there is in a plaster, the more room for voids in the curing process. Keep in mind that as plaster dries and cures, the water molecules (H2O) are driven off leaving voids behind. The lime crystals need to grow into those voids in order to create a strong plaster. If the voids are bigger than the crystals can fill during the curing period, the walls will end up weak. Plaster should therefore be sprayed at the same consistency as it would be hand applied. Exactly how much water needs to be added varies with each load as the sand for plaster is often supplied in bulk with varying amounts of water within it. Therefore it is crucial that the plasterers keep a watchful eye on the mix as it is created to ensure that just enough water is used in each batch.

As with hand applied plaster, the concept of overworking sprayed plaster should be managed as well. Spray it, press it into position with a trowel and then leave it alone. One MUST follow up sprayed plaster with a trowel immediately after it is sprayed to smooth out big irregularities of thickness on the surface and make sure the key with the straw is achieved.

A step that is often missed in lime plaster application is “pressing back.” This is when a trowel is held vertically against the wall and drawn up and/or down over the plaster with adequate force to push the plaster back into the wall. This is only done after the scratch coat and should be completed when the plaster reaches a “leathery” feel. Too soon and the plaster will simply squish around. Too late and the plaster will be too hard to compress. The purpose of this step is two fold. First, it compresses the plaster onto itself, tightening up any voids in the plaster as mentioned earlier. Secondly, it creates an even stronger key/tooth with the straw. Once the pressing back is complete, the scratching should take place immediately leaving marks roughly 1/4″ wide by 1/8″ – 1/4″ deep. Any deeper and the plaster will slump on itself. Any shallower and the brown coat will not have enough tooth to properly attach. The scratches should be made with a scarifier or other tool designed for this specific purpose. Make shift scratching devices often pull mud from the wall or create inadequate scratch patterns. The scratching should be run horizontally as much as possible.

After the scratch coat is complete, it is vital that the walls be kept damp, or misted, for at least the first 3 days. The curing time between coats is a minimum of 10 days and if misting can be done for the entire 10 days, even better. This slows the curing process and allows the plaster to grow into the voids as discussed earlier. Failure to wait the 10 days can cause a weak plaster. Before the application of the next coat it is vital to pre-wet the walls. The night before the second coat’s application, the walls should be completely dampened. The morning of application, they should be misted once again. Failure to fully saturate the walls the night prior will give you a “snap, crackle, pop” effect on the plaster. You will literally be able to hear the prior coat of plaster sucking the moisture out of the new coat. This rapid reduction in moisture ruins the fresh coat of plaster which will likely result in delimitation or chalking of the coat. This dampening MUST happen between both the first/second coat and the second/third coat for proper plaster application. The 10 day cure time and misting must happen after the scratch and brown coats, but not after the final coat as misting of the final coat can cause color to run. Furthermore, the final coat is applied very thin and as such will dry/cure fast enough that misting would have little effect on it.

The brown coat does not receive the pressing back like the scratch coat. Instead, it is burnished with a “devil float” or some other float in a circular form to 1) compress the plaster onto itself and 2) press the plaster into the tooth created by the scratching tool. The final result will be a rough, swirly coat. This is vital to the final coat’s ability to hang onto the scratch/brown below it. If the brown coat is smoothed out, the finish coat will fail and delaminate.

There are so many details to a quality plaster job and so many places to make mistakes. The real question may not be whether to spray or to apply by hand, but rather, what steps need to be taken, no matter which application method is chosen, such that the plaster job will be successful. I strongly recommend learning to plaster on a small project before you decide to tackle your own home. Consider taking a workshop with me to get your hands dirty, literally, or at very least, check out my instructional plastering DVD. Plastering is hard work and takes skill. It’s also what people notice the most about a home when it’s complete. Take the time to learn the process and you will have success.

American Clay Q&A

Over the years I have heard several people ask about the American Clay line of plasters so I felt it was time to contact them to ask them some of these questions.  Here is the Q&A session:

1. How do you handle the fact that clay is more breathable (allows more vapor to pass through it) than typical exterior coatings such as lime and, in some cases, cement based stucco? How do you keep the bales from becoming saturated by moisture that can get into the walls through the clay, but cannot get back out through the exterior coating?

Even though the clay is more permeable, it is also hygroscopic, and holds the vapor in its pore structure.  It also has an affinity for water that is greater than that of the straw, thus helping the straw to dry.  The clay allows the water to dissipate through a larger area and then move out of the wall system to that of lower vapor as the humidity levels drop to the interior of a building space.

For the moisture that moves through the wall and collects on the exterior, the importance of continued permeability remains high.  A lime plaster, even though it is lower than a clay, is still highly permeable to vapor, and also has high dissipation of water, allowing it to move to the outside as the humidity drops to the outside, thus allowing the system to balance and not remain in the wall system.

The importance of having a climate that dries out enough to allow for the dissipation of the moisture is high. Without it, the balance will not be reached and therefore, climate must be taken into consideration when choosing your plaster both exterior and interior.

2. Isn’t the quality of the American Clay finish heavily dependent on the quality of the substrate? In this case, the adhesion and overall quality of the American Clay will be based on the quality of the earthen scratch and brown coats. Does the makeup of those coats effect the finish?

It is true that the American Clay finish is dependent on the quality of the substrate, but that is true of any finish plaster or stucco.  Typically the “makeup” of the coats will determine whether it will work or not as a sound base.  If the substrate is both sound and solid then the American Clay will attach well.  If the base is loose and not very sound, there would be issues.

3. How do you handle wet areas with American Clay such as bathrooms and kitchen walls near sinks? Do you have to treat the finished surface of the clay to waterproof it? Howe does that effect the overall performance of the product?

With the clay, the areas to seal and protect are areas that are going to be regularly exposed to items that will saturate, stain and degrade the material.  Behind a kitchen sink or a bathroom sink (or even around a toilet with young boys and even men that tend to miss often).  For the rest of the areas in the kitchen or bathroom, using the clay to help mitigate and disperse the moisture is an advantage.  Keeping in mind that good ventilation to allow the moisture to dissipate, after a hot shower for example, is still important.

The type of sealer determines how the permeability would be degraded.  A silicate would work great for water but does not block oil stains very well, yet it remains very permeable.  Similarly, a limewash works for water as well, but not oils.  Acrylics are another option but move away from the natural finishes.  They do protect against both water and oils; however, they can reduce moisture transmission out of the system.  Oil based sealers, like polymerized linseed oils are great for protection against all of the above but do not breath.  Wax is a good option, but limits additional coats over the area later.

4. I’ve heard that up to 4 coats of finish are required to get the product to look as beautiful as it does in your advertising. Is that true?

No, with a sound, even base coat, one or two coats is all that is necessary.  If it is taking more coats, the base was either very coarse or not very level. That said, the base may be two coats thick, so the overall plastering process from start to finish can be considered 4 coats.

5. Is there a wait time in between coats for the product application? In other words, does the subsurface need to dry first before it is re-wet for the plaster application?

The base does need to be dry prior to the applications of American Clay.  The need to pre wet your base is dependent on the site conditions (i.e. the difference between Seattle during the wet season, or Tucson in July.  I would not pre wet my base in Seattle, but I would in Tucson).

6. Are there adhesion problems if the base coats are not earthen? Can AC be applied over a lime scratch and brown coat? What issues might one encounter?

The base does not need to be earthen.  Our plasters go over a lime brown without issues, as long as it is a true brown coat with adequate key.  If it is a smooth lime finish, it would require additional prep prior to lay application of either a primer to provide tooth or a bonder to provide adhesion.  Cement brown coats will work in the same manner as lime.  Gypsum brown coats can be an issue, and require a sealer prior to the clay application.  For the mentioned exceptions above, the clay would begin to pull away from the brown coat upon application of the second coat if the detailing noted above was missed.

7. How do you wash the walls over time?

The required washing of the walls that we are used to with paint is not generally required with any natural finish.  A light brushing or vacuuming of the wall to remove cobwebs and dust attached to texture on the wall is typical.  For stains or marks, a very well wrung sponge used to wipe the surface will most always do the trick.  For deeper stains a 25% white vinegar solution sprayed on the surface will help.  Allow this to dry, and then wipe with the sponge mentioned prior.  If it is a stain that cannot be removed with washing, the plaster can be removed and patched with reserved material from the original project.

8. How do you change colors over time if you decide to change a room color? Can the walls be painted or color washed?

The are many ways to change the colors over time.  Painting with any number of materials is possible.  A color wash worked into the clay works well for subtle shifts, and if a complete change is desired, another coat of AC plaster can be applied.

(Note:  Straw Bale Innovations is in no way affiliated with American Clay and this post is purely for informational purposes only)

Review of the DragOn Pro Mortar Sprayer

They say that necessity is the mother of invention, and in the case of Branislav Prvanovic, a Serbian innovator and businessman involved in the building trades, a gigantic straw bale building project turned out to be the mother load of necessities. Charged with the task of rendering 150,000 sqft of straw bale walls on his industrial complex, he knew he had to get innovative and quickly in order to get the job done. Here we enter the story of how a progressive couple, Branislav and Gorica (his wife), living in Serbia came to design and create what may become the new standard for mortar sprayers around the world.

Serbia is a very small country in the Balkan region of Europe that is on it’s way to joining the European Union. This is an exciting time for this tiny nation and Brainslav and Gorica are on the forefront of environmental progress in the building sector of their country. They are both passionate about building their industrial facilities as efficiently and cost effectively as possible. As such, in between 2007–2009, they brought together the best Serbian team of engineers and prepared for investing in the largest straw bale industrial facility in all of Europe (50,000sqft). The team chose straw bale technology because they love how sustainable, cost effective, healthy, and energy efficient it is. In the process they intend to prove that it doesn’t matter if you are dealing with residential, commercial, or industrial projects, straw bale technology can be a solution for each of those situations.

When presented with the mega task of rendering the 150,000sqft of wall surface, they had to devise a solution that would produce excellent quality, be cost effective, and be able to plaster much faster than anything else on the market. Branislav, being the innovator that he is, took to the drawing boards and began to conceptualize a mortar sprayer that would suit their needs. After many renditions, trials and errors, and modifications, they were able to fine tune the mortar sprayer to be a sleek, lightweight and highly-productive tool. At the time, they were calling this sprayer the “Revolutionar”, however, one day Gorica was looking at the sprayer and was struck by how it looked like a dragonfly. The sprayer has been called the DragOn PRO ever since.

The DragOn PRO mortar sprayer is a heavy duty pneumatic tool which delivers all kinds of plasters and rendering mortars to the walls surface quickly. One of the best details is the design ergonomics. It’s balanced well, so it’s possible to plaster for several hours without the strain that is typically associated with plastering work. Okay, it’s still hard work, don’t get me wrong, but it does take less physical strength to deliver the plaster to the wall than using a hawk and trowel. It’s also cool that the DragOn PRO can apply all density mixtures with fillers up to 6mm including mortar of all types, plasters, clay renders, papercrete, and micro concretes. It works in conjunction with a compressor test which generates the force to push the plaster through the sprayer and out of the nozzle. Make sure you have a big enough compressor so that it can keep up with the required air supply!

One of the qualities we love about the DragOn PRO mortar sprayer is that it has been designed to be super easy to learn to use (it takes just minutes and can be used by pretty much anyone). We always appreciate innovations that are geared not only towards professionals but also towards the do-it-yourselfer. It weighs less than a shovel when empty and is actually quite comfortable to use (especially when compared to the job of applying plaster by hand with a trowel all day!). It is pretty much indestructible so one can spray plaster with confidence. That said, if you don’t wash it after each use it will get heavier and heavier each time. I’ve seen that happen with other sprayers, and it makes the job more tiring and less efficient, so take the time to keep the tool clean.

It’s true that other mortar sprayers exist on the market today, however, Branislav and Gorica are confident that the DragOn PRO outperforms them all. They tout that their sprayer is significantly faster and more efficient than other sprayers because of the unique concept of their nozzle design and how it manages to spray the plaster. They have patented this solution in order to protect their innovation, so they obviously believe in it. The reception from buyers around Europe and the Southern Hemisphere has been tremendous. The cost is reasonable and pays itself off after several working days, making it an obvious fit for not only professionals but also for owner-builders with their projects. Branislav and Gorica are also very pleased with how well the sprayer applies plaster in vertical, horizontal, slanted, curved and very high walls. I think the strong pressure of the application really helps in those situations too.

The DragOn PRO can be purchased at either wholesale or retail. The retail cost is 279€ and there is always an additional 10% discount applied for anyone that is building with straw bales. They also offer a retail program if you have an interest in becoming a retailer. By the way, Straw Bale Innovations makes no financial gain from writing about the DragOn PRO sprayer. In fact, we are not retailers or otherwise associated with DragOn, we simply thought this was a great product created by an amazing couple trying to make a positive impact on how green construction is developing in the world and we wanted to share their story.

Plastering is no easy task. Anyone who has done it can attest to the intensity of the labor and the time that it takes to do a job well. The DragOn PRO is a solution for easing this process. So, we want to thank Branislav and Gorica for believing in the benefits of straw bale construction and for creating a product that will make the plastering of bale walls much more manageable for everyone! To visit their website, please go to and to email Branislav with any questions, please write to  To watch a video of the sprayer in action click here.

The Ultimate Plaster Making Machine

Dun, dun dun…… Can you feel the excitement? I just got back from working on a project in Portugal and the plaster machine was one of the coolest I’ve seen. This monster mixed up to 1 1/2 bags of lime plaster at a time (35 kg bags). The capacity was not what made the machine exciting as some of the mortar mixers I use here in the States will mix twice that capacity at once. What was cool was everything that the machine was able to accomplish. Here’s a run down.

The machine should be placed directly behind the pile of sand. The reason is clear: why carry sand when you can use an automatic, winched sled?! That’s right, this baby comes with a remote controlled sand sled that places the sand directly into the holding barrel. That brings us to the next cool part of the machine, the holding barrel. This section of the machine allows you to pre place all of your materials, even water if you choose although I think it’s better not to put the water in at this time, into a holding tank of sorts. That way when you are ready to mix your next batch you simply empty the mixing barrel of the machine and add the next batch, already pre measured and ready to go.

What’s also cool is that this holding barrel is hydraulically lifted, so there’s no strain to your back. You simply hit a switch and the hold thing lifts up and dumps the material into the mixing barrel. Add your water and you’re off. While the plaster is mixing, you can get the next batch pre measured and into the holding barrel. This is especially useful when using a material like Natural Hydraulic Lime because that material has to actively mix for 20 minutes. While it’s mixing, you prepare the next load. It’s a great use of time. Otherwise, a 20 minute mix takes 30 minutes start to finish. This way, it’s 20 minutes on the nose.

Another aspect of working with plaster is moving it from the machine to where you need it. Most machines require a wheel barrow, a string back, a well inflated tire, and some relatively good balance. This is usually not a problem (save the well inflated wheel barrow tire), but it is work. This machine would simply pump the mix from the mixing drum directly to where you need it. In fact, it can pump the material up to 10 stories up! Most of us won’t need that, but it does help to send the mud up a steep driveway or hill where a wheel barrow might end up costing you hundreds in chiropractic repairs.

So now we have mixed our plaster, placed it within inches of where it will be used, and the only thing we have had to lift is a bag and half of lime at 35kg each. Not bad. So how about applying it, any savings there? Of course. The machine uses the same compressed air that drives the mix up the hill to run a plaster spraying gun. This speeds application and does a great job of both leveling the wall on the first shot and penetrating the straw.

The down side to this machine? It costs about $8,000. If you can find one to rent or borrow, go for it. Otherwise, just think about how cool it is and marvel at what we have been able to build as humans! :)

Elephant Dung for Earthen Plaster Available

Anyone looking for elephant dung for their natural plaster? If so, I have a good contact for you. Gavin Wuttken ( from the Point Defiance Zoo and Aquarium in Tacoma, Washington is looking for a good home for some elephant dung. Could you be that good home? If so, please contact him directly to set things up. Good luck.

“Alternative” Interior Wall Finishes

I was recently asked about using different finishes for straw bale walls on the interior. I’m very often asked about using different exterior finishes, but not as often does the topic of interior wall finish come up. Of course, the type, texture and color of plaster is always in question, but more rare is a discussion about using metal panels as a wall finish, or perhaps drywall or even tile.

The answer is that yes, these things can be done; however, “is the amount of extra labor worth it to you?” may be the appropriate question to ask yourself. Keep in mind that straw bale is an organic building material. Where this is most obvious is around curves by windows and doors. At every workshop I teach, people ask me about making a template to measure each window well with to make sure all of the window curves look the same throughout the house. Possible? Sure. Plausible? Not really. The fact of the matter is that each curve will be slightly different. That’s part of the beauty of building with straw bales. So now consider how you might finish an 18″ deep window well that has a natural, undulating curve to it, slightly different on each side of the window, while using metal panels. How do you attach them to the house? How do you adjust for the irregular shapes within the window well?

You can see where the difficulty comes in. The same is true for any material you use that is rigid and “unforgiving” to uneven sub straights. The key is to provide backing that fully supports the material in mind to ITS specifications. This means that you may have to insert framing to support the material every 24″ on center, or provide for nailing on a specific pattern. You’ll need to weigh the pros and cons of each finish you choose and see just what is worth your efforts.

I have seen corrugated metal roofing used in shower stalls and in straw bale barns to great success; however, would I do an entire room with that material? Probably not. I think for specific spaces that require something like this, it is worth it. If you want your walls to look like drywall on the inside, then I suggest you build with drywall, and forgo the straw bale infill, or at least create a hybrid installation system that will eliminate all of the “extra” framing to be notched in to the bales, post stacking.

Keeping Track of Sand When Making Plaster

Mixing plaster is as much of an art as it is a science. It’s important to keep a consistent mix from one batch to the next and this isn’t always easy to accomplish. One of the most common mistakes people make when creating plaster mixes is to lose track of how much sand has been put into the mixer. Have you ever mixed plaster with a bunch of folks helping you? If so, you know exactly what I mean.

Picture this: you’re using a 5 gallon bucket to place sand into the mixer. You need 4 buckets of sand for every bag of lime you add to the mixer. Your helpful friends are filling up the bucket as fast as you empty it and you guys are totally cruising through the mixing process. Suddenly you ask your friend “is that 3 or 4 buckets?” In return you get what a friend of mine calls a “goat face,” a look of complete disconnect. Now you retrace your steps to try and figure out how much sand is in the mix. You look at the plaster tumbling on the paddles in hopes of recognizing the texture of the mix. IN truth, neither of you have any clue how much sand is in the mixer. There’s a better way.

Instead of using one bucket, use 4. Three buckets should be the same color and the last bucket a different color. This way know if you’ve made it to the end of a load. For example, when I mix plaster, I can usually fit 3 bags of lime in the mixer at a time which means I need 12 buckets of sand. Counting those out one by one would be hard to track, so I use the 4 buckets. I put in three white buckets of sand and then an orange one (you could always use another white bucket and just pray paint it or wrap it with tape). As soon as I see that orange bucket go by, I know I’m at the end of a run. Now my helper can fill all 4 buckets again while I add the bag of lime and we’re ready for the next grouping. It’s easy!