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At the end of the fifth day of the May Seven Day Intensive Straw Bale Construction Workshop, a few folks mentioned how much they were looking forward to applying the brown coat because it would be so much easier than the scratch coat applied to the interior of the building. I smiled and so “oh yeah?…okay.” By the end of yesterday, their opinion had changed.
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The fifth day of the May workshop started and ended in mud. The good news is that it was mud we were making and using to plaster our beautiful straw bale structure. We are working with lime plaster and as a result, we had a lot of dust masks around.
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Plastering is a difficult process and site conditions have a big impact on the results. Most people are aware that plastering in direct sun is not a great idea, especially with natural plasters. What many don’t realize is that plastering in cold conditions and/or wind can be equally as damaging to the plaster.
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Vapor barriers often create more damage than they prevent in straw bale houses. Why then are they required in straw bale building codes? The answer is not complicated; however, the impact of vapor barriers on homes of all types is.
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When building a straw bale house, the question of what type of mesh, if any, should be used is a big one. I show the use of 14 gauge welded wire mesh in my DVDs, and that is a great option; however, it also has its downsides like any other application. For one, it is expensive. Secondly, it is a bit harsh on the environment to use so much steel. So, what other options are there?
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One of the great aspects of plaster is that the color of the finish material changes as the sun moves across the sky and as light plays with the surface of the structure. Picking a color for your building can, as a result, be a difficult process. I am sure you have heard of or have yourself had a hard time picking the right color paint for your bedroom from a small chip. Now imagine trying to decide on that color knowing that it will change throughout the day!
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I just received an email from a man I recently started doing some straw bale consulting for about the cost of plaster. He has received three estimates for the plaster work and he was unhappily surprised at the cost. The average cost turned out to be roughly $5 per square foot of bale wall surface. This is about what I expect to pay for plaster work on bale walls. The cost of plaster may be different in your area depending on local labor costs and what type of plaster you use; however, (more…)

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I have been using the Devine Green line of paints for some time and I love them. The colors are great, the quality of the finish is fantastic, and the “Green Building Value” of the product excellent. Let me start this post by saying that the problems I have had are not a result of the paint, but something else entirely. I have run into a new problem with a house we completed some time ago. The paint on the walls is just barely attached to the surface in several places. It may be the result of fine dust in the house while the painting took place. There were tile setters and finish carpenters in the building a few rooms away. That could be the simple answer; however, in the process of my research on the subject I learned that if the plaster has not completely cured, the alkaline levels in the plaster can inhibit the paint from bonding to the walls.
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I just got an email from a man named Greg who has a very interesting idea about plastering a bale house. His concept is a mix between plaster and concrete form work. I think there is merit in the idea and yet at the same time, wonder if the time savings would pan out. I do think that the straight finish of the wall would be impressive. I would like to hear from you all about this idea and what advantages or disadvantages you think it might have. Also, if any of you have a small project that could work as a test building, it would be cool to see how it fares in the “real world.” Here is the email he sent with the idea he proposes:
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Here is an email I received today. My answer is below.
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Andrew,

We have already done the first two coats and wanted specific instruction on
the last as it is the one that will encounter the weather. We have used
ordinary clay, gritty ( lots of facets and sizes of grains) sand and chopped
straw for the first two coats and they were much drier than what you showed
in your DVD. We also didn’t wet down the bales first, but did sponge the first coat
before applying the second. It is very rough so we don’t think we’ll need
the scratch thingy. Our ratio was 3 parts sand to 1 clay and about 1/2
chopped straw. The clay was dry bags purchased through the pottery supplier
in town. It was easier to apply with more clay and we tended to put in less
sand as the walls went along. unfortunately that meant there are a few
cracks now… not really big but there none the less. It seems to be well
stuck on and really hard though. It is weathering were there are direct
winds and rain, mostly the west side of the house.

So really at this point we are just soooo tired and want someone to come do
it and FIX it! We had hoped in the beginning to get someone to use regular
stucco for the final coat and thus have a maintenance free exterior. we have
heard recently though that the mixtures would react differently to climatic
changes and might move or crack relative to each other. what do you think?

Maryann
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Maryann,
I am sorry to hear that you feel you have reached a stopping point. I know how that goes. That said, I think you still have some options to take care of your concerns.
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I recently received the following questions regarding Natural Hydraulic Lime (NHL) plaster:
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As always, we appreciate your response. We finally ordered the lime,
it is arriving this morning. We are scheduled to start tomorrow. Just
lining everything up today. Some final technical questions.

In the formula you call for 4 different grains of sand. In my local
Home Depot I can only find “play sand” and “Masons Sand. I suppose
I’ll have to go to a better source to find the variety of sand. When
I do, what is the proportion of different sands that I need? Probably
this information is on the DVD, yes?
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Gene wrote to me this week asking about the viability of retrofitting an existing structure with straw bales. I get that question a lot and figured it was time to blog about it. Any structure can be wrapped with bales, it is simply a question of how much extra work will be required to make that structure function properly once wrapped. Consider that you will be adding about 2′ to the exterior of the house and that all bale walls need to have adequate roof overhangs to protect them from rain. So, unless your house originally had 4′ overhangs, you will have to extend the roof to accommodate the bales. This means opening up the roof system and “sistering” new rafters to the old ones with enough attachment to support the cantilevered rafter tails. A good rule of thumb is that should be a two to one. If the overhang is 2′ then the attachment needs to be at least 4′ long. Of course then the sheathing will need to be attached and the roofing material feathered back into the existing roof.

Another area of concern are the window and door openings. These will end up recessed into the wall by the thickness of the bales, leaving a large sill that could collect water. Your options here are to move the windows and doors to the outside of the wall using standard bucks, or to slope the sills and cover them with some protective material that will quickly drain any water away from the house. Some options are concrete, granite, or finished wood sills. Doors don’t have this option because they don’t have room for sills.

Finally, will the bales collect moisture against the existing building? If the building is wrapped in a non breathable material like metal siding, the chances are high that the bales will end up soaking in the moisture that collects against the metal surface. A drainage system is a good idea in this case. Something like the product on this website (www.mortarnet.com) is a good idea in this application. Regardless of whether the back of the bales is separated from the existing structure by a drainage channel, the bales need to be fire proofed which means a layer of plaster needs to be added to the bales. This is easy on the face of the new wall, but the back of the bales will not be accessible once the bales are installed. For that reason, each bale needs to have plaster or a clay slip applied to the back before it is installed. This is a slow process, but an important one. The bales could otherwise present a fire risk if not covered. This is most important when using the drainage system but should also be done without a drainage system for added protection.

It sounds like a lot of work, but the results are beautiful and efficient. You may have to work hard to accomplish the wrap, but you will be paid back for years and years with lower utility bills, a more beautiful home, and a higher resale value should you ever decide to leave. I hope this gives you some ideas of what is needed for a bale retrofit.

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Dear Andrew,

We had quite a few days applying the “Scratch Coat” to our straw bale structure. It is so true that the whole process is really about having one stage done as completely before the next stage. But you are the best advocate for this.

Having applied the “Scratch Coat” there are a few questions:

Q: It has been a week since the “Scratch Coat” was applied, how much longer do I mist down the walls and how often?

A: You can stop misting after a week but the longer you mist, often enough to keep the plaster moist, the stronger the cure will be.

Q: What is the optimal time to wait before the “Brown Coat” is applied?

A: Again it is about curing. The longer you wait the better. After you stop misting the walls, you want to wait until the plaster dries out and watch for cracking of the scratch coat. Once the plaster is completely dry, you can prepare for the brown coat.

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It is important that all wood surfaces be covered with roofing felt to separate them from the plaster. If you do not do this, the plaster will adhere to the wood and will be prone to extensive cracking as the wood dries and moves over time. a typical house has a lot of wood members that will need to be isolated so the process can be time consuming. It can also go quickly with a little planning and forethought. Here’s what I suggest. Figure out the major widths of the wood components that need to be covered with the felt. Add 4″ to that width for some overlap (I’ll tell you why in a minute). Now the roofing felt to the chop saw (use an old blade because the felt will gum it up terribly!)and cut the roll into smaller rolls matching the width you determined. Cut slowly to stop the felt from melting to itself rendering it useless. Now you have precut rolls of the size you need to move quickly through the structure. These rolls are not only cut to size, but also easier to carry around the job site and up ladders if necessary.

Now, why did you add 4″ to the measurement of the wood members? When notching your bales, I always tell you to over cut the notch rather than under cut it. If you try and hit the notch size exactly, you will miss most of the time and the trimming of the notch in the bale is hard to accomplish well. This means the bales will be harder to get into place and the time you’ll spend trimming, fine tuning and installing your bales will be huge. If you over cut the notches, you will speed the process immensely; however, you may end up with a bunch of 1″ gaps on the outside of the structure against the posts and beams where the over cut took place. You could stuff these, but it is hard (because they are only a few inches deep) and very time consuming (now you’re back to where you started with lost time!). The extra roofing felt (4″ over cut) acts as backing for the plaster as long as there is no more than an inch or so of space behind the felt. The other 1-3 inches of felt laps onto the bale, bridging the gap. There is no significant affect on the R-Value of the wall and the process is sped up greatly. Again, the faster you can move through the baling process, the sooner you can get the bales protected with plaster.

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When adding a straw bale addition to an existing straw bale house, you have to be sure to create a connection between the two walls (old and new). One way to do this is with dowels or rebar embedded into the old wall and laid in place in between courses of new wall. This allows you to leave the existing plaster in place and still accomplish a connection. Another way is remove the plaster from the existing wall and then use plaster lath on the top of each new course that is bent at 90 degrees and pined to the old wall surface. Use landscape pins on the old and new walls to attach the plaster lath. You will want to offset the new walls in either application so they are not in line with each other. In other words, add a right angle turn from the old wall and offset the new wall by at least one foot. This will help when you plaster because it gives you a stopping point (the corner). Without it, you will see a large plaster scar or will be required to plaster the entire wall (both old and new) to a corner.

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Question from a reader: Do you know a way to apply extremely fine ground sand mixed with natural lime or some other binder (resin) and color and bond it securely to a plywood floor as artificial stone (pattern to be achieved through removable tapes)?
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When using Earth or Lime plasters, it is not necessary to use any mesh or lath. There are advantages to using mesh nonetheless, and there are disadvantages as well. The biggest advantage of using the mesh is the ability to shape the walls and reinforce the plaster in the process. The biggest disadvantage is that more plaster must often be used to even out the walls, especially if the mesh is rigid like a welded wire mesh, for example.
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I recently responded to an email about cracks in lime plaster. The person reported seeing cracks through all three coats of plaster along the joint between the top of the bales and the wood box beam. She has tried a lime wash patch, which made things worse or at least more noticeable, and she was asking what to do. My response is below.
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When you build with bales, one thing is almost 100% guaranteed: you will be plastering your walls. Knowing that, you may be surprised to discover that there is a cost that you should definitely put into your budget that may otherwise be overlooked. That cost is the electrical bill during the plastering phase.
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There is a conversation happening right now on another list serve about woodpeckers destroying plaster on a house. This is not the first time I have heard of this. If you use earthen plasters that are based on local soils, you may encourage local birds to try and nest in your walls.
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