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My name is Andrew Morrison and welcome to my straw bale building site dedicated to anyone interested in building their own straw bale house. If you are brand new to straw bale or are a straw bale construction specialist there's something for you at StrawBale.com.
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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.
The rigid mesh will hold an even plane even if the surface of the bales undulates beneath it. This leaves deep areas that need to be filled with mud in order to remain even with the swells. In such cases, it can actually be more frustrating to use the mesh than it would be to plaster directly onto the bales. If you plan to place your mud directly on the bales, be sure you do a good job of weed whacking. Any loose straw will make the process more difficult as large sections of plaster will get too heavy and simply peel away from the wall. That is a mess and very annoying. So either way, you can end up frustrated! Plastering is hard. Don’t let anyone tell you it isn’t. Once you get the skills from several projects, it gets easier, but it is nothing less than an art that must be learned and improved with time and practice.
Here is a response to a student doing a case study of straw bale homes in North Carolina. He had a good question about how the bales of an existing structure in Alabama might be connected to the foundation. I think the details of the connection are worth mentioning here as well.
I am glad to see that you have chosen such a cool topic for your case study! Perhaps the most important distinction to make is that the homes are made with straw bales, not hay bales. Hay would be a food source for many critters and would also run the risk of fire because of the higher moisture contents within hay bales. Straw on the other hand has no food value and is extremely dry, typically around 8% moisture content during installation.
The old style of construction has changed significantly in recent years so how the bales were attached to the foundation in the building you are studying is hard to say. In today’s homes, we use a system that bolts 4×4 sills to the foundation. Those sills are place on the interior and exterior faces of the bales so each bale is held up n both sides at the bearing points. The space between the 4x4s is filled with gravel and/or rigid insulation. 20 penny nails are then driven into the sills at 4″ on center staggered from one side of the sill to the other (both sills are nailed and treated as separate entities when measuring the layout of the nails). The nails are only driven in until firmly secured in the sills and about 2″- 3″ of nail is still exposed above the sills. The bales are then placed on the nails and held tightly in place by the “grab” of the nails. That is the easiest and most effective way of connecting to the foundation.
This is a response to a comment about bale buildings and their ability to resist fire. The author of the original email challenged the fact that conventional buildings only have a twenty minute burn time and that they do not actually have a chimney affect like I describe. I disagree and you can see my response below.
Thanks for your email. What I refer to in the twenty minute burn time is the rating of the drywall. A standard wall assembly is designed to resist fire for 20 minutes and then the drywall will be burned through. Once in side the drywall, you do have chimneys, albeit small ones that run for at most 10′ and at least 8′. Fire blocking is not required until you reach ten feet in height and wood plates at 8′ or 9′ are the standard in most homes. Consider a “chimney” of 1/2″ drywall (one break in the drywall will allow the flames in), dry 2×6 studs 1 1/4″ of plaster on top of densely packed, silicone rich material with extremely low amounts of oxygen in the material. This is where the comparison is a clear winner for bale building.
The recent fire testing results support this claim. I have seen conventional homes on fire and they get out of control very quickly. In contrast, a plastered bale home will smolder for a long time before any flames actually take hold. That’s where I am coming from on this. I know it seems counter intuitive to think bale homes could last longer than conventional homes when faced with fire, but that is what I have seen and what the studies have shown. Thanks again for your email.
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.
It sounds like the joint between the wood box beam and the plaster is opening up. This usually happens when the wood has not been separated from the plaster. In other words, if the wood was not covered with roofing felt, the plaster would be adhered to the wood. The problem here is that wood moves at a different rate than straw so you get stress fractures at the joint between them. Another potential problem is that the joint was not reinforced with plaster lath or some other structural mesh.
For the same reason stated above you need to span the joint with a structural mesh so that the plaster can hang on to that and the different rates of movement are absorbed and moderated by the mesh. The mixing ratio of the mud could definitely have an affect on things as well. My first assumption, not having seen or heard about the construction of the building, is that it is related to the items above, not the mixing ratio. If so, the only fix is to deal with the problem. If it is a lack of roofing felt, you may need to tear out the plaster and start over in that area.
Shy of such a drastic fix, you could try using fiberglass mesh tape (like drywall tape but get the higher quality plaster tape) placed over the crack and then embedded in fresh mud. This should give the plaster enough strength to withstand the movement of the plaster beneath it. I would certainly try that first.
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.
Be sure to put in enough money to cover the cost of any heaters that you may use to dry the plaster, especially if you plaster during a cold or wet time of year. As an example, we used two plenum heaters in a 3200 SF house we plastered last month and the electrical bill came in at $650. That is a lot of money if you are no expecting the bill. A few little missed amounts like that and you will quickly find yourself in a financial hole! Consider how long you will be plastering and estimate how much electricity you are likely to use. You may need to ask the local rental yard how much electricity the heaters you rent will use in a given day, or how much propane they will need to run. Over estimating is a good idea, especially with the rising cost of energy these days.
Did you know that in the United States construction accounts for 36% of total energy use? That is a huge number when you stop and think about it. Perhaps if the products we used were biproducts of another industry (like, hmmmm……STRAW) we could lower that number a bit.
But hang on, it gets worse. 65% of the United States energy consumption is related to the construction industry. The U.S. uses more energy than the rest of the World as is, and 65% of that energy is used by the construction industry.
The process of building is also responsible for 30% of greenhouse gas emissions. Most people talk about cars when it comes to greenhouse gases, but rarely consider the home they build as an impactful source of pollution. What may seem more understandable, 30% of the raw materials used in the United States go towards construction. Again, if we could focus on the use of bi products like straw, fly ash, and recycled materials, we could have a significant impact on the shape of things in the States. In fact, if people recycled their product waste instead of throwing it away (as is often the case on job sites) we could reduce the 136 million tons of garbage produced annually by construction projects. That’s 30% of the total waste output for the U.S. each year.
As you may already know, the World’s water supply is in trouble and is not large enough to sustain the growth we are seeing worldwide. With that in mind, consider that construction projects account for12 % of potable water consumption in the United States. That is a lot of water and much of it can be seen cleaning out wheelbarrows and washing down the sidewalk after a day at the job site. Conservation has to become the mantra for contractors if we plan to keep our great trade alive without killing the World in the process.
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.
This is especially true of you have bank swallows as they may see your house as one huge river bank! In order to avoid this, be sure to get your finish coat of plaster on the walls as soon as you can. The finish coat has the color and so the birds will no longer look at your house as a possible home.
Woodpeckers are another type of bird that have been seen smacking their heads into walls, at least here in the Northwest. Flickers, a dominantly ground based woodpecker, love to widen holes made by other birds in search of possible food. Other woodpeckers may focus on rafters or other wood members. This may be an indication of wood rot or termites. No matter what type of bird you have attacking your house, it is a good idea to investigate the area they are interested in BEFORE you move them on their way. Be sure to see them as an opportunity to learn about the health of your house and then be sure to remedy what ever is encouraging the birds as soon as possible.
I had a very close call on a job I am working on this week. While I was in Maine on vacation, $10,000 worth of cork flooring was delivered to the job site and set for installation. My project manager noticed that there were blemishes on the cork and stopped the crew from installing it. He had the crew open a random number of boxes of the material and all of them had the same blemishes.
He contacted the flooring company and they routed the call to the distribution center where a representative open an entire pallet of the material and it ALL had the blemishes. It seemed this was just a part of the material and that the blemishes were simply areas that do not take stain, like a knot in wood. We had to clear this with the owners, who live in Alaska right now, before we could install the floor as the sample they originally viewed did not show any blemishes. Thank goodness we did because it turns out the flooring company had sent us the wrong floor! The blemishes quickly became a moot point as we were not looking at the right style of cork to begin with.
The obvious moral here is to pay attention to the materials that are delivered and insure they are in good condition and the right style before you install them. I am glad my project manager was on top of the blemishes; however, I now realize that as I was the one who helped choose the flooring with my clients, I should have given my project manager a sample of the material they chose before I left for Maine. In the future, I will keep samples or pictures of all finish materials on site so that no wrong materials can be installed
If possible, get any plaster that needs to be applied above the roof line in place before the finish roof is installed. If that is not possible, be sure to protect the roof from any dripped plaster. Once on a roof, especially a roof with texture like shingles, shakes, or clay tile, plaster is all but impossible to remove and the roof itself may need to be replaced in sections.
The picture above is an example of how to properly protect a roof while applying plaster. Do not assume you can keep the roof free from debris with careful detail. Instead, assume you WILL spill plaster and protect the roof accordingly. It is an even better plan to schedule the plastering after the roofing felt has been installed but before the finish roof has been completed. As with many other aspects of construction, a little forethought goes a long way!
We are currently building a house where the architect has called for base board trim to be used throughout. That is fairly standard delivery for most homes; however, is much more difficult in bale homes due to the undulations in the bale walls and the large curves in corners.
Making the situation even harder is the fact that the architect has called for stain grade wood to be used. Again, this is possible but difficult. To ensure that the trim follows the undulations of the walls properly, you may need to use 1/2″ stock rather than 3/4″so that the material remains flexible. In addition, you may need to score the back side of the trim to allow it even more flexibility. This is almost always required in corners where the trim is forced to make deep bends to stay tight to the wall. When installing the trim, be sure to use nails and glue to hold it in place. Nails alone may allow the trim to pull away from the wall in places. If you can use paint grade trim, you will find it easier to bridge the gaps with caulk and paint; however, keep the trim as tight to the wall as you can because caulk and paint are no substitute for wood/wall contact.
In many homes, we eliminate the base board trim entirely and finish our plaster to the floor. This is hard to do if a floating floor or wood floor is installed as a gap is required against the wall for expansion. That gap is usually hidden by the trim. For that reason, planning is required for your finish trim when you are building the walls and plastering them. You will need to know what type of flooring will be installed and how that will finish to the wall. You don’t want t o spend the extra time plastering tight to the floor only to realize you will have to install base trim.