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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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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.
I was recently asked if it is possible to do an earthen or cement skim coat over a slab foundation. The answer is yes, you can do a skim coat of either clay/straw (earthen floor) or cement over the top of a concrete slab; however, there are minimum thicknesses that need to be maintained. At least 3″ of concrete are required unless a specialty skim coat is used (this takes extra skill).
There are specialty coating systems available that can be used if you have the skills, but in general, they are much more difficult to finish well. In fact, it may be easier to simply finish the concrete in such a way that the foundation slab can be used as the finish floor of the home. Be sure to protect the floors during construction. If you plan to acid stain the floor, make it a point to know the details of that art. For example, you would want to know that a stack of lumber left on the concrete during construction will cause the stain to fail in that area leaving a blank or discolored straight line that will not look very good at all in the finished floor. You will also have to be very clear with any subs that the slab is the finished floor and inform them that they cannot write notes on the floor with a construction crayon or snap lines with red chalk. There are many things to keep in mind here and some basic knowledge is a must. Knowing what to watch out for ahead of time will be a life saver in the end!
When applying a skim coat of stray and clay, it is a good idea to use about 2″ of material to get proper adhesion and compaction. Be sure to apply the earthen floor in lifts. In other words, apply one inch of material and then let it cure. Moisten the surface of the cured floor and apply another 1/2″ for proper adhesion to the base coat and then apply the final 1/2″ while the previous 1/2″ is still moist. This will ensure a tight bond between all the coats. Compact and finish the floor as you would any earthen floor. In most cases if an earthen floor is used, you can eliminate the concrete slab altogether and build the earthen floor over compacted gravel lifts. A foundation can be poured to carry the loads of the home and then the gravel and earthen floor can be built up inside the foundation.
If an existing concrete slab is to be covered, many options are available and the ones listed above are just two of many.
Welcome to the December 2006 “Building Green” podcast. This is my monthly Q&A session where I answer your green building and straw bale construction questions. This month I answer the following questions:
1. I want to design and build my own house. What are the pros and cons of this?
2. Are two string bales or three string bales the best to build with?
3. How do I install plumbing in a bale wall?
4. How do I run electrical wiring in my bale walls?
5. Can I build a bale house in a humid climate? How about a rainy climate?
To listen to this podcast on your computer please click the following link or right click to download the podcast to your hard drive:Building Green Podcast: December 2006 Edition
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Please click the play button below to listen to this podcast!
Perhaps the most important aspect of straw bale building has nothing to do with bales. In fact, it has everything to do with holes in the walls. Windows and doors present the most likely areas for water infiltration and bale damage in the entire house. For this reason it is extremely important to pay extra attention to these areas during construction. For windows, I use two part flashing. The first is called counter flashing and is put in place before the window or door is set in the opening.
Starting at the bottom, a waterproof membrane is applied to the opening and then built towards the top so that each layer overlaps the one below it. In other words, the top of the counter flashing for the bottom window sill is underneath the bottom of the side jamb flashing, and the top of the side jamb flashing is underneath the bottom of the head flashing. In this way, any water that contacts the counter flashing will always be moving down and always end up on top of the counter flashing. I use adhesive flashing for this application.
Once the counter flashing is in place, I install the windows. After the windows are all secured, I wrap them in an adhesive flashing again starting at the bottom and working my way up to the top. The top most piece of flashing must always be above and on top of the layers underneath it. The adhesive flashing works well because it completely seals to the windows and framing. Be careful not to get straw behind it during installation as that will create areas for water to find its way into the building.
I always set my windows flush with the outside plane of the wall, not inset like in adobe houses. The look is a bit more basic than the adobe feel, but the risk for water infiltration is considerably lower. This is just another detail that is something to consider when designing a home. How can I best protect my bales and thus ensure a long life for my home. A simple change in design allows for better protection and a better ability to flash against the elements.
For doors, you can lower the base of the threshold into the floor if you are using concrete by creating a void during the pour. It is also possible to use sill pans underneath the threshold to improve the seal or even use a large bead of high quality caulking beneath the door threshold. These products greatly improve the installation of the door and are worth the extra effort. The side jambs of the door are flashed in the same manner as windows, from bottom to top as is the door head.