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(photo courtesy of Harvest Build)

Many people have asked me if spraying lime plaster is a good way to go. There are belief structures on either side of the coin. Some people believe that spraying the plaster will improve the adhesion of the plaster to the bales because the plaster is being forced, via compressed air, into the bales. Others believe that hand application provides the best adhesion because the plaster is pushed and shimmied into the bales with arm power. There are other pieces of the puzzle to consider too. How many people do you have available who know how to plaster? How long do you have to get the plaster applied? What is the weather like? Do you have access to a commercial grade plaster spraying machine? Will a small hopper style sprayer work for you?
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There are many details that must be managed in order to produce a quality plaster job. This is true for any type of plaster; however, there are some material specific conditions that must be met when working with Natural Hydraulic Lime (NHL) that are not necessarily common to other materials.
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Bees wax may not be a standard tool in your tool box, but it really should be. If you have ever plastered a house or poured a concrete slab, you know how those materials can dry out your hands. It often goes beyond dry skin and ends up in painful cracked hands. Most people use gloves to try and avoid the affects of the materials, but that never quite works.
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Want to be part of a once a year opportunity? I have several buildings from this year’s straw bale workshops that are in different stages of plastering. This is the perfect way to learn how to plaster with lime because it is necessary to wait a minimum of 10 days in between plaster coats. With my situation, we can do all three coats of plaster on three different buildings over only three days, no need to wait in between coats! Read on for course details.
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For years I used either welded wire mesh or (eeek) chicken wire to shape the space above windows and doors. The chicken wire was horrible, mostly because it never seems to hold a shape, but the welded wire mesh worked pretty well. The biggest problem with the welded wire mesh is that if it is not stuffed well with tightly packed straw or if the straw is packed too tightly, the plaster has a hard time sticking to the lids of the opening.
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There are so many things to consider when choosing a plaster for your straw bale home. I will try and give a quick outline here to get you all started on the path of inquiry. There are many decision to be made and many details to consider in those decisions. The plaster is the thing that most people will notice about your home, so make a wise and well informed decision. Below I will give some pros and cons to Clay, Lime and Cement based plasters. The decision is ultimately yours and I hope the information below will help you decide.
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Photo: R Critchley Plastering

One. All he or she has to do is pick up the phone and call the plastering company!

Okay, that may be an overstatement of how hard it can be to work with a subcontractor when they plaster, but it at least makes my point. Plastering is an art. It is physically exhausting, and long winded. Without the right skills and a large enough crew, you will be setting yourself up for failure and frustration.
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For a long time my crew has used the same mesh (2″x2″ 14 gauge welded wire mesh) to shape windows and door openings. It has always worked very well; however, I have recently found a situation in which that can be quite problematic for the plastering process.
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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…)

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.