Repairing Straw Bale Water Damaged Walls
Repairing water damaged walls in straw bale is a skill that is not required very often, especially in well built homes. If it does though, it's important to know how to recognize it and how to fix it. Below is a series of steps to consider wen dealing with water damaged walls.
Identify the problem exists. I have heard from several home owners over the years who were worried that their bale walls were rotting because they were convinced they could smell mold. In most of those cases, it turns out the mold they were smelling was from bales that were over wet during the plastering process. As soon as the plaster fully dried out, the smell disappeared, never to return. It is important that you don't take huge steps towards fixing a problem that doesn't exist.
Locate the problem. If you are certain that there is in fact a problem, you will need to identify where it is and how far the damage has spread. Keep in mind that bales are like sponges and will pull water and moisture into them even from fair distances. Use a moisture meter to locate the extent of the damage.
Minimize initial plaster damage. When checking for the extent of the problem, do your best to avoid ruining the plaster. After all, you may have moved beyond the extent of the damage in the bales, so why create more problems for yourself in the plaster work? Utilize the access through electrical boxes to probe with your meter. If you need to drill holes in the plaster, make them just barely big enough for the meter's probe to fit through.
Remedy the cause. There is no point in replacing bales or trying to mitigate moisture issues if the source of the moisture is allowed to continue adding moisture to the walls. You have to identify the problem and fix it so that no new water/moisture can be introduced into the walls. The most common sources of water/moisture intrusion are broken pipes (water isolation boxes and walls eliminate 99% of these issues so please use them), roof leaks, and window and door leaks as a result of improper flashing details.
Scale your repair. There is no need to tear open a beautifully plastered wall if the moisture levels are not that high. If values are only slightly elevated (8%-12% moisture content is ideal; however, anything up to 15% is ultimately okay. Values between 15% and 20% are slightly elevated. Sustained values above 20% need more immediate and aggressive attention as mold growth can exist at this level. For lower values, drill holes in the walls and pump in warm/dry air as shown in the photo above. For worse situations, start with the warm air and monitor the levels. If they do not drop, then more aggressive action will be required, including opening up the walls.
Remove rot. If you have rotten bales due to extensive water damage, then those bales must be removed and replaced. This is hard work, but not as bad as you might think. No water damage repair is fun in a bale or conventional house. Bear down and get into it. It will be over before you know it.
Repair the holes, no matter what the size. Once the bales in the wall are fully repaired or replaced, the plaster will need to be repaired. If you only needed to drill air inlet holes, those too will need to be patched. With larger holes, those required for replacing bales, be sure to leave roughly 6" of mesh exposed beyond the removed plaster so that when you replace the new mesh, it overlaps and can be tied into the rest of the wall mesh. Plaster the repair and then skim coat the whole wall to blend everything together.
The good news is that you will likely never have to deal with repairing water damaged straw bale walls. The key is to build your house well from the start and to consider the most common points of entry for water from the start. Pay special attention to window and door openings and how they are framed and flashed. Be careful with roof assemblies and make sure they are properly sealed.
Do not over water your walls during plastering and be careful not to start your plaster during or right before the wet season in your area. Keep in mind that any water you place on/in the walls during plastering will need to escape into the environment and the only way it can do that is if the environment is drier than the walls. Otherwise, that water will stay in the walls until the weather clears enough for it to escape.
Have you ever had to deal with damage in your bale walls? If so, what did you do about it? Did you hire out the repair work or take it on yourself? I hope you'll share your story below in the comments so that you can help others learn from your experience. You may think that comments are just for fun, but they actually help a lot of people make important decisions. I hope you will help out your fellow balers with your own story.
-Andrew Morrison