Repairing Straw Bale Water Damaged Walls

Written by Andrew Morrison

water damaged wallsRepairing 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.

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19 Responses

  1. My hubby and i are considering purchasing a straw built home. I am a property adjuster so am inharently always looking at potential problems. I can quickly spot signs of water damage in a traditional built home, what should i be looking for in a strawbale home. I am in Northern MN. The home has a steel roof with good size overhang and a lot of windows for passive solar. Any info would be great thanks!

  2. Hi Kirsten. I would recommend looking for any discoloration in the plaster, especially in areas where water might be an obvious issue (around and under windows, doors, hose bibs, etc.). You can also use a Delmhurst bale moisture meter to check the moisture content of the bales by poking it through the back of electrical boxes into the straw. Be sure to turn off the power before you do this.

  3. We’re now repairing the SECOND wall beneath a dripping air conditioner in a window. You’d have thought we’d have learned after the first one…

    The entire wall below the window became saturated and collapsed. They’re replacing the sodden, rotten bales with concrete block.

  4. After smelling straw and taking moisture readings, we have stripped back the stucco to find an area that has been subjected to water off a nearby roof overhang. !st order to come is find the problem leakspot. The off-colored straw has been pulled out to the point of healthy straw. We plan to let this area breathe and dry out for a while in our dry Arizona spring. Here is my question: to fill the voids created by straw removal which may only be 6″x6″ and in a vertical cut (following the problem drip line), I was thinking of using expanding spray foam then lath, then stucco. Any foreseeable problems with this idea? We built our SB 15 yrs. ago and have had no problems other than some fine cracking and we love it still. Thank you for responding
    Lon Anderson

  5. Hi Lon. That should work just fine. Be sure to overlap the lath onto the existing straw/lath so that you don’t get cracks along the repair line. You could also use straw and burlap, then covered in lath, for a less environmentally impactful repair.

  6. Good info. I am looking to buy a small straw bale home in Ohio. Owners purchased it a few years ago and do not have much info on it. No plans. They did not live in it for two years but had someone paint outside with proper paint. I am having hard time finding inspector with right moisture meter. Can I buy one and do this myself? Is checking behind the electrical box enough? There is walkway around the house under large overhangs . West comer of the house the walk way is tilted in toward house. I know this would have to be fixed. Should I make sure and get reading of the bales in that corner. Have not ask sellers if they will let me yet. Marg

  7. Hi Marg. You can buy a moisture meter for about $250 or so. Here’s a link to the one I use. I would get readings below every window if there are plugs there, and in any area that might be subject to excess moisture. If you want to get areas without plugs and switches, then you have to drill holes which would than have to be repaired. Often, sellers are not excited about this, but it is worth asking. I believe you would need a 3/4″ hole to insert the meter. If they painted the exterior with latex or oil paint (standard paint) then there could be some moisture issues in the wall depending on the climate, as that paint would lock down the ability for the wall to “exhale.” If they painted the interior with the same or less permeable paint, then you would likely be fine. Those general moisture levels would be prevalent in the straw behind the switches and plugs. Good luck!

  8. Hi, We are in the process of purchasing a straw bale house, we recognize that this house needs a fair bit of work especially fixing up some of the walls and render. There are a number of large holes in the render and straw bale where birds have made nests. especially around the corners where the wall meets the roof. What method would you recommend to fix these holes?

  9. Hi ,
    I have repaired water damage strawbale walls.In a rear wall of a studio where the soil had built up beside the wall and a leaking roof gutter existed, obviously bad building maintenance ..
    The walls were clay render/plaster and suffered weather damage also but the soil built up was the real issue . Only the bottom course was affected and I was able to pull the composted straw out put in some timber struts to hold up the bales above yet they seemed to hold up without support.
    I let it dry a week in dry warm weather then stuffed straw back in and lime rendered over.

    I am pretty sure the clay helped minimised damage ,the hardwood bottom plates were in good condition . And I believe that situation in standard building materials would have been harder to repair .Even though water ran onto the floor inside the building ,the internal clay walls did not need any repair ,they remained intact.
    Now I have a job where a patch of strawbale wall was flooded by an overflowing gutter in an extreme rainstorm . It is under construction and some plastic protection in place for rendering cause the water to hit the wall.
    It had a dry first coat of lime on the wall fairly thick.
    My business partner thinks the lime will help pull the moisture out. I think taking the lime off will help it dry faster. At the moment it is warm and dry,but that wall dosent get sun (Australian south side ).
    The wet area is only the bottom half of a 12 foot wall and 1 1/2 feet wide.
    What do you think ?

  10. Hi John. Sorry for the delay. This message was stuck in my system. It’s hard to know just how much water got into the wall, but if it was just one rainstorm, the chances re good that it will dry out even with the lime in place. I would monitor it for a while and see if the levels drop. Being that the surface of the wall is what was wet, it’s very probable that there is not actually any damage to the wall in reality. I’m curious to know what your results are as you move forward.

  11. Hi Mark. The repair will depend on the type of plaster to some extent. In general, you will want take the following steps, regardless of the plaster type.
    1. Remove any loose plaster. Remove it farther back than any mesh you may wish to replace, by at least 6″ in each direction so that you can
    overlap new mesh onto the old mesh.
    2. Remove the mesh to gain access to the straw, assuming you will need to replace some damaged straw.
    3. Use a moisture meter to determine the moisture content of the bales. Remove any straw that is higher tan 20% or otherwise looks damaged by its
    exposure. You may have to chase this down as the moisture levels may have increased around or below the opening.
    4. Add fresh straw to the hole and pack it with a light clay slip so that it stays in place.
    5. Replace the mesh, overlapping it onto the old mesh by at least 6″. Secure with landscape pins long enough to reach the intact bales behind the
    6. Add plaster to the holes to seal them up.
    7. Complete a skim coat of plaster over the wall to hide the patches.

    Hope this helps.

  12. Hi Andrew,

    Great post! We are actually in the process of building our SB house in France and are applying the clay render. Now, here’s the thing, my partner wanted it to come flush with the wood which would make a massive 15 cm of insulation.

    We’ve done the first 7 cm but at the time of applying I was concerned that it was very wet and the slip may not have been thick enough to protect the straw bale. It smelt very strongly at the beginning but that’s now far better in most places.

    We’ve had a huge amount of shrinkage (around 2-3cm) but my concern is that there are some areas that are still damp despite a good.month of drying.

    We also have marks of mould that are still visible and when I put my hand through the crack the straw isn’t so tightly packed anymore making me concerned that it’s the start of mould…should we be concerned?

  13. Bonjour Severine. That is really hard to say from here without a closer look. I’m a lime plaster man myself, so I have limited experience with clay plasters. I will say that major shrinkage in the clay can be an issue and is likely pointing to too much clay in the mix, relative to the sand, etc. The smell of mold is not uncommon when dealing with fresh plaster as the amount of water added to the walls can be extreme during the plastering process. That smell should go away once things dry out. Again, the shrinkage and any drawing down of the straw would be of bigger concern. You may need to re-stuff areas that have drawn down in order to keep the insulation value of the wall.

  14. Thanks for the great site with a lot of good info. I recently signed a contract to buy a strawbale house near Moab, Utah. It’s usually dry in Moab but there can be short periods of huge downpours. I found out today the house had been under contract twice before but both buyers backed out after inspection, apparently due to the walls and a 20-year-old roof. I guess the builder used a concrete mix layer beneath the stucco and above chicken wire / tarpaper. I read on here that concrete can potentially cause haybales to rot. I haven’t yet gotten my own inspection and will make sure they do moisture tests. But wanted to inform myself before that. Does this building method raise some obvious red flags? In a worst-case scenario where there would be a lot of rot in straw bales, do you have any (very rough) idea what repair costs could be for a 3,000 square foot house?

    Here’s what the builder said about the house. He stands by the way it was built of course, but he emphasizes the strength and says nothing about possible rot.

    “We left a cut out of the stucco in the house, it’s roughly a 3”by 3” piece, which shows the layers.

    Underneath the thin layer of synthetic waterproof stucco on the outside is a ca 1 concrete mix layer, which is over and inside the chicken wire which is over the tarpaper which is over the straw bale, which is insulation inside the post (4×4, not 2×4) and beam construction.

    The same concrete layer including chicken wire and tarpaper is also on the inside walls.

    We could have put the synthetic layer directly on the chicken wire as it is done in plywood construction, but we added the concrete layer for stability and durability.

    Somebody could drive a truck into that house and not get thru the wall, whereas the same could not be said for the soft synthetic stucco over styrofoam on plywood post and beam construction.”


  15. Hi Grant. It sounds like the piece they left open is a simple truth window, so nothing special there. I am not a fan of the system they used. One of the great aspects of straw bale construction is the connection of the plaster to the bales. that adds HUGE amounts of strength for the building. Disconnecting those tow aspects by the inclusion of tar paper is a problem in my opinion. Secondly, the tar paper will greatly reduce the walls ability to breathe and function properly. Chicken wire is garbage for many reasons, but at this stage of the game, the most important reasons are that it does not provide adequate strength to the walls as it allows for movement by stretching and, perhaps more importantly, it is not a galvanized metal so it is likely to rust and dissolve over time.

    I imagine that the “thin layer of waterproof stucco” he refers to is in fact elastomeric plaster. That does not allow for vapor to escape the house AT ALL. Further, the use of a concrete layer is a terrible idea. I’m not a fan of cement based plasters because they are brittle, tend to crack and allow water to enter the walls, don’t breathe, aren’t flexible, and tend to cause damage to the bales for all of these reasons and more. He is talking about concrete, not cement based plaster, which would be even worse. Yes, the structure will be strong because it is basically a ferro-cement home at this point; however, the bales may very well have rotten away over the last twenty years leaving you with no insulation or a pile of rotten straw inside the walls. You can check that by using a moisture meter behind electrical outlets and switches where readings should not exceed 18% (over 20% means mold can sustain itself). You may also want to consider a thermal scan of the walls to see if they are still providing insulation values upwards of R-40 or not.

    Sorry for the bad news, but I would personally want a lot more information about the CURRENT condition of the walls before moving forward. Again, they may be strong because of the concrete, but that does NOT translate to a high quality bale house, just a string concrete wall.

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