A Concern with Painting Plastered Walls in a Straw Bale House

Written by Andrew Morrison

devine green paint canI have been using the Devine Green line for painting plastered walls 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.

Most plasters need about 28 days to fully cure. The biggest problem with this is that the time line usually does not allow for waiting 28 days before the paint is applied. Most critical paths assume that one trade will move quickly to the next. To put off painting would mean putting off cabinets, flooring, and everything else associated with the finish of the house until after the paint is completed.

You will either have to plan for this in your critical path, or paint after all of the finishes are in place. Painting after the installation of the finishes is fine but it means a lot more prep work is in order to protect the finish materials. This is something to consider before you get running down the path towards home construction!

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18 Responses

  1. Why would you paint a plaster wall, especially if it is new construction? I was under the impression that the color is put into the final coat of plaster called the “color coat.” I don’t get why you are painting your walls at all. Perhaps this whole problem should have been avoided in the first place.


  2. Silvia,
    I don’t recommend that my clients use the color coat because if they ever have holes in the wall, like when they move a picture and leave a nail mark behind, it is all but impossible to match the wall color again. With paint, on the other hand, they can easily patch and paint any size hole with ease. I have found that the paint is a much easier wall finish to live with and when the details listed in the original post were addressed, I have not had any problems.

  3. I have a new straw bale fence. I used Ash grove premix stucco to cover it. I found the color coat to cost more than I can afford. Can I prime and paint the stucco. A friend told me not to paint stucco over hay bales, something about the hay bales needing to breath ? I live in Wy. please give me any advice you can. Thanks Rhonda

  4. Hi Rhonda,
    I sure hope you mean straw bales, not hay. I would agree with your friend to some extent; however, the right paint can be applied if it has a higher permeability rate than the stucco. In other words, if it breathes more than the stucco it won’t limit the vapor transfer.On a fence, it doesn’t matter anyway because the bales will likely rot away over time unless it is protected with a roof. That is fine because what you are looking for is the shape of the fence, not the insulation value of the straw. Consider the straw as a form work for the stucco and then the stucco as the actual fence material.

  5. Thanks Andrew for the reply. I’ll probably use a silicate dispersion paint from Eco-House for my exterior.

    But I’d like to use this Devine Green paint for the interior surfaces of my straw bale wall. I talked to my local retailer, who immediately called her distributor. The distributor thinks I should use a primer to avoid the kind of separation problem you mention in this post. Do you use primer with this paint? If so, which primer do you use that doesn’t inhibit breathability?

  6. My painter did use a primer although I don’t remember the name of it. It is specially formulated to work with plastered walls, taking into account their pH levels. Talk to your distributor and they should be able to let you know about what to use. In terms of breathability, I don’t worry as much about that on the inside of the house, I’d rather have a little extra vapor resistance on the interior than I have on the exterior since homes are pressurized from the inside out. In other words, if I can only move say 10 (random number and unit for clarity’s sake) amounts of moisture into my walls from the interior, but I can move 20 out through the exterior, this helps me insure my walls stay dry.

  7. I live in very wet country, northwest WA. I assumed that I would have to paint the exterior plaster to protect it from rain. After watching your DVD and reading some of the posts I’m beginning to wonder. Should I paint the plaster or not? And if I should paint any factors in the paint I should watch for?

  8. If you choose to paint the exterior of the house I strongly recommend that you use silicate paints as they allow vapor to pass through (from the inside out) but stop water from penetrating. If you use a “regular” paint like latex or oil based on the exterior, you will seal the wall and no moisture will be able to escape through the wall. This will trap moisture inside and potentially cause problems in the long term.

  9. So Andrew, if I am reading this right, I don’t HAVE to use a clay paint on my interior straw bale plastered walls? My house was finished in March 2011. It is almost two years old. It is very dark in here on three walls. I didn’t have the money to color them when the house was built but I will this year. Sadly, I may need to sell my straw bale house and want to present it as best as I can. Thanks. Annie

  10. Hi Annie. I think you may have seen article from my blog as it was posted to the Facebook page. Just in case, I will share some details here.

    1. You can use paint on the interior walls, but I would never recommend you use it on the exterior of the house as it is likely to trap moisture in the walls.
    2. Use as natural a paint as you can find.
    3. If you used a clay plaster originally, you will need to use something more specialized like a casein paint or other earth pigmented paints.
    4. If you used lime plaster originally, then I suggest a lime wash or lime paint as the number one option. If you use a non-lime based paint, be sure to check the pH of the wall before you paint. USe a high alkaline primer and make sure to be within the pH levels of the paint manufacturer’s specifications.

    Hope that helps and I hope you can stay in your bale house!!! If you decide to sell, let me know as I am launching a Straw Bale Homes For Sale page on StrawBale.com this year.

  11. IF, this was a lime based product, the walls should have been primed with a lime based primer. Since the walls are exposed to different temperatures , the PH will read differently, in different areas . I have been a Professional Decorative Painter for over 25 years, all high End Experience.. Now, , a simple way to find out whether or not the surface is ready for Painting, apply a strip of blue tape to a part of the wall and make sure, you rub it hard, so, that the tape will stick to the surface. Leave it on the wall for a couple of days, come back and peel the tape as quickly as you can, IF, you have anything on the tape, it will most likely be dust on the walls and we all know, you can’t paint over dust. Cheap paints tend to pulverize over time. We were doing a very large house, which was done with a lime based Plaster from Italy. After the house was power washed, we still had dust on the walls, we did the blue tape test and sure enough, there was dust and there was no way to get rid of the dust. So, I called the Experts in Italy I have been dealing with for years and they recommended a Special Primer they make, which acts almost like a glue, therefore as you apply this material, it glues the dust to the walls and we were able to paint the house. Another large house we did using a Lime based Stucco was just painted, I Don’t even believe they primed the house. I am sure, the paint will start to show signs of the mistake they made.

  12. Does painting the internal walls alter the “feel” you get from them? Part of what I love is that sense of whatever-the-heck-it-actually-is that you get standing in a room with plastered walls. Does painting take that away? If so, does it do so less with the breathable silicate paints?

  13. Hi Ellie. I totally get what you mean. In my opinion, painting doesn’t impact the feel. It just adds color to the walls. If you have lime plaster, you can simply lime paint the walls and that way you are sticking with the same material from base to finish.

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