Limewash is growing mold?

SpychsChickens

In the Brooder
Sep 3, 2020
4
16
18
Decatur, GA
Hello,
My husband and I finished building our first coop about 6 weeks ago. We live in Atlanta, where it can be very humid, but the last month or so humidity has been very low. I whitewashed/limewashed the inside of the coop with hydrated lime at the beginning of September. I noticed yesterday that mold has grown all over every wall (about 125sqft). The reason I went to the trouble of limewashing is because I read it is so beneficial - keeps insects out, fights mold, etc. Any idea why this would have happened? I want to try again, but I'm not about to go through the trouble until I figure out why it happened. I'm afraid I'll end up painting a third time. I am shocked and angry that I now have to repaint this thing. Now I'm not sure what to use since paint fumes are obviously not good for the girls. I know I can find a low VOC paint, but is that the best choice? Did I do something wrong when I whitewashed it?

Thanks for any tips on repainting the inside of my coop.
 

SpychsChickens

In the Brooder
Sep 3, 2020
4
16
18
Decatur, GA
Yes, that's a real possibility. It rained a lot this summer as we were building. We did our best to cover it, but I'm sure it was still exposed to moisture. The thing that is confusing to me is that the areas I didn't limewash (ceiling joists, door frame) don't have a speck of mold on them. The mold is actually on the limewash. Would this happen if moisture came through the wood and reacted with the lime?
 

Ted Brown

Songster
Dec 12, 2018
1,037
2,327
241
near Shawville Quebec Canada
My Coop
I am not an expert.

I did a bit of searching and found that limewash is supposed to be toxic to mold (as you note above). I saw "recipes" that included salt or borax to further enhance this toxicity. So peculiar to say the least.

I also saw an article that says use a spray on mold killer (no rubbing) if one gets mold on limewash (no explanation why it would grow). Quora says " surface can support molds and mildews that use pollen , soil, and other dust as a substrate. The solution is to apply more lime wash at LEAST once a year, often twice." however the article says this happens after some time has elapsed.

Normally limewash is applied more than once to get a whiter colour as opposed to the translucent finish produced by a single coat. 125 sq feet is not a lot of area so I would be tempted to:
  1. Use a mold spray to kill the mold
  2. Add a second coat of limewash using either salt or borax in the mix.
Please note that this is how I would proceed but I encourage you to do your own research as I am guessing a bit here.

Good luck.
 

janego

In the Brooder
Jun 29, 2019
4
31
37
rural France
I'm in northern France and an expert (?!) here suggested that I add some linseed oil to the limewash to avoid mould forming.

I'm a newby to all this and unfortunately whitewashed the coop before receiving this advice, so I only added salt to the lime. It is now dry, but very powdery and dusty - doesn't seem right!
 

Ted Brown

Songster
Dec 12, 2018
1,037
2,327
241
near Shawville Quebec Canada
My Coop
I have not seen anything about using linseed oil with limewash, have done a fair amount of searching; that does not mean it would not work.

A few things that I do know about linseed:
  • It is old school and normally used as a finish on both wood and concrete.
    • With wood it is commonly used in "Danish Oil" which is mixed equal parts of BOILED linseed, turpentine (preferably made from pine) and vanish/polyurethane. In this form it is brilliant. The linseed is a protectorant in that it soaks into the wood, softens and preserves; the turpentine thins the oil and allows the whole mix to penetrate even more into the wood; the varnish acts as a hardener and protects the surface. Also because it soaks in it does not flake as it ages; when an additional coat is needed simply do a quick clean and re-apply, no sanding or other labourous prep required.
      • One caution a painter friend used it on exterior wood windows and it was horrid; would not dry then attracted dust which caused mold to develop. The problem was he used pure linseed not boiled.
    • With concrete it was/is used on floors as a finish and protector. In barns it was applied to neutralize the lime in concrete when new; lime will cause hooves to deteriorate so this was important for cattle that spend a lot of time inside.
It is the latter use that makes me cautious about mixing linseed with limewash. One uses limewash because of it's toxic nature against mites and other small nasties.

It is conceivable that linseed in it's Danish Oil use will deter critters in wood ON IT"S OWN without mixing with limewash. I use it on decks and other outdoor wood pieces with excellent results including slowing rot which results from water causing molds then attracting insects.

However, limewash is very inexpensive, linseed is not.

As to your "It is now dry, but very powdery and dusty " issue @janego - is it possible that your mix was too thick? The normal progression in using it is a light translucent 1st coat that whitens with subsequent applications to get the brightness one wants.

Again I am NOT an expert just a guy with a bit of experience.
 
Last edited:

BigLar368

Chirping
Jun 12, 2020
132
230
73
Southeast Texas
We used to paint our pecan trees with lime white wash in the summer to help with insects. Salt was a a key part of the mix. If we did not use salt they would yellow very quickly and eventually have mold growing on them. We also used a bluing agent to help keep the coating bright white.
 

janego

In the Brooder
Jun 29, 2019
4
31
37
rural France
I have not seen anything about using linseed oil with limewash, have done a fair amount of searching; that does not mean it would not work.

A few things that I do know about linseed:
  • It is old school and normally used as a finish on both wood and concrete.
    • With wood it is commonly used in "Danish Oil" which is mixed equal parts of BOILED linseed, turpentine (preferably made from pine) and vanish/polyurethane. In this form it is brilliant. The linseed is a protectorant in that it soaks into the wood, softens and preserves; the turpentine thins the oil and allows the whole mix to penetrate even more into the wood; the varnish acts as a hardener and protects the surface. Also because it soaks in it does not flake as it ages; when an additional coat is needed simply do a quick clean and re-apply, no sanding or other labourous prep required.
      • One caution a painter friend used it on exterior wood windows and it was horrid; would not dry then attracted dust which caused mold to develop. The problem was he used pure linseed not boiled.
    • With concrete it was/is used on floors as a finish and protector. In barns it was applied to neutralize the lime in concrete when new; lime will cause hooves to deteriorate so this was important for cattle that spend a lot of time inside.
It is the latter use that makes me cautious about mixing linseed with limewash. One uses limewash because of it's toxic nature against mites and other small nasties.

It is conceivable that linseed in it's Danish Oil use will deter critters in wood ON IT"S OWN without mixing with limewash. I use it on decks and other outdoor wood pieces with excellent results including slowing rot which results from water causing molds then attracting insects.

However, limewash is very inexpensive, linseed is not.

As to your "It is now dry, but very powdery and dusty " issue @janego - is it possible that your mix was too thick? The normal progression in using it is a light translucent 1st coat that whitens with subsequent applications to get the brightness one wants.

Again I am NOT an expert just a guy with a bit of experience.
Really interesting info, thank you.
 

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