Cyd Burns

Thanks, I will try adding the borax just in case and do some test patches.

I know it looks like mold from the pictures, but up close it really doesn't. It seems to be more a property of the clay as it dried. Would love to hear ideas on that.

Thanks Gerry!

The second picture with all the black is the original wall color after a single clay coat. The first is the current state of the walls.

After the first coat, we started using a different clay source for the subsequent layers. The first coat came from a pond excavation project and the second was clay on the same property but from about 500 yards away and more surface level. To the naked eye they looked quite different.

It is definitely possible that it is mold. I have had some doubts because up close it is very dry and doesn't seem to correspond to wet spots or ambient moisture. It's pretty hot and dry where we are so don't usually have mold problems.

My current theory is that it is some kind of mineral in the mud oxidizing but have found no other stories of this happening.

Very open to ideas and suggestions! I am wanting to do a finish coat with either white clay or milk paint and am curious if the black will come through that as well.

Hi All,

I am searching the internet with a specific issue that has some up in our slip straw building and haven't seen an answer yet. When we did our first coat of mud plaster over the slip straw, the walls dried to a patchy black. After applying several more coats of a clay, straw, sand combo, the walls are mostly brown but black spots continue to appear. It is possible to sponge them over but they tend to reappear in a few weeks. Any ideas what could be causing the blackening?