molding straw in test cob

Hi

Im experiementing with the clayish soil under my feet to see if i can build with it. Ive been doing test 'bricks' of Cob to find out the best ratio of soil/sand/straw

since its cold and wet outside I have the bricks inside for drying. inside temperature is around 15 degre celsius.

all the bricks with straw in them now has mold on the straw. It is 5 days since I made these test cob bricks.

Any tips or troubleshooting?
did I mix the cob too wet or is indoor humidity + heat just good moldconditions?
I took the straw directly from the storage next too the sheep so it shouldnt be moist. but that is a very airy storage. it has roof and walls so it doesnt rain on the straw but it is in no way airtight.

I will appreciate any tips or troubleshooting

I think it's just bad straw. warmth + wet + *mold spores* = mold. the mold probably came in on your straw from the barn.

buy a new bale - of straw, not hay - , keep it really dry and clean, and use that.

Tys

Ok, thank you!