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gaps at the top of slip straw walls and around wood

 
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My slip straw walls are around 7 years old. I have a yearly problem with gaps opening at the tops of walls and some but not all vertical wood to plaster seams. Most years I will mix up a small batch of plaster and repair this gap only to have it open back up by the winter time making for a cold and drafty house. My typical repair mix is pure clay to three parts sand with some fiber. It is hard to say if this change is due to humidity changes or an ever shrinking wall. I should mention the walls have an earthen plaster. I have tried the burnt sand mastic recommended in one of those books it is a real ass pain to put up. I'm thinking of re coating the walls with a lime plaster. Does anyone have any advice? Will the lime perform better?

thanks
 
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Your mix probably has too much expansive clay in it and is too dense causing it to expand and contract alot in winter, store and release alot of heat, cold, vapor. Thermal and vapor cycles will cause clay to crack, and the mating wood does so at different rates. After repairing the earth plaster again, I'd scratch coat with a less dense more fiber insulating mix with just enough lime to hold more fibers together and very little sand. Lime self heals small cracks, holds less vapor and heat than most clays. The insulating lime plaster will hopefully protect the earth plaster from seeing too much expansion and contraction. Finish coat with more lime. Wet it often as it cures over a month or so.
 
joe craw
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Thanks for the advice! I guess I'll need to wait for warmer weather to do any lime work. Do you have any advice for trimming around windows and covering wood. I have read about using drywall mesh but have no experience with it. Also I assume I will need to score the existing plaster to get a good key for the lime coat. One more thing I have been using human hair in my lime plaster. Is this acceptable?

thanks again
 
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hey joe ... i ve read that people use strips of burlap to cover seams (where different planes/materials meet each other) and to plaster over wood.
they often use a mixture of clay and flour-paste to glue the strips to things.

but thats was for use with earthen-plasters, so i don t know how that would perform with lime.
 
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