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DuncanD

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I have a 8' x 12' office that is a kit shed in the back yard. I purchased the house and the shed has a mold issue that is from below. I have removed the carpet and will remove the plywood subfloor to expose the treated 4x4s that form the base of the structure. Which right now sits on the ground which is covered with gravel. I plan to raise the structure and place it on 4" thick 8"x16"cement blocks to prevent moisture transfer. And treat the 4x4s for mold. My question is four-fold:
1) I am not yet 100% sure the mold is only in the floor. Is there a way to locate mold in walls without demo in the case the mold is from an external leak that isn't showing/testing as moisture on the inside?
2) What would you treat the 4x4s with? RMR-86 was recommended.
3) I also considered cinder blocks with a cutout that the 4x4 would sit in, this would result in a lift height of 6" vs. the 4" for the solid blocks. What recommendations do you have for what I should put under the shed to make it more secure in an earthquake so it doesn't slide off the blocks, and what is best to prevent moisture transfer?
4) What should I put on top of the 4x4s if the space inside is heated and cooled with minisplit with outside temp range from upper 40s to occasional high 80s (I am near ocean/fog so less temp range). The 4x4s will continue to be open to the air to allow circulation from the sides of the structure. Should I put a vapor barrier on top of the 4x4s before subfloor and flooring? Ideally I would also like to put some rigid insulation in over the subfloor and top it with luxury vinyl planing, but have concerns about the moisture transfer the temp difference will create.
Thank you for your guidance.
 

moldguy

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For locating hidden mold without demolition, professional moisture meters and thermal imaging cameras can be highly effective at detecting potential problem areas - you can learn more about comprehensive mold inspection equipment here. For treating the 4x4s, while RMR-86 works, I'd recommend a EPA-registered fungicidal coating that both kills and prevents future growth, followed by a moisture-resistant sealant. For the foundation, I'd suggest the 6" cinder blocks with cutouts as they provide better elevation and ventilation - secure them with construction adhesive rated for exterior use and consider adding adjustable post bases anchored to concrete footings in your high seismic zone. As for the floor assembly, definitely install a 6-mil polyethylene vapor barrier over the 4x4s, then add your subfloor, rigid foam insulation (minimum 1" thick with taped seams), and finally the LVP - this layering will help manage both moisture and temperature differentials. Have you considered installing a small powered vent or dehumidifier to help maintain optimal moisture levels once everything is rebuilt?
 

Fitter30

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I'd call tyvek. Plastic doesn't breathe. 1 800 448 9835
For mold Concrobium
RH travels from high to low
 
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