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Discussion Starter · #1 ·
I'm scratching my head over a situation that I thought I might ask about here:

We have a storage shed in our backyard that was experiencing some rot in the 2x4's and plywood that made up its floor. As a quick-and-dirty solution, I cut out the old wood, used pressure-treated 2x4's to replace the framing and 1/2" MDF instead of the plywood. Although MDF is more typically used in interior applications, I figured it would be less susceptible to rot than plywood would be. After installing this I put some plastic bins, buckets, etc in the shed for storage.

A month later, I was moving some of the bins and noticed a light green powder on the MDF under them. I pulled all of the stored containers out of the shed, and found the powdery material was under all of them. At first I was concerned this might be a mold, so I cleaned out the shed with diluted bleach. Now, however, I'm thinking maybe it wasn't mold but rather something leaching out of the MDF as a result of exposure to moisture (it only occurred under bins and buckets and so on which kept humidity trapped).

Does this leaching scenario sound like it makes sense? Would it be best to seal the MDF with paint? Thanks for any ideas.
 

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MDF will swell and flake like when it gets wet. Sealing with paint is probably a good idea. MDF is probably not a good solution anywhere where there is moisture but its done so might as well stay with it. If you paint it with water based paint you'll get almost a texture type grain raised on it. Us a sealer if you don't want this.
 

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Discussion Starter · #3 ·
Thanks, Jack. I woudn't call this just swelling and flaking -- it's a pretty distinct powder collecting on the surface.

If it seems in the end like it's not working, it wouldn't be all that time-consuming to replace the MDF. Is there a material available in a ~1/2" sheet that would be more appropriate here?
 

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I would suspect this to be

some type of mold spore. MDF (paper pulp and resins) has no outside uses. Remove it and refloor with 5/4 pressure treated deck boards or pressure treated plywood.

Ed
 
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