Powder on FRT plywood

[Inspectorjoe]

This was in a 22 year old center unit townhouse. It had soffit vents but no upper vents. What I assumed was FRT plywood (couldn't find anything stamped on it) had a white powder matching the grain of the wood. It didn't appear at all on the adjacent flakeboard sheathing.

I don't recall ever seeing this before. I'm guessing is powder is the chemical(s) that was used to treat it. Anybody know if this is a problem?

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[Brandon Whitmore]

I don't know if it's a problem, but saw that on a new construction townhouse last week.

Here's an excerpt from Inspectapedia: FRT plywood is produced by pressure treating plywood with fire retardant chemicals. During the mid 1980s, the search for lower hygroscopic (i.e., less moisture-absorbing) chemical compounds to treat plywood resulted in a change from ammonium sulfates that cause fastener corrosion to ammonium phosphate salts. Ammonium phosphate salts with additional treatments using buffers, such as Borax, and organic and less acidic chemicals were developed to decrease fastener corrosion and raise the threshold temperatures of fire-retardant materials.

http://www.inspectapedia.com/structure/FRTplywood.htm

[Scottpat]

This was in a 22 year old center unit townhouse. It had soffit vents but no upper vents. What I assumed was FRT plywood (couldn't find anything stamped on it) had a white powder matching the grain of the wood. It didn't appear at all on the adjacent flakeboard sheathing.

I don't recall ever seeing this before. I'm guessing is powder is the chemical(s) that was used to treat it. Anybody know if this is a problem?

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It does not look like FRT plywood (most of what I see has a very dark color to it), but it looks like a chemical leaching out of the wood.

[Marc]

What is 'FRT'?

Marc

[Scottpat]

What is 'FRT'?

Marc

FRT or flame resistant plywood.

http://www.inspectapedia.com/structure/FRTplywood.htm

[hausdok]

The OSB next to the plywood is telling you that there'd been a problem and some plywood was torn off and been replaced with OSB. They probably stripped off some fungi-infected plywood and treated what remains with some borate-based fungicide and what you're seeing is the borate.

If there's no upper ventilation I hope you told them to get some or they'll be repeating the exercise some time down the road.

ONE TEAM - ONE FIGHT!!!

Mike

[John Dirks Jr]

I had seen similar in the past. Here's that thread.

https://inspectorsjournal.com/forum/top ... IC_ID=9557

[Inspectorjoe]

Thanks John, that's it. I didn't do a search here, because I read every post and have a pretty good memory for what's been discussed ..... at least I thought I did.

Brandon, thanks for the Inspectapedia link. A Google search had already taken me there, but I couldn't tie what I saw to the info there.

Mike, the roof was original, as well as the sheathing of course. Seeing no upper vents while I was outside, I was certain when I got into the attic, I was going to find lots of mold on the north side sheathing. I couldn't believe it - nothing. The only moisture signs were slightly rusty roofing nails. The 22 year old 3 tab roof was in remarkably good shape too. I was actually really uneasy coming up with a recommendation for the roof. Common sense said that it's time to replace it, but aside from a few nail pops, it was perfectly fine. I did of course, recommend adding upper vents.

Thanks everybody.

[Brandon Whitmore]

The OSB next to the plywood is telling you that there'd been a problem and some plywood was torn off and been replaced with OSB.

Mike,

That sheathing is on a townhouse. Don't they usually run OSB in the field, and FRT plywood on the edges abutting neighboring units? Since this is in a center townhouse, I would bet that there's OSB in the middle, and plywood at the ends.

[Inspectorjoe]

That was the setup.

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