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substance on attic sheathing


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This house was built in 1983. It has had at least one new roof covering and much of the original plywood was replaced with OSB. On the remaining original plywood was this white substance. It looked like salt. It was grainy and hard like that and on most pieces it followed the grain of the plywood. It has been falling down and could be seen sprinkled around on the insulation and the top of the hatch cover.

What is it? Is it a by product of the wood treatment? Maybe FRT?

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I think it will attack the organisms that are most vulnerable to it first. It might be some kind of wood rot fungi that the species of wood that those surface flitches of those particular pieces of plywood are most vulnerable to.

ONE TEAM - ONE FIGHT!!!

Mike

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I was once told by a contractor that that is concrete over spray or the like. According to him that is very common at a construction site (like the stack of sheathing is next to a concrete mixer).

But a word of caution on this, this same contractor also told me it's a common practice of his to use lintels as a ramp from the street to curb.

But yes, I once went into a crawl with a mold and moisture guy on my heals and we discussed it a bit and he said yes it is mold. He gave me the probable type but words with more than 15 letters in them don't stick in my head too easy.

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It's the organic salts leaching out of the fire-resistant treated plywood (FRTP). It was installed in townhomes and condos throughout the 80s and early 90s.

Really? Man...I knew I was on to something. I feel better now, although it's helpful to get a scare now and then.

What causes the leaching?

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What causes the leaching?

Primarily moisture and it doesn't require "excessive" moisture to cause the leaching.

The salts used back then were highly hygroscopic. Inadequate ventilation, a bath fan blowing into the attic, a humidifier set too high are some causes of moisture condensing in winter. However, our mid-Atlantic summer humidity is all it takes to create what's shown in your first pic.

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Bill, isn't 1983 before the time of FRT? Around here, I first started seeing it in 1987.

FRTP was being marketed in the late 70s. 1980 is a common start date, listed in publications, for residential installations. I did litigation support for one of the first lawsuits and one of the communities being represented was built 1981-82.
And I've never seen it used for a single family home.
I was guessing it was an attached home 'cuz 2 of John's pictures shows a block wall adjacent to the area in question.
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Bill, isn't 1983 before the time of FRT? Around here, I first started seeing it in 1987.

FRTP was being marketed in the late 70s. 1980 is a common start date, listed in publications, for residential installations. I did litigation support for one of the first lawsuits and one of the communities being represented was built 1981-82.
And I've never seen it used for a single family home.
I was guessing it was an attached home 'cuz 2 of John's pictures shows a block wall adjacent to the area in question.

Its a townhome. 1983.

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It's the organic salts leaching out of the fire-resistant treated plywood (FRTP). It was installed in townhomes and condos throughout the 80s and early 90s.

Bill, do you have any written documentation supporting that? Could use it for my reports.

I first learned of it from one of the defendant's experts. He said that it happens when the product is installed where humidity nears 90%. With a high moisture content, the salts migrate to the surface and crystallize.

I've also read about it, but the files for that case are long gone. I had some papers and publications from the Forest Products Lab of the US Forrest Service that I think discuss it.

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  • 3 weeks later...

This house was built in 1983. It has had at least one new roof covering and much of the original plywood was replaced with OSB. On the remaining original plywood was this white substance. It looked like salt. It was grainy and hard like that and on most pieces it followed the grain of the plywood. It has been falling down and could be seen sprinkled around on the insulation and the top of the hatch cover.

What is it? Is it a by product of the wood treatment? Maybe FRT?

Click to Enlarge
tn_2009517165035_HPIM6457.jpg

72.65 KB

Click to Enlarge
tn_2009517165211_HPIM6462.jpg

59.88 KB

Click to Enlarge
tn_2009517165233_HPIM6466.jpg

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John, you left out the most important detail... what did it taste like?

Seriously.. I'd guess it was probably a mold/fungus and recommend further evaluation by a qualified mold professional. Did you see any stains indicating a leak into the attic? Was the bathroom vent fans emptying into the attic? Can't say I've seen anything like that, although I do sometimes see black-ish colored mold on attic sheathing often from bathroom fans venting into the attic.

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