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Plywood delamination


Chris Bernhardt
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Moisture, but heat helps it along. In climates where there's a lot of humidity, like North Carolina for instance, the stuff will break down sooner under similar conditions than it will in California, New Mexico or Southern Cal where the air is drier.

The glue is water soluble in most grades. Keep the plywood damp long enough and sooner or later the glue starts to break down.

ONE TEAM - ONE FIGHT!!!

Mike

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I never see delamination of plywood in dry conditions here in Texas. We get lots of heat with 150 degree attics for months on end and no problems. Ad moisture to the mix and it will wrinkle up quickly.

I agree with the others, moisture is the key but moisture acts faster with heat.

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. . . The glue is water soluble in most grades. Keep the plywood damp long enough and sooner or later the glue starts to break down.

I've always understood that if the plywood panel has a APA stamp that says "exterior" or "exposure 1" then the glue is fully waterproof.

- Jim Katen, Oregon

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. . . The glue is water soluble in most grades. Keep the plywood damp long enough and sooner or later the glue starts to break down.

I've always understood that if the plywood panel has a APA stamp that says "exterior" or "exposure 1" then the glue is fully waterproof.

- Jim Katen, Oregon

How long has the product been around Jim?

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. . . The glue is water soluble in most grades. Keep the plywood damp long enough and sooner or later the glue starts to break down.

I've always understood that if the plywood panel has a APA stamp that says "exterior" or "exposure 1" then the glue is fully waterproof.

- Jim Katen, Oregon

How long has the product been around Jim?

What product? Exposure 1 plywood with fully waterproof glue? I think it's been around as long as I can remember.

- Jim Katen, Oregon

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I checked on the APA site yesterday. They've been using resin-based heat-cured glues since the 40's and Exterior grade Exposure 1 is supposed to be waterproof. They used water soluble (caseine?) glues until the 30's.

I should have realized that; during WWII my father built PT boats out of that early resin based glue plywood.

ONE TEAM - ONE FIGHT!!!

Mike

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  • 3 weeks later...

On a plywood panel stamped "exposure1" or "exterior" the glue lines themselves are waterproof. If the product is manufactured correctly the glue lines will not fail due to moisture as they are a phenolic resin that polymerizes with heat and pressure during the laminating process.

If the glue line itself does fail, it is due to problems in manufacturing or occasionally allowable knots or open areas in the veneers that do not bond well. Both of which are hurried along with exposure to moisture.

That being said, in my years in plywood claims, the main cause of all delamination claims are exposure to moisture causing the wood fiber itself to break down. That is why even though the glue is water proof, it is important to protect the wood from moisture, especially the panel edges and ends. Moisture can enter the wood fiber and rot it or cause it to swell and pull apart from the other plies. Heat by itself will not cause delamination, but can hurry along the process when the panels are not protected. Proper installation using paint, sealants, and flashing will avoid the vast majority of problems with plywood delamination.

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Moisture, but heat helps it along. In climates where there's a lot of humidity, like North Carolina for instance, the stuff will break down sooner under similar conditions than it will in California, New Mexico or Southern Cal where the air is drier.

Mike

About 12 years ago when I was on the Space Shuttle program we were required to develop a new glue to seal the J slots at the solid rocket motor joints because of EPA environmental concerns. Thiokol came up with a glue and performed extensive tests in Utah with a final test on a full sized rocket at their horizontal test facility. Everything worked fine so it was approved for use on a vehicle.

I was on the post flight inspection team at KSC and when we got the first motors with the new glue back after launch and broke the first joint you could hear a collective gasp in the building. We had burn char very deep into the J seal joint, much deeper than any ever seen before. This meant the char was much closer to the o-rings that seal the joint.

After weeks of investigation the conclusion was that the glue worked well when tested in the dry climate of Utah but lost much of its adhesive power when applied in humid Florida.

The one lesson we learned over and over again is that no matter how well you research and test a system or component you are never going to know with 100% certainty how it will perform in the field. This holds true whether you are building houses or rockets.

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The one lesson we learned over and over again is that no matter how well you research and test a system or component you are never going to know with 100% certainty how it will perform in the field. This holds true whether you are building houses or rockets.

That is some truth right there........accelerated wear studies in the lab are nice, but the real R&D in building is done on the backs of the consumer in real houses.

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