Chris Bernhardt Posted April 30, 2009 Report Share Posted April 30, 2009 What causes plywood roof decking to delaminate? Is it moisture or heat? Chris, Oregon Quote Link to comment Share on other sites More sharing options...
Jerry Lozier Posted May 1, 2009 Report Share Posted May 1, 2009 What causes plywood roof decking to delaminate? Is it moisture or heat? Chris, Oregon usually moisture related...lack of ventilation/ condensation, don't know about heat...although excessive heat can cook asphalt shingles, I don't know that it would cause delamination Quote Link to comment Share on other sites More sharing options...
kurt Posted May 1, 2009 Report Share Posted May 1, 2009 I've seen the old 3 ply junk delam from (what I think is) heat. Of course, that stuff was worthless. Quote Link to comment Share on other sites More sharing options...
Bill Kibbel Posted May 1, 2009 Report Share Posted May 1, 2009 Is it moisture or heat? Heated moisture. I use steam to soften glue. Quote Link to comment Share on other sites More sharing options...
waynesoper Posted May 1, 2009 Report Share Posted May 1, 2009 Moisture. Hot or cold, Moisture Quote Link to comment Share on other sites More sharing options...
hausdok Posted May 1, 2009 Report Share Posted May 1, 2009 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 Quote Link to comment Share on other sites More sharing options...
inspector57 Posted May 1, 2009 Report Share Posted May 1, 2009 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. Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted May 1, 2009 Report Share Posted May 1, 2009 . . . 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 Quote Link to comment Share on other sites More sharing options...
hausdok Posted May 1, 2009 Report Share Posted May 1, 2009 Hi Jim, You're right. I'm all wet (Pun intended). OT - OF!!! M. Quote Link to comment Share on other sites More sharing options...
Terence McCann Posted May 1, 2009 Report Share Posted May 1, 2009 . . . 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? Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted May 1, 2009 Report Share Posted May 1, 2009 . . . 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 Quote Link to comment Share on other sites More sharing options...
hausdok Posted May 1, 2009 Report Share Posted May 1, 2009 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 Quote Link to comment Share on other sites More sharing options...
BigRob Posted May 22, 2009 Report Share Posted May 22, 2009 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. Quote Link to comment Share on other sites More sharing options...
bjloden Posted May 25, 2009 Report Share Posted May 25, 2009 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. Quote Link to comment Share on other sites More sharing options...
kurt Posted May 25, 2009 Report Share Posted May 25, 2009 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. Quote Link to comment Share on other sites More sharing options...
Jerry Simon Posted May 25, 2009 Report Share Posted May 25, 2009 It's like when I did a job for a gentleman a few years back...his job was selling composite deck materials. I asked him how the stuff will hold up over time. He replied "We'll find out". Now I hear composite deck materials are starting to have problems... Quote Link to comment Share on other sites More sharing options...
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