"I'm sure Greg is right. The PFE documents did refer to "curling,
checking and cracking," but as it happens the shop sketch I saw did
have about a 1/8 inch gap between the plywood sheets. Is that an
inadequate gap, Greg? That gap was in addition to the T-section metal
seal strip (with the "leg" of the T down between the sheets).
"As for it being an "installation error," I have no doubt that
PFE followed the instructions of the Douglas Fir Plywood Association --
whatever they may have been <g>.
Well, let's see we use and 1/8" gap and then we fill that gap with a piece of "TEE" section sheet metal and the gap was in addition to the width of the metal??? HMMM something doesn't add up and I wonder if it was as confusing to the shop crew as it is to this reader? So was the gap intended to be greater than 1/8", like say ¼" and then the metal? I can see that there might have been an installation issue, but the only way to be sure is look at the drawings, then compare that to the practice...It's diffecult to picture as the metal strip would have to "float" or the plywood would have to "float" the two couldn't be rigid UNLESS the gap was properly maitnained. Gone are the cars and the verifaction, regardless the experiment was not repeated by PFE.
If the veneers held across the panel and large sheets of veneer didn't come off it was not a production issue with the plywood. Generally, if there is an issue with a glue line on plywood it was done at a given point and restricted to a few sheets not a complete run or shift produced. But without the evidence we will never know for sure. Remember, these types of plywood panels were not made just for the railroads use but marine use or cooler/freezer use where moisture was constantly present and I can tell you they did last. Again, we would have to put all the pieces of the puzzle together to see what was the cause of the failure. As Dennis mentions perhap the experiment would have worked if the plywood was sheathed with a moisture resistant coating as a cover veneer like those used by sign painters(we call these overlays and they are usually resin soaked paper). These are commonly used today as concrete form and other uses. We certainly know more today about plywood then they did then and most application errors are avoided. This reads to me as an issue that was caused to the plywood when it was installedt that caused restricted expansion and the veneers buckled across the face veneers.
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