PL Premium

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PL Premium

Postby QueticoBill » Sun Feb 12, 2017 2:46 pm

PL Premium seems to be the most popular choice here for adhesive for rigid foam, even over the PL 300 designed for foam. If you've built an "average" size teardrop with ply-foam- ply walls and roof, any idea of how much PL you used? A case of 28 ounce tubes? More or less?

And if you've squeezed and notch trowled, which would you do next time?

Thanks!
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Re: PL Premium

Postby rruff » Sun Feb 12, 2017 4:42 pm

I heavily texture the foam with a carpet seam roller and use a fine notched trowel to spread the adhesive evenly on the surface. I used more than I expected, but I don't think it's too bad, came to ~.12 lb/sq ft per side gluing to luan. If you are gluing foam to foam I'd expect a little more.

So both sides would be .24 lb/sq ft. The big tubes are 28 oz or 1.76. So for instance if your trailer is 200 sq ft it would be 200 x .24 / 1.76 = 27.3 tubes.

I'd encourage you to test the application yourself though and see what you come up with.

BTW, IME PL300 isn't nearly as strong. I have no idea why the manufacturer advises against PLP for foam, since I've never heard of anyone having an issue with it.
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Re: PL Premium

Postby KCStudly » Mon Feb 13, 2017 8:21 am

rruff wrote:IME PL300 isn't nearly as strong. I have no idea why the manufacturer advises against PLP for foam, since I've never heard of anyone having an issue with it.

My guess is that it has to do with the typically intended application, hanging foam board on vertical gypsum or concrete walls prior to having another wall board material fastened down over it. The foam will swell and contract at a different thermal rate and the rubbery consistency of the PL300 will allow for more give, especially when applied as per the MFG's instructions (i.e. thick vertical beads placed 12 inches apart). My interpretation of the instructions is that they really only intend for the PL300 to "baste stitch" the foam board in place, that the spacing and thickness of the recommended beads allows for a chimney affect that allows the adhesive to cure, and that the long term fastening is by what ever mechanical method is used to secure the overlay.

PLP, on the other hand, cures much harder and may not result in a very flexible bond.

Either method troweled or spread on will likely run into curing issues due to creating and airtight seal around the perimeter before the center has cured. (I used kerf chimneys in my foam to combat this.)
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Re: PL Premium

Postby rruff » Mon Feb 13, 2017 12:02 pm

KCStudly wrote:Either method troweled or spread on will likely run into curing issues due to creating and airtight seal around the perimeter before the center has cured. (I used kerf chimneys in my foam to combat this.)


What's a kerf chimney? For foam to foam bonding it makes sense that air would not get to the center of a large panel, but with plywood I think the air goes through the wood. Cured readily on my small samples anyway.
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Re: PL Premium

Postby KCStudly » Mon Feb 13, 2017 1:46 pm

On my hatch and front radius, where I laminated two layers of 3/4 thk foam on to the inner plywood skin, not only did I kerf the tighter radii of the profile to about 9/16 deep (made saw cut reliefs to allow it to bend), I also kerfed 1/4 deep everywhere else so that that the troweled PL was fully ventilated. Then, later, I when back and stuffed little strips of foam (ala the foam ear plug method) int o the ends of the kerfs to seal them up. You can see pictures here. Also, that's about the same time I experimented with the foam dust/TB2/vinyl spackle mixture.
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Re: PL Premium

Postby yrock87 » Mon Feb 13, 2017 5:39 pm

I used three different glues for my foam to ply bonds. PL premium (5 tubes total) Gorilla Glue (1.5 32 oz bottles) and 3M Fastbond (1 gallon) I think that the Gorilla glue was the easiest to work with. although the PL Premium may have provided a better bond (just an impression when applying. I have had no issues to support this impression) I gouped on and then used a fine notched trowel to spread out in both cases.

The 3M fastbond is a water based contact cement that I was not impressed with. it was the most finicky, the most expensive, and I was able to get some bond failure in test pieces.

I used TB2 for all the wood to wood joining, specifically internal frame to ply skin. I used nearly a gallon of TB2.
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Re: PL Premium

Postby rruff » Mon Feb 13, 2017 6:02 pm

KCStudly wrote:On my hatch and front radius, where I laminated two layers of 3/4 thk foam on to the inner plywood skin, not only did I kerf the tighter radii of the profile to about 9/16 deep (made saw cut reliefs to allow it to bend), I also kerfed 1/4 deep everywhere else so that that the troweled PL was fully ventilated.


I see, that should work well. :thumbsup:

Now that I've found a cheap source for epoxy (US Composites, ~$55/gal shipped) and silica thickener (System 3 Amazon $11.48. 5 qt), that might be the best way to go for panel gluing. No need to worry about air.
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