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Old Dec 12, 2003, 03:35 AM
splatman is offline
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which is better for foam sheeting---3M 77 or probond?


Have a big can of the old-formula 3M 77. Should I use this or probond for sheeting a large foamie?



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Old Dec 12, 2003, 03:47 AM
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ProBond is better, different. While the 3M leave no time to reposition the skin (tacks instantly) ProBond allow this as its gluey for a while. Cure time about the same.

ProBond also expand a little so you get bettet skin contact. Last plus is it wont wear of age or hot/humid conditions. 3M can delaminate if left direct in the sun for too long.
Old Dec 12, 2003, 07:56 AM
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I whole heartedly agree with Haldor. I actually lost the washout angle on a wing panel. Was fine when built, then later relaxed to nuetral. Caused some intense moments..

Steve
Old Dec 12, 2003, 08:05 AM
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Thanks for the advice, gentlemen! I will invest in a bottle of probond. Will this work without vac-bagging? I intend to put wieght on the wing blanks (lined with wax paper). Should i put the PB on the skins or foam?
Old Dec 12, 2003, 08:08 AM
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Apply the PB to the skins. A very thin layer is all that is necc. Spread it thin with a plastic card. You only need to wet it.

Steve
Old Dec 12, 2003, 09:41 AM
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Do a couple of tests first


PU glue works well but I needed a little practice. I used Gorilla Glue since I've seen reported that it doesn't foam as much. My first test was a thin layer on balsa squeegied pretty well and some white beaded FOME with no added water. I didn't care for the amount of adhesion. It stuck very well to the balsa but didn't penetrate the FOME well.

Second test was a more generous layer of PU (didn't squeegie it as thin) and some water on the FOME. It stuck well but lifted the wood a bit even though it was weighted during cure.

Last test was a well squeegied layer of PU on the wood and a sponge dampening of the FOME and I got great adhesion on both.

BTW, all tests were also done at the same time with 1/64 ply. I cut the FOME down layer by layer until I got to the glue joint to see what was really going on.

Very instructive and only took a few minutes to set the tests up.

jtm
Last edited by Jim Miller; Dec 12, 2003 at 01:23 PM.


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