coring w/ urethane foam sheet?

jonesg

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Feb 22, 2008
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wandering around home depot last nite, pondering how to core a molded hardtop on my T top.

I looked at the 1 inch polyurethane foam insulation sheets, the ones backed with foil. is this stuff polyester proof?

If so, I think this could be a great coring material, remove foil, score it and work resin putty in with a spreader. Anyone tried it ?
 

oops!

Supreme Mariner
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Oct 18, 2007
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12,932
Re: coring w/ urethane foam sheet?

hi jonesy....

the resin will chew right thru it
 

jonesg

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Feb 22, 2008
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Re: coring w/ urethane foam sheet?

I'm still gonna try it.
hahaha
 

jonesg

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Re: coring w/ urethane foam sheet?

Hey ya can't try it if you don't buy it.!

BTW, it works the nuts.!

I peeled the silver backing off a 10x10 inch square sheet,
slit into 1 inch squares with utility knife, not cutting through the blue backing on the other side, its slices very clean.

I placed it over a compound curve (couple of old tools on the bench) , mixed up some poly with cabosil, catalized and worked it into the slits with a putty knife, then pressed mat onto that and wet out the mat with straight unthickened poly resin w/ a hot shot of mekp, it got REAL hot and set rock hard after 10 minutes in the sun.
I did kinda slop a lot of resin on the matting.

The urethane I grabbed is spongey soft like extruded styrene foam, don't know if you would want to walk on it but for coring my roof its gonna be perfect. Absolutely no reaction with the resin.

So the plan is to use the whiteboard I was originally going to use for the roof as a mold surface, heres my plan,
cut whiteboard to outline to the shape of roof,
apply modelling putty around the perimeter to form a molding lip,
wax/polish x4 and lay up 2or 3 layers of mat,
apply the foam with poly resin putty ,
after it sets, peel the backing off the urethane foamboard...
and then mat/resin over the whole shebang.
Install some hard mounting points for mounting to the steel tube framework. (ply?).

Pity I don't have any more resin now.:rolleyes:
 

MushCreek

Petty Officer 2nd Class
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Jun 20, 2009
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150
Re: coring w/ urethane foam sheet?

Urethane foam is fine with polyester- that's what they make surf board blanks out of. It's styrofoam that melts with polyester, but you can laminate it with epoxy resin.
 

ondarvr

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Apr 6, 2005
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11,527
Re: coring w/ urethane foam sheet?

The only problem you'll run into is how weak the foam is, for a non stressed part it may be OK, but for anything else it won't work well. Even if you increase the laminate thickness to make up for the lack of strength in the foam, the foam will still fail causing problems.
 

jonesg

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Feb 22, 2008
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7,198
Re: coring w/ urethane foam sheet?

exactly my thoughts, this could only work in a deck if the run was short and w/ vertical braces or honeycomb, but on sides or tops where no-one can walk its going to be fine. Theres no way to get on my top anyway.

the original coring in my deck was honeycomb cardboard, it had flattened out.
I wet some out with resin and it was quite good, apparently they didn't wet it out properly with resin when new and it collapsed over the yrs.
Never heard of cardboard honeycomb coring. Probably just another idea that went away.
 

oops!

Supreme Mariner
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Oct 18, 2007
Messages
12,932
Re: coring w/ urethane foam sheet?

good 4 u bud....add another material for the boat building list...:)
 
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