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Old 10-17-2010, 10:55 AM   #173 (permalink)
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Originally Posted by Weather Spotter View Post
This might have been covered, but what thickens is the foam?
I normally do not use an expanding foam, like Great Stuff Foam. Why? I have noticed that this foam continues to expand for some time. It was used in the areas of the old motorcycle fairing, and in the hot, summer sun, areas of the fairing bubbled slightly and distorted the paint job.

Now I use expanding foam in areas where if it does expand slightly later on, does make much difference.

Originally Posted by Weather Spotter View Post
...I can not seem to find anything over 1" think and that is blue Dow board....
The foam I used was Owens Corning Foamular, found at Home Depot. A 2" thick, 8Ft board was about $20, and this is half price compared to the blue board that was used on the motorcycle fairing over 15 years ago, so the price has come down over the years.

Originally Posted by Weather Spotter View Post
... I do not think that will work well....
It really depends on how you design it.

But the two inch board is actually 4 times stronger in bending strength compared to the 1" board, and the two inch board is only slightly heavier than the 1" board after glassing both sides, and is much stronger and resistive to bending forces.

The objective of a composite is to simply have the filler material (foam) hold the two outer layers apart (fiberglass) at a constant thickness. Some people claim you can lighten your composite even more by removing part of the foam core when finished, but I think that the foam adds so little to the weight to leave it intact after completion.

I have had issues glueing two thinner boards together to make a thicker board, so maybe my technique is not the best, but I use a thin layer of resin to bond them together, after sanding both surfaces to clear-off the shiny finish. The subpar adhesion has shown up where the two layers get sanded down and "feathered", and then I discover that the bonding process is suspect.

I have not tried expanding foam to bond the two together as it needs air exposure to expand, and there is no air between the two boards to allow this to happen properly. If there is air, then there are also air gaps, and that is not good regarding mechanical strength.


Last edited by 3-Wheeler; 10-17-2010 at 11:06 AM..
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