a ? about fiberglassing over foam

Have any of you got any ideas or tricks to be able to fiberglass over foam, without it disentigrating the foam ???, i have heard of people coating the foam first with latex paint, or a water based polycrylic, (but i haven't had much success with either of them). Any ideas ???. ( also... i am using poly resin, not epoxy ). Thanks.

 

Use the correct foam for the job, or use epoxy.

Depends on what you're doing.

 

I just thought someone may have come up with a solution or way to use the rigid blue or pink foam for projects or items like dock boxes or live tanks etc., and then be able to cover them with fiberglass, have you got any barrier coat suggestions ???. ( maybe using a wax or wax paper would work, but it doesn't really bond to anything ).

 

I was cut short in answering the question.

You can buy polyester resin that is compatible with normal white EPS foam.

You can get this from Composites One.

http://www.ccponline.com/tds.asp?id=538

 

Thats cool, thanks, that may be just what i am looking for. do you have any idea of the cost per gallon ?, i think i am paying about $26 a gal. now for the regular poly resin.

 

It will cost more and the minimum amount is 5 gallons. This is a specialty product and costs more due to higher raw material prices and the low volume being made.

 

I did what you want to do. I bought the pink foam from Home Depot and encase it in fiberglass. However, I used epoxy resin. No need for special foams or special resins.

 

Hi Ike, how has the epoxy fiberglass held up on the pink Home Depot foam? I have been looking into using this foam as the core in a sandwich construction for a small dingy, but keep reading about delamination issues.

 

As far as I know it's fine. On my boat its buried under the sole so without pulling up the sole I have no way to see it. But since it was bagged so that water can't get to it, I believe it's doing fine. I don't know how it would work as a core. It isn't a structural foam, and is only 2 lb density. Plus that, it's a styrene foam. I haven't seen anyone using styrene foams in sandwich construction. Usually it's polyurethane or polyvinyls

 

Most of the Rutan experimental aircraft used extruded polystyrene for the wings and other parts of the structure. Some of them were rated for +-9g loading. Of course Rutan knew how to design with this stuff in mind, so there are strong fiberglass shear webs incorporated and the wing spar caps are several layers of uni tapering from thickest in the center to thinnest at the wingtips. Most of the aircraft are still flying. Some were scrapped when embedded hardware for the removable wings developed corrosion problems which would have required new wings to be built.

There were a few that broke up in flight because the builder did not follow the laminate schedule given to hold on the wingtips, for instance. So it is possible to make durable things from extruded polystyrene, especially when you plan to use a hotwire to cut very accurate shapes, like airfoil sections. But you need to be careful, it is a low density foam. If your laminate is too thin, and you are going to stand on it, a human being on 1 foot is a fair amount of pressure and potentially bending stress. One layer of bid is not going to do as a laminate. Especially so with light fabrics. Take a bit of a look at how they make surfboards, they are of course not intended to last forever but will give you an idea at the minimum strength end of the scale.

 

Do not build with low density xps foams anything really important.

It works fine for say a livewell or cooler, but a big mistake for hulls. The shear strength is simply too poor. The hull can't take any punishment like bumping bottom or a dock. It will delaminate.

For something like a livewell, a bit of delamination is not the end of the world and another layer of glass can be added if it delams creating a functionally solid layup in repairs.

Another way to leverage foam is with plywood. A light plywood sheathing with foam glues makes the stuff pretty strong; the shear issue is mitigated because of the strength of the 'skin' of plywood.

There are factual documentations about shear ratings for various cores here. I am not in the mood to search for them.