glassing over stryofoam

I plan to make a prototype of a new small boat in the Spring. The boat has a few unique features and lots of rounded edges. It is approximately 11 feet long. I have found a supplier who will sell me 2 large blocks of styrofoam which I will cut and shape and then cover in fiberglass similiar to the homemade surfboard technique. Just wondering if anyone has tried this method before on a similiar project and/or any suggestions welcomed.

 

If you use epoxy it is OK. Otherwise you need to put a layer of paper glued on to keep the styrene from disolving the foam

 

Ron; That method is in frequent use. Perhaps not the easiest or best way to build a boat but it does indeed work. Styrofoam tends to absorb quite a lot of resin on the first laminate ply. Try to find foam that has the smallest cells. There are numerous grades of styrofoam. Be picky about the one that you choose and your job will easier and have more skin strength. By all means avoid polyester resin as it will disolve styrofoam in a heartbeat. Epoxy costs more but in the end it is worth the difference.

Good luck with your project.

 

I have heard that a layer or 2 of regular latex house paint(interior or exterior) will protect the styrofoam from polyester resin, though I have not yet tried it for myself. Get the mis-mixed batch from your local home improvement store to save mucho dinero.

 

....and test it first on a sacrificial piece.

 

...and God help you if there is even a pin hole for the resin to penetrate through!

-Tom

 

If you want a good bond you should vacuum bag it or apply pressure over the entire surface in some other way. You also need a porous interlayer so the air can get out from between the vacuum bag and the glass cloth when you apply the vacuum.

The foam blank also adds a lot more weight than you think. Will roughly double the weight for something lightweight like a sailing dinghy. Not so significant if it is for a heavier powered hull. There is some advantage if you can leave the internals with some hollow.

Rick W

 

As Gonzo wrote, there's no problem if you use epoxy.
I made a smaller object (bow extension) over a styrofoam core. Painted the foam to seal it against the polyester resin and succeeded in glassing. But while the resin hardened, fumes found their way in and made the core shrink considerably. On an 11 ft long object, something is bound to go wrong.

 

Just a thought for the 'pot' to keep it bubbling - would a final coat of plaster over the styrefoam (which can be smoothed off and faired easily) provide a good surface for the fibreglass ?

Perhaps a few coats of varnish or similar would make the job of cleaning up the insides a bit easier.

 

Thats what I used

Blue styrofoam
Slurry of epoxy and qcells to seal and reduce amount of resin drank
Epoxy and glass over top

 

Styrofoam is quite weak and the fiberglass skin may be prone to delaminating from the foam in areas where loads are applied. It might be better to vacuum bag a thin layer of higher density foam onto the styro blank to give the whole thing a better chance of survival.
I would also use epoxy without question. It doesn't cost much more but is so much stronger and gives a much better result.
11ft is the length of a moth. Is that what you're building?

 

No it is not a Moth - it is a totally new design with a few unique features, I have not seen anything like it. I am going to go to the Toronto boat show next weekend to see if there is anything like it being produced but I have searched the internet and have not found anything like it. Eventually I would like to have a low priced version made in plastic but initially this styrofoam/fiberglass version might be the best way to do a prototype. Do you have any thoughts as to the thickenss and the number of layers of fiberglass over the styrofoam?

 

I like the idea of plaster over the styrofoam but how do you think water will affect the plaster or is the assumption the fiberglass would keep the water from getting to the plaster?
Re: varnish - are you suggesting the varnish goes on to the plaster?

 

We use to put newspaper with white glue on styrofoam for surfboards. Never had any of the problems people are talking about. Make sure everything is well covered.

 

Great idea. thanks. Ron S