glassing over stryofoam

There are polyesters that are compatible with EPS foam, Styrogaurd works well, so it is an option.

 

Ok so epoxy (unthinned) can go on Tv packing polystyrene, but then you have to continue with epoxy because polyester wont go on top of epoxy.

BUT what if you used polyester resin on top of the epoxy while it was still drying, say 2 hours, would you get a molecular bond, if this was so one could continue with polyester resin.

 

The chemistry is too different, sometimes the uncured epoxy will keep the polyester from curing correctly. But like I said in the previous post, polyesters can be used, there are special formulas for this purpose.

 

27 years ago I made a windsurfing board with epoxy and glass fiber on a polystyrene core. It was never good as a windsurfing board; It needed to immideately get up on plane and I wasn't good enough to start that way. It's mostly been used by children when playing in the water. It's still holding up well in spite of the abuse it gets on the rocky beaches. Not a single breach of the epoxy/glass skin and no delamination. It's stored outdoors, under a house, when not in use.

We were a few engineering students making ourselves windsurfing boards. Two of them were into chemistry and could get epoxy and glass fiber at low cost. We didn't prepare the styrofoam blocks in any other way than cutting to shape and sanding the surface. Efter that we just put the epoxy and glass fiber on in the usual way, without letting it cure totally between layers. No vacuum bagging or any other special tricks. I don't remember the surface weight of the layers or how many layers we used. The end result was a very light board compared to the commercially available alternatives at the time (that we could afford).

The key to long life is the UV-stopping paint on any plastic. For an 11' prototype I don't see any reason to use anything but epoxy. The possible savings with polyester + protection of the polystyrene core can hardly be worth the risk that you damage the core. According to the expertise you get a stronger skin using less epoxy if vacuum bagging, but it isn't necessary for your prototype if you don't have the equipment for it.

Erik

 

Erik - I'm surprised (and happy for you) with your success there. The plain styro boards I've seen without any higher density foam at the high load points have all got heel dents and many also delam at the dent location. Perhaps you are using a slightly higher density core or perhaps you are using more glass?
27 years ago would be 1983 - I'm not surprised you could make a lighter board than production ones back then. They were mostly rotomoulded plastic which is robust enough to survive cyclones but not really that performance oriented by today's standards.
If longevity is important then I would still recommend a thin layer of higher density foam or increasing the skin thickness to the point where compression of the styro is very unlikely. The latter option will be heavy, the former will involve more work and skill in building.

 

It was the chemistry students, not me, who arranged all the materials through industry contacts. At the time I didn't really bother with details like the density of the foam blocks. At least the chemistry students knew what they were doing, so it's probably correct as you say that the foam blocks were of a high density type suitable for the purpose.

Erik

 

What is the problem here guys? You keep figuring ways to use polyester over styrene foam. Plaster, paper, varnish, and whatever else. Just use epoxy if the body must be cheap assed foam. If the boat is to be worth a damn and the builder is determined to use foam, then for the sake of common sense and decent craftsmanship, use good foam such as Klegecell or a polyurethane foam at the least. In the final analysis the cost of material for a small boat like this is negligable when compared to the extensive labor that it takes to do the job. So use the best and most appropriate material you can find. Styrofoam is for making beer coolers not boats.

 

Beer coolers and boats are of the same family.

 

In my book, they're synonymous.

 

Eventually I would like to make this boat in plastic - for production. The styrofoam approach is to allow me to make a prototype on my own that will look professional and actually float so that I can test the concept.
Every edge is rounded which may make this method ideal. This boat definitely has a few unique features. So far I plan to use closed cell Expandable Polystyrene with a compressive strentgh of 15-20psi, cover it with epoxy and fiberglass cloth. I found a supplier who will sell me an 11 foot block of foam that I will carve.

 

Ron
I made a hull from foam but I used 1" thick sheets that were cut to correspond with 1" waterlines. It allowed quite good control over the shape. The flat pieces are cut to the waterline and then minimal shaping of the steps so they blend. Less carving by eye or template.

I tested this plug as a hull with a single layer of 200gsm carbon fibre. I did not vacuum bag it and I did not get good adhesion along the flatish sides. The curved bottom was fine. That is the reason why I suggested vacuum bagging. If you do not get good adhesion water will intrude and pump the bond causing gradual delamination. If you go to a total layup of about 800gsm with glass then the foam is really only acting as a former and not playing a structural role. You could remove the foam and replace it with some stiffeners if required.

There was a similar boat built with a milled foam plug that was very accurate but the milling was not cheap. That plug was covered in plastic to enable release leaving a shell using a total of 600gsm CF.

My foam boat is now a male plug. I have only use it once to pull a new hull.

Rick W

 

I do not anything about vacuum bagging..is it difficult?

 

do you have any pictures of your foam plug?

 

oh and what type of plastic did you use - is this something you paint or trowel on?

 

I used epoxy. You can pour it on and roll it in. I use a fine paint roller.

Vacuum bagging is not particularly difficult. It is usual to use peel ply on the epoxied glass, a breathable layer over this that allows the air to find its way out and a light plastic cover to provide a seal. This is taped to a table or back on itself if fully unclosed in one go.

It is best to practice the process before you set out on the job. You need to decide how you cut and lay the glass cloth to avoid creases. You can do say 4 layers of 200gsm cloth in one go. The first layer might be starting to cure before you finish but it will still be flexibble enough to pull down. Don't do it in really cold weather, hot weather or humid weather if you want a good job. It is probably best to do the bottom and deck at different times.

The black boat is the original plug with CF cover and the yellow one is the boat I pulled from the black hull.

You can use a vacuum cleaner to pull the vacuum but it is noisy for the few hours it will take to cure. I have also used foam rubber to apply even pressure on smaller parts just taped down. You can get little vacuum pumps for about $100 that are suitable. You do not need to pull a perfect vacuum. The vacuum is an easy way to get even pressure over a large area without using heavy weights.

Vacuum bagging will give a much better result. If there are any convex surfaces then it will be very difficult to get a good bond without applying pressure in some way. I have even used bags of sand but vacuum is common practice for this sort of stuff. You will find many references if you google. Some is overkill and that is why it is best to test a process for your own needs.

Rick W