Fiberglass Bodywork Question

[donpearsall]

I have been making changes to my M/C body for years now and this year I am making big changes. I always use the rigid foam insulation to make the shape, then fiberglass over that. But the polyester resin melts the foam. I have been looking for a decent filler/barrier for the foam for a long time. I have tried body filler (lots of sanding, can only be applied in small areas at a time), drywall mud (easy to sand but takes forever to dry and cracks easily), packing tape, latex paint (can't sand it), etc etc.

What I am looking for is a roll-on, fast drying thick filler that is very easy to sand and won't be affected by the resin.

Any ideas?

Thanks
Don

[wobblywalrus]

Duratec is what I have been using to put a finish on wood molds.   www.duratec1.com

[tauruck]

Don, Polyester resin won't work on that foam "ever".

You need to use an Epoxy resin. All the body fillers are Polyester based and create all kinds of problems with that foam.

Buy a nice Epoxy two part resin system along with fumed silica, cotton flocks and microballoons  from your supplier. Mix your own filler using those agents and cover the foam with the mix.
It won't chow the foam and is easy to sand. Roll on it won't, you'll need to use a spatula like the one for body filler.

Put it on in thin layers and let it cure overnight and you should be good to go.
If you need more help PM or email me 24/7.

Mike.

[Elmo Rodge]

As far as foam goes, you need urethane foam.  Polyester won't melt it. Wayno

[johnneilson]

Don,

Have used plaster as a barrier to the foam.
Goes on thick, easy to sand shape and seals up well with spray primer.
The primer holds wax very well, only drawback is that life is short.
Duratec is very hard and durable, just make sure you like the shape.

J

[sofadriver]

Don, I use the adhesive backed aluminum tape from Home Depot. $8 for 150'. Easily formed. Works great as a barrier (resins won't go through it)
and the glass separates easily from it. You can find it in the heating duct area.

Still wanting to chat with you B4 Speedweek.

Mike

[robfrey]

Don, Polyester resin won't work on that foam "ever".

You need to use an Epoxy resin. All the body fillers are Polyester based and create all kinds of problems with that foam.

Buy a nice Epoxy two part resin system along with fumed silica, cotton flocks and microballoons  from your supplier. Mix your own filler using those agents and cover the foam with the mix.
It won't chow the foam and is easy to sand. Roll on it won't, you'll need to use a spatula like the one for body filler.

Put it on in thin layers and let it cure overnight and you should be good to go.
If you need more help PM or email me 24/7.

Mike.

Mike is right on the money here. Sealing the foam has always been a challenge for us and so far, this method works the best of all we tried.
While you at at it, why not convert over to epoxy based resin for your actual parts or have you been doing that already? Since Eric turned me on to the epoxy, I don't want anything to do with that stinky polyester based stuff anymore.

[tauruck]

Rob, the smell is one thing but nothing beats the "Polly Wobble" as I call it.
Those beautiful waves you see when looking at a Polyester part made with a little too much hardener .

I know this is LSR and weight is not viewed in the same light as in other forms of racing but Epoxy beats Polyester every time.

Polyester is supposed to be user friendly in that the masses can master it with very little know how. I think that's wrong.
How many people like working with fiberglass?. Not many. It's the chopped strand mat and Polyester that make you hate the stuff and have given "composites" a bad name.
Heck I even hate it.

Epoxy wets out better, cures at a predetermined time and offers way better stiffness pound for pound.
It sands better and won't shrink. Not more expensive either because you'll use two thirds less for the same in Polly.

[donpearsall]

Thanks for all the suggestions everyone. I will make one more suggestion on what NOT to use, and that is paraffin  wax. That makes a mess and leaves runs and drips that have to be smoothed.
I am very familiar with epoxy resin after having built 3 experimental aircraft with foam and epoxy.  I just default to using polyester resin because it is available everywhere and less expensive. Epoxy is only sold at specialty stores.

However the Boeing Carbon Fiber wing factory is just 3 miles from me, so maybe I can make friends....

Thanks again,
Don

[tauruck]

Don, you should make friends there.

That would be a great advantage. Aviation has strict rules on shelf life that don't apply to race cars or bikes.

[Speed Limit 1000]

Don, you should make friends there.

That would be a great advantage. Aviation has strict rules on shelf life that don't apply to race cars or bikes.

You might find someone with an interest in LSR willing to help

[sofadriver]

Not more expensive either because you'll use two thirds less for the same in Polly.

Tauruck, can you explain a little more? I've used both but never really compared them.

[tauruck]

I can but I work in metric terms. Comparisons will be the same.

450 gr/m2 Chopped strand mat uses 1Kg Polyester resin per layer per m2=1,450Kg.
161gr/m2 woven glass cloth uses 220gr Epoxy resin per 2 layers per m2=542gr.
Post cured the Epoxy is much stiffer and lighter.
If you get into working with the Epoxy you'll eventually find that it wets out way better due to the lower viscosity and as experience grows you'll be using less fabric to resin.
A resin rich part is a waste of money.
Your Epoxy supplier can tailor make resins for your requirement as well. You tell him what you want it to do performance wise and how long the pot life should be and it will make life easier.
You can use styrene coffee cups for mixing small batches and there are many fillers you can use to alter viscosity and create pastes for filling in tight spots like short radius 90* corners where the fabric nine times out of ten will bridge.

[Ron Gibson]

Mike
What material (cloth or mat), layers and cure time would you recommend for something like a carb scoop with nothing flat, fairly small size, compound curves. etc. I don't have a lot of experience with glass and non with epoxy resins.

TIA
Ron

[johnneilson]

Ron,

look into twill weave material.
It typically will conform to complex shapes easier than normal weave.

J