Fiberglass question?

OK fiberglass experts. I've worked a little bit with fiberglas before (negative mold, gelcoat, using mat / cloth, resin) and I've done a good amount of casting (mostly resin / silicone molds) and I have a fiberglass question.

I want to make something out of fiberglass, but I don't want to create a mold for it. Mainly because:

- I don't intend on making copies, it will be a one off "build up"
- It's OK that the detail is slightly softer / smoother
- the time spent (or saved) from not making a mold in the first place.

So is it possible to keep the benefits of fiberglass (thin / light) and keep it to more of a "build up / one off" process?

I'm thinking of sculpting something in pink foam, and laying fiberglass cloth on top, to give it a hard shell. I was hoping to some how lay the fabric on top, spread the resin, roll out the air pockets, and when it cures, somehow be able to separate and remove the pink foam underneath. Not sure if it could be separated?

I've seen people make elaborate shapes for "sub boxes" for their cars, by cutting crazy MDF shapes, and stretching some kind of cloth (is it fleece or T-shirt material, or is it some special material?) over the form creating some pretty elaborate shapes. They then build up on top (or sometimes underneath?). I was wondering if this kind of technique could be used?

I don't want to use regular mat as I want the top layer to be somewhat uniform, and I'd prefer not to apply bondo on top.

Would this be a good approach? Will this be durable enough? Can I separate the cured glass / cloth surface from the foam (what could I use to separate them?).

Sorry for all the questions, but I'm typing / thinking aloud.

Thanks in advance!

Might want to ask a mod to move this to the replica props would have better results then the modeling section.lol

Ill add this real quick. You cant fiberglass over pink foam unless you seal it first, the resin will melt the foam.

well fiberglass itself will not give a smooth finish if its placed on top of a form. You will probably have to apply a surfacer or at least sand it a lot.

If you go down the foam route you will have to seal it as IED says or it'll blister through the foam in seconds.

Personally I'd make the shape from foam, then before fiberglassing, cut it in half so that it's easier to remove the foam. Seal then fiberglass the two halves then join them back together with a strip of internal fiberglass.

Epoxy fiberglass won't eat the foam, polyester definitely will though. I use epoxy over foam all the time.

Put on several layers of glass fabric, not mat, the fabric is stronger, until you have a nice hard shell, then flip it over and chip away the foam.

Sealing the foam will get a better result though, because the smoother the surface before you fiberglass, the smoother the final result.

Thanks guys, I'll try to get a mod to move this post.

REL: what kind / brand of fabric do you use? In terms of sealing, how do you seal the foam? Can I just use paint (acrylic?)

Thanks in advance!

two things, go the epoxy route, as said you won't eat the foam, then to melt the foam on the back side, use a laquer thinner, won't harm the cured fiberglass but will totaly eat away the pink foam, leaving just the fiberglass part. Now if you want to go the polyester layup resin, then use ordinary latex house paint with no tolulene in it to seal the surface for fiberglassing, hope this helps...
Will

pandatrooper said:

what kind / brand of fabric do you use?

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If you go with epoxy you have to verify the fabric or mat is compatible, the boding agents they use to hold the fibers in the mat or fabric is different for epoxy, all companies should specify if it's epoxy compatible mat/fabric... As for type mat or fabric that will depend greatly on the shape you are working, if it does't have many or extreme highs and lows you can and might be able to get by with a single piece of fabric worked over the object with no seams or overlapping, leaving a nice solid easier to smooth finish... If it has lots of ups and down or tight areas you will probably have better luck with a mat, the weight of the mat is dependent on how extreme the surface is... Lighter weight mat will form much easier then heavy gauge but will require more layers...

In terms of sealing, how do you seal the foam? Can I just use paint (acrylic?)

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A good acrylic paint like Bulls Eye 123, or watered down Elmers (white) glue and last but not least you can get real fancy and go with a fancy product like Foam Coat http://www.fxsupply.com/materials/foamcoat.html

IED BOUNTY HUNT said:

Ill add this real quick. You cant fiberglass over pink foam unless you seal it first, the resin will melt the foam.

Click to expand...

Add a layer of Alum Foil on top of the foam and make sure the seams (overlaps) all go the same direction..

At least that is what I have learned.

Heres a few shots of a load of fiberglassing I did for a custom build:



I used MDF as basic shapes.
I then stretched cheapo lycra over the forms to build up the shape. This was simply stapled to the formers. I then gave this lycra form a coat of resin, which sealed it and made it rigid. I then fiberglassed matted under neath the shape to make it super-firm, which also kept the outer face very smooth.



I then skim coated the outer layer with body filler, and used that as the painting base


Lots of sanding involved but no mold, and very light!



I have made shapes as you say, with foam/polystyrene. If you use spray mount lightly on kitchen foil, you can smooth the foil over your shape very neatly so covering the form with fiberglass is pretty easy.
Jesomite is resin free but you have to use their own brand of matting. Glass fiber matting has a resin bonding agent in it which helps it do its job, which wont work with jesmonite. You can get very fine matting and very course matting. I find the fine stuff hard to really get around awkward shapes, normally I just choose a 'medium' matting. The courseness is set by the weight, if I remember. Its far cheaper to buy in rolls than in little packs too ;_)
Hope this helps.
D

This is a great help, just what I needed. Thanks guys!

Something? A little bigger hint would be nice, but a picture speaks a thousand words.

IMO, making a waste mold will save time and effort. The amount of time and effort to laminate over something and then smooth with Bondo is quite large as compared to this:

Carve you foam shape as desired. Coat with Vaseline. Cover with 1" of stone (plaster), reinforce with cheese cloth if item is big. Once cured, bust the foam out of the plaster shell. Let plaster dry for a week for all the moisture to escape and sand smooth any rough spots. A spring steel scaper works great.

Now seal it with several coats of lacquer. Sand in between coats. Apply several coats of wax, polishing inbetween coats. If available, spray in several coats of PVA (green mold release, best if sprayed. Can be brushed)

Now you can lay fiberglass into the waste-mold. Once gel-cured, trim the excess fiberglass around the edge of the mold. When fully cured, smash mold on ground.

You will have a fiberglass piece that will require some cleanup, but not as much as lamiating over the foam.

I hope that makes sense.

If you do the plug thing, and endup sanding, and grinding, do wear a repirator. fiberglass/resin dust is not something you want to suck in. Then water/wipe down the whole area after each time. dust lingers, builds, and you inhale it.
also patching and filling does not give you a chemical bond. hence you can get time related de-lamination. why I prefer old school of clay sculpt, mold, and stomp the piece all in one shot, so I don't have to patch fill, and join pieces together later on.

This might help , it's how i did my Kroenen mask using plastic wrap to seperate the fiberglass from the original shape .






Worked pretty Good