tc4 drft

I'm building a new hatch for my TC31. So far, I have a 1/8" sheet of plastic the same size as where the hatch needs to sit, and a carved out peice of "carving foam". I'll be mounting the sheet of plastic to a peice of wood, also the same shape as the hatch hole. I hope we're on the same page here.
1. I need to attach the foam to the plastic. Would CA glue work? Silicone? The foam is really grainey.
2. Once attached, what should I cover it with to fill in all the gaps? Bondo? Whatever it is, I need to be able to make a plaster mould of it.
3. When I have the plaster mould ready, I want to do a gelcoat, and a fiberglass cloth. What all do I need? What oz. fiberglass cloth, resin, release agent...is a catalyst needed?
Has anyone done this before? My LHS said it's a lost art, and my body shop said cloth and resin is all I need, which is not true.

Flabum

with what you have now, you can attach the foam to the plastic with epoxy. I would use a piece of wood instead of the plastic since you will be adding bondo to it and bondo will stick better to wood than plastic. Once you have the bondo covering the foam and wood and as smooth and perfect as you can get it, spray the whole thing with gel-coat. wet sand and polish the gel-coat until it is flawless. Next get some Maguires mold release wax and start waxing. 6 - 8 coats without touching the part with your fingers. You will then be ready to make the mold. Spray thye waxed part with a different color gel-coat (so u can see the proper coverage). After the gel cures, start laying it up with fiberglass. once it is all done, seperate the parts and you will now have a mold.

tc4 drft

Where does the plaster come in? If I lay it up on the outside of the mold, won't the hatch will be larger than the mold? I think I read somewhere that this is a male mold? I want to do a female mold. I pretty much have the shape that I want now...I was planning on putting plaster of paris over it, pull the mock up out of the plaster, then gelcoat and layup the fiberglass inside the plaster cast. I dunno...this is my first attempt at this...let me know. Thanks!

DocJones199

Hi There,

What you are doing is simple. You can do this project with a plaster mold if you want to. You will, however have some finishing work to do on your final part because the porous nature of the plaster will leave marks on the surface of the piece that you make. If you choose to use plaster as the mold, you will want to follow these steps. First of all, you can smooth out the inside of plaster mold with glazing putty from the auto store. I would use the cheap, air drying red stuff. This stuff sands easy and should be softer than the plaster. Once the inside is as smooth as you can get it, apply at least 5 or 6 coats of mold release wax. There are many brands of mold release wax, both McGuires and Part All are good products. With the wax dry, you need to apply two thin coats of PVA. PVA is a parting agent that is used in fiberglass molding. Let the PVA dry (it can be brushed on or sprayed on). Don't try this without PVA!!! Now you are ready to apply gelcoat and fiberglass. Your part is small so I would brush in the gelcoat. Gelcoat has to be catalyzed with MEKP. Follow the manufacturers instructions for the MEKP to Gelcoat mix. Brush a nice thick layer of this into the mold. Let it cure to the point where it is tacky to the touch and doesn't stick to your glove. With the gelcoat still tacky, apply the fiberglass resin and chopped mat. I would use 1.5 ounce mat for this, maybe two layers. The resin needs to be catalyzed with MEKP per manufaturers instructions. Use a brush to saturate the mat with resin then lay the mat into your mold. Use the brush to push the mat into the mold. "Work" the mat like this for at least a few minutes. You can let the fiberglass cure to the point where it is stiff but still very flexible and then use a knife to trim the excess. This should get you a part. The only problem with this is that between fiberglass resin, gelcoat, mat, MEKP, parting wax, PVA and your other supplies this part will probably cost you over $100. There is a manual available with all this info and nice pictures to guide you online. If you do a Google search under fiberglass mold manual it will be on the first page. The whole set is informative and only about $20. Good luck. I hope that this helps.

tc4 drft

It should.....thanks Doc!

Thin water

I have made a bunch of molds for all kinds of stuff. I have made plaster molds (for casting sinkers, downriggers and musket balls), fiberglass molds (Radio boxes, poling platforms, rc hulls, hatches etc...) sand molds for casting aluminum (all types of machine parts, toy guns, an entire lathe etc..) etc... If you use the gel coat over your "Plug" (This is the best way to make a good part) sand it very smooth. Do not use any automotive paint on it if you use PVA, some paints will bond to the PVA better than they do primer. PVA needs to be sprayed on or your nice finish will have molded in brush strokes. If you can make the plug correctly (no negitive draft, good gel coat finish etc... ) send it to me and I will pop you a little mold off of it. It will only cost me a couple of bucks at most since I have the stuff. If you buy a small amount of everything you need you will spend a bunch of money, may or may not produce a good part and have a bunch of junk you will never use left over.

Good luck with it.

JIM