Fiberglassing Tips?

Billy the Hero

Member

• Nov 18, 2016

• #1

So for the past few months, I've primarily used plaster bandages to make my mother molds. But seeing as they're rather...unsuited for the project I'm currently working on, I figured it be a good time as any to get into fiberglassing. While it's rather straightforward (mix up right amount of hardner into resin, brush on fiberglass cloth, etc etc) for a mold with a lot of nooks and crannies, I found it's too easy for bubbles to pop up while I'm letting it cure. It doesn't help that where I live is currently cold (below 60 most of the week with overcasts), so it takes too long to cure without going overboard with my hardner.

Any tips?

 

cavx

Master Member

• Nov 18, 2016

• #2

How big are these molds? If you can, make yourself a heat box to place the parts in. This will speed up the exo and set the resin off.

 

Billy the Hero

Member

• Nov 18, 2016

• #3

cavx said:

How big are these molds? If you can, make yourself a heat box to place the parts in. This will speed up the exo and set the resin off.

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The central piece is approximately 90x40cm. Good idea about the heatbox, my crappy homemade vaccuforming machine should be laying around in my workshop somewhere...

 

DizzyStrmtroopr

Well-Known Member

• Nov 19, 2016

• #4

why not just cover the outside of the existing plaster shells with fiberglass? that's what I do. when the silicone cures on my item I use 2 layers of plaster bandages then after a couple days slather polyester resin and glass on that. still have to wear gloves when I slush cast though, but the fiberglass holds the pressure of clamps on 2 part molds while the plaster underneath still allows air in during demolding

 

cavx

Master Member

• Nov 19, 2016

• #5

I agree with Billy the Hero. I really don't like using plaster if another medium is available. Not that I like fibre glass either. I made a jacket using D65 and pet mesh (fibre glass reinforced screen mesh) once. It held the weight during the pour.

 

Last edited by a moderator: Nov 8, 2018

Duncanator

Sr Member

RPF PREMIUM MEMBER

• Nov 19, 2016

• #6

A heat box is a good idea for cold climates. It doesn't have to be hot, just warm. For small ones, I've simply used a 75watt lightbulb under a foil lined box.
Cold temps can stop the chemical reaction the resin needs in order to cure fully.

Case in point: I laid up a jacket mold on a cold evening, and left it in the garage to harden overnight. The next day it was still gooey and jelly-like. After a couple more days, it was still the same. The cold weather had killed the exothermic reaction in the middle of the curing process, and nothing I tried could get it to cure. This was with an epoxy fiberglassing resin. I'm not sure how susceptible polyester resin is to the affects of cold weather, but I'm sure it suffers a similar fate if left in too cold an environment.

 

cavx

Master Member

• Nov 19, 2016

• #7

I think if you can heat it up within a few hours, you will be OK. Left overnight might be too late and especially leaving it a few days. I'd say a throw away now unless you hit with a another coat with higher amounts of CAT. That may generate enough heat, but I doubt it. Ideally you want the room temp to be at least 23 degrees C.

 

Billy the Hero

Member

• Nov 19, 2016

• #8

Alright. I've redone my mother mold today and it's sitting to cure under my vaccuforming machine. It's sitting at a toasty ~32°C/90°F and it's beginning to cure in its high spots already.

 

Spyhunter2k

Sr Member

RPF PREMIUM MEMBER

• Nov 20, 2016

• #9

I switched to room-temp cure epoxy resin and started doing my molding inside during the cold months. The resin is 100% solids, meaning no stinky solvent to evaporate and breathe in. There's virtually no smell.

I make my mother molds from about 20-30 oz. of cloth reinforcement, followed by packing on 1/4 to 1/2" later of fine sand mixed with epoxy resin to a peanut-butter consistency, followed by another 20-30 oz. of cloth reinforcement.

Adding the sand layer reduces cost while rapidly increasing the thickness of the mother mold. It also allows you to layup the entire mother mold in one go, as you need so little resin mixed with the sand that the total exotherm of the entire layup doesn't get very high.

 

Last edited: Nov 20, 2016

cavx

Master Member

• Nov 20, 2016

• #10

Spyhunter2k said:

I switched to room-temp cure epoxy resin and started doing my molding inside during the cold months. The resin is 100% solids, meaning no stinky solvent to evaporate and breathe in. There's virtually no smell.

Click to expand...

I have also seen (and used myself) polyester casting resin used. No smell and sets up in room temp.