How to prepare metal plug for mould making

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#1

Does anyone practice a good method for prep the plug made from metal sheet.

Plug is like box depth 10cm 60cmwidth and 30cmlength
I had such thing filled with putty and painted with 2k acrylic paint , then 3 coats of PVA , next tooling gelcoat , tooling resin and put at the end to oven overnight at 55C

I was very dissapointed when i couldnt demould it , the mould land in trash in pieces , some paint lefted on mould some on plug.

I have no idea what happened and Im not sure if making same steps as above but with frekote will help?!

real pain in ass

#2

Did you use any wax?

Frekote system and sealer is definitely a better release usually.

I have no experience for moulding from acrylic paint, usually I use polyurethane paints.

Any paint system should also be very well cured.

http://www.rexco-usa.com/why-molds-stick/

#3

I’m going to assume your mold had draft and what you experienced was the part sticking to the mold surface. If that is the case, I’d say your PVA was probably too thin and porous. If you have a good, solid PVA surface, there is no reason the part should stick (at least none that I’ve ever heard of).

#4

You still need to wax it before PVA

#5

I’ve made lots of on-off quikie molds and use PVA as a parting film. I never wax before PVA and I’ve never had an issue. In fact, I think it is a waste of time to wax before the PVA. If you have a good film the wax does nothing for you. The PVA acts as a complete barrier between the laminate and the substrate.

Sometimes I’ll put a coat of wax on after the PVA if I want to pull more than one part. I’ve pulled three or four parts off without having to touch up the PVA.

#6

I’ve went the exact opposite. I used to wax and pva, but now only wax. Even 3 coats of wax at 5 minutes apart (buffing in between) is sufficient enough to pull my polyester gelcoat off easily.

#7

try that on a 20 ft boathull, and report back :smiley:

PVA alone is sticky as hell. The wax isn’t there for release, it’s there for slip.

#8

3 coats? You sir, are braver than I.

Normally, I prefer a properly waxed or, better still, polymer release agent to PVA on real molds. I was referring to quickly built, somewhat rough molds. Rough, of course, is a relative term. I’m talking about MDF and body filler, maybe sanded to 400 grit. Or an old composite part that is beat up that you are using as a basis for a new part.

I haven’t done a with a 20 foot boat hull but I have done a 31 footer. Just turn it upside down and shake. Watch your toes! :cry: :bigsmile:

#9

I had the same problem. Painted a fender with 2K and then we polished this to an absolute shine. The polishing alone took two days. Left the plug over the weekend and on Monday we put 12 coats or Mirror glaze. On Tuesday we did the tooling gelcoat and resin. Left the part for 3 days.

When we pulled the part everything stuck together. Managed to save the mould but the plug was damaged beyond repair. We even used acetone to remove paint from the mould.

Sounds the same like your problem….

I was told that the 2k takes time to dry and therefore with the heat of the resin this “melted” and stuck to the resin. So I guess the best option would be to bake the part with the 2k before you continue with the rest of your mould.

#10

Johan I think you get to the point of the problem , cheers