Mold contamination question

[Pelle]

We're having a problem with some kind of contamination in the deck mold for a small OD keel boat that we are producing. The contamination makes the gelcoat "bead" like water on a waxed surface. I can not be removed by the usual solvents or cleaners but only by light sanding and polishing but then it returns after making one or two decks. Does anyone have any ideas what it could be and any experiecne wheter it possible to get rid of? Some kind of silicone maybe?

[yokebutt]

Very odd, what type of mold release do you use? Are you using the same wax for the hull mold without problems, and doing it in the same shop under the same conditions and with the same equipment? Are you using the same gelcoat on hull and deck?

Silicone is one of the worst contaminants around, wouldn't surprise me if that is what it is.

If everything else is the same, perhaps you should try a test-patch with a different type of gelcoat if that is the only variable that isn't the same as the hull.

[cyclops]

You have to isolate which part is causeing the problem by applying the gel coat on some other material and see if it occurs. Put a different brand of gell coat on the mold. No problem, change the gel coat. Still a problem? Get some Tech. Assistance from several Mfgrs.

[Pelle]

Thx for your replys

I'm pretty sure the problem is in the mold......

We use the same gelcoat and mold release in the hull mold and innerliner molds which is in the same workshop and no problems. We also tried a few different gelcoats but all behave the same. The difference is that the deck mold is considerably older than the other molds which where rebuilt a few years ago. The tech support at the supplier we use has no clue so I figured I'd ask here

Ah well, maybe time for building a new deck mold too ....

[cyclops]

LOOK! I only sell the stuff.

[yokebutt]

Pelle, Your question is still bugging me. If the problem was surface contamination, (like silicone) I'd think it would show up immediately, not after a couple of parts. It really sounds as if something is precipitating out of the mold-surface, although I hasten to confess, I have absolutely no f-ing idea what that would be.

So, if you want to test that hypothesis, you could try heating a small section of the mold to the same temperature the laminate has while curing, and see if anything ugly comes creeping out.

Admittedly, this is a very far-fetched idea, but it's the only thing I can imagine going on.

Disclaimer: Absolutely no warranties expressed or implied.

Good luck,
Jocke.

[Pelle]

We tried heating but nothing happens. Thx for trying. ... The decision has been made to build a new mould so the problem will be solved albeit by an expenesive way.

[chandler]

Maybe outgassing from whatever your using as a primer or adhesive, they have to cure also before being coated with anything.

[gonzo]

That happens on surfboard re-gelcoat jobs after a repair if the gelcoat doesn't have enough wax. Is the gelcoat you use come with wax in it already?

[Robjl]

Pelle,
We call it "fisheyeing", it is usually a silicon problem. I've solved it in the past by applying PVA mould release in addition over the polished mould release system. The surface finish isn't quite as good though.
I've seen a hull repainted twice after a silicon handprint came through next to a porthole... yes twice. The bloody silicon just wouldn't dissolve with solvent.
I think there may be some spcial solvents that may help.
Cheers,

[rxcomposite]

I beleive it is silicon migration. The mold might have been contaminated. It will keep coming back as it tries to float to the surface. It is like stain in a fabric. Wise move to make a new mold.

Silicon is bad as it transfer to the part. Over a period of time, it migrates to the surface and you cannot paint it or in some cases, the layers delaminate. I have used silicon release in the early days.

[ABoatGuy]

Anybody ever wax the mold with automotive wax? Probably a long shot. Most are full of silicone and will make gelcoat behave like this.

[rxcomposite]

Originally Posted by ABoatGuy

Anybody ever wax the mold with automotive wax? Probably a long shot. Most are full of silicone and will make gelcoat behave like this.

Use carnauba based wax. I have even used floor wax in an emergency in a non critical mold.

Most mold release are carnauba based. Always read the material content.

[fiberglass jack]

have u tried using pva as a release agent after u wax ur mold spray some pva on it polyvinalachahol should do the trick

[fiberglass jack]

has anyone in your shop use armoural leather cleaner its has a lot of silacone