Release agent hit or miss

[SaulOhio]

Sometimes things go really well with molding hydrofoils, sometimes they don't. I've been cutting molds out of expanded PVC with my CNC machine, and using a PVA release agent after filling the pores with automotive glazing putty. As you can see from the pictures, sometimes the mold comes apart from the hydrofoil really easily and clean, sometimes its a huge job, and damages the mold.

I never have any problems when I use HDPE, but thats much more expensive, not easy to get in the right sizes, and harder to sand after carving it.

The other half of the mold is in pieces, completely ruined.

At least the hydrofoil came out great. This is my biggest yet, for super light winds.

[rynhardt]

I've used PVA release agent in the past, but only on waxed surfaces. Typically a gel coat or painted mould with at least 6 layers of carnuba wax. Then release agent.
Even with a smooth surface, the wax layer is recommended to reduce surface reactivity.

[SaulOhio]

I've used PVA release agent in the past, but only on waxed surfaces. Typically a gel coat or painted mould with at least 6 layers of carnuba wax. Then release agent.
Even with a smooth surface, the wax layer is recommended to reduce surface reactivity.

Is it possible to put the wax on top of the PVA, so the PVA stays on the mold, and the hydrofoil comes out clean, without the PVA sticking to it?

[rynhardt]

Probably not. The PVA should wash off with water, which is what made the system work in my case (I'm making the assumption that you are using a similar process).
The way I understand it is that the wax is the main release layer, and the PVA a backup.

My experience has been that applying the PVA is a one shot process, i.e you need to get a nice even liquid layer in place and not go over a dried piece of PVA, otherwise it wrinkles.

And once the PVA layer is in place, it's very thin and you need to handle it with care.

[rynhardt]

[Bille]

...
The way I understand it is that the wax is the main release layer, and the PVA a backup.

My experience has been that applying the PVA is a one shot process, i.e you need to get a nice even liquid layer in place and not go over a dried piece of PVA, otherwise it wrinkles.

And once the PVA layer is in place, it's very thin and you need to handle it with care.

What He said !

And also -- if you coat your mold , with a thin layer of epoxy , (the same hardness) as
the one used in the part , then wax, then PVA -----
you should Never run into that problem you had, ever again.
I use :
Meguiars Mold Release #8 , for the wax.

Bille

[Bille]

My first Bad experience with a blank , not separating from the mold
i made of it ; happened because the blank was coated with lacquer spray
paint, and i only used wax on it . The epoxy used in the mold, was harder
than the lacquer ; the wax didn't do it's job, (needed some PVA) as well.
I destroyed the blank, removing it from the mold ; the epoxy surface-coat
of the mold, was fine !

NOW i make the final coat of the blank, (object to be molded) is
done in epoxy, and i only need wax to get a separation
but
i still use both wax and PVA because i ain't very lucky !

Polyester is Not as hard as epoxy ; so like the lacquer , it will need a
coat of wax And PVA to get a good separation when using epoxy
as the surfacing agent.

If your surface-coat on the mold , is epoxy , and your laying
up a polyester part on it ; all Ya need is wax to insure a separation ---
but i still use PVA as well just to make Sure.

If your surface coat on the mold is Polyester , and your laying up
an epoxy part --------- ; now you need wax (And) PVA .

Bille