alternate covering for plug release

I have a small ply trimaran with one missing ama. I want to use the ama as a plug to make a temporary female mold for one or two pulls. This ama has a painted surface that can't be waxed and which I don't wish to harm. I have thought of using a long and wide length of window shrink wrap or possibly that self sticking shipping film that is quite stretchy. Anyone use either of these with polyester resin? What other options are out there? Finish is not important as I'll do a light sand before painting. Thanks.

 

It depends on how much you are willing to spend.You may get away with multiple strips of brown parcel tape.It won't be pretty and will need work and I wouldn't even start before trying a small test area to confirm that your chosen resin won't attack the tape.For a more certain outcome,one of the self adhesive PTFE coated self adhesive cloths will work.PTFE COATED GLASS CLOTH WITH ADHESIVE https://www.gteek.com/ptfe-coated-glass-cloth-with-adhesive-side

 

What kind of paint does it have that can't be waxed?

 

Thanks wet feet. That suggestion of brown parcel tape is a good one, though I'll try it in a different way. I'm going to order that and some stretch wrap packing film from amazon (both items are inexpensive) and test for resin compatibility. If that works I'll stretch the film on the hull and tape the seams with the parcel tape and also tape down the film on the top deck, which won't be part of the mold. The parcel tape will leave a tape depth indentation in the female mold where the seems were taped. This can be filled in with a piece of tape for the one or two pulls. Fingers crossed.

 

I'm not a fan of shrink wrap. It tends to get embedded easily into the matrix in my experiences. I've never use partall without wax, but I'd investigate partall. Your reluctance to use wax is perplexing. There are many different waxes that can work; so you can avoid compounds you don't want near the boat..

 

Hi Cando,

The packing tape often leaves the adhesive behind, takes some washing of with turps or similar.

Try a control area with multiple layers of PVA, quite a thickness can be achieved, washes out with water.

Regards from Jeff.

 

Hi Jeff. To clarify, I was intending to use the brown adhesive parcel tape only to hold the stretch wrap packing film (not adhesive) to the next row of packing film lengthwise on the hull, because the stretch film is only 18 inches wide. The adhesive tape will not come in contact with the hull paint itself, just the outside of the stretch film. In this scenario with the stretch film completely covering the hull, is the PVA even necessary, either on the hull paint or on the outside of the stretch wrap?

 

Don't bother with stretch wrap. It will crinkle up from the exotherm from whatever resin you are planning to use for your casting.

As Gonzo asked
What paint can't be waxed?

 

Hi Cando,

PVA is the best composites insurance policy you can invest in, with a really heavy thickness it may compromise the surface finish a bit, sometimes it enhances it say off a wet & dry sanded surface. For some reason I prefer the green tint... apparently exactly same as blue. Some years ago we were manufacturing some inside corner moldings to round out a head compartment and using 150mm PVC plumbing pipes as the tool, polyester loves to bite into PVC and become one & we did have a stick up(lucky the tooling so low cost), the PVA a lifesaver.
There's a great article some 20 plus years ago in pro boat magazine that describes the spray process... though it really is just misting and patience that's required, it is possible to brush or sponge it on but will always have brush or overlap marks.

Before melamine finishes were so easily available often fast low cost tooling just made with timber/masonite and a coat of shellac, some johnsons floor wax and a sponge over with PVA enough to pull a decent part for a quick wet n dry sand and polish.

All the best.

Regards from Jeff.