"wmbjk" skrev i en meddelelse
...

That surface needs to be as non-porous as possible. Seal it with
whatever your fiberglass supplier has on hand and recommends. Furane
is one product, sprays easily, dries fast, sands readily, polishes
shiny, smells terrible. It's not very durable though.

The supplier is a local Home Depot clone w. highschool student employees, so
I doubt they have any recommandations :-)... They do have a boating supply
dept, wich is where I found the fibreglass stuff..

I found some silicon based mold release designed for Polyester resins at an
electronics supply place.. I just ordered a couple of cans..

How do I keep the fibreglass from sticking to the mold?

After sealing the surface, use a specialty type paste wax. Apply wax,
let dry as recommended (perhaps overnight), and buff. Do about 6
coats. Do not try to speed the process. You might also bake the mold
in a warm oven between coats to help get the wax to penetrate the
surface. For at least the first part, apply a couple of coats of PVA
(from the fiberglass supplier). Spray it on if you can, it won't brush
very well on a waxed surface.

Any clue if boatwax will work?

PVA is regular (white) wood glue ?... I could add a little destilled water
and spray it on

Someone mentioned using babypowder on the mold as a release.. Will that
work?

Any tips that may come in handy?

I can't tell you how many times I've heard that folks making their
first piece don't get the mold sealed and waxed properly, and end up
with the mold and the part permanently bonded together. So you might
try sealing and waxing some samples first to test that your technique
is adequate. The first release on a new mold can be troublesome. Try
getting a little compressed air into one corner. If that doesn't work,
try getting some water into the released areas to dissolve the PVA.
After the first release, add another coat of wax. If the first part
was tough to release, you might use PVA on the second one as well. But
if the mold is properly prepped, all releases after the first one
should be easy. The tail on your horn doesn't appear to have much
taper, and the part is going to shrink around the mold. So expect the
part to have a good grip on your mold in that area. You might make the
first part a single layer thick. That will give you some layup
practice, and enable you to peel the part off the mold if it's stuck
in some areas.

I could integrate a quickrelease fitting for the airhose in the mold, so I
can blow air between the mold and the piece..

I could do just a few layers on the mold, let it harden and add more layers
after I remove it from the mold... This would help the shrinking problem to
some degree, or am I way off track ?

Thanks for the input so far!

/peter