"Garland Gray II" wrote in message
...
If I were to wax the outside of a piece of 2 1/2 inch pvc pipe about 6
feet long, and then lay up several layers of fiberglass and epoxy, would
the resulting tube slide off the pvc easily enough after curing ? Or would
I need to first wrap the pipe with sheet plastic or similar ?
Thanks !

It will release but only with great difficulty. The GRP part will shrink as
it cures and that will make the release VERY difficult even though the GRP
is not stuck to the mould. What we normally do is engineer some flanges
into the layup such that we have something to pull against because we will
be exerting great amounts of force with clamps, presses, wedges, compressed
air etc. The part needs to be able to witstand these forces and you need
some way and place to apply these forces. The flanges or metal chains laid
into the part can later be cut off. Likewise, you may need to engineer some
sort of bearing piece in your PVC pipe. Or maybe use a 6' long theaded rod
with nuts to apply force like a bearing puller. Still, the part needs to be
strong enough to not buckle.

Instead of wrapping with plastic sheet, we frequently use clear packing tape
in 2" widths as a mould release. You tape up the part with clear tape, then
wax then lay up. Do not use masking tape - sometimes the wax on the masking
tape inhibits full cure of the poly resin.

The easist way would be to buy polystyrene foam rods of the correct diameter
from a craft store. Tape up and lay up. Melt out the foam with acetone or
lacquer thinner when cured and pull out the clear tape. This is the most
stress free way. Only problem is that the foam rod may deform (bend) during
curing. Same as with PVC tubes. .... I just re-read that you will be using
epoxy. In that case, with foam rods, don't even bother with a release agent
or tape since epoxy resin will not dissolve your foam. And if you are using
a low shrink epoxy, you will not get much deformation if at all.

Or do what Peter hk said. That'll work.

Here's a tip - we've all been taught to "wax on, wax off". I do it
different - "wax on, wax on, wax on" let the wax harden up and do not wipe
off. Layup over that. The part comes up with alot of wax transfer and
swirls marks but those are easy to polish out. I do this even when making
production molds because I refuse to risk a stuck plug and mold.

Arnold sg