On 3 Jan 2009 09:17:01 -0600, nothermark wrote:

On Fri, 02 Jan 2009 22:14:36 -0500, Pete Keillor
wrote:

On 2 Jan 2009 20:54:02 -0600, nothermark wrote:

On Fri, 02 Jan 2009 01:59:20 GMT, Dan@ (Pirateer guy) wrote:

On Thu, 01 Jan 2009 21:49:40 +0000, IanM
wrote:

My news wrote:
Any comment if Epoxy over Polyester will work?

No problem if the polyester is *well* cured. Months or years not weeks.
Abrade surface thoroughly first.

Also make sure you de-wax the surface before sanding.
Ummm what wax?

Polyester uses a free radical cure with the reactive diluent styrene.
Oxygen activates the inhibitor, so a wax is incorporated into the
resin-styrene solution. The wax migrates to the surface during cure
to prevent oxygen exposure and allow complete cure. Otherwise, the
stuff won't cure on the surface. You need to remove this residual wax
as it'll prevent adhesion of the epoxy.

Pete Keillor

But won't sanding take care of that?

Of course it will.

If you are going to make a repair to a fiberglass structure you will
want to sand off all the paint or gelcoat, right down to bare
fiberglass, usually using a fairly aggressive sandpaper - 24 grit, for
example. This will eliminate any wax that might have remained after
the original polyester was applied. After sanding wipe the area with
acetone and clean wipes, paper towels, etc.

That is about all there is to it. Regardless what you are bonding to,
aggressive sandpaper to give a good coarse finish for the epoxy to
bond to and clean.

One last caveat. There are basically two types of fiberglass cloth.
One for use with polyester and one for epoxy. The "epoxy" cloth can be
used with polyester but the "polyester" cloth cannot be used with
epoxy. The reason is that some kinds of "polyester" cloth is made with
a "starch" or binder that dissolves in polyester but not in epoxy and
epoxy will not completely wet that type of cloth.

Everyone in the business know about this so when you buy cloth just
specify that it for use with "XXXXXX" resin.
Cheers,

Bruce
(bruceinbangkokatgmaildotcom)