[WWP] Amines, Epoxy, Polyester

From: Judith Franklin Blumhorst, DC (DrJudyB@pacbell.net)
Date: Fri May 12 2000 - 09:57:48 PDT


Scott,

You're right on the methodology -- wash, then sand. I can never remember
the correct order, so I wash, sand, and then sand again. You're also
correct about some specialty resins that don't blush.

But regarding water vs. alcohol vs acetone, I think we're getting a few
things mixed up here. I could be wrong, but here's how I remember it.

IIRC, all my references say that the amine blush, with highly polar NH3
molecules (?), is water soluable. It's not waxy (waxes are long-chain
hydrophobic, non-polar molecules). They recommend plain water, which is
definitely not an epoxy solvent. Alcohol, which is hydrophilic and polar,
with all it's OH groups would do it (and I don't believe it's an epoxy
solvent either) . Actetone, with polar COOH groups. might, but I'd have to
look up my chemistry to be sure.

Acetone is definitely a polyester solvent if the resin isn't fully cured
(but not a good thinner; monomer styrene is much better). After full cure,
acetone won't harm either polyester or epoxy resin. I'm not sure if
acetone's an epoxy solvent or not -- I think it IS in the early stages of
curing -- I've used acetone to clean tools, but I can't remember if I used
it for epoxy or polyester resin.

So I'd err on the safe side and avoid acetone with both polyester and opoxy
resins unless the stuff is old enough to be unquestionably fully cured. All
in all, water gets the job of removing the amines done, is cheap and doesn't
hurt the epoxy.

Polyester resin and gelcoat usually have waxes (surfacing wax or PVA) added
to provide the air barrier needed get the surface to cure. (alternatively,
you can cover a polyester repair with mylar film to seal our air). Most
boats, including our potters, are laid up with polyester-type resin and
polyester gelcoat. Before doing any repair, you have to be sure you remove
the wax or else the new resin doesn't "key" into the underlying resin.
Acetone will remove wax (keep turning the cloth and use lots of rags).
Alcohol will not remove the wax.

I use denatured alcohol for removing excess bedding material. Not for
anything else.

If I'm wrong on this, somebody please correct me.

Judy B
-----Original Message-----
From: Scott Pack [mailto:scott.pack@pictureiq.com]
Sent: Friday, May 12, 2000 9:33 AM
Cc: Potter Email List
Subject: Re: [WWP] Have the "keel" galvanized?

> blushing" which can affect how your bottom paint cures. In any event, you
> have to lightly sand the epoxy for the paint to grip, and then wash it
> thoroughly with water to remove the amines. And try a test section to
make
> sure your bottom paint cures over epoxy. Micron CSC paint cured fine over
> new epoxy on my keel last November.

Some but not all epoxies when cured form a waxy layer on top, which is the
amine
blush. You should remove the waxy amine blush layer before sanding, since
it
will just gum up the sandpaper. I don't think water will remove the wax
though. Acetone or denatured alcohol will do the job. Go easy on the
rubbing
since both are epoxy solvents and the epoxy is unlikely fully cured.

-Scott

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