thinning epoxy

[prkaye]

1) What is the best way to thin West Systems epoxy for brushing onto fiberglass surfaces (e.g. inside of wheelpants) to fill the weave and pinholes? Acetone or paint thinner? I don't want to risk damaging the existing layup.

2) For very rough surfaces like the insides of the wheel pants I thought of first brushing a coat of unthinned epoxy. Then after this dries, a coat of thinned epoxy for the remaining pinholes (this is not a surface to be painted, just want to seal it against dirt and grime). Does this sound like a reasonable plan?

[dedgemon]

Why seal the wheelpants?
They're already epoxy.
Its just added work and weight.

[marchudson]

When covering pinholes and such, I kind of subscribe to DanH's advice, don't thin epoxy. I've been using straight epoxy on top of fiberglass parts to seal pinholes and small scratches with good results.

Great fiberglass read http://www.maddyhome.com/canardpages...chapter_25.htm

Good discussion on pinholes
http://www.vansairforce.com/communit...glass+pinholes

Good luck

[RVadmirer]

See this from their web site:

There are two methods of temporarily thinning epoxy. One is to heat the mixture and the other is to add solvent to the mix. The goal of both methods is to reduce the epoxy?s viscosity. This article explains what happens to WEST SYSTEM epoxy when it is thinned either by heating the components or adding solvent to the mixture.

Web Page:
http://209.20.76.247/ss/thinning-west-system-epoxy/

[Transporter]

In the FWIW category, I don't recommend thinning West System epoxy. You can roll on a thin coat of West System (regular mix) with a short roller (foam cover is okay).

If you need thinner epoxy, I recommend System 3 Clear Coat. It's extremely thin (like water...).

Yeah, I know...some guys thin with Acetone. Some guys have trouble getting it to harden properly too.

Good luck,
Mike

[instructor_bill]

? Adding a small amount of one of these solvents has a significant effect on the
viscosity of the epoxy. For example, adding 5% lacquer thinner makes about
a 60% reduction in viscosity (Figure 4).
? Adding 5% lacquer thinner to epoxy reduces the epoxy?s compressive
strength by 35%?a big hit in the mechanical properties of WEST SYSTEM
epoxy (Figure 5). The addition of more than 5% solvent results in an
excessively flexible cured material. Thinning epoxy with solvent causes
enough loss of strength that we (and most other reputable epoxy formulators)
cannot recommend using it as a structural adhesive.
? Adding a volatile solvent extends the pot life and cure time of epoxy and
jeopardizes the reliability and predictability of cure. Additionally, with slow rate
of cure, it takes longer before work can be sanded.
? Adding volatile solvent may cause shrinkage of the cured epoxy. Applying
thinned epoxy in large, confined areas (like consolidating a large pocket of
rotted wood) is likely to trap some of the solvent. In thick applications, the
epoxy cures very quickly and not all of the solvent has time to evaporate
before the epoxy hardens. Over time, the solvent works its way out and as
this happens, the cured epoxy shrinks and in many instances cracks.
Shrinkage also causes print through. You may have a surface sanded smooth
only to have the resin shrink. This shrinkage often reveals the texture of the
substrate. Shrinkage can continue to be a problem until all the trapped
solvent works its way out of the cured epoxy.
? Adding solvents, especially acetone, alters the color of the cured epoxy.
While the effects are not immediate, adding acetone to epoxy causes the
color to change from slightly amber to very dark amber.
? Adding solvent results in a temporary reduction in viscosity. Volatile solvents
evaporate quickly as they are agitated during brushing or rolling, causing the
viscosity to continually change as time passes.
? Adding solvent to epoxy may damage the substrate. Many materials
(Styrofoam? for example) are not attacked by epoxy but may be attacked by
the solvent used to thin the epoxy. Be certain to test the substrate with the
solvent before using it to thin the epoxy.
? Adding volatile solvent to WEST SYSTEM epoxy has some adverse health
and safety effects. WEST SYSTEM epoxy components are nonflammable but
the chance of fire or explosion goes up in proportion to the amount of solvent
you add. Also, the vapors of many volatile solvents are hazardous to your
health and proper ventilation is mandatory to prevent inhaling harmful
quantities of them.
? Adding volatile solvent to epoxy which is then applied as a coating may cause
problems with various regulatory agencies. If your business is inspected for
air quality, adding volatile solvents to WEST SYSTEM epoxy may make your
business non-compliant.
? Adding solvent to epoxy to enhance fiberglass wet-out will result in more
?drain out? of the resin on a vertical surface. The fabric will wet-out quickly but
it may become resin starved when too much epoxy runs out of the fabric

[Bob Axsom]

I don't use West Systems so I have no idea how it works - I use EZ-Poxy. Several years ago the RVator had an article on finishing the surface of fiberglass parts and I follow that somewhat. I found that all of the store bought fillers were a disappointment. I mix my own with micro balloon and slather it on and 24 hours later sand it off. Then I mix a batch of epoxy resin as usual with EZ-Poxy 24 hour hardner then cut it 50% with acetone as described in the RVator article and paint it on. I flew like that for a year before painting. No Problem five years after painting. I never thin epoxy for fiberglass structure, only surface finish.

Bob Axsom

[skylor]

Originally Posted by prkaye

1) What is the best way to thin West Systems epoxy for brushing onto fiberglass surfaces (e.g. inside of wheelpants) to fill the weave and pinholes? Acetone or paint thinner? I don't want to risk damaging the existing layup.

2) For very rough surfaces like the insides of the wheel pants I thought of first brushing a coat of unthinned epoxy. Then after this dries, a coat of thinned epoxy for the remaining pinholes (this is not a surface to be painted, just want to seal it against dirt and grime). Does this sound like a reasonable plan?

I've tried thinning west with solvent, and I've tried thinning with heat for filling pinholes and voids. Neither method gave me really acceptable results when the epoxy was brushed or rolled on

Then I tried this:

1. Apply a small amount of West to the surface of the part with a brush.

2. Use a squeegee to thoroughly distribute the epoxy AND remove the excess.

3. Allow epoxy to cure to a tacky state only, then repeat steps one and 2.

Perform this about 5 times in a row, with no sanding in between. You will be amazed how economical this method is on resin, AND it will fill all of the voids.

I typically like to finish the parts with 1 or 2 brushed coats of epoxy followed by sanding smooth, but don't sand back into the glass cloth. This results in a really nicely finished part with no pinholes, and the weave of the cloth completely hidden.

Skylor

[SHIPCHIEF]

I've tried brushing on the thinned West System reccomended in the best of RV-ator, also brushing on non-thinned West. They both worked in 50 degree F weather. The foamy brushed on resin seems to have settled in and released the bubbles plus filled a high percentage of the pits.
I've top coated with brushed on PPG DP primer with zero pinholes.
I also seal coated my fiberglass canopy skirt with DP-90 LF, with reducer added. Zero pinholes, but there are faint brush strokes on all 3 methods.
My paint rep prefers DP primer direct over the fiberglass, the color of the primer should be as close to the final color as possible with the slim color selection of primers. After that, I'm going to try DP-4000 spray on and sand down primer for smoothness before the color coat.

[rocketbob]

I throw the resin in the microwave for 10 seconds before mixing. Works great for thinning it.