Epoxy over Gel coat troubles
 

I am repairing a fibreglass hull that has quite a few hairline cracks
and deep gouges over the hull. I sanded the hull using 180 grit wet &
dry and cleaned out the gouges using a small grinder. The hull has been
left to thoroughly dry for a few weeks after a good cleaning, and then
wiped over with acetone. I have applied some epoxy resin over a small
ares to test, the idea was for the resin to weep into the hairline
cracks and gouges to seal them before applying any required filler. I
used a roller to apply the resin to the hull and it looked good for a
couple of minutes, then it all went wrong. The resin formed hundreds of
little globules/islands and no amount of brushing or using a roller
would give me a smooth even coat.
What has happened???

Regards Bruce

On Sun, 27 Feb 2005 19:13:58 -0800, b.stevens wrote:

I am repairing a fibreglass hull that has quite a few hairline cracks
and deep gouges over the hull. I sanded the hull using 180 grit wet &
dry and cleaned out the gouges using a small grinder. The hull has been
left to thoroughly dry for a few weeks after a good cleaning, and then
wiped over with acetone. I have applied some epoxy resin over a small
ares to test, the idea was for the resin to weep into the hairline
cracks and gouges to seal them before applying any required filler. I
used a roller to apply the resin to the hull and it looked good for a
couple of minutes, then it all went wrong. The resin formed hundreds of
little globules/islands and no amount of brushing or using a roller
would give me a smooth even coat.
What has happened???


I'm not sure. Did the epoxy cure or not? It sounds like you kept messing
with it after it started to cure. Aren't you glad you just did a small
test area? Can you use a slower epoxy mixture?

Also, why didn't you use an epoxy fairing compound or primer instead of
resin? I don't think painting a boat with resin is a normal procedure, but
I could be wrong.

Regards Bruce

--Mac

wrote:

I am repairing a fibreglass hull that has quite a few hairline cracks
and deep gouges over the hull. I sanded the hull using 180 grit wet &
dry and cleaned out the gouges using a small grinder. The hull has been
left to thoroughly dry for a few weeks after a good cleaning, and then
wiped over with acetone. I have applied some epoxy resin over a small
ares to test, the idea was for the resin to weep into the hairline
cracks and gouges to seal them before applying any required filler. I
used a roller to apply the resin to the hull and it looked good for a
couple of minutes, then it all went wrong. The resin formed hundreds of
little globules/islands and no amount of brushing or using a roller
would give me a smooth even coat.
What has happened???

Regards Bruce

---------------

I can answer you with confidence...

some epoxies, including at least one that we carry, have excessive surface
tension and will bead up if applied as a thin coat (like brushing it on) on
a smooth surface. Fix: either make the surface a lot rougher or switch to a
different epoxy. Not sure, but adding pigment or 'filler' to the epoxy
might also solve the surface tension issue with the epoxy.

regards
paul

"Living on Earth is expensive, but it does include
a free trip around the Sun every year."

============================================
PAUL OMAN Progressive Epoxy Polymers, Inc.
Frog Pond Hollow - 48 Wildwood Dr
Pittsfield NH 03263


http://www.epoxyproducts.com

wrote in message
oups.com...
I am repairing a fibreglass hull that has quite a few hairline cracks
and deep gouges over the hull. I sanded the hull using 180 grit wet &
dry and cleaned out the gouges using a small grinder. The hull has been
left to thoroughly dry for a few weeks after a good cleaning, and then
wiped over with acetone. I have applied some epoxy resin over a small
ares to test, the idea was for the resin to weep into the hairline
cracks and gouges to seal them before applying any required filler. I
used a roller to apply the resin to the hull and it looked good for a
couple of minutes, then it all went wrong. The resin formed hundreds of
little globules/islands and no amount of brushing or using a roller
would give me a smooth even coat.
What has happened???

Regards Bruce


##** Hello Bruce, I've done an fair amount of Epoxy repair and the problem
you describe sounds like gassing which happens when some type chemical
evaporates through the epoxy layer. Also any kind of silicone contaminate
will cause similar problems. I usually wipe down any surface with white
vinegar and then wash with soap and water before applying resin.Hope this
may help.

Rey

Thanks, for all the advise so far. I did'nt think of surface tension as
being a problem. I can try another band but what type ??. I know the
resin had not started to cure before the problem started and as far as
I can tell the surface is pretty clean. Gassing might be present, but
this would give little bumps correct.

Bruce

On Mon, 28 Feb 2005 16:58:14 -0800, b.stevens wrote:

Thanks, for all the advise so far. I did'nt think of surface tension as
being a problem. I can try another band but what type ??. I know the
resin had not started to cure before the problem started and as far as
I can tell the surface is pretty clean. Gassing might be present, but
this would give little bumps correct.

Bruce

If it was caused by beading of the epoxy, then maybe just adding some kind
of filler to the epoxy you've got would help. In any event, it would be
a good experiment. If you have done this kind of thing before, then you
will have your own ideas about how much filler to add to the resin.

If you haven't done this kind of thing before then let me just say make
sure you add enough filler to get a substantially thicker texture,
otherwise the results of the experiment may be inconclusive. If you want
to be really scientific about it, you could prepare 2 or 3 different
mixtures with differing amounts of filler, and see whether any of them
bead up on you.

As I said elsewhere, you may want to just get an epoxy primer and use that.

--Mac

we deal with this all the time. there are two solutions: 1 is to change
the surface energy of the epoxy by adding a fisheye preventer, or
wetting agent, which you can get from an automotive paint store. 2, is
to add cabosil (colloidal silica) , to thicken the epoxy until it
wont bead up. it often makes sense to put on an unthickened coat (which
will seep into cracks much better) and then follow immediately with a
thickened coat, which will not bead up. good luck. Dick Pereli

Bruce,
It sounds like you are making more work for your self than you need to. If
the repair is above the waterline, any good quality marine polyester
filler(3m premium) is the product of choice for the gouges. As for the
stress cracks in the gelcoat, it is necessary to find our what is causing
the crack or the repair will comeback the second the stress is applied to
that area. Repairing stress cracks around stanchions, is worthless unless
you beef up the bottom side of the stanchion...even then there is no
guarantee that the crack will come back. Paul was correct in suggesting the
addition of a thickening agent for the stress crack. The pooling is the
result of surface tension and adding any wetting agent not approved by the
manufacturer is a very bad idea. There is no telling what kind of chemical
reaction is going to occur. I always use epoxy below the waterline and
polyester above..mainly because of cost.
Good luck
Bruce

--
Shield Finishes and Nauticoat Marine Finish Systems
www.shieldfinishes.com

On Mon, 28 Feb 2005 17:56:32 -0600, "Reynaud" wrote:


wrote in message
roups.com...
I am repairing a fibreglass hull that has quite a few hairline cracks
and deep gouges over the hull. I sanded the hull using 180 grit wet &
dry and cleaned out the gouges using a small grinder. The hull has been
left to thoroughly dry for a few weeks after a good cleaning, and then
wiped over with acetone. I have applied some epoxy resin over a small

All acetones are not created equal. Many sold to the consumer have numerous
impurities that cause problems. I use a solvent wash (Interlux 202 ) with good
results. Other manufacturers have similar products. I pay the extra money
because of problems with what is sold by the mass market stores.

Also 180 grit is a little fine for a pure epoxy coat. I would use 120 grit. 180
to 220 grits are for finish primers and color coats. Check the manufacturers
recommendations for the particular product that you are using.

Hairline crack filling is not straight epoxy's strong point, it is usually much
to viscous for that. Epoxy primers are what you use for hairline cracks, then
use an appropriate filler for the dings and imperfections that primer can't
cover.

If there are numerous problems then start with a high build primer.

Note: Any proper surface prep most often involves multiple coats of primer and
filler with sanding in between until the surface is ready for the finish primer
and color coats.

JJ


ares to test, the idea was for the resin to weep into the hairline
cracks and gouges to seal them before applying any required filler. I
used a roller to apply the resin to the hull and it looked good for a
couple of minutes, then it all went wrong. The resin formed hundreds of
little globules/islands and no amount of brushing or using a roller
would give me a smooth even coat.
What has happened???

Regards Bruce


##** Hello Bruce, I've done an fair amount of Epoxy repair and the problem
you describe sounds like gassing which happens when some type chemical
evaporates through the epoxy layer. Also any kind of silicone contaminate
will cause similar problems. I usually wipe down any surface with white
vinegar and then wash with soap and water before applying resin.Hope this
may help.

Rey


James Johnson
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