Epoxy or Poly for poly repairs?
 

Hi,

I'm doing some repairs to my Catalina 36, which is made from polyester
resin/glass over wood (like most "fibreglass" boats). Should I stick with poly
resin, or go with epoxy? I know epoxy is "better", but I'm concerned that it
wouldn't stick well to the existing poly, and that the (poly?) gelcoat won't
stick to it.

Suggestions?

Lloyd Sumpter
"Far Cove" Catalina 36

Epoxy or Poly for poly repairs?
 

Secondary bonds with polyester are not strong. Sand thoroughly and use epoxy.

Whoever's compiling the FAQ, add this one.

Lloyd Sumpter wrote:

Hi,

I'm doing some repairs to my Catalina 36, which is made from polyester
resin/glass over wood (like most "fibreglass" boats). Should I stick with poly
resin, or go with epoxy? I know epoxy is "better", but I'm concerned that it
wouldn't stick well to the existing poly, and that the (poly?) gelcoat won't
stick to it.

Suggestions?

Lloyd Sumpter
"Far Cove" Catalina 36

Epoxy or Poly for poly repairs?
 

Well the problem lies in the fact that the polyester gelcoat would not stick to
the epoxy.

You will have to use poly. I won't stick as well, but will have to do.

Rich

Epoxy or Poly for poly repairs?
 

On Sun, 28 Dec 2003 20:09:18 +0000, Toolowd wrote:

Well the problem lies in the fact that the polyester gelcoat would not stick to
the epoxy.

You will have to use poly. I won't stick as well, but will have to do.

Rich

Yeah, that's it exactly.

The boat BUILDERs that I ask this question invariably recommend epoxy. The boat
REPAIRers I ask usually say "use the same material that's the If it's poly,
use poly..."

Building a boat from scratch: epoxy, no question. Repairs on FRP/gelcoat? Jury's
still out...

Lloyd

Epoxy or Poly for poly repairs?
 

Don't use gelcoat. LPU paints weather better and are easier to work with than
gelcoat.

Toolowd wrote:

Well the problem lies in the fact that the polyester gelcoat would not stick to
the epoxy.

You will have to use poly. I won't stick as well, but will have to do.

Rich

Epoxy or Poly for poly repairs?
 

Use geloat over epoxy if you care to do so. You just have to do a lighg
sand on the epoxy so there is some tooth there. You have to do the same
with polyester or vinylester, because the cohesive bond with gelcoat
(which is also polyester) is poor (lust like any other polyester).
The only advantage to a gelcoat finish on a repair is that it is
relatively good for a color match and as it is applied thinker than any
paint, it can be wet sanded to fair the surface.
If you were planning to paint anyway, blow off the gelcoat job.
Matt Colie

Jim Conlin wrote:
Don't use gelcoat. LPU paints weather better and are easier to work with than
gelcoat.

Toolowd wrote:


Well the problem lies in the fact that the polyester gelcoat would not stick to
the epoxy.

You will have to use poly. I won't stick as well, but will have to do.

Rich

Epoxy or Poly for poly repairs?
 

Toolowd wrote:

Well the problem lies in the fact that the polyester gelcoat would not stick to
the epoxy.


True in most cases, but System Three make an epoxy formulated
specifically to go under polyester. I've used it many times and never
had a failed bond.

Look at their SB112 epoxy resin.

http://www.systemthree.com

Definitely use epoxy for the repairs.

Brian Cleverly

You will have to use poly. I won't stick as well, but will have to do.

Rich

Epoxy or Poly for poly repairs?
 

I watched a video on boat repair recently in which polyester and gelcoat
were used to repair a crack in a polyester boat below the waterline. The
inside of the hull was sanded down and 2 layers of mat applied. Then
the finish on the outside was sanded, then some putty filler followed by
gelcoat were put on with lots of sanding with different grits at each stage.

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Epoxy or Poly for poly repairs?
 

Toolowd wrote:
Well the problem lies in the fact that the polyester gelcoat would not stick to
the epoxy.

You will have to use poly. I won't stick as well, but will have to do.

Gelcoat is purely cosmetic and I'm far more concerned with the strength
of the underlying repair, so epoxy gets the nod for that. I've applied
gelcoat over epoxy repairs and it works fine as long as you sand the
epoxy surface.

--
Regards

Brian

Epoxy or Poly for poly repairs?
 

On Mon, 29 Dec 2003 03:58:11 +0000, William R. Watt wrote:

I watched a video on boat repair recently in which polyester and gelcoat were
used to repair a crack in a polyester boat below the waterline. The inside of
the hull was sanded down and 2 layers of mat applied. Then the finish on the
outside was sanded, then some putty filler followed by gelcoat were put on with
lots of sanding with different grits at each stage.


Yup - that's the way I was taught.

Lloyd

Epoxy or Poly for poly repairs?
 

On Mon, 29 Dec 2003 11:59:53 +0000, Brian Nystrom wrote:

Toolowd wrote:
Well the problem lies in the fact that the polyester gelcoat would not stick
to the epoxy.

You will have to use poly. I won't stick as well, but will have to do.

Gelcoat is purely cosmetic and I'm far more concerned with the strength of the
underlying repair, so epoxy gets the nod for that. I've applied gelcoat over
epoxy repairs and it works fine as long as you sand the epoxy surface.

Sounds like I may need a "two-part solution" ;)

For the jobs that need strength (like the stringers), I'll use epoxy, and
hope the gelcoat sticks ok. For the gouges, scratches, cracks, etc. that are
"purely cosmetic" I'll use poly/gelcoat.

Lloyd

Epoxy or Poly for poly repairs?
 

Lloyd Sumpter wrote:

On Mon, 29 Dec 2003 11:59:53 +0000, Brian Nystrom wrote:


Toolowd wrote:

Well the problem lies in the fact that the polyester gelcoat would not stick
to the epoxy.

You will have to use poly. I won't stick as well, but will have to do.

Gelcoat is purely cosmetic and I'm far more concerned with the strength of the
underlying repair, so epoxy gets the nod for that. I've applied gelcoat over
epoxy repairs and it works fine as long as you sand the epoxy surface.


Sounds like I may need a "two-part solution" ;)

For the jobs that need strength (like the stringers), I'll use epoxy, and
hope the gelcoat sticks ok. For the gouges, scratches, cracks, etc. that are
"purely cosmetic" I'll use poly/gelcoat.

That sounds like a sensible approach to me.

--
Regards

Brian

Epoxy or Poly for poly repairs?
 

I'm doing some repairs to my Catalina 36, which is made from polyester
resin/glass over wood (like most "fibreglass" boats). Should I stick with
poly
resin, or go with epoxy? I know epoxy is "better", but I'm concerned that it
wouldn't stick well to the existing poly, and that the (poly?) gelcoat won't
stick to it.

Suggestions?

Lloyd,

Based on my 30 years (mostly as an amateur repairing my own and friend's boats,
a few summer jobs and one "inbetween serious IT employment" stint at Waterat,
probabably the best small high performance boat builder in the galaxy"), I
would NEVER use polyester resin to do a repair. Repair with epoxy. Sand the
area you are repairing well and the epoxy will stick to it much better than
polyester will.

As for gelcoat (polyester) sticking to epoxy. It works for me. Just build up
the repair with epoxy and whatever glass, Kevlar, carbon fiber, etc.
reinforcements you intend to use, level it with epoxy and filler, sand with 60
or 100 grit and gelcoat it. Hint - you can tint the last epoxy layer with some
of the gelcoat, so the substrate is close to the color of the gelcoat. Don't
use much gelcoat for this, just enough to color the epoxy resin, and don't
bother catalysing it. Always mix fillers, tints, etc. into epoxy AFTER mixing
the resin and hardner.

Alexander "Ali" Meller
505s 7200, 8776, 7080
Albacore 4862
Laser 11166, 173969

Epoxy or Poly for poly repairs?
 

On Thu, 01 Jan 2004 00:41:06 +0000, Alexander A. Meller wrote:


I'm doing some repairs to my Catalina 36, which is made from polyester
resin/glass over wood (like most "fibreglass" boats). Should I stick with poly
resin, or go with epoxy? I know epoxy is "better", but I'm concerned that it
wouldn't stick well to the existing poly, and that the (poly?) gelcoat won't
stick to it.

Suggestions?

Lloyd,

Based on my 30 years (mostly as an amateur repairing my own and friend's boats,
a few summer jobs and one "inbetween serious IT employment" stint at Waterat,
probabably the best small high performance boat builder in the galaxy"), I would
NEVER use polyester resin to do a repair. Repair with epoxy. Sand the area you
are repairing well and the epoxy will stick to it much better than polyester
will.

As for gelcoat (polyester) sticking to epoxy. It works for me. Just build up
the repair with epoxy and whatever glass, Kevlar, carbon fiber, etc.
reinforcements you intend to use, level it with epoxy and filler, sand with 60
or 100 grit and gelcoat it. Hint - you can tint the last epoxy layer with some
of the gelcoat, so the substrate is close to the color of the gelcoat. Don't
use much gelcoat for this, just enough to color the epoxy resin, and don't
bother catalysing it. Always mix fillers, tints, etc. into epoxy AFTER mixing
the resin and hardner.


Interesting - I've never heard of this. I was taught to use the same material
for repairs as original - the theory being a "perfect" repair would be
indistinguishable from the rest of the hull - even with xray, etc. (talking
about cosmetic repairs here...)

Interesting tip on mixing gelcoat with epoxy.

Lloyd

Epoxy or Poly for poly repairs?
 

Do you mean mixing in the gelcoat or the pigment with the epoxy?

"Lloyd Sumpter" wrote in message
...
On Thu, 01 Jan 2004 00:41:06 +0000, Alexander A. Meller wrote:


I'm doing some repairs to my Catalina 36, which is made from
polyester
resin/glass over wood (like most "fibreglass" boats). Should I stick
with poly
resin, or go with epoxy? I know epoxy is "better", but I'm concerned
that it
wouldn't stick well to the existing poly, and that the (poly?) gelcoat
won't
stick to it.

Suggestions?

Lloyd,

Based on my 30 years (mostly as an amateur repairing my own and friend's
boats,
a few summer jobs and one "inbetween serious IT employment" stint at
Waterat,
probabably the best small high performance boat builder in the galaxy"),
I would
NEVER use polyester resin to do a repair. Repair with epoxy. Sand the
area you
are repairing well and the epoxy will stick to it much better than
polyester
will.

As for gelcoat (polyester) sticking to epoxy. It works for me. Just
build up
the repair with epoxy and whatever glass, Kevlar, carbon fiber, etc.
reinforcements you intend to use, level it with epoxy and filler, sand
with 60
or 100 grit and gelcoat it. Hint - you can tint the last epoxy layer
with some
of the gelcoat, so the substrate is close to the color of the gelcoat.
Don't
use much gelcoat for this, just enough to color the epoxy resin, and
don't
bother catalysing it. Always mix fillers, tints, etc. into epoxy AFTER
mixing
the resin and hardner.


Interesting - I've never heard of this. I was taught to use the same
material
for repairs as original - the theory being a "perfect" repair would be
indistinguishable from the rest of the hull - even with xray, etc.
(talking
about cosmetic repairs here...)

Interesting tip on mixing gelcoat with epoxy.

Lloyd