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Charlie,

I've gotten polyester resin and hardener at many hardware stores as well
as boat stores. Beware using non-marine polyester filler, but the resin
is fine.

Both epoxy and polyester have their advantages and disadvantages. I
prefer, in general, to repair polyester boats with polyester resins so
as to not create problems for future repairs. As you note, polyester
will not adhere to epoxy. In fact, polyester isn't really an adhesive.
It forms a mechanical bond with the cured resin. This is why it's
important to rough sand a taper around the hole, at least 3 inches, to
give a good bond. When patching, I like to lay up all layers in one day,
without letting the resin completely cure between layers. I let them
kick off and become hard, but the next layer can still chemically bond,
saving some sanding and probably giving a stronger layup. BTW, if you
let epoxy cure, you need to wash the amine blush off with soap and
water, and then dry the surface, before continuing.

Polyester is air-inhibited, so the surface will not cure completely in
the air. That's why very thin applications don't work very well. The
normal way to get the surface to cure is to coat it with PVA (poly-vinyl
alcohol). On small boat repairs, I typically just sand it smooth and
spray it with appliance enamel.

Polyester gives off a lot of styrene, which is what you smell. If you're
working indoors, use a respirator. If you're working with large
quantities and frequently, use a respirator. If you're patching a
Sunfish outside, the fumes will likely blow away. Prefer working from
the windward side, and hold your breath for a moment if you smell it. I
have a respirator but no longer use it when doing small patches like
this. When I do use it, I load my beard up with glove-cote to seal the
airflow around the respirator.

I've done a lot of repairs on Sunfish and other small boats when my
grandkids were in a junior sailing program. Kids are hard on boats, and
they often need patches. The method of working outlined in
emerged from
that. It will not give the most pristine results, but they will be
reasonably good, strong, and functional. If you're working on a
show-quality boat, you'll want a seasoned professional working on it.

The biggest resin job I've done was helping a friend replace the rotten
plywood deck of his 21' center console with Coosa board covered with
glass. Another friend was mixing the resin for us as fast as they could,
and we went through several gallons on one hot afternoon. That was about
20 years ago and that boat is still rock solid.

I've also done a lot of deck re-coring on my Alberg 30, also with
polyester. That requires a little more care than the small boat repairs.
When I repaired the forward edge of the bow, I used epoxy because I was
concerned about getting enough grip across the width with the polyester.
But otherwise, I've used polyester and have no trouble getting insurance.

Oh, epoxy resins have remarkably different characteristics depending on
trace amounts of additives in the resin and/or hardener. I had a great
conversation some decades back with the chemist for a boat builder who
built with epoxy. That chemistry is not for amateurs like me. It's also
a warning that not all epoxies are alike.

Use what you want. I'm not interested in re-engineering an old Sunfish,
so I use what's worked for it it's whole life.

? - George

On 7/6/20 5:52 AM, Signal Charlie wrote:
> Hey George
>
> You are correct, the Pettit Rep was trying to sell me something. But his
> experience with the insurance company, maybe just one company, came from
> his previous life as a big boat repair guy. I think they key bit of info
> I picked up from his story was that the epoxy resin supposedly made a
> stronger repair. So I don't want to report my story wrong or try to
> influence folks one way or another, it is possible that the _insurance
> company_ was wrong.
>
> Please tell us more about your experience with polyester resins. I have
> heard that they are a lot cheaper than epoxy resin and good to?use for
> large?projects. I have not noticed them for sale at my favorite haunts,
> but I haven't looked for them. I don't know where to look for them or
> who the?best manufacturers and suppliers?are. Do you have a favorite and
> have you worked with them a lot? I also hear they smell bad and were
> more hazardous to work with than epoxy. Let's see, what else...this info
> below came from the web (Ref:
> ) Some
> of the info sounds like sales talk, other bits of the info are in line
> with what the Team Epoxy folks repeat.
>
>
>? ? ?EPOXY RESIN CHARACTERISTICS:
>
>? ?* -Epoxy is extremely strong and has great flexural strength. Our
>? ? ?300/21 <>?and
>? ? ?400/21
>? ? ?<>?epoxy
>? ? ?resins have a flexural strength of 17,500 psi. Our 300/11
>? ? ?<>?and
>? ? ?400/11 epoxy resins have a flexural strength of 12,800 psi.
>? ?* -Epoxy has a great shelf life. While we guarantee our epoxy resins
>? ? ?for 6 months, you can reasonably expect the epoxy to last at least a
>? ? ?few years properly? stored on the shelf.
>? ?* -You cannot vary the cure time of epoxy resin. Epoxy resin’s cure
>? ? ?time is determined by the hardener and the temperature. Our 300
>? ? ?resin with 21 hardener has a cure time of 24 hours at 70 F. Our 5
>? ? ?Minute Epoxy
>? ? ?<>?has
>? ? ?a cure time of 60 minutes at 70 F. Adding more hardener will not
>? ? ?make it cure more quickly! Too much hardener will actually make the
>? ? ?cured epoxy rubbery. You can decrease the cure time by raising the
>? ? ?ambient temperature around the epoxy resin. For every 10 F the
>? ? ?temperature is raised above 70F, you can cut the cure time by 10%.
>? ? ?However, don’t raise the temperature over 100 F.
>? ?* -A gallon of epoxy generally costs slightly more than polyester resin.
>? ?* -Epoxies like ours that are 100% solids are low to no VOC. They have
>? ? ?a hardly any odor. Epoxy is also non-flammable.
>? ?* -Epoxy cures fully when applied as a thin film, making it ideal for
>? ? ?adhesive applications.
>? ?* -Epoxy does not shrink when cured.
>? ?* -Epoxy is very resistant to wear, cracking, peeling, corrosion and
>? ? ?damage from chemical and environmental degradation.
>? ?* -Once cured, epoxy is moisture resistant.
>? ?* -Epoxy is not, on its own, UV resistant. Some epoxies have a UV
>? ? ?resistant additive added to them that works moderately well.
>? ? ?However, the best way to ensure that your epoxy doesn’t yellow or
>? ? ?breakdown from UV rays is to top coat it with clear UV resistant
>? ? ?urethane. Then, you will have the strength and durability of the
>? ? ?epoxy and the UV protection of the urethane.
>? ?* -Epoxy generally has a bonding strength of up to 2,000 psi.
>? ?* -Epoxy will not bond to polyethylene, polypropylene, EPDM, anodized
>? ? ?aluminum, Teflon or Tedlar.
>
>
>? ? ?POLYESTER RESIN CHARACTERISTICS:
>
>? ?* -Polyester resin is brittle and prone to micro-cracking.
>? ?* -The shelf life of polyester resin is about 6 months – 1 year.
>? ?* -You can vary the cure time of polyester resin by adding more or
>? ? ?less of MEKP catalyst.
>? ?* -Polyester resin generally costs slightly less than epoxy resin.
>? ?* -Polyester off-gases VOCs and has strong, flammable fumes.
>? ?* Polyester resin does not cure well as a thin film, so it doesn’t
>? ? ?work well as an adhesive.
>? ?* -The larger the pour, the more polyester resin shrinks when cured.
>? ?* -Polyester resin is UV resistant and does not need to be top coated
>? ? ?to prevent yellowing or degradation from sunlight.
>? ?* -Once cured, polyester resin is water permeable, meaning water can
>? ? ?pass through it eventually.
>? ?* -The bonding strength of polyester resin is generally less than 500 psi.
>? ?* -Polyester resin will not bond to epoxy resin.
--
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? ?When I remember bygone days? ? ? ? ? ? ? ? ? ? ? ? ?George Dinwiddie
? ?I think how evening follows morn;? ? ? ? ? ? gdinwiddie@...
? ?So many I loved were not yet dead,? ? ? ? ? ?
? ?So many I love were not yet born.? ? ? ? ? ? ? ? ? ? ? ? ? also see:
? ? ? ? ? ? ? ? 'The Middle' by Ogden Nash? ? ?
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