Polyester vs Sunlight

[44'cruisingcat]

A question for the resin experts: how well does polyester resin cope with direct exposure to sunlight? Like for years.

I know epoxy has to be kept out of the sun, but I've never heard anything like that said about polyester.

Does it last well in the sun?

[Wotname]

About as well as polyester line and polyester sails etc.

[boatman61]

Take a look at your gel coat.. how's it doing.??

[Island Time O25]

Epoxy can be made less affected by the sun using a special UV blocking hardener. I think, if I remember correctly, V140. My boat builder friend calls it "Florida additive" and says any outside hull repairs should be made with this hardener. Not sure if there is a similar item for poly but will ask when I'll talk to him.

[boatman61]

From the West System site.. no mention of uv resistant hardeners.



Add final finish coatings to your structure to provide UV protection, extra moisture resistance and more durability.
Paint or varnish applied over an epoxy barrier coat is intended to decorate the surface and protect the epoxy from sunlight. In so doing, the finish coating extends the life of the epoxy moisture barrier, which in turn provides a stable base that extends the life of the finish coating. Together, the two form a protective system far more durable than either coating by itself.
This page covers:
The importance of UV protection
Finding the most compatible coating
Coating types – at a glance
The importance of UV protection
Protection from sunlight is a primary consideration in the selection of a final coating. Long term UV (ultraviolet) protection of the barrier coat depends on the effectiveness with which the finish coating resists UV and retains its pigmentation and/or shield of UV filters on the surface of the epoxy barrier coat. A high gloss finish reflects a higher proportion of the light from the surface than a dull finish. Therefore, a white coating- especially a high gloss white –is much more durable.

1. Identify the WEST SYSTEM products that best suits your needs
(WEST SYSTEM)
... filler and hardener selection guides Whether you are looking for a fire-resistant additive, a filler for fairing or a hardener that gives a natural wood finish, you will identify which WEST SYSTEM product ...
2. Choosing WEST SYSTEM hardeners, fillers and additives
(WEST SYSTEM)
Whether you are looking for a hardener that gives a natural wood finish, a filler for fairing or a fire-resistant additive, you will identify here which WEST SYSTEM® product is suitable. In the following ...
3. WEST SYSTEM 205 Fast Hardener
(Hardeners)
... mixed with WEST SYSTEM 105 Epoxy Resin® in a five-part resin to one-part hardener ratio, the cured resin/hardener mixture yields a rigid, high-strength, moisture-resistant solid with excellent bonding ...
4. WEST SYSTEM 206 Slow Hardener
(Hardeners)
... with 105 Epoxy Resin® in a five-part resin to one-part hardener ratio, the cured resin/hardener mixture yields a rigid, high-strength, moisture-resistant solid with excellent bonding and coating properties. ...
5. Finish coatings
(Support)
... polyurethanes. They are durable and chemically resistant, but offer limited UV protection compared to the linear polyurethanes. Antifouling paints ...

[Wotname]

Originally Posted by Island Time O25

Epoxy can be made less affected by the sun using a special UV blocking hardener. I think, if I remember correctly, V140. My boat builder friend calls it "Florida additive" and says any outside hull repairs should be made with this hardener. Not sure if there is a similar item for poly but will ask when I'll talk to him.

There, fixed

[Benz]

Polyester resin will yellow over time in the sun, and begin to oxidize slowly off (this is why gelcoat gets chalky if not waxed regularly. Look at those forehatches that used to be popular where there was just bare fiberglass in order to let light in. They are all yellow and usually the chopped strand mat is really printing through or even coming up in hairs.
Takes a long time, but I prefer to keep gelcoat or paint on my polyester stuff.

[boatman61]

Originally Posted by Island Time O25

Epoxy can be made less affected by the sun using a special UV blocking hardener. I think, if I remember correctly, V140. My boat builder friend calls it "Florida additive" and says any outside hull repairs should be made with this hardener. Not sure if there is a similar item for poly but will ask when I'll talk to him.

PRODUCT DATA SHEET: POTA-POX PLUS - SERIES V140
https://www.tnemec.com/resources/product/PDS/V140.pdf · PDF file
PRODUCT DATA SHEET SERIES V140 PRODUCT PROFILE GENERIC DESCRIPTION Polyamidoamine Epoxy COMMON USAGE Innovative potable water coating which offers high-build edge protection and allows for application at a wide range of temperatures (down to 35°F or 2°C with 44-700 Accelerator). For use on the interior and exterior of steel or concrete

[Boatguy30]

Extremely well, lots of early glass boats had hatches made with no gelcoat in the center. Lots of 60s and 70s boats still sailing with these hatches. Probably does loose some strength maybe 50% in 40-50 years?

[a64pilot]

Actually Polyster resin is effected by UV and pretty seriously so, but it does take years.
The Agricultural airplane I used to manufacture had a chemical hopper that was made from Polyester, we did not gelcoat or paint it as we wanted it to be see thru so that at a glance you could see how much chemical was in the hopper. After years it would turn orange and wear, and even start showing glass at about 15 yrs or so. The fix was of course to “hot coat” the hopper with just resin to wet the exposed glass back out, but any resin I believe should have either a gel coat or paint to protect it from UV.

[SaylorMade]

Isn't gelcoat = polyester?
Holding up well on my 40 yo boat

[a64pilot]

Originally Posted by SaylorMade

Isn't gelcoat = polyester?
Holding up well on my 40 yo boat

Yes, but it has pigment in it that protects it a little like paint does or that’s my understanding anyway, but I am no composites Guy

[jimbunyard]

Following three pictures are a polyester windsurfer laid up, by me, in 1987. It has been kept outside, uncovered, since then...for the last 10 years on top of an old fiberglass skiff with 4 other unused boards.

It was made from high quality clear polyester laminating resin, if there were UV inhibitors in the resin they were not advertised.

The first picture shows the date, 2/87, and my name, written on the 1/8" spruce stringer. The blue specs are metallic paint additive mixed into the final 'hot' coat, given to me by a friend when such things seemed to matter. There is a slight yellowing in the resin, but at least as much is from the polyurethane foam the board is made from (in a fit of laziness I didn't paint the bottom white as should be done).

The second picture just shows the condition of the bottom after 31 years of neglect (I washed it off for the picture)

The third shows the top, also just washed. The cloth showing is not because of deterioration of the resin, but because of the use of the wrong type of cloth (got an unknown half roll included in a lot at a tool sale). As can be seen, the top is in reasonably good shape, though mildew has grown through the nonskid section pretty bad (who knows what I used for non skid...I've tried all kinds of off-the-wall stuff sand, salt, sugar, etc....) and also certain parts of the un-non-skidded sections. Yes, the nose of the board is yellow...

So yes, polyester resin holds up very well indeed to UV. However, that isn't to say that it won't last longer with proper maintenance, certain additives or a top coat that is more UV resistant than the polyester resin itself is...

[IslandHop]

Looks like softvill there, come across plenty old, neglected , rotten, surfboards and fg boats around here. Yes fg will rot eventually some worse than others. First it gets soft, really weak, and yellow

[IslandHop]

Forgot about ecopoxy, says uv inhibitors come mixed in and doesn't yellow. Eco friendly, sustainable. Never tried the stuff was going to ask for experiences here