Author Topic: Using polyester resins on an epoxy board.  (Read 9424 times)

TallDude

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Using polyester resins on an epoxy board.
« on: September 13, 2014, 12:00:00 PM »
First of all, Don't use polyester resins directly onto EPS foam! It will melt the foam.
That being said, there are applications where top coating a board that was glassed using an epoxy resin with polyester top coat can be useful. I know a few glassers who like using color pigments to do art on a board. They prefer to use polyester resin because they are familiar with the flow, blend, and workable time. If they have multiple boards they are finishing, they will use Polyester top coats over both polyester resin and epoxy. I wasn't sure if that was a good idea, but they didn't seem to be having problems with it. I've been thinking about playing with pigments and had not seen any of these glassers doing pigments with epoxy. I would prefer not to use polyester resins... :P  The manufacturers of the pigments say they are for both polyester and epoxy resins, but I haven't seen anything on how the ratios will effect cure times, and bond?
I found this research paper on bonding polyester to epoxy resins. For you who have to know the specifics......
http://www.westsystem.com/ss/polyester-over-epoxy/
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8'8" L-41 ST and a whole pile of boards I rarely use.

Jeroensurf

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Re: Using polyester resins on an epoxy board.
« Reply #1 on: September 14, 2014, 08:48:23 AM »
Windsurfers always use Epoxi and often with pigment.
Works fine.

PonoBill

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Re: Using polyester resins on an epoxy board.
« Reply #2 on: September 14, 2014, 09:59:34 AM »
I still wouldn't do it, even after reading the West Systems paper. First of all, why bother. But ester resins are much more water-permeable than epoxies. The west systems paper is using the resin essentially as a hotcoat. I'm not sure it would work the same with glass in it. I sure wouldn't use a sandable resin with wax in it on top of epoxy. But the bottom line is I can't see a great reason other than tradition.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Bean

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Re: Using polyester resins on an epoxy board.
« Reply #3 on: September 14, 2014, 12:23:33 PM »
One issue with epoxy is that it takes significantly more time to produce a nice gloss finish.  With polyester resin, you might start buffing after 400-600 but you need to get down to 1500-2000 grit before even considering buffing epoxy.  Not that big deal for repairs, but a real time sucker for production.

magentawave

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Re: Using polyester resins on an epoxy board.
« Reply #4 on: September 16, 2014, 01:01:27 PM »
My thinking before was that epoxy would adhere to almost anything but polyester resin would not adhere to epoxy. So I was surprised recently to see surfboards laminated with epoxy but polyester resin was used for the hot coat. Anyone know how well that holds up?
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TallDude

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Re: Using polyester resins on an epoxy board.
« Reply #5 on: September 16, 2014, 01:38:52 PM »
Read the research paper link on my initial post. A wax to the hot mix and ?
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andygere

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Re: Using polyester resins on an epoxy board.
« Reply #6 on: September 19, 2014, 04:21:13 PM »
I have a custom epoxy board with a resin tint.  It looks great, but the board is a sanded finish, not gloss.  As noted above, it's a lot of work to get a poly style gloss from epoxy.  I've grown to like sanded finish boards, it's easier to make repairs look good on them, and you can get a nice luster using wipe on acrylic sealers.  Fiberglass Supply sells a good one.

I would avoid polyester on epoxy for the simple reason that you will only get a mechanical bond, and I would expect durability to be poor as a result.  Most production boards are painted instead of tinted for the simple reason that clear epoxies that are tintable are more expensive, and that the finish work on the blank/sandwich would have to be much nicer if you could see it through a clear or semi-opaque tint. That said, nice airbrush and pinline work with clear epoxy on top can look almost as good as a tinted cut lap job, and it's less labor intensive.

Resin tint epoxy board


Air brush with clear epoxy

Dwight (DW)

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Re: Using polyester resins on an epoxy board.
« Reply #7 on: September 19, 2014, 04:48:41 PM »
I know of one company with a polyester resin in testing, that was developed just for hot coating on epoxy. Some guys really want that high gloss bad.

I've seen the test boards with it. They are pretty.

andygere

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Re: Using polyester resins on an epoxy board.
« Reply #8 on: September 20, 2014, 11:20:15 AM »
System Three sells a surfboard specific epoxy resin that is supposed to finish glossy like polyester.  I've never used it, but it looks interesting.  It's their SB-112 Epoxy.  The spec sheet for it advertises that polyester resin can be bonded directly to SB-112 without using tie coats.  It can also be pigmented, though there is no mention of tinting. Perhaps this is the way to get poly gloss on an epoxy board. Anybody with experience using this product?  I've used System Three Silvertip epoxy, and it's an excellent product.

http://www.systemthree.com/store/pc/SB-112-c12.htm

supthecreek

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Re: Using polyester resins on an epoxy board.
« Reply #9 on: September 20, 2014, 06:41:30 PM »
Great thread... very informative...thanks!

Now I know why they "Paint" SUP's... that baffled me in the beginning... sorta still does.... tinted resin doesn't scrape off with paddle hits.... maybe they should use the expensive tintable Epoxy just on the rails.

PonoBill

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Re: Using polyester resins on an epoxy board.
« Reply #10 on: September 21, 2014, 10:28:27 AM »
I'm going to try the reverse--epoxy on polyester, which the interweb tells me works just fine as long as the surface prep is good. The Ama from one of the Hood River Canoe Club OC6's has been leaking like crazy. I sanded it down, put a little air into it and used my ultrasonic leak detector on it--sounded like a calliope--stress cracks under the 'iako pillars, pinholes everywhere, leaky lashing holes and leaks on the bottom from rock strikes. The lashing holes have PVC pipe pressed into drilled holes. I'm not sure how I'm going to seal those, and even if it matters. They're pretty high out of the water.

It's drying out in my shop, I expect to make my first ama repair attempt in a couple of days when it's to be fully dry. I'll keep y'all posted on how it goes in case you need to fix an Ama.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

TallDude

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Re: Using polyester resins on an epoxy board.
« Reply #11 on: September 21, 2014, 10:47:23 AM »
Maybe try to make a temporary box out of foam sheets or even plywood, then stick a couple of shop lights or small space heater in the box. A 90 or 100 deg. post cure will probably get a stronger cure and possibly better bond. I don't know if it would be counter productive heating the polyester. You think it could weaken the bond?
It's not overhead to me!
8'8" L-41 ST and a whole pile of boards I rarely use.

PonoBill

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Re: Using polyester resins on an epoxy board.
« Reply #12 on: September 21, 2014, 11:32:02 AM »
I let it drain overnight, and now it's sitting in the sun. I'd pump dry air through it, but it makes my compressor run continuously, so no.

I plan to take the surface where the major cracks are down into the glass, use three layers of 6oz S-glass that I can't use for much because it's too stiff, and vacuum bag it to get as good a mechanical bond as I can. Then tape the seams with some heavy fiberglass tape the club has. they also have some kind of roll-on epoxy barrier stuff that I'll use as a hotcoat. the stuff will build to about 1/4" according to the spec sheet, but I'm just going to give it one coat, then paint it with rattlecan white. Might not be perfect, but it will be better than having a gallon of water in it.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

 


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