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Old 11-06-2012, 17:00   #1
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Waxed vs UNwaxed Poly resin

I'm starting a project on my boat, and I'll be using polyester resin. I know there are advantages to epoxy, but cost isn't one. My hull is polyester, and so I'll get decent strength (sufficient for my project) from polyester.

I'm using brand new resin, and it says "contains no wax." I know what that is supposed to mean, although I've never used it before. I just completed a small part, and the work went well. My mix ratio appears to have been good, as it was workable for about 1/2 hour, and cured rock hard the next morning. It has cured for a day now, and I'm pleased.

Here's my question. As an "UNwaxed" resin, it should cure tacky (at least that's my understanding). The glass work, as well as the 1/8" left in the tub, both cured shinny, hard, and not the least bit "tacky." That doesn't sound like what I expected! The can clearly says "contains no wax." The product is MarPro, targeted for the trades market, so it has little information on the can -- but tradesmen expect it to mean what it does say.

Can anyone tell me how to tell if it is really unwaxed? Can I tell if it is waxed? And the million dollar question -- can I safely put gelcoat over this?

Thanks

Harry
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Old 11-06-2012, 17:53   #2
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Re: Waxed vs UNwaxed Poly resin

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Originally Posted by sailingharry View Post
I'm starting a project on my boat, and I'll be using polyester resin. I know there are advantages to epoxy, but cost isn't one. My hull is polyester, and so I'll get decent strength (sufficient for my project) from polyester.

I'm using brand new resin, and it says "contains no wax." I know what that is supposed to mean, although I've never used it before. I just completed a small part, and the work went well. My mix ratio appears to have been good, as it was workable for about 1/2 hour, and cured rock hard the next morning. It has cured for a day now, and I'm pleased.

Here's my question. As an "UNwaxed" resin, it should cure tacky (at least that's my understanding). The glass work, as well as the 1/8" left in the tub, both cured shinny, hard, and not the least bit "tacky." That doesn't sound like what I expected! The can clearly says "contains no wax." The product is MarPro, targeted for the trades market, so it has little information on the can -- but tradesmen expect it to mean what it does say.

Can anyone tell me how to tell if it is really unwaxed? Can I tell if it is waxed? And the million dollar question -- can I safely put gelcoat over this?

Thanks

Harry

If you acetone wipe the layup does it get sticky again? If so there is no surface cure and probably no wax. Wax only affects surface cure, and often you can't really tell the difference with resin unless you have quite a bit of experience, especially since a really hot batch will come close to a surface cure, particularly if you are using polyester isotropic resin instead of orthotropic resin, which you probably are. You can definitely safely gelcoat over it. You should have a 24 hour window to catch a chemical bond. A light scratch up to remove any fuzzies or drips is generally called for even when chemical bonding. If you are concerned about wax content acetone wipe thoroughly before coating, this will remove any wax residue and make the resin sticky again.
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Old 11-06-2012, 18:47   #3
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Re: Waxed vs UNwaxed Poly resin

^^^What he said^^^^ Couldn't have said it better
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Old 11-06-2012, 19:02   #4
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Re: Waxed vs UNwaxed Poly resin

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^^^What he said^^^^ Couldn't have said it better


I would add that you should never, ever buy anything which IS pre-waxed. This is a terrible mistake propogated by even the manufacterers who will happily sell you prewaxed resin or gel. And in fact many pro's will use a prewaxed gel for repairs. I believe it leads to nothing but trouble and has much to do with the mysterious problems many report with surface curing gel properly. Personally I add my own surface curing agent (in the old days we would actually melt wax into styrene monomer), which allows me to spray the usual 3-4 thin coats on a repair and only add the wax into the final coat. It's just common sense that if you do this with prewaxed gel unless you spray only one coat you are going to have problems, as you need to wait for the gel to flash between coats and the wax will rise to the surface on each succesive coat. This can cause all sorts of wierd effects, like cratering in the gel and alligation, that you want to stay away from. And I can't imagine why you would ever want to wax resin for a surface cure, I think that that is done mostly for the surfboard market, where they have strange ways when it comes to laminating. So buy your own surface cure and stay away from that prewaxed stuff, IMHO. Even when I brush a bilge laminate it takes more than one coat to cover...
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Old 11-06-2012, 19:14   #5
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Re: Waxed vs UNwaxed Poly resin

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If you acetone wipe the layup does it get sticky again? If so there is no surface cure and probably no wax.

If you are concerned about wax content acetone wipe thoroughly before coating, this will remove any wax residue and make the resin sticky again.
Minaret,

Thanks, your answer is comforting (especially the part where you say it can be hard to tell). But your very last sentence contradicts your very first sentence. Will acetone make waxed resin sticky again?

With regard to the chemical bond, I was under the impression that the "window" was measured in weeks, not hours. I'm not terribly worried about a strong chemical bond, as it's just gelcoating a bilge area, but it is good information to know the details.

Oh, with regard to another reply about pre-waxed product, I agree with you -- I have 4 gallons of resin, and a gallon of gelcoat, all unwaxed. And then I have a bottle of wax. I will be doing glasswork in the bilges, followed by a coat of gelcoat, followed by a coat of self-waxed gelocoat.

Thanks again!

Harry
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Old 11-06-2012, 20:13   #6
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Re: Waxed vs UNwaxed Poly resin

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Originally Posted by sailingharry View Post
Minaret,

Thanks, your answer is comforting (especially the part where you say it can be hard to tell). But your very last sentence contradicts your very first sentence. Will acetone make waxed resin sticky again?

With regard to the chemical bond, I was under the impression that the "window" was measured in weeks, not hours. I'm not terribly worried about a strong chemical bond, as it's just gelcoating a bilge area, but it is good information to know the details.

Oh, with regard to another reply about pre-waxed product, I agree with you -- I have 4 gallons of resin, and a gallon of gelcoat, all unwaxed. And then I have a bottle of wax. I will be doing glasswork in the bilges, followed by a coat of gelcoat, followed by a coat of self-waxed gelocoat.

Thanks again!

Harry
Sorry, I could definitely see where that would come across as contradictory. All I can say is that when you acetone wipe resin which has been waxed and is surface cured, it does get a little sticky again (ie you can leave a fingerprint), but if you acetone wipe unwaxed resin with no surface cure it will get VERY sticky! The difference is pretty extreme. I only mentioned that an acetone wipe will create sticky as well as removing the wax because I believe it helps the bond even on surface cured resin and thus should be done in any case, though obviously this is a moot point because if it's surface cured you need to sand it anyway. The impression you have of very long chemical bond windows is with ortho resin, which is what many manufacterers use to build boats in the factory. Most poly resin used in repair work is iso though, and doesn't have as long a window for a good chemical bond. You can acetone wipe an ortho hull built years ago and it too will get very sticky, which is why they use it when building. A 24 hr window would really screw you when trying to laminate a big boat...
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