Gelcoat questions

[boatster]

Ok so I long since forgone the idea of superglue . I am now going to attempt gelcoat to fill the cracks as well as finish layer ontop of some fiberglass repairs. My question is, since gelcoat is a polyester resin, thus sticky when exposed to air, can I add wax/hotcoat to the gelcoat so that it sets nonsticky. I am completely familiar with surfboard construction which uses clear laminating polyester resin then a final coat of wax added laminating resin to create the "hot coat" which isn't sticky. This final coat is then wetsanded to smooth out the finish. Is boat poly resin essentially the same as surfboard poly resin?

 

[petrolhead]

Re: Gelcoat questions

The resin is essentially the same stuff, Solution MW is the wax additive for gelcoat.<br />BTW it's only the gelcoat that remains tacky in contact with air, layup resin dries, otherwise the inside of anything you moulded in GRP would remain forever tacky!

 

[boatster]

Re: Gelcoat questions

Hey Petrolhead,<br /><br />but laminating resin dries sticky. You mean to tell me the poly resin used to bond the fibreglass under the gelcoat dries nonsticky? That seems odd to me. But then again I kinda wonder why the fibreglass under gelcoat when exposed to water soaks it in. In surfboard construction the fibreglass laminated in poly resin doesn't have osmosis problems at all. Only the light foam underneath does. Can someone clear up this difference in layup schedule between say a surfboard and a boat? I've never had any of my fibreglass surfboards soak water into the glass weave like on a boat. What am I missing here? Do boat builders not soak the fibreglass with enough poly resin for weight savings or something?<br /> <br />Thanks<br />Adam

 

[boatster]

Re: Gelcoat questions

I just found a nonsticky gelcoat on the Evercoat website. I think I'm going to return the regular "sticky" gelcoat and get this stuff.<br />You can find it on http://www.evercoat.com <br /><br />It seems easy enough. They also say you can spray it on with a 10% dilution of acetone.<br /><br />Heres the description:<br />The highest quality ISO NPG marine finish gel coat to permanently repair or replace original, high-glass finish. The product cures to a hard finish and does not require Evercoat Mold Release (# 105685) to attain a fully cured surface. Use to fill gouges, chips, scrapes and deep scratches in the fiberglass gel coat. One Step Finish Gel Coat is a non-run, non-sag formulation of flexible polyester resins to produce resiliency and toughness. Evercoat Coloring Agents may be used to tint the material to desired color. Reduce with Evercoat Acetone (10%) to thin for sprayer applications.

 

[petrolhead]

Re: Gelcoat questions

I don't know what brand of resin you use boatster, but I do a lot of GRP work in my business and the layup resin never dries tacky, it would be a real pain in the arse if it did because I'd have to add wax to the final coat of resin every time I moulded something!<br />I'm surprised that you're still using poly resin for surfboards, my last 3 boards have all been epoxy, much lighter and stronger, and you can use polystyrene foam for the core and it doesn't dissolve.<br />As for poly resin soaking up water, I assume you're talking about osmosis? This takes quite a long time and boats which are immersed in water permanently would be far more likely to suffer than a surfboard which is only wet for a couple of hours at most.

 

[boatster]

Re: Gelcoat questions

Good point Petrolhead. I didn't think of the duration a board spends in the water. <br /><br />Regarding epoxy boards. They don't feel the same as poly. Thats a debate that can go on forever!! I have one Epoxy board (Patagonia), its really stiff. I will give epoxy boards another shot sometime in the future. Right now I'm dialed into my polys <br /><br />So can I just add the same wax addative used in surfboard hotcoats/sandcoats in my gelcoat then? And regarding the tackyness, there must be something I'm missing in your explination. I know Laminating resin won't be tacky if not exposed to air so maybe theres a step in your manufacturing process that I'm missing.

 

[boatster]

Re: Gelcoat questions

I get it now. If your putting laminating resin in a mold then its like vacuum bagging (surface not exposed to the air) thats why your layups aren't tacky. However if you say lay laminating resin on a surface (patch) with say fibreglass exposed to the air it'll be tacky and will compound sandpaper if you try sanding it. So its really about the process. So anyways is "Solution MW" the same as the wax used in the final step of poly surfboards? Can I use that wax? Thanks.<br /><br />Adam

 

[petrolhead]

Re: Gelcoat questions

I normally work with female moulds, first a coat or two of gelcoat goes on the inside, this stays tacky on the inside (where it's in contact with air) when cured, so it's easy to press pieces of glasscloth on the inside and they stay put. Then I apply the layup resin, enough to saturate the cloth, this dries completely, no tackiness and no need for further finishing, no additives needed, just resin and hardener.<br />When it comes out of the mould the outer surface of the gelcoat, where it was in contact with the mould, is completely dry of course.<br /><br />When you're laying up surfboards you're working the other way round, from the inside out, maybe the resin you use is designed to stay tacky, that would make sense as it makes positioning the glasscloth easier.<br />When I do layups like that I just use my normal layup resin (Scott-Bader), and finish with gelcoat, then I have to use the wax additive with the gelcoat because of course it's in contact with the air, otherwise it'd stay tacky.

 

[BillP]

Re: Gelcoat questions

Petrolhead,<br /><br />Whoa dude, cowabunga, hang ten...<br />Here in the states laminating resin is normally tacky and finishing resin not. Virtually all of the resin mfgs lead this in their product lines. <br /><br />Laminating is used to glass surfboards same as boats. It is more critical in boat construction because they typically skin the first lamination with veil to reduce print through and let it kick. Then go back and finish laminating over the tacky surface without having to prep. <br /><br />Like boaster says, they laminate surfboards and then do a fill coat (aka hot coat) with wax added to the laminating resin to build up a thick tack free and sandable surface. Surfboards are glassed in one operation (about 5-6 minutes worth) and could be done with finishing resin but it isn't cost effective or practical. It would have to be sanded to allow a fill coat. The fill coat is kicked (can you say 20-30cc per pint in 90F temps?)so quickly it builds very high and drips actually harden before they hit the floor.<br /><br />Finishing resin (more expensive than laminating resin)is tackless and used for the final gloss coat...then buffed out for final gloss. This is industry standard thoughout the frp industry here.<br /><br />Polystyrene foam and epoxy was used in surfboards back in the early 60s but fell out of grace soon thereafter. The blanks were premolded and no shaping required before glass. I don't know why it isn't the norm on epoxy boards now but my guess is it can't be shaped (planed & sanded with precision)as easy as polyurethane foam. Preshaped boards (aka popouts) just don't sell well...everybody wants a custom shape.

 

[petrolhead]

Re: Gelcoat questions

The polyester resins I use only come in two forms, Resin A is the laminating resin, it cures to a non-tacky finish. Resin B is the gelcoat and cures to a non-tacky finish where it's in contact with the mould, but remains tacky where it's exposed to air, e.g. on the inside of a female mould before the glass is applied.<br />If I understand you correctly you have 3 types of resin in the US, a laminating resin and a gelcoat which both remain tacky, and a finishing resin which cures to a non-tacky finish?<br />So if you were to lay up inside a female mould you'd need to apply gelcoat, then glass cloth with laminating resin, then a further coat of finishing resin or laminating resin with added wax? Sounds a bit long winded to me!<br />I can see the point of using finishing resin on something like a surfboard, where the finish coat is applied last and needs to be perfect, but to add it to the inside of an item that doesn't need a particularly good finish, simply to get rid of the tackiness sounds an expensive and time consuming way of doing things. <br /><br />I think the preformed polystyrene surfboard blanks you are referring to were blow moulded foam, the stuff that has an obvious beaded structure and is quite crumbly, also quite difficult to get a good surface finish, like packaging foam?<br />The stuff I use is EXTRUDED foam which is very different, it has a much finer structure and can be carved easily and precisely, it can be sanded to a very fine finish. We use lots of it at work for sculpting, and often skin it with glass/epoxy if a durable surface finish is required. <br />This is also the foam that my recent epoxy surfboards have used for the cores.

 

[BillP]

Re: Gelcoat questions

petrolhead,<br /><br />Laminating resin will lose it's tack over time and most boat mfgs don't bother to coat the final interior laminations. A tacky surface lets them come back days later and install bulkheads, stringers, innerliners, etc without more sanding. The tacky surface is superior for bonding and less work. Tacky areas are also sealed under the innerliner, etc and under normal conditions there isn't a reason to make it tack free. The mfgs that do coat it use opague gelcoat for cosmetics only.<br /><br />Boat builders don't use finishing resin just to clear seal off the tack. It is too expensive. In that case they just add wax to laminating resin (or in the last batch while glassing)...like the surfboard guys do. But like I said earlier, gelcoat is used as a cosmetic media and it drys tack free.<br /><br />Yep, the polystyrene surfboard blanks I remember looked like coolers. I had one and used epoxy to glass it with. <br /> <br />What are you laminating?

 

[petrolhead]

Re: Gelcoat questions

What are you laminating?

I'm a professional model and prop maker, doing lots of work for film and TV, so I end up making all sorts of weird stuff in polystyrene and often it needs to be skinned to make it more durable, sometimes we just skin it with strips of paper glued on, like papier mache, or if it needs to be stronger then glass/epoxy.<br />Also we use the "lost poly" moulding process quite a lot, where the poly core is dissolved out afterwards with acetone leaving a very lightweight epoxy/glass monocoque.

 

[boatster]

Re: Gelcoat questions

Whoah, like tubular brah....! <br /><br />Just because we surf doesn't mean we're all Spicoli stoners, at least I'm not. <br /><br />Anyways, I'm gonna mess around with the gelcoat and add some wax to see what happens. Best way to understand how to apply this stuff is to figure how it behaves.

 

[Terry H]

Re: Gelcoat questions

boatster..alls you need to do is to seal the gel and it will cure...there have been times when I used spray furniture wax, latex paint, spray paint from can. I like the spray furniture wax on gel patches cause it wipes of easily, you just need to spray it on as you finish the patch. I've also use the clear shipping tape from 3M, you can get real creative, but alls you have to do is seal the gel...just a thought

 

[boatster]

Re: Gelcoat questions

Thanks Chief,<br /><br />thats a good idea.