gel coat

[amcc]

Hi, I dont know if this is the right site for me but here goes, I have a GRP Mirror Dinghy and I am repairing the gunwhale which I have done with Fibreglass Resin,I was unsure of getting the colour right which is grey so decided to sand the lot, I am now ready for the gelcoat, I have the wax additive but dont know whether to brush or spayany advice would be very mach appreciated. I hope someone can help.

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[aitchw]

Sorry but you shouldn't have done that. Re gelcoating large areas is a nightmare. You should have restricted yourself to repairing the damaged area.

Having said that, hopefully someone will be able to give sufficient guidance to make a job of it.

Good luck.

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[Hardley]

Definatley spray wax on, make sure you cover all the gel coat.
It is near impossible to get a complete colour match, unless you are prepared to go to a lot of trouble.
As has been said you should have just repaired/gelcoated the damaged part, too late now, but gel coat thinned down with acatone can be sprayed on, using modellers spray gun with gas cylinder attached,straining to get any bits out first. But mask every thing nearby up with masking tape & newspaper, roll the edge of masking tape back 1/8 inch so that gel coat blends in & does not leave a built up edge. Normally you can put coat upon coat without stopping.

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[bruce]

got to ask, what is 'wax additive', have not heard it on this side of the pond. check 'westsystem.com', they have lots of 'glass' help.

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[Hardley]

'wax additive', is a substance, that when sprayed on gelcoat keeps the air off of it, gelcoat does not harden if the air gets to it.
I first heard of it several years ago when I purchased some videos on gelcoat repairs. made by a Yank boat repairer, so you do have it over there.

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[Ruthie]

Polyester resin with wax added - sometimes refered to as finishing resin.

As already said, you can get problems with gel coat not hardening fully if it's exposed to the air. Not normally a problem during original lay-up 'cos the gel coat is up against the mould. I believe the problem is the result of styrene - which plays an important role in polymerisation - evaporating too fast when in contact with the air.

I read somewhere that one trick is to add extra styren to compensate. The wax additive is another dodge - it works by migrating to the surface and forming a seal.

Ruthie

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[Ruthie]

oops - forgot to add... the other simple trick is to tape a sheet of polythene (or similar) over the new gel coat to keep the air out, and the styrene in. Not too practical if you're spraying an entire hull though!

Ruthie

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[JimMcMillan]

Been there done that,tried to gelcoat hatch cover with all additives etc and it just would not harden properly, disaster for all the reasons already stated. Sprayed the actual hatch with a good quality(vehicle paint) 2 part paint which I had mixed to match. Perfect.

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[snowleopard]

i am accustomed to using 'wax in styrene' which is added to gel coat to make the surface set.

polyester resin is 'air inhibited' so the surface layer remains tacky. this is a good thing for gelcoat as it helps the subsequent laminations to bond. laminating resin contains a small percentage of wax which floats up to form an airtight micro layer on the surface allowing the surface to set. when adding more resin it is vital to sand off this wax layer. flow coat is a gelcoat with wax added so you can paint it over a laminate.

i've never heard of a wax you apply over the surface but see no reason why it shouldn't work. you could probably brush or sparay it after the resin has hardened.

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[gjgm]

no.. laminating resin should not have any wax in it... As you say at the beginning there is laminating resin/gelcoat which is air inhibited... meaning it wont set in contact with air.. thats great for laminating as the surface remains tacky for the next layer of laminate.
then there is flowcoat which has wax added which can ONLY be used as a topcoat because even other gelcoat wont bond to it. the purpose is that it is blocked from air and will harden.
So , for final gelcoat, you need to block from air.. either melamine,clingfilm,wax.. whatever.
In this case, theres no option but for flowcoat, or gelcoat with wax by any other name, as he ll never manage to seal a gunwhale from air i d guess. and then alot of careful wet+dry,finishing compound , wax/polish.
hell of a job.
Think maybe a resin finish (which will harden in air) and then some paint/spray.

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[MLBURGE]

wax in styrene i only use mixed in with the gelcoat at 2% by weight for exterior coating.- 'The right humidity plays a part in obtaining an effective result'

gelcoat is not recomended as a paint and should only really be used over freshly applied mat or tissue to become part of the laminate.

It can be rolled on or brushed (not sponge type rollers) and i suppose if its thinned enough could be sprayed (it's not recommended to thin with acetone). as said you will have a lot of work getting a good finish. and maybe better going for a good quality two-pack paint and you will probably find it easier to apply.

good luck whatever you do

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[amcc]

Thanks to everyone who got back to me about my gel coat, but its left me a bit confused, the wax additive is a little bottle of wax which you add to the gel coat so that the surface drys, now the confused part some say that you can thin the gel coat with acetone to enabel it to be sprayed, well I contacted Allscot Plastics who supplied my GRP materials and they said that you cant thin gel coat with acetone and that I should just brush it on, hence the confusion. So here is another question for you I was at Poole in Dorset last month and saw a GRP supplier next to the Sunseeker Factory at the harbour who ofered free advice, unfortunately at that time I didnt know there was so much to this game, so now I wonder if anyone out there knows the phone number of this company Thanks Again

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[Ruthie]

I don't know the number off-hand, but I'll probably be passing the place in the next day or two and will let you know...

Ruthie

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[MLBURGE]

Hi as said acetone is not recomended to thin gelcoat this is not my personal opinion, it is the advice from my grp supplier (glasplies) and other fabrication companies i know say the same. It is to do with areas of the gelcoat not curing fully due to acetone not evaporating completely.

Having said that i have on occassion thinned the gelcoat with acetone and it has hardened fine but the cure i couldn't be sure, ive only used it like this for plug making and jobs where its not important. I wouldn't use it mixed on a proffesional basis.

Its not recomended but you might be ok.

It would be bad information for any supplier to suggest it's ok and i doubt they would.

I have found the best way for exterior coating is to use a mini roller (like an emulsion radiator roller 'sponge rollers will melt and fall apart') thin coats with the wax additive 'only on the final coat' also allow time between coats otherwise the gelcoat can react with the previous coat. The way to tell if the gelcoat is ready for the next is to touch it with your 'clean finger' it will always stay tacky without the wax but if any colour is on your finger its not ready, leave it until you can touch the surface and no gelcoat colour is present on your fingertip then proceed.



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