GELCOAT APPLICATION-help

rivonia

rivonia

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Hi folks,

we had some gelcoat work done lots of little area. It was SPRAYED on and naturaly a thinner was used to stop the spray nozzle from blocking.

Well it has remained SOFT and attracts dirt. We have asked a lot of people about application and everyone says "DO NOT USE THINNERS"

Now is there an expert out there who can state catagoricaly (sp) the correct way to apply gelcoat to small areas.

Thanks

Peter
 
Yes, ask International paints !

I hear they're very helpful to enquiries like this.

I have used Gelshield and always understood thinners is a definite no-no.

Hope you get a successful outcome.
 
Seajet said:
Yes, ask International paints !

I hear they're very helpful to enquiries like this.

I have used Gelshield and always understood thinners is a definite no-no.

Hope you get a successful outcome.
Click to expand...

Gelshield is quite different from gelcoat, it's epoxy innit?
 
Gelcoat needs to have air excluded to cure (e.g. in a mould). Flowcoat cures in the open as it has a wax additive that migrates to the surface and seals the gel from air. You need to know what product has been used.
 
I wouldn't mind betting that's the problem - either the thinner has allowed the disolved wax to run out of the gelcoat resin, or there was never any in there to start with. If it's in the sort of place that lends itself to such things, try sticking parcel tape to it and the surrounding area so that the air is excluded and then warm it a bit with something like a hair dryer. If the wax is still in there, it MIGHT go off. If it doesn't, all I can think of would be to scrape it off and do it again, I'm afraid.
 
Many thanks for all the replies. I have also gone to two companies who apply GELCOAT and both have stated that it appears that the incorrect thinners were used OR the wrong paint??

Well we shall see as I am going back to the people who applied it to get a re-do and naturally
i will be wanting to know what paint it is and how it is to be applied. We went away as my wife is allergic to many smells.

Thanks again

Peter
 
There seems to be a little confusion here. Gelcoat is polyester resin with almost the same composition as the resin that the boat is built from, plus a thickener. It is a decorative surface layer laid down in the mould before the grp is laid up. When repairing surface damage it is normal to use flowcoat, which as said earlier has some wax added to it to ensure that it cures to a hard, non-sticky finish. It is not paint.

I am not an authority on the subject but I would have thought that thinning gelcoat defeated the object of the thickening, which is intended to ensure that it does not sag down vertical surfaces. As suggested by Avocet, thinning with a solvent could conceivably cause migration of the wax and lead to stickiness in the cured surface.
 
Peter,

I hope this site helps answer some of your questions.

http://www.fiberglasswarehouse.com/gelcoat_application.php

No way am I an expert, but have always done my own repairs.

I always use styrene to thin gelcoat, not acetone.

Wax or "styrene with wax" is added if the repair is not covered, to exclude air.

Without knowing the facts it would appear that wax wasn't added.
 
bigwow said:
The gelcoat needs to be covered with peel ply to exclude the air on an external repair.
Click to expand...

Peel ply won't give you a nice gloss finish.
But then you might intend to sand it anyway.
You can use ordinary polythene in some circumstances.
Spraying with the right thinner and wax seems to be an accepted technique.

The key thing is that whatever technique is used, a skilled operator good at that method will be able to get it right, but others will make a hash of it.
Even good operators can have the odd failure, they usually sort it before the customer sees.

Whatever, it's gone wrong.
Tell them, and ask them how they intend to sort it.
If you are not convinced, ask to see other work they have done.

It can be put right.
 
lw395 said:
Peel ply won't give you a nice gloss finish.
But then you might intend to sand it anyway.
You can use ordinary polythene in some circumstances.
Spraying with the right thinner and wax seems to be an accepted technique.

The key thing is that whatever technique is used, a skilled operator good at that method will be able to get it right, but others will make a hash of it.
Even good operators can have the odd failure, they usually sort it before the customer sees.

Whatever, it's gone wrong.
Tell them, and ask them how they intend to sort it.
If you are not convinced, ask to see other work they have done.

It can be put right.
Click to expand...

Hmm thats the thing. The so called expert was originaly a CAR paint sprayer and so used the same tecnique. It was done in Nth Cyprus we are now in Turkey and will return to Nth Cyprus during Oct for the winter. Any way they will have to re-do it whatever as it is awful.

Thank you all for the advice once again

Peter
 
rivonia said:
Hi folks,

we had some gelcoat work done lots of little area. It was SPRAYED on and naturaly a thinner was used to stop the spray nozzle from blocking.

Well it has remained SOFT and attracts dirt. We have asked a lot of people about application and everyone says "DO NOT USE THINNERS"

Now is there an expert out there who can state catagoricaly (sp) the correct way to apply gelcoat to small areas.

Thanks

Peter
Click to expand...

Hi Peter,
As others have said the sticky surface may be due to air inhibition of the surface of the gelcoat exposed to the air. If so flatting back may provide a solution. However if an organic solvent has been added to the gelcoat it may be necessary to strip it off and start again.

If the gel coat was being sprayed it sounds like there was quite a large area to be dealt with otherwise brush application would have been preferable.

When spraying gelcoat it is usually necessary to use the correct spray equipment. The thixotropic agent in the gel coat, required to allow a wet film thickness on vertical surfaces (typically 0.38 mm – 15 thou’ in "old money") will prevent good flow of the gel coat through a gravity cup type spray gun. It is usual therefore to use a small pressure pot gun. The best will have the pressure pot mounted immediately under the gun.

When spraying it is best to use a gelcoat designed for spraying. If the only gelcoat available has been formulated for brushing application it can be thinned for spraying with a little styrene monomer. Not more that 10% (ideally 5%) as the gelcoat will loose flexibility the more styrene is added. Styrene will crosslink with the polyester in the curing process and thus will not render the cured gelcoat soft.
Organic solvents such as acetone etc. must not be used as thinners as the gelcoat will not cure properly. If the final surface of the sprayed gelcoat is to be flatted and polished then wax solution should be added as others have said. Somewhere between 1% and 2% is normal. As the wax is dissolved in styrene monomer any percentage of thinning styrene should be reduced in proportion.

If applying the gel coat to a mould prior to glass fiber lay-up, wax solution should not be added as the sticky, air inhibited, exposed surface of the gelcoat will re-polymerize with the lay-up resin ensuring a good bond between gelcoat and lay-up. A wax solution will reduce this adhesion.

A solvent such as acetone will have to be used to clean the spray equipment after the spray application but it must not be mixed with the gelcoat.

Hope this helps.

Cheers,
"Basil"
 
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