Why o why will my gel coat not dry, I’ve done everything that they said....

It is generally accepted that you do not do GRP work Gel or laminating in less than 15C temperature - otherwise curing is seriously affected.

Depending on the polyester as well - many will stay 'tacky' on the surface as it oxidises and fails to set ... but underneath that very thin top film - its set ok. Clingfilm is the usual answer to it - but again if temp is low - no g'tee at all.
 
Homer J said:
How long should I expect it to take to cure in current temps?
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May.
If its a sailing boat with a closeable cabin you could put a heater in the bilges and close the cabin door. That would warm up the grp hull from the inside and help the gel coat to dry/cure.
Its a trick I used years ago when I had a bodyshop and hand painted transit vans or sprayed them where if you put a heater inside it would warm up the panels and halve the drying time.
 
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Homer J said:
Well I was very pleased with the title but less pleased with the result.
Sunday pm - sanded scratches, acetone to remove grease, mixed gel coat with 2% and double checked. Applied.
Monday pm gel coat still tacky. Phone supplier- they said exclude air, I said thanks for not putting that in the instructions, now what do I do?
They said apply a new coat over the top and clingfilm. Well I went to town to exclude air contact, clingfilm and lashings of exterior masking tape.
Today took off a patch to test and it’s still tacky

what went wrong? It’s not the hardener I checked about 15 times and was really accurate

so - too cold?
or something to do with the first coat

what should I do now? If I have to start again how do I remove the still tackygel coat?

why did I think it should be easier than this? Lucky we now all have weeks to resolve it, if not the funds to do it.

i have plenty of bog roll and antiseptic spray of anyone would like to tackle it for me with payment in inflation proof currency.
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Is it just surface tackiness, or has the whole mess failed to cure?

I've got a bit on my boat which has a tacky surface, it's because I'm using a mix of 'gelcoat' and 'topcoat' to get the colour near enough. The topcoat has wax added, the gelcoat does not. You can buy wax to add, in styrene as a solution.
The surface stickiness can be cleaned off with acetone to some extent, and then just cut back with w&d paper. Or just scrape with a blade.

Damp and cold don't help, catalyst can go stale.
If you warm the work with a hot air gun before applying resin, that dries it too.
If covering gelcoat to exclude air, I tend to get better results with plain polythene than clingfilm.
Masking tape is porous and not going to help, except to hold polythene in place.
Sometimes a piece cut fro mthe side of a plastic milk bottle holds the resin in place, excludes air and gives a fair surface.

I use a little plastic pipette to measure catalyst, it's more repeatable.

Step back from the boat, do a test piece,
 
I haven't had to apply gelcoat for some years but the kit I used then included some powdered wax which I added in some proportion or other and it set fine.
 
I've used various marine and general Gelcoat's and never had any problem with non curing. But I never did it in cold weather or damp weather.
I used to be friendly with a guy at Strand Glass in Portsmouth ... he explained many things in those days ... most I've forgotten now ..
 
They used genuine Beneteau gel coat, sanded, cleaned with acetone, mixed, applied, sanded after a couple of hours. I watched them. They gave me some after the job was finished, I used it to fill in some chips before it eventually went off after a couple of years in the locker. Never had to put peel ply or cling film on!
 
It is very possible that your hardner/catalyst is old and expired. That stuff has a definite shelf life of one year or less. I went through this exact problem several years ago. Scraped the soft gelcoat off and started again with a fresh bottle of catalyst.
 
Beneteau381 said:
They used genuine Beneteau gel coat, sanded, cleaned with acetone, mixed, applied, sanded after a couple of hours. I watched them. They gave me some after the job was finished, I used it to fill in some chips before it eventually went off after a couple of years in the locker. Never had to put peel ply or cling film on!
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One of the desirable and designed-in properties of raw gelcoat is that it cures to firm quite quickly, but leaves a tacky surface where air is present. That's so that it can sprayed onto the surface of a mould and quickly be hard enough for laminating to begin, but it needs to stay tacky so that it can form a good bond with the resin layer. If it didn't solidify beneath the tacky surface it would be badly disturbed by the metal rollers pushing the reinforcement down into it. Clever stuff. (It's also way harder and more UV resistant than a coloured laminating resin would be).

Yachtbuilders could sell you raw gelcoat, but what they (or more likely their supplier) actually do is premix it with wax so that it cures without the sticky surface. It's no use at all in a mould, but perfect for repairs. A fiver says that's what your team will have used.
 
anoccasionalyachtsman said:
One of the desirable and designed-in properties of raw gelcoat is that it cures to firm quite quickly, but leaves a tacky surface where air is present. That's so that it can sprayed onto the surface of a mould and quickly be hard enough for laminating to begin, but it needs to stay tacky so that it can form a good bond with the resin layer. If it didn't solidify beneath the tacky surface it would be badly disturbed by the metal rollers pushing the reinforcement down into it. Clever stuff. (It's also way harder and more UV resistant than a coloured laminating resin would be).

Yachtbuilders could sell you raw gelcoat, but what they (or more likely their supplier) actually do is premix it with wax so that it cures without the sticky surface. It's no use at all in a mould, but perfect for repairs. A fiver says that's what your team will have used.
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The only flaw in your long description is that Polyester resin in its very nature reacts with oxygen to remain tacky on its surface - it has nothing to do with Gelcoat designed to stay tacky for laminating to ....
In fact Gelcoat if you care to push a GRP panel to destruction will show you that Gelcoat does not adhere totally or integrate with the laminated GRP its on. It creates a hard cosmetic skin that can be cracked away.
 
Refueler said:
The only flaw in your long description is that Polyester resin in its very nature reacts with oxygen to remain tacky on its surface - it has nothing to do with Gelcoat designed to stay tacky for laminating to ....
In fact Gelcoat if you care to push a GRP panel to destruction will show you that Gelcoat does not adhere totally or integrate with the laminated GRP its on. It creates a hard cosmetic skin that can be cracked away.
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In fewer words then. I disagree with you.
 
Refueler said:
The only flaw in your long description is that Polyester resin in its very nature reacts with oxygen to remain tacky on its surface - it has nothing to do with Gelcoat designed to stay tacky for laminating to ....
In fact Gelcoat if you care to push a GRP panel to destruction will show you that Gelcoat does not adhere totally or integrate with the laminated GRP its on. It creates a hard cosmetic skin that can be cracked away.
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Polyester layup resin does not remain tacky like gelcoat. Not for very long anyway.
The properties of the two versions of polyester resin are optimised. (I can never remember which is resin A and which is B)
If you colour some layup resin and use it as gel coat, it will not bond nearly so well, it will crack off much more readily than proper gelcoat.

If you mean gelcoat/flowcoat which has been applied after the layup resin has cured, yes I'd agree that doesn't bond nearly so well, if you test that to destruction it will tend to crack off much more readily than gelcoat which went on first.
Same as if you use a polyester gelcoat to cover an epoxy repair. You can make it stick well enough, but not nearly like original gelcoat.
 
Well here‘s an update.

if I had set out to make the boat much worse and look awful then I’d be feeling pretty pleased with myself tonight.
how on God‘s green earth can something be so difficult?.....

Not only did it not set despite following all the manufacturers and forum advice it would not come off with acetone and Only smeared a residue with sandpaper. It appears the only things that it will adhere to with any tenacity is skin and clothing.

Talk about dispiriting. I was totally pissed off with it, even sanding with 1,200 grit paper has had no result on the bit I want to shift but has totally destroyed the shine on the nearby gel coat.

in summary then I have made It worse than it was before. It doesn’t go like this for the people on bloody Utube.

I hope this social distancing doesn’t go on too long or I will have destroyed the entire house by the time it’s finished.

anyone now how to go into stasis for 12 weeks? I think everyone at my house will be better off.
 
Hi

There are a few things to consider here. Top of which are as follows

If you are meaning just to repair a small chip in the gel coat, it should be fairly simple as long as you have the hardner ratio right.

But as some have said. Ideally when repairing any fibreglass surface, you want the ambient temperature to be certainly above 15, if not 18oC. At the very least, the bare exposed glass should not still be damp or worse.

Added to that, I’ve often been witness to others and myself putting a repair on the Underside of a hull, then returning the next day and wondering why it hasn’t set. Only for it to rain a little but what’s happened is that the rain water has ran down the centre line of the hull and over the presumed sheltered area of the repair.
 
Normally, the gelcoat they sell you for repairs contains 'accelerator'.
when catalyst is andded, it should set in something like an hour at 20degC.
So, it's not hard to get the work warm using a black'n'decker hot air gun, even working outside.
You will sometimes see the pro's using fanheaters and hairdryers, maybe IR lamps.
Sometimes with a little tent of polythene etc over the work.
The pro's don't hibernate, they do a lot of work on boats in the winter.

When you've cocked it by not having wax in the gel, or your polythene covering goes awol, and you're left with a sticky surface, it can either be wet sanded, or gently scraped with a blade, once the body of the repair has set.

As I said before, it's good to do a little test piece, particularly if you suspect any of the materials are past their sell by date.
Normally if you can get the resin out of the tin, it will work.
The materials are pretty cheap in the scheme of things, so maybe buying fresh is worthwhile.
What's costly/valuable is generally knowing what exact colour gel to use.

And get some of these
Pipettes Graduated, Polyethylene, Dropper 5ml 3ml 2ml 1ml 0.5ml 0.2ml - UK | eBay
If you measure the catalyst, you have a better chance of one batch behaving like the last.
 
QBhoy said:
Hi

There are a few things to consider here. Top of which are as follows

If you are meaning just to repair a small chip in the gel coat, it should be fairly simple as long as you have the hardner ratio right.

But as some have said. Ideally when repairing any fibreglass surface, you want the ambient temperature to be certainly above 15, if not 18oC. At the very least, the bare exposed glass should not still be damp or worse.

Added to that, I’ve often been witness to others and myself putting a repair on the Underside of a hull, then returning the next day and wondering why it hasn’t set. Only for it to rain a little but what’s happened is that the rain water has ran down the centre line of the hull and over the presumed sheltered area of the repair.
Click to expand...


I fitted an 8KW Westerbeke genset to our boat three years ago.

I prepared two 19mm squares of marine ply with protruding 12mm bolts. Th bolts welded to square washers which were screwed to the top plate to stop them turning, bottom plate cut out to take them so as to leave a flat surface.

The edges were chamfered - 3 inch shallow chamfer - and the plate sikaflexed and screwed down to make the bed for the genset mounts.

I glassed the chamfered edges using tri radial strips of matting and resin, several layers, rollered down hard to exclude air bubbles.

Came back to the boat three days later - still wet! Brown trouser job!

Asked the yard expert who said give it some gentle heat for a couple of days. I left a 1 KW oil radiator in the generator garage for two days, all OK.

I also measured and followed instructions very carefully.

Temperature was the key in my case.

I agree with Refueler about the adhesion of gelcoat to matting.

When you have crashed as many racing motorbikes as I have fitted with GRP streamlining there is plenty of evidence from the bits swept up after a crash to show he is on the money.
 
Homer J said:
Well I was very pleased with the title but less pleased with the result.
Sunday pm - sanded scratches, acetone to remove grease, mixed gel coat with 2% and double checked. Applied.
Monday pm gel coat still tacky. Phone supplier- they said exclude air, I said thanks for not putting that in the instructions, now what do I do?
They said apply a new coat over the top and clingfilm. Well I went to town to exclude air contact, clingfilm and lashings of exterior masking tape.
Today took off a patch to test and it’s still tacky

what went wrong? It’s not the hardener I checked about 15 times and was really accurate

so - too cold?
or something to do with the first coat

what should I do now? If I have to start again how do I remove the still tackygel coat?

why did I think it should be easier than this? Lucky we now all have weeks to resolve it, if not the funds to do it.

i have plenty of bog roll and antiseptic spray of anyone would like to tackle it for me with payment in inflation proof currency.
Click to expand...

I did some similar repairs over 30 years ago with similar problems. In the end i covered them with sellotape. And warmed the area with a hair dryer. The 2 combined did the trick for me.
 
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