Gell coat to catalyst 100 to 1 mix

[Ribtecer]

Hi Everyone.

I am in the middle of a Rib rebuild and currently the boat is inverted and i am repairing some bodged gelcoat repairs, red hull with old white gel repairs!!!

Anyway, ground it all back and ready to start the repairs with the correct colour.

The gelcoat repair is a tin of 500ml of gel and a small pot of catalyst, the mix is apparently catalyst at 2%.

Bearing in mind I want to mix small amounts many times, how on earth do I work that out? I am told a 50% margin of error is ok, but not enough catalyst and it won't go off and too much it won't go either.

Any advice or easy tips, much appreciated.

Thank you.

Ribtecer

[jwalker]

1% to 2% is fine but the speed of cure is temperature dependent. If it's very warm, 1%, if it's cold, 2% and anything in between. In general, the less catalyst you can get away with the better because it lies inside the resin very slowly releasing itself, possibly over years!

If you take a litre of resin to weigh 1 kilo [ which it doesn't ] but it's close enough, then your 500mls of resin can be set off by using 5 - 10mls of catalyst.

If you don't have a dispensing bottle, then you can use a syringe to meter out the catalyst with sufficient accuracy.

Adding pigment will retard the cure so time to cure will be longer. Dark pigments more than light ones tend to have greater effect. Black in particular can markedly retard the cure.

It's a bit 'suck it and see' until you've built up a little experience with the materials. Good luck with it, I'm sure it'll be fine.

[jeffstevens763@g]

Agree with JW you will have more catalyst than you need to cure the gel coat you have, just do a teaspoon full as a trial. When I do mine I use a hair dryer to bring the temp up to start the reaction working outside or in the cold.

[beamishken]

Remember you need to exclude the air from the gelcoat so it cures or it will remain forever tacky and difficult to sand
Either tape over the last coat with something like cellotape or packing tape or if its a larger area add wax to the gelcoat to create flowcoat

[Ribtecer]

Originally Posted by beamishken

Remember you need to exclude the air from the gelcoat so it cures or it will remain forever tacky and difficult to sand
Either tape over the last coat with something like cellotape or packing tape or if its a larger area add wax to the gelcoat to create flowcoat

Really? I thought it needed air to go off, to release the chemicals from within and therefore go hard.

My plan was to paint it on layer by layer to build it up and then wet'n dry it back flat with the rest of the hull.

So should I tape over each layer as it goes off?

[beamishken]

No it stays tacky so subsequent coats (or the glass layup in the mould) will stick to it, it wont fully cure untill you exclude the air so you either add an appropriate wax which migrates to the top and excludes the air or apply a tape over the top to exclude the air but only need to do this on the last coat

[jwalker]

Originally Posted by Ribtecer

Really? I thought it needed air to go off, to release the chemicals from within and therefore go hard.

No, it doesn't work like that.

Originally Posted by Ribtecer

My plan was to paint it on layer by layer to build it up and then wet'n dry it back flat with the rest of the hull.

Apply the gel as thickly as possible, if it's too thin it may never set. You can put multiple layers of masking tape alongside the gouge marks to add extra depth if necessary. The gel is thixotropic so it will pretty much stay put once you stop moving it. Peel the tape off as soon as the gel is stable, try not to let it set in place by the gel - extra work sanding!

[Ribtecer]

Thanks Guys

I am in the middle of this today, I will provide a status report later.

"Thixotropic" thats a new on on me.������

[office888]

Originally Posted by Ribtecer

Thanks Guys

I am in the middle of this today, I will provide a status report later.

"Thixotropic" thats a new on on me.������

Thickening / vertical cling additives.

9% Low hydrogen MEKP, most gelcoats are a 20-24 minute gel time in a lab, meaning they will reach a thin film cure in about 90 minutes when initiated at the manufacturers recommendation.

At 21c, the target is usually 2%.

Production type laminating gelcoats are an air inhibited cure, meaning they will remain tacky. In order to reach a total cure, it must be sealed from the air. Either by wax additive, PVA, or by laminating glass over it in a mold.

[Ribtecer]

Originally Posted by office888

Thickening / vertical cling additives.

9% Low hydrogen MEKP, most gelcoats are a 20-24 minute gel time in a lab, meaning they will reach a thin film cure in about 90 minutes when initiated at the manufacturers recommendation.

At 21c, the target is usually 2%.

Production type laminating gelcoats are an air inhibited cure, meaning they will remain tacky. In order to reach a total cure, it must be sealed from the air. Either by wax additive, PVA, or by laminating glass over it in a mold.

PVA, that's interesting.

I mixed and applied about 6 hours ago and its still tacky. I did cover it in cling film but after an hour or so i got nervous and removed it.

I would say it's is going off, but slowly.

Can I cover it in a PVA solution? If so what PVA/water mix?

The reason I took off the Cling Film was I was worried about sanding thru the film, but PVA seems a good plan.

Thanks again for all this help.

[office888]

Originally Posted by Ribtecer

PVA, that's interesting.

I mixed and applied about 6 hours ago and its still tacky. I did cover it in cling film but after an hour or so i got nervous and removed it.

I would say it's is going off, but slowly.

Can I cover it in a PVA solution? If so what PVA/water mix?

The reason I took off the Cling Film was I was worried about sanding thru the film, but PVA seems a good plan.

Thanks again for all this help.

Because you removed the cling film, it is now inhibited.

straight PVA, no water. Some hairsprays work fine. It will likely not work now though, now that the gelcoat has already partially cross linked.

I’d just apply another coat of gelcoat on top, and either mix wax additive in to the gelcoat, or spray some PVA on at the end.

Plastic wrap will not stick to gelcoat.

[Pikey Dave]

I use bog standard brown parcel tape, because it’s what I had to hand. Works perfectly & peels off no problem. Sand down with 600 grit wet & dry with plenty of water & washing up liquid. Work down to 1800 grit, finish with G3 compound & polish.
Works for me.

[Ribtecer]

Originally Posted by office888

Because you removed the cling film, it is now inhibited.

straight PVA, no water. Some hairsprays work fine. It will likely not work now though, now that the gelcoat has already partially cross linked.

I’d just apply another coat of gelcoat on top, and either mix wax additive in to the gelcoat, or spray some PVA on at the end.

Plastic wrap will not stick to gelcoat.

Tonight I have my wood burner on and I bought in a small scoop of waste gelcoat and it's gone off very quickly with the heat.

Now I'm thinking wave a heat gun over it tomorrow, what do we think?

[Pikey Dave]

Originally Posted by Ribtecer

Tonight I have my wood burner on and I bought in a small scoop of waste gelcoat and it's gone off very quickly with the heat.



Now I'm thinking wave a heat gun over it tomorrow, what do we think?

Heat & humidity play a big part in resin work.

[beamishken]

Originally Posted by Pikey Dave

I use bog standard brown parcel tape, because it’s what I had to hand. Works perfectly & peels off no problem. Sand down with 600 grit wet & dry with plenty of water & washing up liquid. Work down to 1800 grit, finish with G3 compound & polish.
Works for me.

Thats pretty much what I said in post #4 then it got all technical and big words, confused the issue and ended in a sticky mess.
Oh well maybe next time[emoji6]

[Ribtecer]

Originally Posted by beamishken

Thats pretty much what I said in post #4 then it got all technical and big words, confused the issue and ended in a sticky mess.
Oh well maybe next time[emoji6]

OK - point taken, should have listened to the simple approach, defiantly will next time.

That said, what's my next move?

1. Heat it up what's there?

2. Put parcel tape on it now?

3. Put more on and parcel tape it?

[beamishken]

I think I'd go for another coat and tape over and leave untill fully cured with the help of some heat.
Thats assuming you are confident the first mix was correctly mixed and it has cured and just left the top surface tacky.
If theres any doubt about the cure, then removing and starting again might be the best option

[Ribtecer]

Thanks for the advice beamishken, and for sticking with me thru this.

This morning I checked on it and it is going, but slowly. The bit I bought in and put.in front of the fire last night is rock solid.

I think I am going to wave my heat gun over it for a bit and see if I can't heat it up and set it off. If not tonight I might try putting more on with parcel tape.

Is there any value in putting tape on it now?

Thanks again.

[beamishken]

I'm not sure about the value of putting tape on now as its not something I've tried. I have in the past washed some of the stickiness off with acetone or thinners then continued sanding but found it clogged the paper until you had sanded right past the sticky layer

[jeffstevens763@g]

ive never used gel coat as an external coat but as said by others exclude the air and it will go off one way is vacuum packs expensive but what the pros use. i guess you could wax spray over the tacky surface for it to set never done it but worth a trial.

all my stuff i flow coat as an external finish a vid below on the difference between the two.
it's worth going on this site they have projects explaining the different ways of doing stuff also if you ring up they are more than accommodating pointing you in the right direction and products to use.

https://www.youtube.com/watch?v=rY_Nf1hPado