gelcoat mix ratio??

[DavidJ]

Sealine have kindly supplied me with some gelcoat and catalyst (from the factory) to fill a deep scratch which I have put in the boat. (damn!) What ratio should I use and any tips on how to measure that ratio because the white stuff is a thick custard consistency and the catalyst is a clear and a watery consistency.
David

 

[MLBURGE]

I usually use about 10 cc's of catalyst for filling work and 15 cc's for moulding's per 1lb of gelcoat.

If it's an average day out of the sun then mix say 4 oz of gelcoat (measure this on some kitchen scales) to 2.5 cc's of catalyst which is just under 1 level teaspoon.

I don't know if you have experience, but the job should be masked and prepared properly and cleaned with some wet and dry and some acetone or thinners you may want to use a filler powder or a wax addative to make the gelcoat non tacky.

Let me know if you want more info about the job,it can be quite difficult to get an invisible repair but is possible.

 

[mustard]

Try to keep the catalyst level to 2% (about 10 cc per lb) max and work at 21 deg C - 25 Deg as higher temps/ratios can discolour the Gelcoat. Lower temps simple delay gel/cure times, but too low can cause problems. TRy not to use in direct sunlight, as this can affect the UV additive in the resin. A full teaspoon (do not use a metallic teaspoon!!) is 5cc. Keep the liquid catalyst away from soap, rust and eyes!!

We sell a number of gel coats and have found that good colour match can be made if you assume the gelcoat they have supplied is the same they originally used. It should be - most boat manufacturers stay with proven products. Worth asking if you haven't. Gelcoats do not fade, UV degrade or chalk these days as much as they used too. Wax in Styrene solution added to the mix means you can sand the gel coat thru various grades of waterpaper, (400-1000gt) and then buff with a good polishing compound (we recommend Farecla G4). You can get an almost invisible repair with time & care.

Do not add fillers (other than choppped strands if needed for bulk or support - do not use for cosmetic work), as they are never used in original gelcoats, and shrink & expand at different rates.

We have, in the past, added small quantities of pigments to get a closer match, but this is tricky.

Let me know if we can help further....

 

[DavidJ]

Not done the job before but keen to get it right without learning by making mistakes. I would really appreciate your advice on this and I'm sure others would find it useful also.
look forward to more wisdom
David

 

[jfm]

2-3% catalyst will be ok at 15-20 deg C ambient temp.

Gelcoat will not harden when exposed to air, so the surface will remain tacky while the body of the material hardens. As mentioned above, you can add a wax to the mix (also about 2-3%) to avoid this effect and make the surface harden.

If you are buidling a boat, the gelcoat/catalyst should be mixed precisely. But if a small repair it doesn't matter. So a teaspoon sized splash of catalyst to a 2/3 full jam jar of gelcoat will be ok

If you are working on vertical surfaces it will be hard to stop the gelcoat running. It's nowhere near as stiff as say body filler. If so, support it by taping over with masking tape till it dries, then file/grind/ sand paper/polish off the excess

 

[DavidJ]

Mus and MLB
Thanks for your excellent answers to my request.
How much time do I have from mixing to the compound to starting to set.
I've heard that you have to put clingfilm over the repair to help it go off and I guess to get a smooth finish as well. Is this your recommendation.
David

 

[mustard]

You should have 18-20 minutes gel time @2% (The time before its unueseable) at ambient temps but then allow at least 12-18 hours to cure before sanding. Full & final cure can be up to 7 days. The idea of using cling film is as an oxygen barrier instead of wax solution. The wax rises to the surface and acts as a barrier, in the same way as cling film, and prevents the "stickiness". But use wax in Styrene solution in preference, because it enhances the sanding and final finishing and buffing, in the same way as polishing an apple brings out the shine. IMHO its better to sand this back & buff than use cling film. Generally most waxes are paraffin wax solutions, but we find canuba wax combi's are far better for final shines/finishes. Use at around 3% (30 cc per kg, 12cc per lb) for the best finish. Too much wax causes pitting and rejection.

 

[DavidJ]

Thanks Mus for your detailed reply.
The Styrene solution is something I hadn't heard of before. Is it a specialist thing or can it be bought from chandlers
David

 

[mustard]

Should get it from a chandlers. Ask for 5% solution. If not e-mail me, will send some FOC.

 

[MLBURGE]

yes don't use a metalic teaspoon,and i did say just under a level teaspoon which is about 2.5-3 cc's.

wax in styrene is really only available from fibreglass supplier's such as glassplies which is who i use.

To do your job simply, is to first rub the area that is going to be filled with a 400 wet and dry paper get it really clean and white.Then mask the area and clean it with acetone or cellulose thinners ,don't touch it or anything because this may show as a greese mark when finally polished.

Fillers can be used as long as the scratch isn't 2in deep silica powder,fillite,or the most simple is talc powder.

Mix some gelcoat and catalyst to 4oz to just under a level teaspoon with some talk powder for simplisity babypowder will do and use this to fill only the main depth of the scratch as the white will be darker than the original.allow this to harden for at least 3 hours.As the gelcoat will stay surface tacky without the wax,the way to tell if it's gone off is to push your finger on to the gelcoat and if there is white on your finger it is not off and leave it for a further period.

Then mix some more gelcoat "no filler" and apply this covering the whole scratch area an old butter lid cut down makes a good spatula apply this as good as you can it's not that hard.

Let this dry overnight,it will remain surface tacky as all resins do but you don't have to use the wax,because as soon as you give it a rub with a 400 wet dry paper (try to fill it so you don't need any courser) the surface tack will go.

Then carfully (will take time) rub the area with 400 until it's smooth then 1200 until it's perfect then use,as i do g4 compound (available from car body shop's) as it dosn't contain amonia,then a mirror finish polish.A t-cut polish may do the job.

If done with time and care you should have an invisable repair,a few tip's for you---Add a few drop's of washing up liquid with the water for wet/drying
-Use a soft flat sanding block when wet drying.
-Mix the gelcoat slowly with a flat clean stick/will avoid tiny air bubbles.
-Good luck whatever you do.

 

[DavidJ]

MLB
That's excelent. It's a bit frightening how much I did'nt know and was about to attempt the job.
David

 

[MLBURGE]

David if you are worried about attempting the job,which is fair enough we are talking about your pride and joy.then see if you can find an old bit of fibreglass an old gas locker or anything that has a gelcoat finish even an old dingy there must be some old grp junk around your marina.

Then angle grind a scratch similar to what is on the boat and undertake the filling attempt,and practice until you get an acceptable result you should be able to do it with a bit of care.Don't try the boat until you feel confident enough, if you have trouble then get someone to do it for you.

 

[DavidJ]

Yea, good idea.
I do like to develop DIY skills so will see handing over to someone else as a bit of a defeat, so I will try your suggestion first.
What do you mix it on, can I use a piece of clean wood.
David

 

[MLBURGE]

The best thing is to get some old butter dishes/cut down plastic milk bottles or any old plastic bottles, just cut them down clean and dry them.

One thing i have remembered i have used it a few years ago is that there is a two tube gel coat filler paste which should be available from any good chandlers it comes in a yellow box and could make the job alot easier for you you just mix it as instuctions and apply,cost's under a tenner i think.(just check the colour match to the boat)

See how you go, and get some of those plastic gloves from a local petrol station if you hav'nt got any.

 

[DavidJ]

Yes I though about the two part filler but I want the exact colour match and I've got the correct gelcoat from Sealine.
Plastic gloves...good idea
I take it when we talk of 2% it is by volume not weight.
thanks
David

 

[MLBURGE]

All fibreglass resins and addatives are measured by weight .

1lb of resin/gelcoat add - 2% by weight of catalyst or wax will work out to 10cc's

4 oz of resin/gelcoat add -2% by weight of catalyst will work out to 2.5 cc's

I would'nt mix any more than 4 oz to start with because you may waste alot see how you go and mix more or less just keep the catalyst at the same ratio.

Go 4 oz gelcoat and a teaspoon (plastic) of catalyst about 3/4 full because of the shape of the spoon this will give you 2.5 ish cc's although full will give you 5cc's.

 

[kingfisher]

Mylar

After you apply the gelcoat, stick a strip of clear mylar on top. It will leave a near-perfect finish.

My supplier of gelcoat (VOSS chemie), has it. In dutch it's "hostafaan"-foil. In french its "hostaphane"-foil.

Don't know about cling film, though. Try it first with a dallop of gelcoat-mix and/or acetone, to see whether the solvents in the gelcoat are compatible with the film.

Use a block when sanding. If you sand with your hand, you'll just enhance the existing indentations.

Does anybody know how you can sand mechanicaly with wet paper. I learned early in life that electric sanders and water don't mix. Pneumatic machinery ?

Group of people on the pontoon: skipper is the one with the toolbox.
http://sirocco31.tripod.com

 

[DavidJ]

Re: Mylar

Good point about the clingfilm test. I hadn't thought of that. It would be a real shame to finish a good job and have the cling film melt everywhere.
Mylar...that's an interesting one
thanks
David

 

[mustard]

Re: Mylar

Mylar's fine but you do get join marks where the gel coat spreads onto the masked areas, and you still have to sand the join. Never done it successfully but stand to be corrected. Clingfilm shoudn't be affected by any solvents in resin, but its hard to get flat. Have used over curved surfaces where we can stretch it to cover evenly. There are probably real crafstmen out there who do it all the time - I guess its just practice....

To finish after wet & drying to 800 gt (100 gt is better) we use a great product from America. Its a machine glaze - a paste you use sparingly and it fills the sand marks, even swirl marks, as it buffs. We get a perfect gloss finish. Before we went thru all the grades, then used pastes that gound out the swirl marks until we got a shine. New way is much faster. Use electric machines as there is no water involved, just small quantities of this paste. Water based so safe to use as well. Air tools, using a small hand held orbital sander with a softish pad and water paper is the best way if you have large areas or frequent use - but of course you then need compressors and airlines.

 

[gjgm]

lots of experienced advice already. Try lining the 1/4" outside of the scratch with masking tape to ensure you dont spread the gelocoat all over the place. Can save some panic! Best advice I can offer is that as long as the deep scratch hasnt done any structural damage, then dont fret.. if it isnt perfect first time, just sand it out again. Getting a perfect invisible match is probably a job for someone with a lot of experience, but you should be able to do a pretty good job. It might seem a bit complicated all these ratios etc, but if you can mix araldite i m sure you ll manage!

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