colouring gel coat

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Ardenfour

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My eggshell-blue grp on the deck and cabin top has various chips and gouges that I'd like to fill. So how do I match the colour, and what could I add to white gelcoat to arrive at a close match?
 
Gelcoat isn't white, it's a kind of clear pink before it has been pigmented. You need to find the coloured pigment that you want - fine tune with other pigments if necessary like an artist and mix it in with the gel. If I remember (long time since I've done this - white is 10% max pigment by weight but for other colours 5% or less. Black really doesn't need much pigment at all for example)
Saw a pro colour matching once, he spent quite some time getting the pigment colour right and had 3 or 4 different pigments in use. Did a great job.
If you're applying gel for a repair then you will most probably need to put wax additive in it too unless you intend to exclude all the air with resin proof tape. Gelcoat will remain tacky on the surface unless you do one of these.

You can get anything GRP related from CFS supplies in Cornwall and I believe there is at least one other good supplier on the East coast somewhere. Someone will be along with that soon...
 
G12 said:
... and I believe there is at least one other good supplier on the East coast somewhere. Someone will be along with that soon...
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I think you may mean East Coast Fibreglass Supplies. (No connection except as satisfied customer.)

I was lucky enough to get a good match with one of their gelcoat repair kits (over 100 colours, I think - see http://www.ecfibreglasssupplies.co.uk/c-1041-gelcoat-repair-kits.aspx) so that avoided mixing to shade. I bought the colour card from them (essential to get the colour match) and then chose the kit. Not absolutely perfect, but very close and good enough for me on for the stippled non-slip - and very little hassle compared with mixing pigments, I imagine (one of those jobs I'd put off, for that reason!). The card and kit were not expensive IMO for a very reasonable amount of materials for 'touching up'. Worth a look and perhaps buying the shade card at least to try.

PS They probably also do pigments etc. to mix your own, so another potential supplier if you go down that route.
 
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Matching gel coat colour requires a skilled eye as even white has tints of blue green pink and yellow. The technique is to mix white with various tints until you get a match then add hardener and apply. The colour card and are mix from CFS sounds good.
 
That's what I used to do with a red hull. I'd mix without hardener and smear some on alongside the area to be filled. If not right, wipe off and adjust.
 
Javelin said:
I do this for a living but its easier to watch this vid than for me to explain.
http://boatworkstoday.com/archives/1512
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Thanks for that. I take it from that video that for small quantities the whole colour matching process has to be repeated each time, as no record was made of the amounts of different pigments added. Is there any way to 'fix' the recipe for small quantities - how small are the weights/volumes of pigments which would typically have to be measured?
 
I have also done a bit of this matching and found that old white gel coat also needs a smidgen of black in it to get a closer match. colour card sounds quite a good idea if you can get a close enough match, but I also found that the mixed gel coat also sets a nats shade darker so you really need to have a few small trials beforehand to get it right.

I suppose a lot depends on how fussy you are on the repair match?

Philip
 
Obviously if you get it right you can't see the repair and this is always the aim.
The hardest is on molded non-slip which is a bitch to get right.

I find with white boats that I add yellow normally and on odd occasions some grey.
For eggshell blue I'd start with white and add a tiny touch of blue until matched.

Now for the tricky bit.
If you use topcoat/flowcoat gel it will go off un-sticky however if the repair is more than a couple of mill deep you run a high risk of air bubbles that will appear when you sand back.
You shouldn't recoat over top or flowcoat as its pre mixed with wax that comes to the surface during curing.
This wax needs to be sanded off before the next coat.
So I usually use normal gelcoat and put on 2 or 3 light coats but un waxed gell will not cure totally and remains sticky so I have to mix the last coat with a little Wax in Styrene so it sets of hard.
You can cheat sometimes on the last coat by waiting 10 minutes after you apply the last coat and then carefully putting a piece of tape over it to cut off the oxygen if you don't have any wax though frankly its cheap as chips.

Finishing I scribble over the cured gel with black marker pen and sand off with 320 grit - then repeat this process with 800, 1000, 1500 and 3000 grit wet and dry.
Then finish off with 3m cutting compound and buff.
 
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Javelin said:
Obviously if you get it right you can't see the repair and this is always the aim.
The hardest is on molded non-slip which is a bitch to get right.

I find with white boats that I add yellow normally and on odd occasions some grey.
For eggshell blue I'd start with white and add a tiny touch of blue until matched.

Now for the tricky bit.
If you use topcoat/flowcoat gel it will go off un-sticky however if the repair is more than a couple of mill deep you run a high risk of air bubbles that will appear when you sand back.
You shouldn't recoat over top or flowcoat as its pre mixed with wax that comes to the surface during curing.
This wax needs to be sanded off before the next coat.
So I usually use normal gelcoat and put on 2 or 3 light coats but un waxed gell will not cure totally and remains sticky so I have to mix the last coat with a little Wax in Styrene so it sets of hard.
You can cheat sometimes on the last coat by waiting 10 minutes after you apply the last coat and then carefully putting a piece of tape over it to cut off the oxygen if you don't have any wax though frankly its cheap as chips.

Finishing I scribble over the cured gel with black marker pen and sand off with 320 grit - then repeat this process with 800, 1000, 1500 and 3000 grit wet and dry.
Then finish off with 3m cutting compound and buff.
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That's good advice.

Also really enjoy the boat works today series of videos, about the only one that goes into the matching process well.
 
Javelin, can I pick your brains please: I have to strip and repair a large area of crazed gelcoat, about maybe 6 sq ft (damage from last winter's storms). While I am not too desperate on colour match, Shannon Green and perfectioned already, how best to lay on a new gelcoat?
 
Ardenfour said:
My eggshell-blue grp on the deck and cabin top has various chips and gouges that I'd like to fill. So how do I match the colour, and what could I add to white gelcoat to arrive at a close match?
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This is one of those jobs ( like plastering or glasscutting) where intelligence is no substitute for experience. You can potter round yourself with tints from Eastcoast ( ahelpful outfit) and I have done so myself. But if you want a really good match, put your hand in your pocket and go for the local guy who does this all the time.
 
We all know that it's only a matter of time before the nice new gel coat starts to fade at a different rate than the older original coat.

This can be reduced by saving the material that has been sanded off and reuse this older material in the new mix as it has been exposed to UV and fade slower.

You just need to make sure the area being sanded to harvest the pigment is very clean before you start sanding.

Good luck and fair winds. :)
 
I repaired a t50 powerboat recently with both impact damage and a lot of crazing. You can see the photos at
http://www.southwoldboatyard.com/?p=450

You have a choice with crazing one you have removed the reason it crazed it the first place. Normally due to flex.
You can tackle each craze individually as I'm doing here,
grinding out each craze line that I've marked with pen using a dremil or similar
vent011.jpg


or you grind back the whole area and start again. which is what I did here,
vent005.jpg


Assuming you have a colour match you need to build up layers of gel, I can usually do four layers a day in reasonable conditions.
Make sure the last one you do is waxed.
The I usually sand back flat, removing any wax and will roll another three coats on.
Then its sanding back as I mentioned before.

The temptation is to put it on too thick which is fine until you want to get a decent finish.
If you get any air bubbles in a layer then you might get away with using a drill bit to chamfer the hole and re-gell it or as I have done in the past, start again.
 
Thanks, lots of good information. The largest chip I need to repair is about finger nail sized, no big areas. Does the pigment need to be of a 'gel coat product', or can I mix any kind of colouring, eg inkjet ink with white gel coat?
 
you might get away with it - have used a touch of anti foul as the pigment is concentrated, however the base was pre-pigmented white so the blue I added was insignificant.
I make no guarantees and I certainly wouldn't do it on a customers boat.
Try it - if it doesn't work you can always grind it out and try again.
 
Thanks for that. Crazing is due to impact, the craze lines follow where the top hat frames are inside. There are lots of them, but on the other hand much of the gel is still attached and sound and it may be possible with some patience to dremel out each line and certainly easier to fill than replaster.
 
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