Gel coat to hardenner ratio.

[davidpbo]

Gel coat to hardener ratio.

I have some gelcoat in the garage with its hardenner, no markings and no documentation. Bought from a fibreglass supplier at a boat jumble some years ago. I realise it may be
useless but want to mix a sample.

I will attempt to estimate the volume of the two containers but can anyone give me an idea what the likely ratio might be. Looks to me as though it might be 1 to 4 or 5.

A boat builder friend told me gel coat will go off in free air but that there is a deposit that has to be cleaned off. Is this correct.

 

[gjgm]

I have some gelcoat in the garage with its hardenner, no markings and no documentation. Bought from a fibreglass supplier at a boat jumble some years ago. I realise it may be
useless but want to mix a sample.

I will attempt to estimate the volume of the two containers but can anyone give me an idea what the likely ratio might be. Looks to me as though it might be 1 to 4 or 5.

A boat builder friend told me gel coat will go off in free air but that there is a deposit that has to be cleaned off. Is this correct.

First, gelcoat is a polyesyer resin, with pigment;the other common resin is epoxy.
For gel and polyester resin,1-2 pct I think , mix ratio. Or, in an eggcup quantity, a few drops, maybe. To give some perspective a 1-2litre can of polyester resin will have a bottle of catalyst half the size of a tube of toothpaste- certainly nothing like 1/5.. that is epoxy ratios.
Epoxy gives of a wax "blush", and that needs to be washed off, and then sanded to get a good bond-that is why with epoxy, you want to keep going, and not take a break!
Unlike epoxy, the polyester gelcoat mix ratio isnt so critical, it just sets faster.
The resin in the gel will probably evaporate or whatever it does if you keep it too long- polyester resins have a sell by date.
Gelcoat can have styrene in it or wax, as polyester resin wont set in air- but that is only the top surface- below that, it will set. You can try anything from clingfilm to furniture polish as a test, or just wipe the top surface off with acetone once the rest has set.
Gel with wax etc in it can be called flowcoat.. the boat manufacturer can spray it on places like bilges and it will fully set. You wouldnt use flowcoat in a mold though, as obviously the fibreglass and resin wouldnt stick to the wax.

 

[Bodach na mara]

The gel coat that I used to use came with liquid hardner. The mixing ratio was between 1 and 2 percent, ie between 1 to 100 and 1 to 50. I have never met anything like you describe that would be 1 to 2 or similar. The ratio was not that critical in that it would still go off, but if too much catalyst was used it went off very fast.

Epoxy is different. Ratios like 1:3 or 1:5 are common and must be adhered to as closely as you can. If not, it will not cure properly. You really need to know the correct ratio.

 

[davidpbo]

Thank you, that was more or less my understanding. I sand and clean cured epoxy surfaces as a matter of course.
When I checked materials it was indeed a tiny drop of activator.*A test mix is hopefully going off now all looked well withe tin and additive.

Can i use multiple coats to get a thicker finish?

Can I thicken the gel coat with any additives?
The area I have to apply it to is slightly sloping.
Colloidal silica? I WILL get rid of that pot.
.

 

[sailorman]

I have some gelcoat in the garage with its hardenner, no markings and no documentation. Bought from a fibreglass supplier at a boat jumble some years ago. I realise it may be
useless but want to mix a sample.

I will attempt to estimate the volume of the two containers but can anyone give me an idea what the likely ratio might be. Looks to me as though it might be 1 to 4 or 5.

A boat builder friend told me gel coat will go off in free air but that there is a deposit that has to be cleaned off. Is this correct.

2%

 

[davidpbo]

Could I use epoxy resin with pigment for the top coat?. I have both.

UV Stability??

 

[TQA]

Could I use epoxy resin with pigment for the top coat?. I have both.

UV Stability??

Epoxy resin sticks better but it is not UV resistant.

Using something old esp . as you are clearly not sure what it is sounds like it might

' spoil the ship'

well maybe.

 

[davidpbo]

The ship is already spoiled.
I know what I have is polyester Gelcoat.
I have mixed a sample to see if it cures correctly.
If it does I can't see why I can't use it.

I do also have epoxy resin and a colour additive.

It would not be the end of the world if I had to redo the final finish or have it redone.

 

[nigelmercier]

Gelcoat will cure to a tacky finish, so will need to be sanded. If the catalyst is a clear liquid it is probably MEKP, so 1% will give a slow cure, 2% normal, 4% or more is fast.

 

[Tanqueray]

Nigelmercier is spot on.

Treat MEKP with respect however!

You can relax because yours will be stabilised with this stuff.

This is very unlikely to happen (well, almost very unlikely anyway)

 

[William_H]

Gel coat

No epoxy does deteriorate with UV going sort of chalky. Gel coat is polyester resin. As said a few percent by volume of MEKP hardener. I would tend to err with too much. It may go hard in the pot before application but will harden on the job quicker especially in low temps. Polyester resin needs a catalyst. It is usaully mixed in before sale but it may have been omitted consider if it won't go hard. Usual past sell by date deterioration is that the resin goes hard or thick in storage.
However I would advocate a polyurethane 2 pack paint in lieu of gelcoat. it sticks like epoxy but is good in UV. good luck olewill

 

[oldsaltoz]

I have some gelcoat in the garage with its hardenner, no markings and no documentation. Bought from a fibreglass supplier at a boat jumble some years ago. I realise it may be
useless but want to mix a sample.

I will attempt to estimate the volume of the two containers but can anyone give me an idea what the likely ratio might be. Looks to me as though it might be 1 to 4 or 5.

A boat builder friend told me gel coat will go off in free air but that there is a deposit that has to be cleaned off. Is this correct.

Think of Gel-coat as Poly resin with coloured powder mixed in and no added wax. This lack of wax means it will set only if covered and air is excluded.

The normal ration of resin to catalyst is just over 1% but should not go over 2.5%. However as at least one third of the gelcoat is particulate and not resin a mix of just 1.oo % should be fine.

Flow -coat on the other hand will have wax added, I suspect this might be what you have, (Gel-coat = no wax. Flow-coat has wax)

Both are essentially the same compound except flow cot has wax and gel-coat has no wax so must be sealed to cure.

Good luck and fair winds.

 

[gjgm]

poly on top of poly is fine
epoxy on top of poly is fine
poly wont bond on top of epoxy (generally)
Gel (I know.. is poly) can be made to adhere to epoxy, but the epoxy needs to be extremely well set ..weeks, perhaps. Many say it wont set, but West Systems ought to know, and they say it will (in the end!)

 

[davidpbo]

Hmmm just bought some flowcoat.

The epoxy has had a few days to set, I was planning on abrading, wiping with solvent cleaner and painting with flowcoat.

Surely that will key it into the epoxy?

 

[nigelmercier]

The epoxy has had a few days to set, I was planning on abrading, wiping with solvent cleaner and painting with flowcoat. Surely that will key it into the epoxy?

With those steps beforehand, it should be fine.

 

[gjgm]

Hmmm just bought some flowcoat.

The epoxy has had a few days to set, I was planning on abrading, wiping with solvent cleaner and painting with flowcoat.

Surely that will key it into the epoxy?

I think I would wait alot longer, because if it doesnt bond you are going to have to do it again.

 

[davidpbo]

I think I would wait alot longer, because if it doesnt bond you are going to have to do it again.

I want to go sailing. If I have to redo the top coat of two small definable areas at the end of the season so be it.

The alternative is, I am going to have to fair the repair before I coat it. I could add the flowcoat before the epoxy fairing is fully cured, would that work?

Otherwise is probably going to be fair today coat and flowcoat when I have left it for at least a day, more if I can.

 

[gjgm]

I want to go sailing. If I have to redo the top coat of two small definable areas at the end of the season so be it.

The alternative is, I am going to have to fair the repair before I coat it. I could add the flowcoat before the epoxy fairing is fully cured, would that work?

Otherwise is probably going to be fair today coat and flowcoat when I have left it for at least a day, more if I can.

ok, if it is only a small repair there perhaps isnt much downside- not much hardship to redo it another time. If it was something you were going to spend hours on...I think I would just do a temporary slap on, and blend/match polish and wax in a month or two

 

[nigelmercier]

I want to go sailing...

Go sailing, finish the job later.

 

[oldsaltoz]

Hmmm just bought some flowcoat.

The epoxy has had a few days to set, I was planning on abrading, wiping with solvent cleaner and painting with flow-coat.

Surely that will key it into the epoxy?

Note that the curing of the existing epoxy will leave a resudue on the surface.

It is critical that this is washed off BEFORE sanding,

You can use Acetone or a somple plastic kitchen scourer (Scotch-bright) starting at the top and working down (in the direction of water flow) and lightly scrub till beads of water no longer form on the finish indicating the residue has gone. TIP: keep the hose running the whole time to flush away the residue as the work your way down.

You will need a 40 or 50 grit grit sanding to get the right roughness.

The flow-coat will self level so not a problem.

Good luck and fair winds.