Catalyst to Gel Coat Ratio

[davidpbo]

Hi folks,

Bought some Gel coat at a boat jumble about 18 Months ago. Label on catalyst bottle says Pro-composites Ltd. Thinking about using it to do a repair. Might try fabricating something simple first off boat.

Firstly is it likely to be too old? it has been stored in house to stop from getting too cold.

Secondly, unfortunately catalyst spilt somewhat and has semi destroyed label.

It says it is something methyl ethyl ketone peroxide and that the dosage is 2ml per ??? (obliterated).

Is it MEKP or is ther a word or two missing?

What is the dosage 2ml per 100ml or something else?

I have epoxy resin and hardener (probably of the same vintage) would the the hardener for the resin be the same?

TIA

David

 

[VicS]

Surprised Brendan has not responded to this

Try this old thread http://www.ybw.com/forums/showflat.php?C...&PHPSESSID=

Also might find something in www.topcatsail.co.uk/GRP-REPAIR-MANUAL.pdf

 

[30boat]

It may have gone off so mix some and make sure it hardens properly.You'll have to exclude all oxigen or it will stay tacky.

 

[William_H]

Epoxy resin is hardened by mixing 2 parts sometimes at 2to1 sometimes 1to1 but the parts become part of the final structure. If the ratios are incorrect then molecules of one will not be attached to molecules of the other giving a weakness and non hardening. No epoxy heardener is no good to you.
Polyester resin is a rssin usually mixed with a catalyst before delivery. It is hardened by adding an oxidiser which generates heat and causes the hardening. The hardener MEKP does not seem to be a critical coposite part of the matrix so actual quantity of hadener is not so critical. Too much hardener and you risk the resin getting too hot and going off in the pot before lay up while too little means it will not go hard quickly enough. However ambient temperature affects the speed of going off to a great degree.
So in UK cool temps 2ml per 100ml might be OK but be quick in laying the resin on. In warm summer conditions that 2ml might better be 2ml per litre for a long pot life.

I usually use it in small quantities such that a splash (1/4 teaspoon will harden about 1/2 cup of resin in a few hours. You should experiment a bit.
If it gets hot in the pot or goes suddenly viscous it is too late throw it away don't try to use it by rushing the layup.
good luck olewill

 

[nimbusgb]

2% is usual so your 2ml to 100ml is right ( about 20 drops from the dropper bottle ). As someone else suggested, mix up a couple of tablespoons full to test the stuff out.

I had some gel stored in a cupboard on the boat in the med for 2 years, 40 degree summer, 0 degree winters and it still worked fine last week.

 

[lw395]

I think the catalyst can vary in concentration/additives, but 1% is typical. It is not that critical, provided mixing is adequate. I tend to measure with a small syringe for repeatability.
Self-heating of large batches can be an issue, better to work in stages where possible.
And remember the disposable polythene gloves!

 

[pappaecho]

The problem with aged polyester resins is not the hardener or catalyst. but the fact that the activator in the resin deteriorates.

By all means try a small amount of resin with the hardener, say 2%.
If it does not cure then you will have to get a small amount of activator from the manufacturer

 

[vyv_cox]

I guess you know that gel coat is only the thickened surface layer? You'll need some layup resin and glass as well to make something. I have no idea at all whether you could lay up epoxy onto new gelcoat but I wouldn't risk it for the cost involved.