Gel coat catalyst ratios

[lumphammer]

I have a 0.75 litre tin of matched gel coat and a tube of catalyst. Out of the tin I probably only need a spoonful to fill the cracks I'm repairing. What is the easiest way to get the proportions of gel-coat to catalyst right? Is the ratio as critical as I understand it is for epoxy?

And on a related question does the gelcoat in its tin have a shelf life?

TIA

 

[prv]

The ratio is not critical to the final strength in the same way as for epoxy. What it will do is change the reaction speed. I usually use 2% catalyst, but go up to 3% in cold weather or where it's a simple job (ie not much working time needed) and I want it to hurry up so I can get on to the next bit.

I use 3ml plastic pipettes for the catalyst, which give reasonable precision:

For the resin or gelcoat, I use graduated mixing cups - they look rather like the sort of flimsy plastic pint glass you sometimes get at outdoor events, but with a measuring scale on the side. Some places charge silly prices for them, but they're cheap as chips on ebay, so I use one for each mix, apply direct from the cup, and stuff the used gloves and brushes into it at the end and throw the whole lot away.

Pete

 

[VicS]

Or for a "spoonfull" use a plastic medicine measure .. usually marked at 5cm³ intervals to 20 or 30 cm³ .. and a 1cm³ teat pipette.

Yes it does have a shelf life and so does the catalyst.

The gel coat is Ok while it is still fluid. The catalyst is OK while it will "set" a trial batch

 

[oldsaltoz]

Because Gel coat has a high mass of solids (about 50%) you do not need a lot of catayst, just half a percent will mean it sets as fast as 'normal' with a dose around i.5%.

Any more is just a waste of catalyst.

The same applies to flow coat. =(Gel Coat with added wax).

Good luck and fair winds.