I need to take a mould from a grp non skid surface on a boat so I can match it on an area I'm repairing. Is your silicone suitable for this or would I be better finding a thicker putty type silicone? If it will work, what sort sort of thickness would I have to make it?

I have carried out just such a repair or rather I have had to let in a 2 ft section of deck where the shroud plate pulled out in a dismasting incident. I made a splash mould and new deck section but I wanted to cover the joins with a thin moulded gel. I made a mould with condensation cure silicone from E.C. It is about 8mm thick. 

Saul, have you tried warming it up a bit? I believe an issue with RTV silicones is they suck the heat out of the process, so thermoset resins may not reach the temperature they need to fully cure. If you warm everything up to about 30-40 degrees Celsius, you might find that solves the curing tacky issue. 

Thanks for the reply Saul. I've since read somewhere that the condensation cure can have curing issues, so maybe the addition cure would be better. My repair will be out in the algarve sunshine so hopefully heat won't be a problem!

Condensation curing silicones are generally very good at curing. Addition cure silicones can be inhibited by several materials.

In terms of resin curing, most resins cure fine in condensation cured silicones, except for waterclear resins which due to thier nature are often very moisture sensitive and thus the moisture found in a condensation cure silicone can cause problems.  This shouldn't be the case for typical polyester gelcoats or laminating resins.

You may find that due to the uneven surface, the wax additive is not working as effective as it might be on a flat surface. Remember though that the wax additive only works on surfaces exposed to air facing upwards as the wax will float.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant