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?

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