Here's a really good link:

: At the present time I am in the process of building a plug of a kayak from
: which I want to cast a fibergglass mold. From this mold I intend to build
: my kayak. In the past I have had problems with the mold not separating
: well from my plug. I have made my plug from regular seaming compound
: because it is soft and easily sanded,however, after I have applied my
: parting compound to the plug I find that the resin which I use to make the
: mold of the plug eats its way through the parting compound into the plug
: and six months of work is ruined. I am looking for something to coat my
: plug which is made of seaming compound so that it will become a barrier to
: the effects of the resin and will prevent it from reacting with my plug.
: Has anyone out there got any idea what I can use as an effective
: barrier????? Thanks