: I could have sworn I had heard/read somewhere that Nick used to add
: a small amount (maybe a TSP) to his resin for fill coats to
: increase the viscosity. Personally I'm not sure I would...

On final fill coats I sometimes add a very small amount of cabosil to the resin. It helps reduce fisheyes from any small pits in the weave.

About a tablespoon per cup of resin on the suggestion of MAS epoxies. Mix the epoxy, add the cabosil, and let it sit for a little bit. This will let the air get out of the cabosil and the result is very clear. Cloudiness from cabosil is mostly just air trapped in the mix. Cabosil is silica, or glass so is capable as being about as clear as fiberglass.

Spread out thin, the epoxy is not cloudy even if there is still a little air trapped.

I would not suggest it for seal coats before glassing.