Aerosil (Cabosil) fumed silica is hydrophillic (readily absorbs water)?

[naturewaterboy]

I was just looking at the Aerosil website, and read that Aerosil is hydrophillic, meaning that it readily absorbs water. Even when the Aerosil is mixed with epoxy or other resin, isn't some of it on the surface, and wouldn't this mean that it would absorb some water? I know that we paint or gelcoat over the top of a repair that has Aerosil, but would a scratch in the paint expose Aerosil, thereby allowing it to absorb water?

[PAR]

Silica absorbs resin, becomes entombed in it and doesn't cause any issues, once the goo cures. If you have silica that isn't mixed into the resin (which you have to intentional do, because of the mixing qualities of the stuff) then sure you could have some problems. If your mixing skills are causing unsaturated silica to be in the cured resin, you have other problems to deal with, like resin/hardener having incomplete mixture and clumps of silica or other filler material messing up a batch.

The first time you try to mix silica into epoxy, you'll see what I mean. You have to be real sloppy or intentionally not want to mix it in to have unsaturated fluff in you cured resin.

If you had a pile of silica to your resin, sometimes you can get clumps, which are more difficult to mix into the resin. Run the silica through a flour sifter (don't let your wife catch you, and don't ask how I know), which will break up the clumps and provide a smooth, easier to mix batch. Often it's best to learn by doing, rather then reading . . .

[naturewaterboy]

thanks PAR, I've mixed a lot of it with epoxy, but just reading that it likes water concerned me. So it is ok to put below waterline on the outside of the hull?