Fumed Silica Thixotropic Powder

Yes. There is no problem with adding both glass bubbles (micro balloons) and fumed silica to a resin at the same time. In fact, this is quite common for creating a thixotropic filler for applications like filling and fairing on radio controlled planes/boats.

The fumed silica we stock is not hydrophobic and is described as hydrophilic.

Yes, we'd normally suggest adding the fumed silica it to the resin and mixing it in thoroughly first before you add the hardener to the resin. This will give you unlimited time to mix in the fumed silica, which can take a while (many minutes of vigorous stirring) to develop its effect properly.

In terms of the dilution effect of the hardener, it will have the effect you might predict; adding 50% hardener (for a 2:1 mix-ratio resin) to the thickened resin will reduce the thixotropic effect of the fumed silica by 1/3 so you would need to account for this when determining if you have reached the right thixotropy when adding to the resin side only.

For typical percentages of fumed silica, the effect on the volume of resin is so small that it's probably unnecessary to even factor the density change of the resin. If you did want to mitigate any ratio discrepancies, you could just measure out the correct volume of resin and hardener (at 2:1) before you add the fumed silica to the resin.

Likewise, if you were mixing the resin by weight (not volume) the weight of fumed silica is likely to be so small as to allow it to be ignored but if you wanted to be absolutely sure you could weight out the the correct ratio before adding the fumed silica.

Yes, our Fumed Silica can be used to thicken most epoxy resins. The more you add, the thicker it gets - in small quantities you can turn a typical resin into a thixotropic gelcoat consistency. At even higher amounts, you can even end up with a thick paste.

Our 'Fumed Silica' is Aerosil 200. The datasheet for the whole Aerosil range can be found on the Aerosil website. When looking at the datasheet, always look at the values for the Aerosil 200.

Although fumed silica will start to have an affect even at quite low quantities, in order to achieve a thick paste you would need to add quite a bit to your resin. One person's idea of a thick paste might be different to another but a good guide would be perhaps 100% by volume (so one cup of resin to one cup of fumed silica) would be a good starting point for a thick paste.