I have worked with colloidal silica thickened epoxy a whole lot. I bought a 30 gallon bag of it years ago for a recore project and store it in an plastic garbage can. Its versatile stuff. I will often use a little milled fiberglass to really make it bombroof. My method is a pretty similar to texlans but with a few differences:
1. I use a respirator. This stuff is really nasty for the lungs
2. Find a wind-free area. I have been known to set up sheets of plywood, tarps or other temporary barriers.
3. I use quart containers. Old yoghurt tubs are great.
4. I like to use two large size tongue depressors doubled up since the thickened epoxy is pretty stiff (I have tried paint sticks but I prefer the doubled up tongue depressors, seems like more control and ability to scrape sides of the bucket easily)
5. Make sure the epoxy is flowing well. Might require warming as Loren mentioned above.
6. Mix the epoxy for 30 seconds to a minute.
7. I add the silica in two or more batches, with the first being 1/2-2/3 the final amount. I'll mix the first batch well then gradually add more until the desired consistency is achieved. It's easy to get too much.
8. If I have added the right amount of silica in the first batch I don't lose too much of it, unless it's windy. If in doubt, I'll start with smaller batches of silica.
9 I never use more than 4-6 pumps of epoxy per pot. Trying to mix a large batch is very difficult.
10. Using the tongue depressors, I scoop the epoxy up and gently fold it over the silica, kind of like cake batter. I only start stirring it once most of the silica is folded in. If you start stirring immediately it all poofs out of the container.
11. I use two new "tongue depressors" for each batch.
Double-ditto on the respirator/good quality mask. Silica is worse than fiberglass in the lungs. It'll kill you, long and slow like.
I used to use doubled up tongue depressors, but on larger batches I kept breaking them and even if i didn't, the epoxy that got between the sticks always bothered me (more waste..)
I (ironically) just mixed a pretty big batch (6 pumps epoxy, 3 pumps resin.. I use 2-1 Marinepoxy for most of my stuff (cures more flexible than 3-1 or 5-1 like west, less cracking on impact and works better with the thermal expansion/contraction of wood substrates) yesterday. I thought about videoing the process and posting it here to show the technique, but I was already mixing so fail on that. I'll try to remember to demo next batch i do..
The key to my technique is to tip the container so that you can get the broad side of your mixing stick over as much silica as possible, and then push it down into/through the epoxy, then bring it back up through the epoxy and repeat. it's a very deliberate motion, similar to your folding action just the other way around. I had mixed in 3-batches of silica in about 3.5 minutes, it went really fast.
Last thing to note, before it's really thickened, the silica tends to bead/clump up a lot. Don't waste too much time trying to smooth it out until it's closer to the consistency you're trying to achieve, just add more silica and go back to folding it in. As it gets thicker, it seems like the sheer of the viscosity helps to tear apart the clumps and it becomes smooth really fast at that point.
