Also, there are different types of fumed silica. The type most people use is "M5", or the hydrophilic type. There are fumed silicas that are hydrophobic (typically, long or large organic chains are attached to them). Regardless of the type of fumed silica you use, the results are the same--it isn't a rigidizer, it isn't colloidal silica, and it isnt protecting you from ceramic fiber. 

Where do you get your information Alex? Perhaps provide some cites.

In what way is fumed silica not colloidal? Before you answer that look up what colloidal means.

Frosty The Lucky.

It's about as colloidal as colloidal gets.

My Kastolite is flaking where I added a thin coat to level the floor. Im assuming the coat was too thin, or maybe I didn't butter properly?  I don't think it's a problem yet, but I'd like to fix it. I was thinking I could scrape off the flaking layer, then reapply the Kastolite, or maybe Satanite?  I've read that Satanite is good for patching, I've never used it.   Then re-coat with Plistix.  Will this approach work? What is recommended for a patching material? 

Thanks

The fumed silica I got from Amazon got quite hard, except on the front and back edges of the lining, not sure why.   I'm careful to keep the layer of the ridgidizer supplied by the manufacturer undamaged just in case. 

How thin a layer was it and how did you cure it? Kastolite is used as a patch in factory RR car size furnaces, patching with it is no problem.

Frosty The Lucky.

It varied, since I was trying to level the floor,  but anywhere from 3/8 to zero. Cured by bagging with a wet towel for a week,  dried about a week,  then fired a little,  then gradually up to a lot. The mix was a little coarse,  I might have gotten the ratio off, it was a small batch. 

3/8" should be safe but you want it uniform rather than "level. Different thicknesses can cause thick spots to break from pressure as it expands, the thicker it is the more pressure it exerts and thinner is weaker. 

Most of us who've made these things got hung up on plumb and level, especially floors. They really only need to be reasonably flat so thin work is evenly supported. 

Frosty The Lucky.