Re: 493 Progress?

I use all these materials in my trade (masonry heater and oven construction).

Calcium Silicate board (one trade name CalSil board) is relatively inexpensive and tolerant of relatively high temperatures. It can be somewhat brittle and breaks down to a white powder. It has very little bending ability so you will see typical 12" wide boards commonly 3' long or more to make curves (as in #493). Its big advantage is it has a high compressive strength in use (I have built masonry fireplaces on it to keep heat from traveling down into the foundation).

Mineral wool insulation (not the same as rock wool) is very similar to fiberglass insulation (irritating fibers when applying) but holds up much better to heat, retaining its loft when fiberglass breaks down. It does not have a high compressive strength like CalSil board, but if compressed will usually return to shape when released. Mineral wool can be purchased in flexible form (like typical fiberglass batts) or with a binding resin in more rigid form referred to as mineral wool board. A particularly useful form comes in wide rolls with a foiled side to reflect heat.

Ceramic wool is the most commonly used industrial replacement for asbestos as both have higher insulative ability per thickness measure than CalSil Board and mineral wool. It has very little compressive strength and if compressed often does not return to its uncompressed shape so that placement takes a great deal of care if insulative ability is a large factor. It is also the most expensive of these three insulative materials.

I have watched the various restoration photos and seen examples of all these in lagging applications. I agree with Kelly that CalSil board is not fun, though I'd recommend mineral wool over fiberglass.

Timothy