Hi-temp cement advice please

snipped-for-privacy@whidbey.com fired this volley in news: snipped-for-privacy@4ax.com:

It's probably unlikely, but if the builders knew of this then, sodium silicate (water-glass) solution added to the concrete will increase its ability to manage direct heat.

It also changes the curing characteristics, so experiment or research it before doing.

Lloyd

I don't have a clue, but if it were me, spending that much effort, I'd use a refractory concrete, just in case. Google "refractory concrete" and you'll find a bunch of products.

My dad built a big outdoor grill from brick and firebrick (for the firebox) about the time I was born, using a mix of regular concrete and crushed firebrick ("grog") for the mortar, I saw it about 40 years later and it was still going strong. But I don't know if he was just lucky, or if he got it right.

If the "3 to 1 concrete mix" cited in the article has worked inside the fire boxes for all these years, it ought to work outside as well. I assume that means 3 parts sand to 1 part concrete and no aggregate. This stuff (with which I once had an initmate relationship*) is probably pretty close if you don't want to mix your own.

Been known for at least a hundred years. What you realy want is some kind of refractory cement. Fire-Rok is one brand out there.

You want concrete that has no moisture in it - or concrete that can let the moisture out without splitting the concrete. Using fine plastic fibers in the agregate allows the plastic to melt and extrude, relieving the stem pressure.

I'd put in a refractory cement - AL based comes in a bag. Refractory cement isn't a water based cement. Portland cement has water stored in the cement.

I use refractory cement - a different process - and it is in my furnace. I melt Al and Brass. I don't want it to spit or explode.

If you spill some Al or Brass on the concrete floor - it will pop a chunk out with steam explosion.

Mart> My brother and I are welding up a couple of replicas of a "Klamath

Plenty of refractory cement is water based, I use 1600C and 1650C capable refractory castable frequently, and some 1800C from time to time, all work by adding water. The key is in the drying out and commissioning the cast parts to dry out any initial excess water and then driving off the chemically bound water. The binder isn't Portland cement as that won't take the heat, but an alumina silicate based cement.

Re-reading the article it says, as Ned pointed out, that a 3 to 1 mixture of sand and cement is what they used and these stoves are still in fine shape 80 years later. The Klamath Stove has the concrete directly exposed to the fire. The stoves my brother and I are making will have steel against the concrete so I don't think it will be getting all that hot. Eric

I missed that Ned. It does indeed look like plain old concrete will work. Thanks, Eric

'Sounds like a cool stove. Good luck with it.

BTW, I've seen fire rings in campgrounds that were laid right on top of concrete, and it sure looked like regular ol' concrete.

If carrying the entire thing around is a problem, there is always foam concrete, which is more lightweight. I don't know about the maximum temperature it can take, though.

You start out with water and it starts the chemical actions. When you burn out the furnace - steam it out - the water steams out and nothing is left. It is rock hard. High temp.

Mart> >> I'd put in a refractory cement - AL based comes in a bag.

Do we need special cement in the concrete mix?

I was out of town so am late to reply. Sorry. Anyway take a look at

It is kind of interesting even if you are not going to build one. Near the back of the article is a section on how to make vermiculite cement. Worth thinking about.

Dan