Homemade Thermix

[pgmr]

AFAICT, Thermix is simply a lightweight concrete using portland cement and vermiculite/perlite. Other than the, "but it doesn't have a UL listing!!" argument, what's to prevent one from mixing his own and saving 2/3 the cost?

I've used loose vermiculite in the past with great success. Only complaint was that the fines could work past the block off plate and fall onto the stove. More a nuisance than a problem.

Anyone already done this and want to share the experience and formula used?

 

[pgmr]

Here I go talking to myself again!

Just found a good pdf ((broken link removed to http://www.perlite.org/perlite_info/guides/lightweight_insulating_concrete/general/perlite_concrete.pdf)) with formulas, strengths and even K values. It suggests using an air entrainment additive which will increase the cost somewhat.

I would guess that the lightest mix would be the one to use, since it would have more aggregate and voids and most closely matches the Thermix dry weight of ~ 20lbs/cf.

 

[elmoleaf]

Had the same thought & found the same website.
If/when I try it, I'm considering a 1:6 mix (portland to perlite).
Home foundry users often make their own refractory using the same idea, except substituting furnace cement for the portland cement.

 

[pgmr]

Thanks for the reply, Elmo.

I have a really small test batch curing now. Not sure about the air entrainment admixture - some sites say that a detergent can be used, but for the mix to be as dry and granular as Thermix suggests, it doesn't seem like it would do much. I'll probably just skip it.

 

[pgmr]

Mixed up 10 gallons of thermal concrete yesterday to seal the block off plate area (see https://www.hearth.com/talk/threads/15534/). Not sure of the formula used. Filled my mixing tray with perlite and added enough cement and water to get the perlite fully incorporated in the mix, yet not soupy. Didn't bother with an air entrainment additive. Some fell through during the installation, of course, but assuming it is fully surrounding the pipe where it goes through the block off plate, it should keep the loose fill perlite above it from working it's way through over time.

 

[pgmr]

Found the downside to this the other day. With liner cemented to block off plate and perlite packed around it, it was impossible to lift up to uninstall old insert. Had to cut liner off near stove to remove it. Will be putting in a slip joint section of ss smooth wall liner before new insert gets installed to allow future removal w/o cutting liner.

 

[Corey]

If anyone is looking to make their own with the air plus additive - it's pretty cheap. One place to order:

http://www.concretecountertopsupply.com/store/ccp0-prodshow/AirPlus.html (3 bucks for 8 ounces) which is mixed @ ~1% the weight of cement.

I've ordered concrete countertop stuff from these guys. Seem to have good service and fast shipping. (I have no other affiliation with them) Though for such a low price, it makes you wonder if it isn't just a bag of detergent.

 

[Wet1]

If anyone is looking to make their own with the air plus additive - it's pretty cheap. One place to order:

http://www.concretecountertopsupply.com/store/ccp0-prodshow/AirPlus.html (3 bucks for 8 ounces) which is mixed @ ~1% the weight of cement.

I've ordered concrete countertop stuff from these guys. Seem to have good service and fast shipping. (I have no other affiliation with them) Though for such a low price, it makes you wonder if it isn't just a bag of detergent.

I was going to order this product, but I noticed it only increases entrained air in concrete by 1/4 to 1%... I'm not sure it's really worth the hassle/time/expense.

 

[Corey]

That is interesting - had not looked at the detailed specs before. That does seem like a pretty small bump, but not exactly sure when they say, "increases...by 1/4 to 1%". So if the concrete originally had 2% air, this would get it to 3% - which would be 1/3 more 'air' or if they are saying at 2%, you get one percent more as in 2 x 1.01 = 2.02%. Surely it would be the former case. Also note the 1% increase is for one 8 ounce bag in a 8-12 cubic yard truck of concrete. If the product usage would allow, it is pretty economical to mix a much higher ratio for a single flue lining - ie one 8 ounce bag for a couple bags of cement.

There is also a product called "super air plus" which claims to go up to 16% air when used at 4-6 oz / 100 pounds (of cement, not total concrete)

(broken link removed to http://www.concrete-texturing.com/documents/SuperAirPlus.pdf)