High Heat Mortar Mix question Newbie Forum Discuss High Heat Mortar Mix question in the Good Background Information forums; Originally Posted by david s I would not buy the stuff on Ebay because it has a short shelf life- ...

[windage]

Originally Posted by david s

I would not buy the stuff on Ebay because it has a short shelf life- about 6 months. You could get it and find that it's already gone off. Buy it from a reputable refractory supplier. It is expensive and tricky to work with- it goes off fast and is quite temperature dependent

David, do you have some recipes for me to try? I am dissapointed in my alum sil cement for lack of stickiness and diffucult to work-i-ness..

[david s]

Try the poor mans mix 3:1:1:1 sand, portland cement, lime, fire clay. But be careful the lime is particularly drying on the hands, you end up losing a layer of skin. Use rubber gloves and or barrier cream.

[windage]

That blend does work with portland, but not with alum sil, the lime is a no-no and sets it off in just a few (2-3) minutes..

[david s]

The lime also acts as an accelerant with calcium silicate cement. Because the stuff is expensive it is a waste if it goes off too fast.

[windage]

Finally, success! After a long discussion with the US rep for the REFCON MG by Calcem, I was pointed in the right direction, 2 issues were giving me fits; lack of stickiness and short "pot time, or work time".
1) lime is the enemy of aluminum silicate based cements, the residue in my work tools was enough to set it off in 3 to 5 minutes, and the Forno Bravo formula posted as adding one part lime is REALLY off base. Bought a new tub, trowel and fresh blending buckets..now "work time" is as long as I need. No more lime contamination.
2) stickiness was a function of adding more sand for more "surface area" to hold the water. I also tried his tip of adding a few drops of dish soap to entrain air...not sure if that helped or not...so the mixture I am using to lay (soaked) brick; 6 sand, 2 cement, 1 clay. I may even drop cement to 1 part when I parge the outside of the dome.

thanks guys

[windage]

Finally, success! After a long discussion with the US rep for the REFCON MG by Calcem, I was pointed in the right direction, 2 issues were giving me fits; lack of stickiness and short "pot time, or work time".
1) lime is the enemy of Calcium Aluminate based cements, the residue in my work tools was enough to set it off in 3 to 5 minutes, and the Forno Bravo formula posted as adding one part lime is REALLY off base. Bought a new tub, trowel and fresh blending buckets..now "work time" is as long as I need. No more lime contamination.
2) stickiness was a function of adding more sand for more "surface area" to hold the water. I also tried his tip of adding a few drops of dish soap to entrain air...not sure if that helped or not...so the mixture I am using to lay (soaked) brick; 6 sand, 2 cement, 1 clay. I may even drop cement to 1 part when I parge the outside of the dome.

thanks guys

[fxpose]

Please correct me if I'm wrong, but my understanding of homebrew formula is based on using lime with portland cement, and no other type of cement.

George

[dmun]

Please correct me if I'm wrong, but my understanding of homebrew formula is based on using lime with portland cement, and no other type of cement.

You're right. Portland only.

That blend does work with portland, but not with alum sil, the lime is a no-no and sets it off in just a few (2-3) minutes..

This was discussed in the High heat mortar primer (High Heat Mortar Primer) thread:

A quote from the thread by David S.:

When using calcium aluminate cement I found that adding lime in the mix made the mixture "go off" really quickly. On researching this I found, from the manufacturers (can't remember which one) that they said "do not add lime as it acts as an accellerant, which is exactly what I had found. Do not add lime if you want to keep it workable for a reasonable period (eg 1/2 - 3/4 hr or so) .The calcium aluminate cement is very temp dependant. Use chilled water if using on a hot day and don't leave the stuff in the sun to get hot.

There's much less practical experience with using the calcium aluminate mortar here. It has the reputation of being difficult.

[windage]

as dmun pointed out; "There's much less practical experience with using the calcium aluminate mortar here. It has the reputation of being difficult."

My initial search on this forum for "calcium aluminate" mortar turns up the Forno Bravo tuturial which instructs one to add lime in the recipe...it was only when that turned out so bad, did I do further searching and discovered the lime no-no issue. Further, I want to add that simply using old tools or mixing pans that have portland based residue on them also triggers the same "hot to trot" set up time.

I just share this info as there is very little about that product here. I also want to add my experience as being more favorable than previous posts would indicate.

[windage]

I have been converted! Happy day! The cal alum recipe is working great. I had to go buy one of those small (4cuft) Kobalt mixers at Lowes today, $300 to mix the components dry, but made things much faster.
3 benefits I discovered;1) no lime issues with hands or leaching later, 2) no "small joint" mandate. The cal alum cement is a stand alone (and castable) refractory, in other words, at 2624f (Calucem's refcon mg) it can take the heat without degrading (made the bricks around the arch / transition go faster) so gaps full of mortar may not look as professional, but they're fine. And 3), not only is it water resistant, (like portland), it's stronger/faster.

So, guys, take another look at the cal alum (CA) cements for your project. It may not deserve the knocks it has recieved.

And will someone tell FornoBrave to please change / update their page about CA high temp mortars....it cost me several weeks, I was not in a "gosple mood" and was "fixin't slap granny" over it.

More pics posted over at the "commercial-81 inch" thread.

And as always, thanks for the encouragement.