Refractory Mortar Poll

[dmun]

Re: Refractory Mortar Poll

I think that there's been anecdotal evidence that the homebrew mortar is less prone to cracking than other options, and this may explain why.

[david s]

Re: Refractory Mortar Poll

Jamie,
good research and you explained it well. One small point that some people get confused about is the difference between quartz inversion and vitrification. Quartz inversion takes place at exactly 573 C and at this point there is considerable expansion and this stage should be taken through slowly to avoid cracking. This is practically impossible in a WFO and would probably be only achieved at the top of the dome anyhow. Vitrification is when the clay begins to melt depending on the content of the fluxes it contains. It renders the clay body non porous ie. a vitrified clay pot will be waterproof even though it is unglazed. We never get our WFO's anywhere near the temps required to do this.

[david s]

Re: Refractory Mortar Poll

Sorry I should have added that the quartz inversion is the process that renders the irreversible change in the clay that will not let it turn back into mud if watered.

[JayMez]

Re: Refractory Mortar Poll

I used a mixture of refactory clay and refactory sand - no cement component at all. The whys and wherefores are in this thread:

http://www.fornobravo.com/forum/f8/h...clay-2783.html

I think some other forum members have used this kind of mortar since (dvonk for one).... and it still seems to be working fine after nearly two years of use. Of course the intresting question would be what its like after 20 years or 100.

I'll be sure to let you know when we get there

What is the ratio of this mix? What is it called? I was interested in building a temporary dome and your mix was reccomended to me but where do I get me hands on some?

[Tscarborough]

Re: Refractory Mortar Poll

Regarding the portland cement. I have always held that the aggregate in concrete is what causes disintegration of concrete at high temps. While this is also true, I spoke to a friend at Texas Lehigh Cement, and he ran it down for me. Cured Type I cement paste itself begins to fail at 520 degrees Fahrenheit. The aggregate in concrete (not mortar) generally causes explosive disintegration around the same time.

For a mortar with only sharp sand, it will be the cement paste that fails first. Lime does not begin failing until 900 degrees plus, AND it is able to heal itself through a process called "autogenous healing".

Fire clay added to the mix will raise the failure temperature by adding calcium aluminate but it does so at the cost of tensile strength.

The main things to be sure of for a good heat resistant mortar:

Aggregate is the most important. Clean, graded silica sand is optimal, with quartzite next.

For anything that will have direct flame, the joint should be as small as possible, and a very fine aggregate should be used. For anything NOT exposed to direct flame, the aggregate can be standard C144 masonry sand, and the LOWEST possible strength mortar should be used.

The fact of the matter is that it is not that critical in practice. Mix your mud, slap those ladrillo together and fire it up!

[windage]

Re: Refractory Mortar Poll

I am playing with alum sil homebrew...following the "FB" reciepe of 3 sand, 1 fireclay, 1 lime, 1 cement..the mix hardens in 3 to 5 minutes and is not sticky.
I read on here earlier that one guy said to leave the lime out, it seems to "set-off" the mix. I tried a small batch in the same ratios, but without the lime and it seemed to have longer pot life, but still not sticky.
Seems that the alum silc. cement doesn't act like the portland with regards to the stickiness.
Next I will try increasing the fireclay in an attempt to get stickiness, without the lime, of course.

Has anyone else had this lack of stickiness issue when using aluminum silicate cement and how did you deal with it?

[Lars]

Re: Refractory Mortar Poll

Hi Windage,
Boy, I have not posted in months.

I did make many posts on this topic. My oven wintered pretty well. my mortar has been fired and heated many times. The oven works better this spring than last summer.

One thing I noticed in all the 'wintering' was a weird crystal growing on my joints. I think it is due to the lime content. When you mix up my brew ( from earlier post) you get a VERY workable mixture.Sticky and oozy. If it were fired hard, theoretically, the only thing left is the aggregate and the fire clay. I think if I had it to do over again, I might use even less lime.

Besides the expense, I did not want to go to the extreme of the aluminum/sil cement because it is a real unknown commodity. Hardly anyone uses it -- and I consulted with guys who build kilns. They assured me that what I was using would work well. I believe it has.

I must say, though, the bricks and mortar inside an oven seem to get pretty brittle sounding. I try not to 'knock' them when manipulating the fire, etc.

Good luck... Make Pizza.

Lars.

[windage]

Re: Refractory Mortar Poll

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

[windage]

Re: Refractory Mortar Poll

I meant Calcium Aluminate...sorry about the confusion

[david s]

Re: Refractory Mortar Poll

Windage,
Your continued reference to Aluminium silicate had me thinking I was missing something. I thought you meant Calcium aluminate.
On the subject of adding clay to make a mortar more sticky- this is standard practice that brickies use. Sometimes they use lime for the same reason, but it is harder on the skin than clay. The problem with all clays is that they shrink (approx 10%) when drying which would lead to cracking, so the addition of clay should not be in too high a proportion.

[david s]

Re: Refractory Mortar Poll

Potters who want to reduce the shrinkage of a clay body add grog (crushed fired clay) which will not shrink. This in turn will reduce the shrinkage of the body because of the proportion of a non shrinking material. Sand would do the same, but for the potter not a good material because the sand will melt at higher temps (1000 C+)

[Glosta]

Re: Refractory Mortar Poll

I am using Heat Stop 50 dry mix. It worked fine in fireplace, is waterproof and sets up quicker than I can work. Heat Stop 50 is $50.00 per 50 lb bag at masonary suppliers is MASS. Glosta

[lwalper]

Re: Refractory Mortar Poll

I've been using the non-aluminate homebrew. It seems to work well - at least in the construction phase. It will be interesting to see how it responds to heat??

BTW, there is very little demand in this area for fireclay. My local materials source purchased a pallet of fireclay a couple of years ago for one job, sold two bags of the stuff, and there the rest of it sits. Mine is the first purchase of this particular item in the past two years. I wonder why the local brick masons don't use it in fireplace builds??or maybe there are not that many fireplaces being installed? I seem to see chimneys going up. Hmmm . . .??

[WoodchuckDad]

Re: Refractory Mortar Poll

Heatstop 50. My reasons are simple. I am anal retentive as all heck. I would constantly be second guessing myself for using a home brew. I just open the bag, scoop it into a bucket and mix it up. And while it is expensive, running down the different ingredients and mixing them together and figuring out how to store them so I have them ready when I need them takes time. And time is the one thing I have less of than anything else.