High Heat Mortar Primer

[david s]

The reason I use silica sand is because it has sharp grains rather than rounded ones which I think provides better grip when bonded with the other materials. It is also closer to pure silica so has less impurities which can be more inclined to create adverse chemical reactions under high heat conditions. Don't worry about it melting though because pure silica melts at something like 1500C and needs fluxes to bring it's melting point down to about 900C which is still way higher than our range.
Clay may contain some silica but among other things has a higher content of alumina.
Brickies sand often contains some mud and other impurities, which helps make the mortar workable.This is ideal for normal mortar. Because we use lime and fireclay in the mix these ingredients help to make the mortar workable. So IMO silica sand is the preferred choice. Excuse the longwinded reply.

[azpizzanut]

Hi les,

Silica sand sold by masonry suppliers is uniform in composition. Other sands have varying amounts of silica and other sand materials. Silica sand is sold in various mesh sizes here in the U.S. from 30 to 200. I've used the 60 and 120 mesh silica sand with good results for Poor Man's mortar. Silica sand is often used for sand blasting applications. If your masonry supplier doesn't carry the mesh size you want then possibly a welding supplier will have it available.

Cheers,

[les.farrell@activ8.net.au]

Thanks for that Bob, sorry I took so long to reply, I work away from home and just got back.
I will check out our suppliers.
Cheers,
Les

[les.farrell@activ8.net.au]

Thanks David, much appreciated, I'll look around, there is a sand supplier in Bundy and I think he has what I'm looking for,
Regards,
Les

[Hank10746]

Originally Posted by james

Hello all,

The topic of mortar comes up often, so we are making this a sticky posting that will always be at the top of the "Getting Started" forum for reference.

Here is some good background information on the high heat mortar you should use to assemble a Forno Bravo Casa or Premio pre-cast oven, or to build a brick Pompeii Oven.

The best solution is to use Refrax, or another pre-mixed true refractory mortar. We stock Refrax and highly recommend it. It is pre-mixed (just add water), sets hard, is easy to work with, fully cured quickly, and is heat resistent to 1700F. Basically, it's made specifically for pizza ovens and fireplaces.

If you don't want to worry about shipping Refrax, or want to save some money, you can make a fire clay/Portland cement mortar. Fire clay is a heat resistent clay made up of aluminate and silica. When you mix fire clay with Portland cement, sand and lime, you get a mortar that is more heat resistant than concrete (Portland cement with a sand and gravel aggretate), though less resiliant or thermally conductive than a true aluminate mortar.

Here in Sonoma county, you can get fire clay from our big, local masonry supply company, SBI -- who is also a Forno Bravo oven dealer.

Here is the recipe for fire clay mortar, where you measure by volume (use a bucket or shovel to measure):

1 part portland
3 parts sand
1 part lime
1 part fire clay

In between Refrax and fire clay/Portland cement mortar, you can make your own aluminate mortar. It is hard to work with, as calcium aluminate can be challenging. If you get the mix, or water wrong, it won't set correctly. It partially sets very quickly, and you cannot re-hydrate it, so you have to mix it and use it in small batches. Still, if you are trying to save money and want/need the heat resilience, heat conductivity and longevity of a true aluminate mortar, it works.

1 part calcium aluminate
3 parts sand
1 part lime
1 part fire clay

-James
__________________

Hi
I found this and thought it might help in it lime or portland cement should not be used. Thought it might help

High Alumina Cement Construction method:
1. When preparing refractory concrete, fix on the aggregate according to using condition. Choose the proper capacity graduation to make maximum density. Be noted to match and adapt with cementing material.
2. According to certain proportion, add water and mix by man or machine into mortar and then begin casting construction. Use up the ready mortar within 40 min. Calcium Aluminate Cement’s hydration heat concentrate on early stage. Casting thickness should not exceed 3 cm each time. Water curing immediately when concrete goes hardening and the curing time should not less than 3 days.
3. When prepare expanding cement, Calcium Aluminate clinker’s dosage is 73-76%, CaSO4·2H2O dosage is 24-27%. When prepare self-stressing cement, the mixing ratio of CaSO4·2H2O should be increased.

High Alumina Cement Notice:
1. In order to avoid uncontrollable setting time, do not mix with Portland cement, lime etc of which separate out calcium hydroxide cementing material. Before use, clean all the mixing machinery. [/COLOR]2. Steam curing to accelerate concrete’s hardening. The curing temperature should not higher than 50?.
3. Refractory concrete’s late strength decline big, design should according to the lowest stable strength. CA-50 bonded concrete’s lowest stable strength should be determined by the lowest strength of 7-14 days of demoulding sample curing in 20?±1? water.

[arriflex]

Just to throw another option out there, if one has access to "Glass block mortar" there is a very easy way. Glass block mortar is generally:

1 part portland
1 part lime
4 part sand

If you had a source for pre-mixed glass block mortar, and you wanted:

1 part portland
1 part lime
4 part sand
2 part fireclay

Then you would mix three parts of the glass block mortar with one part of fireclay:

3 part glass block mortar (pre-mixed)
1 part fireclay

There was previous discussion regarding the potential for using Type-N pre-mixed mortar; I would caution anyone considering that option to be aware that the ratio of sand in Type-N is 6 parts to one part each portland and lime.

Finally, and someone please correct me if I'm wrong on this, "parts" are very specifically measured by volume not weight. My baker's head wants badly to weigh parts rather than measure their volume which would lead to a major error as portland weighs more than twice what lime does per volume.

arri

[DTHERR]

Has anyone else tried the "calcium aluminoslicate" home brew ? I use it everyday in my countertops as a additive so have access to it so cost is negligible .. Does it make a better refractory mortar then the portland brew?