High Heat Mortar Primer Getting Started Discuss High Heat Mortar Primer in the Pizza Oven Design and Installation forums; Not absolutely sure,but I think the masonary cement is 50% portland and 50% lime anyway. You might need to contact ...

[david s]

Not absolutely sure,but I think the masonary cement is 50% portland and 50% lime anyway. You might need to contact the manufacturer for specs. or just do the mix yourself.

[tdibratt]

Went to a local masons yard and turns out I was able to buy Portland Lime. It is a mix of portland cement and lime 1:1.

Perfect.

[Dutchoven]

Not really sure how I missed this posting and apologize for it...type N masonry cement is mixed at 50/50 portland to lime as is portland lime mix...in this instance it should be 2 parts cement 1 fireclay and 3 sand...that is exactly what I used for our oven build and it dried nice and hard quite quickly...although we haven't fired it yet I am confident in it as a mix...that will also work well for rendering the dome if that is how you plan to finish it as the type N is a bit stickier than other types of mortar...for the render you can add more sand...typically type N gets anywhere from 6 to 9 parts sand when being used to lay brick
Best
Dutch

[Lars]

I, too, had many questions about mortar.
Originally I got a high test bucket of dark refractory mortar to try out. It didn't seem to adhere to fire bricks very well, and needed to be fired to set. Furthermore, it dissolved when wet the next day.

Then I consulted a potter, actually two of them, who had built many kilns. They BOTH recommended the fire clay, portland sand lime mix.

Knowing the portland is just to knit things together and keep the rain from washing away the clay until it gets fired, I decided to put together the 'mix' of different recipes I have seen. I have worked with many different mortars, and the 3:2:1 ( and 1/2) recipe is GREAT --- fine quartz sand, fire clay, portland, and lime.

The fluffy adherent mixture is twice the fireclay to portland ratio. The FINE sand is good to keep the small mortar joints ( as possible) and this stuff sticks nicely ( I am up to the 7th chain with no forms.

The clay really retains the moisture a long time, so this allows the portland to set up very nicely without getting all the moisture sucked out of the mix.

As I understand it, the mortar is really a space filler, and not necessarily an agent of adhesion. It should get hard ( the fireclay) when fired, and the portland, ( as I have read) will begin to lose strength on the cool down phase.

I have been cutting all my bricks at an angle so every piece is a wedge. Theoretically it would stand with just spacers in the back, and hopefully the clay will harden and become at least that ( and hopefully more )

Just what I have learned so far. Let me know if I am way off base!

Lars.

[Abear]

Sounds great - thanks for the tip! In Houston, all we have in the ground is clay - you need TNT to dig a hole around here Just a clarification: When you say fire clay, you mean straight clay say, dug from my backyard? No additives, right?

[RTflorida]

Fire clay is a specific type of clay with the same refractory characteristics as firebricks.
It has an unusually high content of alumina (24% - 40%) and an overal alumina/silica content of 55%-60%.
Although naturally occuring and found all over the world, there is no way for any of us to judge whether the soil around your home contains fireclay. You may simply have "pain in the ass, I can't dig a whole" clay. If you are serious about using materials found around your home, I would research exactly what the characteristics of fireclay are in nature.
The cheapest and easiest solution is to go to a pottery, refractory, or brick supplier. Fireclay is cheap around here, it is $5 for 15 lbs or $15 for 40 lbs, depending on the supplier.

RT

[timo]

I just picked up 4 50# bags of fireclay from Clay Products in Spring Grove, Illinois. They were $11.40 a bag. I plan on using the mix your own method.

I have found many brick yards want to sell you the Heatstop for $74 instead of the 100% fireclay. Could be due to newer construction rules? Anyway, are there any more reports out there from home brewers and their results?

Thanks,

Timo

[Lars]

Timo,

Yes, I have posted many times about my ( I am pretty sure) success with my wonderful mortar recipe -- 3:2:1:1/2 ( Fine Sand, Fire Clay, Portland, Lime) I have started my first curing fires and do not have anything more to report at this time. So far I still REALLY like the mortar I used, but I haven't gotten anywhere near totally up to temperature. It's so hot, it may be a week before I continue with the curing/insulation.

I suspect that the high dollar mortar manufacturers pushed through regulations to force people to buy their stuff. ( just conjecture with no basis in fact that I am aware of)

Great price on that fire clay, by the way. I think I paid $25 for a 90lb. bag, but someone had brought it up special from another state. I am finished and won't be needing much of the 50lb. bag I have left. I have been mixing it into my (regular) brick mortar for a little light brown color.

Lars.

[Mierkmike]

I made up my refractory morter using the 1113 mix. I was later told by another oven builder that the Portland cement will disenagrate at 600 degrees and the bricks will get loose and fall in. Has anybody experienced this?

[karl]

It is not really the mortar which keeps the bricks from falling in. It is the lining up of the bricks in a certain diameter. If all bricks keep their position and there are contact points between each bricks and it's neighbour bricks (in 2D) the rings should not collapse. But often there are certain areas (in particular in the transition between the oven and the opening) where there are voids which have been filled with mortar. If such mortar disintegrate the ring of bricks may collapse.

karl