High Heat Mortar Primer

[karl]

Re: High Heat Mortar Primer

CaMaHa7

Is it correct that you plan to cast your dome and not use bricks with high heat mortar in between?

I have no experience in casting a pizza oven dome. But I would be very hesitant in doing so without a structural reinforced concrete dome. Dense high heat castablel concrete may good (I do not now), but you should consider reinforcement by using iron reinforcement. Refractory cast needs to cure and sinter at the right temperature to obtain strength and I am not used to think of such a concrete as a structural layer. But I am not an expert here.

I guess the dome diameter and diameter/height ratio comes in as a parameter. Unless this is a very small build I would consult someone who has done this before.

Karl

[Brad Low]

Hi
Looking for some advice. We've found a product at Bunnings in Oz which is a premix of sand, cement and hydrated lime https://dingocement.com.au/product/m...ix-handy-pack/ We called Dingo and they let us know the ratio is 3-4 parts sand: 1 part cement: 1 part lime. We're adding 1 part fireclay to this for our mortar. Can anyone see any issues with using this product that we haven't realised? Or has anyone used this product?
Cheers
Brad

[Campmaki]

Hello from frosty Wisconsin, I had very good luck with using a home brew mortar. My quantities were, 3 parts silica sand, 1 part lime, 1 part cement, 1 part fireclay. I used a paddle on a electric drill to mix. Mix only the amount you will use in a short time, as it sets fast. I dry mixed before adding water. My posts/ pictures are under Campmaki, hope this helps.

[shanxk8]

Hi all, I've been trying the 1:3:1:1 home brew mortar with my outer arch today (after using heat stop 50 for my dome). but I am finding that the bricks are not sticking together very well with the home brew. It seems to be setting, just not adhering to the bricks

Any suggestions?

[wotavidone]

Hi all, I've been trying the 1:3:1:1 home brew mortar with my outer arch today (after using heat stop 50 for my dome). but I am finding that the bricks are not sticking together very well with the home brew. It seems to be setting, just not adhering to the bricks

Any suggestions?

Aaand......here goes the great wet/dry debate.
Are they firebricks? Are they clean? Are they wet or dry?
Did you use proper hydrated lime - NOT agricultural lime from the garden shop?
I belong to the clean and dry school, I think. Until next week when I might change my mind.
My thinking is that a clean, dry, hopefully slightly porous brick will suck some of your lime loaded water from the mortar into the brick and help greatly with adhesion.
I washed my bricks and let them dry out for a while. Of course in summer, on a hot day a completely dry brick might suck too much water out of your mortar and screw it up so ypu might want your brick damp rather than completely dry.

The lime must be slaked lime or hydrated lime. i.e calcium hydroxide.
This stuff will combine with carbon dioxide from the air to form calcium carbonate (lime stone) in situ, thus binding your aggregates together and taking the place of the mix of calcium silicates in the Portland cement that may eventually decompose from the heat.

Lime from the garden shop is probably crushed limestone, calcium carbonate. Won't undergo the carbonation reaction, because it already has, so won't contribute any set/adhesion/strength to the mortar.

[JRPizza]

Great advice! Bricks being too wet gave me some adhesion problems early in my build. I learned to just hit the edges with a damp sponge enough to wipe of any residue from cutting and to see the moisture suck in about a quarter inch or so. With the right consistence of mortar the dry(ish) bricks will really "grab" onto it.

[agrasyuk]

Hi all, I've been trying the 1:3:1:1 home brew mortar with my outer arch today (after using heat stop 50 for my dome). but I am finding that the bricks are not sticking together very well with the home brew. It seems to be setting, just not adhering to the bricks

Any suggestions?

Another vote to make sure bricks are clean. While I don't wet the bricks for purpose of them being damp I do wash them throughout - both my angle grinder and radial arm saw leave heavy coat of dust.

You saying an arch this means you building on some sort of support. Is it completely stationary? Do you have situation where you dislodge fresh already set bricks wile tapping the new ones in?

Im having a hunch that type of sand may also play a role . Built my oven with "playsand" , was a joy to work with. Now that I'm using masons sand , from a very respected manufacturer I notice mortar behaves worlds apart different as it is sharper.

In your situation I would probably try and increase water content for bit more sloppy mortar (had to do it for my sharper sand otherwise it lumped).

[shanxk8]

Here's an example, they are fire bricks, clean and wetted with a dunk then wipe with sponge. I am using jointing sand.

It could be that tapping of subsequent bricks in the arch has dislodged earlier bricks. Guess I will have to slow down, the heat stop didn't have the same problem.

[shanxk8]

Maybe I will try dry bricks with just a sponge wipe today .
and yes, I am using type s lime . Returned the type n the other day and got proper kind .

[Pizzahorse]

Hi,

I picked up a bag of heat stop 50, and got super scared by the carcinogen warnings (I think it said to throw out your clothes if they got contaminated).

What dust precautions should we be taking? Are any of the other high heat mortar methods easier or safer in this regard?

[Pizzahorse]

What would happen if I mix Portland cement with sand and lime, but skip the fireclay?

[Gulf]

Depending on the ratios, just general purpose mortar.

[Pizzahorse]

Right, so if I just use general purpose mortar, will my structure fall down, or will I just lose some of the refractory quality and not get as hot a cook?

[Pizzahorse]

Or what if I use regular clay instead of fireclay?

Am I being nuts here? Why does nobody else

[mongota]

Right, so if I just use general purpose mortar, will my structure fall down, or will I just lose some of the refractory quality and not get as hot a cook?

If you use a portland cement/sand/lime mixture - which is "mortar" - the portland cement can lose some of its structural integrity at the high temperatures seen in a WFO. You could be left with less binder in the mix, and what is left in the firebrick joints can powder away over time.

Will your structure collapse? Not likely. The dome is built in compression. You could end up with partial gaps between bricks if the mortar does decay, but the dome should maintain its shape. I could see potential issues regarding the structural integrity of a vent arch with compromised mortar, as the arch shape, depending on its geometry and whether is is buttressed or not, may not inherently be a "strong" as a dome. However - the vent arch typically sees lower temperatures than the brick inside the cooking dome.

Might you occasionally end up with grit in your food from the decaying mortar? It's possible.

In the end, you can build a dome with basic mortar, but it may not be the best way to build.