Refractory Cement

[Bob79]

Hello everyone!

I am based in Sudbury, Suffolk UK and me and my husband are building a wood fired oven and have no prior construction experience. AT ALL! Progress has been slow (and scary!) - foundations dug in 2017, foundation and block stand finished in 2018 and we are hoping to finish the rest of it this year. It all started when we stayed in a holiday cottage that had a pizza oven and we were renting a flat without a garden.....thus the vision was created!!

We are following the FB plans for a 42" Pompeii oven, pretty much to the letter so far with extra research on the web, especially this site - so thank you for the help provided so far!

We have a stand made from concrete blocks with everyone other gap filled with concrete and rebar with a 4" slab and on top of that a 5:1 vermiculite and cement mix which is 3.5" thick - a bit less than we had planned but still within guidelines. Not mixed as per the notes - we used larger particle vermiculate and hoped that the cement mixer would break it down to a smaller size. There are no steam pipes because the notes don't include them but some people are including them in their ovens.

The floor of the heart will be made of storage heater bricks trimmed down to size so soldier bricks can be laid around the edge using firebricks and then the dome will be formed out of half bricks (so there will be big gaps) - the question I have is what mortar do I use? The FB notes suggest a high heat mortar which can be bought or made up using sand, cement, fireclay and lime (10:2:6:3). Where I am getting confused is most of the sites selling mortar suggest using it to 6mm thickness max and using a heat proof screed to fill the bigger gaps but looking at other builds it looks as though just mortar is used.

My question is can I use the homemade refractory mortar to both cement the bricks together and fill the gaps on the outside of the oven?

I've posted a pic of where we are so far so you can see progress (sorry cancel that, I can't get them to upload at the moment) - all comments and guidance greatfully received!

Thanks in advance
Roberta

[Gulf]

The suggested recipe for "home brew" is now 3 parts sand, 1 part portland cement, 1 part hydrated lime, and 1 part fireclay. Yes, home brew can be used for mortaring larger joints than the commercial refractory cements. Up to about 3/4" (19.05 mm). Since you will be using half brick there will be some extremely large joints to the outside. (I'm assuming that you will be using a bolster to cut the brick?) But, I also read that the heater bricks will be "trimmed down to size"? Will ya'll be using a wet saw to trim them?

[Bob79]

Hi Joe,

Thank you for the recipe for homebrew, there are quite a few different ones out there so it's good to get a recommendation. In order to fill the big gaps will it be OK to use the homebrew or is there another recipe we need?

We are borrowing a 12" disc cutter to cut both the storage heater bricks and the fire bricks. I'll be on hand with the hose as I was when cut the concrete blocks for the base (and they cut like butter but I know that heat bricks contain metal so may be tougher) . Hopefully this will be ok?!


Thank you very much for your help, it is really appreciated

Super best wishes
Roberta

[Gulf]

Not really another recipe but, you can place/pack some firebrick slivers or crushed firebrick rubble into the larger outside joints as you are pointing them. That will help on the mortar shrinkage. That being said, we've seen several half brick builds done with just the "homebrew" recipe wihout doing that. I can't remember any issues that came up.

[Merula]

Can't get powdered clay. What can I use instead?

[david s]

There are a couple of sources you could try.
Builders supplies: ask for Bricklayers clay or fireclay.
Pottery suppliers: ask for ball clay or slip casting powders

If either of these turn a blank you can easily dig your own, but it takes some effort.
Dig down below the topsoil where you should find a layer of clay. Allow it to dry completely then break it into lumps no bigger than your fist. Place into a 20 litre bucket until about 1/2 full, then cover with water to about 3/4 full and soak it for three days to allow clay to break down. Then stir with a paint stirrer and electric drill until the consistency is no thicker than pouring cream. Allow to sit for two days then pour off the water and floating debris that forms at the top. Heavy material will fall to the bottom, which you can leave behind. It’s the finer stuff in the middle that you want. Run this stuff through a coarse (say about 1.0 mm) sieve. Pour out onto a cement sheet, allow to dry, then pulverise and re-sieve. Simple but time and effort intensive.