Ive done the mock up combustion chamber and now i want to build on-site. Im using refractory bricks all the way through from the feed hole to the heat riser. My question is this:
Can i use the same cob mixture used in making the bench to act as mortar for the combustion chamber and heat riser? Are there any cons with this method and if so, what is the best method of sealing off and keeping in place all the bricks in the J-unit?
Thank you in advance..the winter is around the corner and time is of the essence!
True refractory mortars add fireclay to the mix. It also is mixed up thinner so you don't end up with a thick joint. There is a lot more information here.
In the past, I've used regular clay I dug from the backyard, and it seemed to work well. (Of course, I live on top of one of the world's largest kaolin deposits, so that makes it easier.)
posted 6 years ago
Thank you John,
One question..when using clay as mortar did you mix it with anything, i.e. sand?
posted 6 years ago
Oh yes, the clay is just an addition to the regular cement/sand mortar. The easiest way to go for a small job is to buy the premixed sacks of mortar that are sold in the concrete block aisle of you local home improvement store and then add maybe half as much sifted clay. When you add water to this mix, you are not looking for the thick milkshake like consistency of block mortar, but add more water until it is thin and soupy. When you butter your bricks, it should only be about 1/8" thick (or less) and you won't be able to get much mortar out of the joint if you tap on the brick. It also helps to work with wet bricks when you are laying them, as you want the mortar to flow easily over the surface of the brick.
In this video, you can see that he is slapping on the mortar very thin, like a plaster.
If that plaster sets up between two bricks, it holds them together, but there isn't much surface area of the joint exposed to the heat. And if a little clay on the surface of the joint gets vitrified from the heat, no problem.