Maximum mortar joint on inner oven surface?

[Les]

Re: Maximum mortar joint on inner oven surface?

Remember the goal here is to cook with the oven not spend allbyou tone building it.

Ouch... I was just responding to the words "not practical". I equate it to never - never say never.

David - when it comes to cutting, you are the master. Your approach to the build was awesome.

Les...

[Roadkyng]

Re: Maximum mortar joint on inner oven surface?

partially agree. It is not refractory in the sense it is not fired. From what the retailer told me it takes a heat of 1800 to 2100 degrees to properly fire a fireclay mixture. It is refractory compared to a standard sand mix in that it withstands much more heat. From reading it appears the homebrew mix is used in building kilns.
My joints are as narrow in the interior as possible and do not exceed 1/4". Now the exterior is another matter!

Since the home-brew mortar is non-refractory, it will let heat escape at a greater rate than a true refractory mortar.

If I was running a kiln or blast furnace 24/7 I would care about the excess running costs.

[Tscarborough]

Re: Maximum mortar joint on inner oven surface?

Portland cement itself is not refractory, but can handle high heat. What causes problems is the aggregate. Fine silica sand is no problem, but other manufactured sands can be. If they are composed of various types of other minerals, they will explosively de-laminate (spall) when exposed to high temperatures. The best practice is to minimize joint size on any face exposed to direct flame.

ASTM C-144 is the aggregate standard for mortar that is NOT exposed to direct flame, and it allows for the use of manufactured sand so long as it is graded properly. This is important because properly graded aggregate will prevent shrinkage cracking which is a very real problem with most refractory mortars due to the fineness and homogeneous gradation of the aggregate.