Refractory Recipes

I am copying this here for easy reference.  Originally posted to BackYardMetalCasting.

The "2 bucks" furnace formula
	The refractory mix is composed of Portland cement (1.5 parts), silica sand (2 parts), perlite (1.5 parts) and fireclay (2 parts). The first three components are mixed together thoroughly. I used a 1-gallon bucket to measure the parts. Less than one bag of perlite was necessary for the bucket furnace and I had about a gallon and a quarter of refractory left over. Tip: Build the body for a coffee can furnace and use the remaining refractory for that. Or mold the remainder into plinth blocks or bricks.

This one is from Traditional Oven

Refractory mortar mixing formulas

10 : 3 : 1.5 - Sand, Calcium Aluminate cement, Fireclay.

If you found hard locating refractory cement don't worry, here is one mixing formula with Portland cement plus lime available in ordinary building stores.

There are two Portland cement types, get the common gray in color, the other one is white decorative used for around pools etc. where a white effects are required.

Lime is calcium it takes over the cement in hot conditions (Portland will gradually burn out, it is used only for the mortar to set while working.)

10 : 6 : 2 : 3 – Sand, Fire Clay, Portland cement, and Lime.

Mixing heat resistant mortar

First mix all dry ingredients well. Then in small amounts start adding clean water at room temperature while continuing mixing.

Mix into peanut butter consistency. Apply thinly between firebricks and only in those places where needed e.g. in "V" sections between arched bricks on outside. Inside the arch - these bricks should be in line next to each other touching without gaps.

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Note that the above formula is for mortar.   Given that it is 2+3 parts of cement + lime I am thinking that 5 parts of perlite would work to make it more insulation.