Expansion

[JRHill]

Hi Folks, I'm new here - 1st post,

I'm building an oven for personal use, 36x28x32" high, domed. Firebrick is 3.5x3.5x16 nominal. All is solid except for the front side which is steel (doors, wood fuel feed, etc). I'm concerned about the steel expansion/contraction of the front over time on the mortar joints. I could make it solid which would be great for support on the front side with my concern, or I could make it float with a gasket.

Using salvaged brick and fondeu, will skim coat overall with std mortar mix. What are "best practices" here, I'm not a mason? Contents will be pork, geese, lamb and whatever tasty thing is at hand ;-)

Best,
JRH

[dakzaag]

JR,
Couple of things, cant really tell how you are venting this thing, looks like directly out the top which will make it challenging to get up to decent temperature. Secondly it is really tall and so it will be somewhat inefficient and again affect maximum temperature. I see you don't have any insulation under the floor, so once again you will find it challenging to get to high temp.

It will work for slow cooked stuff like roasts and whole hog, which ironically are very near by so you do have that going for you. If you want high temp pizza then you are going to need to change the design a little. I think if you are committed to the existing structure, then don't worry too much how you mount the doors because it will not get hot enough to have serious expansion and contraction issues. I would be a bit worried about stability if your doors are very heavy, I could see a heavy door pulling a hinge right off the side wall or breaking the wall itself. Spread the weight of the door out as much as you can.

Looks like you might be planning to move this around some, so build a little reinforcement into the structure to handle the forces of moving it around. Maybe fiber in the stucco mix? Glass fiber reinforced concrete comes to mind. Very interesting build, let us know how it works out.

[JRHill]

Thanks for your input, Dakzaag. A few clarifications: inside dimensions are 25.5" wide by 27" deep, 29.5 high. There is a 6" elbow on the back side for the chimney pipe & cap. The firebox and the cooking chamber will be separated by a removable 1/4" base plate. the firebox will be 8" high On the inside back wall with be a 2.5 x 10" steel channel to draft the firebox out through the chimney (which will add some more heating surface area). The front will be a 3/16 steel plate mounted to the front face of the brick and the base with left and right doors for the cooking chamber and a bottom hinged door for the firebox.

So its the steel expanding on the front that concerns me. If I drill over sized holes through the front assembly so the expansion doesn't put any force on the brick via the anchor screws (the whole front assy would "float"), I lose any support it could add. I can easily make the inside steel pieces float sufficiently so there won't be any stress from those pieces.

And thanks for the hole hog idea! We raise kunekune pigs which finish out around 85# hanging. Now I'm going to plan a bushing on each side for a rotisserie rod ;-) We have an existing rocked fire pit on the behind the stove that we've used for cooking for years, but I think the pig would cook great in the oven.

[david s]

You are correct about the expansion of the steel being a problem. Because steel is way more thermally conductive than brick it will heat up much faster than the brick causing it to expand before the brick has time to catch up. If you can allow for this expansion to occur without placing stress on the brick structure you should be ok, if not expect some severe cracking in your brick structure.