Warped Firebrick

[watchthenanacrossing]

Hey everyone,

Need some help here figuring something out. I fired my newly built oven last night, and after a while the firebrick flooring became uneven. The gaps in between each brick increased like the bricks shrank, and then a couple corners of the bricks popped up. Today I took one out because they became loose enough, and they were warped into a bow shape. Why did the firebricks warp? I've never heard of that.

The firebricks are rated up to 2000 degrees, so I don't know why they would warp.

Let me know if you have an answer. Thanks!

[Gulf]

That's a new one on me. I have some warped firebrick, but they were wire cut (extruded) not pressed. They were that way from the kiln. Do you have the manufacturers name and information from your supplier? If you have a pic of a left over brick, it would be great. Also. please include the exact dimisions of the brick.

[watchthenanacrossing]

Here's a couple photos of the bricks. You can tell more of the warp in the one where I'm pressing on it.

The company is Vogelzang. I haven't tried to contact them yet. The dimensions are 9" x 4.5" x 1.25".

[Gulf]

Those appear to be pumice firebrick for a wood heater. They are not a dense firebrick like you want for the oven floor.

EDIT: Pumice firebrick are soft, light, and have some insulative qualities that help protect and extend the life of some metal wood burning stoves/heaters. Particularly the pellet stoves. They may yield some insulative qualities if you decide to place a layer of dense firebrick splits over them. Get the dense fiebrick splits from a local brick yard.

[Gulf]

Also, I'm not sure what I am looking at in the background of the pics. Do you have any insulation under the oven floor and dome?

[watchthenanacrossing]

Well the info for the bricks on the box says it can be used for ovens. It's made of ceramic materials, and like I said it's rated up to 2,000 degrees. I guess they are just for linings? Do you have any suggestions where to get firebricks?

I have insulating materials under the concrete slab but not in between the firebricks and slab. The bricks lay directly on top of the slab. Did I mess up?

[Gulf]

All I have to go by is the appearance of the brick in your pics. You haven't included any information from the box other than "Vogelzang" and rated to 2000 degrees. If you have any other info from the box such as the company's product number, it would be helpful.

Dense firebrick (full thick and splits) can be bought at most any brickyard that sells to brick layers and contractors.

The insulation under the structural concrete is useless. The insulation needs to be between the dense firebrick.and the structural concrete. The concrete will suck most of the heat from your oven. Even if you were ever able to get it hot enough for pizza the concrete underneath would spall. You may want to download the $3 plans from Forno Bravo and do a little research before you continue,.

[watchthenanacrossing]

This is the only info on the box.

I guess I'm gonna have to figure out how to get an insulation layer underneath the firebrick. I'm not sure my reasoning for building it that way. As you can see from the photo, this is a clay oven build. The bricks were put down, then the cob dome was formed around the bricks. I can take the bricks out now since they "shrunk", so I'm gonna have to figure out what to put down for insulation and how to fit new firebricks in. Makes me sick thinking of having to take a sledge to it after the time and money put into it already.

[Gulf]

I may be wrong on the "pumice". but, they do appear to be very porous. I would be very interested in how much one of those spits weigh.
EDIT: Also, how easy are they to abrade.

Here is Forno Bravo's Brick Primer.

[Gulf]

I did a little research on the Vogelzang firebrick. I really couldn't find much information on exactly what they were made of. I found some Amazon links to FB-1 and FB-01 that listed the shipping weight of around 25 lbs. That is consistant with the weight of 6 dense firebrick splits. Those links pictured what appeared to be a yellow smooth type of brick. Again, consistant with a dense firebrick.

However, Menard's links a pictures similar to what you show in your post. Vogelzang Universal Firebrick FB-1. They list the shipping weight as 12.18 lbs. That is about 1/2 the weight of a 6 dense firebrick.

My advice is to leave the brick you have in place and lay another floor of dense firebrick splits over them.

[watchthenanacrossing]

Yea I did get these at Menards. It would be the FB-1's. I found a description elsewhere that does say pumice. One brick weighs in at 1 lb 14 oz (850 g). I can see how this one looks more porous than others that I've just researched.

If I lay another floor of firebrick (proper ones) on top of the others, will that affect the performance of the oven? Will taking my internal dome height from 16" to 14.75" (roughly) create any problems? My door height would also go from 12" to 10.75".

[Gulf]

A dense firebrick floor will protect the very soft FB-1 brick (I'm going to call them insulation firebrick IFB). It will hold the heat a little better. It will also give you a floor that will not easily abrade from rough contact with wood, pokers, peels, pots, and pans. The dome and door height is no where near as much of a concern as the cooking surface imo. It is just a quick fix to help rescue the time that you have already invested.

I don't know how far you want to go with this rescue, but you may want to try and place the IFB under the dome as well. If this can be done it will greatly improve your oven's performance.

An undercut saw should slice through the clay fairly easily (you may have to drill another hole in the blade to move the handle backward to increase the depth of the cut). Place a very thin ripping on the IFB to serve as gauge and to protect it from the saw .(I will mail you some formica if you can't find anything locally). Get a wood block the thickness of the IFB to use as a gauge for the exterior of the dome. Cut just enough to remove clay and place one IFB at a time under the dome. Keep advancing the guages, saw, and placing the IFB underneath until you get all the way around. Keep the saw the saw inplace just beyond what you are replacing.

I've done this with wood. Never seen it done with clay. I don't see why it wouldn't work in this case.

[watchthenanacrossing]

Okay, I'll have to see how difficult it would be to cut into it. It's cured so it's hard like concrete.

How will sticking the IFBs under the dome increase the performance as opposed to just trying to fit them against the wall? My thought is that I could cut the IFBs to fit as closely to the wall, then patch any space left between the IFBs and wall with my cob mix to seal it up. This is if it's too difficult to cut into the wall and slide them under.

[Gulf]

Okay, I'll have to see how difficult it would be to cut into it. It's cured so it's hard like concrete.

The cob may be dry and firm but, it is not vitrified. Nor is it what I call "cured" unless you added some portland to the mix.

How will sticking the IFBs under the dome increase the performance as opposed to just trying to fit them against the wall?

The dome sitting directly on the concrete will leak loose vast amounts of heat. I'm not sure just how much improvement there will be by adding IFB spits under the dome. I'm as interested in protecting that concrete from spalling as I am about improving the oven's performance. Russell UtahBeehiver has a list of thermal characteristics of many insulating materials including some IFB. But, then we would need to learn for sure what the Vogelzang FB-1 brick consisted of to make that determination.

My thought is that I could cut the IFBs to fit as closely to the wall, then patch any space left between the IFBs and wall with my cob mix to seal it up. This is if it's too difficult to cut into the wall and slide them under.

I thought that your IFB floor was already in place and the cob dome was formed around it?

[watchthenanacrossing]

No, no portland. Just clay, straw, and sand.

Sorry, little confusion. When I say IFB, I meant the new ones that would go on top of the first ones. Like I said, my thought would be to cut the IFBs to fit as closely to the wall, then fill the space that was left with the cob mix.

I'll see what that person recommends for IFBs.