Another pizza oven DIY newb

[Electromet]

Hi, everyone.

My name is Mike and I got hooked on the possibility of building our own outdoor pizza oven after watching a YouTube project by an user named "Artisan Made". A week and a half ago we broke ground on our own 40" Tuscan-style oven. As of noon today we have completed the floor insulation of 4" vermicrete. After a few days of curing, we start laying the floor bricks. We are stoked! I ran into this site a couple weeks ago, and I have found it to be and incredible resource. I'm looking forward to becoming a regular contributor when I figure out which end is up with our project. -Mike

[david s]

The first mistake you have made is to build over moist vermicrete, trapping the moisture in the underfloor insulation layer. It takes a couple of weeks in ideal drying conditions to rid a 4” vermicrete layer of most of its moisture. Don’t fear because the fire will eventually dry it out. Builders failing to dry their underfloor vermicrete have reported it taking months to dry out completely and after many cooking fires. Ovens in this situation are reported to improve performance with each firing for a long time. The underfloor moisture is the most difficult and last area of moisture to be purged. Providing a suitable exit will also assist enormously. Suggest you do plenty of research here before proceeding. You tube videos typically provide short easy sounding solutions, but often with poor and misleading information by inexperienced builders.
The recommended vermiculite (or perlite) ratio for underfloor insulation is 5:1 which provides sufficient strength and insulation value as well as reasonable permeability which allows moisture to pass relatively easily.

Vermicrete insulating slab copy.doc.zip

[Electromet]

David S.-- Thanks for the timely reply. I have not yet started laying the firebrick floor. I had intended to wait a few days before I started laying the floor, but now I will wait a couple weeks. I just went on a road trip this morning to retrieve 250 firebrick. I can use the time to cut most of them in half for the dome. Thanks also for the research document. -Mike

[david s]

Cutting all the bricks in half first creates more wastage, because you have to do 5 cuts. The attached drawing shows how you can do it with only three cuts. Also as the courses rise, the diameter reduces, so the angle to be cut gets greater, therefore it's better to do the cuts as you go, adjusting the angle for each brick course.

[Electromet]

Obviously, the angle is exaggerated on your sketch. Do you know the formula to calculate the exact angle for each course? I'm making a 48" O.D. oven with a 40" I.D.. My firebrick are 9"X4.5".

[david s]

You could work it out using some basic geometry knowing the brick dimensions and the internal radius. But it’s way easier to just adjust your cutting jig slightly as each course rises. Minor errors in angle will be adjusted by the thickness of the mortar joints.
The angles on my drawing may appear to be exaggerated, but the lower courses will be less although the upper courses will be much more.

[Electromet]

Yeah. I've seen a few projects where all the fire bricks are cut square with the outside gap quite large. I guess it's better to keep adjacent edges fairly parallel. You have probably already figured out I know nothing about masonry.

[UtahBeehiver]

You do not need to worry about the gap on the outside, mortar will fill this in. Take a look at JRPizza's build, the bevel of the brick does not need to be along the whole depth (ID to OD) of the dome brick only near the first top inch of the interior face to avoid what is call the inverted "V" joint. See pic below.

[JRPizza]

What I tried to do is minimize the gaps between the internal (fire facing) surfaces of the bricks to limit exposure of the mortar to direct flames. Part of this was before I knew that folks actually cast domes from homebrew , but part of it was because I thought it made the interior of the oven look "neater".

[Electromet]

Thanks, guys. I think I might actually get the gist of it.