Tapered Cuts

[JoeT62]

A question - looking at some of the domes with taper cut bricks, I can't help but think "maybe I should..."

I was wondering if those who have done the tapered brick cuts could comment on how they measure those angles for cutting, and whether they recommend it.

[Unofornaio]

Hey Joe,
While I haven't built a dome oven (yet) I have built 2 roman style ovens and worked with fire brick for many years and I can tell you that the weak link in the building process with fire brick is the mortar joint. When I build the pizza oven here at the house I will cutting each and every brick to fit as tight as possible. the plan is to document every single cut variation.

[jahysea]

Hi Joe,

I would highly recommend tapering the sides if you have a wetsaw for the duration of the bricklaying portion of your project.

I rented one on the days I spent forming the dome & found that to be a good solution.

I cut bricks into simple trapezoids starting at about the 5th chain and realized I should have started earlier. The half bricks looked a little like this:
_
/_\

Some folks may have tried to create trapezoids that are larger on the outside to allow for less mortar use. This would provide a better dome because brick and mortar have different thermal expansion values. I deemed it too difficult and used the "simple trapezoid" approach. My trapeziods were tight on the inside of the oven but had mortar gaps on the outside.

The first chain I spent a lot of time measuring for the correct angle, cutting bricks, etc.

I eventually realized you just needed to dry place 3-4 half-bricks and estimate the amount of angle you need visually by eye and measure distance in from the corner. Then find or cut a scrap slice of brick the thickness of that distance. I started at something like 1/4 inch from memory. Place this piece of scrap on the saw under the edge of your half brick that is away from the blade, tilting the half brick toward the saw blade. Run the brick through the saw, then turn it 180 degrees and run the other side through.

Be slightly conservative with your cuts, make a couple and see if you like the fit. If they are still too wide on top, cut a steeper angle by using a thicker shim scrap.

Each chain the angles in the trapezoid get more aggressive.

When you get to your last chain or two, you will find the process easier if you use quarter bricks instead of half bricks.

[Balty Knowles]

You can use a straight edge from the center of the floor to mark the correct angle on each brick. Cut 3 or 4 & dry fit to make sure the angle is correct. You can also use this method to mark the wedge angle.

See pic this is how I started mine.

Rgds

Balty

[Hendo]

Originally Posted by jahysea

Some folks may have tried to create trapezoids that are larger on the outside to allow for less mortar use. This would provide a better dome because brick and mortar have different thermal expansion values.

Wouldn't this depend on the composition of the mortar? My mortar consists of 40% alumina and 60% silica - the same as the bricks. So I was hoping it would have an identical thermal expansion coefficient to the bricks? Yes/No???

[RTflorida]

I used a very similar approach to Balty. Measuring, cutting and installing 3 bricks at a time. I also varied the widths of my bricks to keep the mortar lines from the previous course as centered as possible....this resulted in the angles not being constant, resulting in only doing 3 at a time. Was a slow and tedious process but I achieved my goal of a very tight fit and minimal mortar.
As many have stated; if there it to be a failure (crack), it will occur along a mortar line.
In hindsight, I would do the same again....just figure out a faster way of achieving the same result.

[Unofornaio]

Originally Posted by Hendo

Wouldn't this depend on the composition of the mortar? My mortar consists of 40% alumina and 60% silica - the same as the bricks. So I was hoping it would have an identical thermal expansion coefficient to the bricks? Yes/No???

Excellent point as far as expansion properties. I guess it would be safe to assume they would react the same since they are the same material. Then again a difference I would think is the bricks are baked which I'm sure changes its properties to a degree. I have always used fire clay to lay fire brick, I don't know much about the 60-40 mix but it sounds very interesting.

[JoeT62]

Originally Posted by Balty Knowles

You can use a straight edge from the center of the floor to mark the correct angle on each brick. Cut 3 or 4 & dry fit to make sure the angle is correct. You can also use this method to mark the wedge angle.

I love that idea. Simple enough for even me! Looking at your photos, it looks like you also tapered the soldier course as well? Also, do you make wedge cuts on all four surfaces to get the trapezoid? Or just the two lateral surfaces and one of the superior or inferior?

[JoeT62]

Originally Posted by jahysea

Hi Joe,

I would highly recommend tapering the sides if you have a wetsaw for the duration of the bricklaying portion of your project.

I rented one on the days I spent forming the dome & found that to be a good solution.

I cut bricks into simple trapezoids starting at about the 5th chain and realized I should have started earlier. The half bricks looked a little like this:
_
/_\

Some folks may have tried to create trapezoids that are larger on the outside to allow for less mortar use. This would provide a better dome because brick and mortar have different thermal expansion values. I deemed it too difficult and used the "simple trapezoid" approach. My trapeziods were tight on the inside of the oven but had mortar gaps on the outside.

The first chain I spent a lot of time measuring for the correct angle, cutting bricks, etc.

I eventually realized you just needed to dry place 3-4 half-bricks and estimate the amount of angle you need visually by eye and measure distance in from the corner. Then find or cut a scrap slice of brick the thickness of that distance. I started at something like 1/4 inch from memory. Place this piece of scrap on the saw under the edge of your half brick that is away from the blade, tilting the half brick toward the saw blade. Run the brick through the saw, then turn it 180 degrees and run the other side through.

Be slightly conservative with your cuts, make a couple and see if you like the fit. If they are still too wide on top, cut a steeper angle by using a thicker shim scrap.

Each chain the angles in the trapezoid get more aggressive.

When you get to your last chain or two, you will find the process easier if you use quarter bricks instead of half bricks.

Excellent advice! Thank you. I will indeed have a wetsaw for the whole process, so I think taking the extra time here will be worth it.

[Hendo]

Originally Posted by Unofornaio

I don't know much about the 60-40 mix but it sounds very interesting.

It's Shinagawa's SHIRABOND 50 airset mortar. See info sheet at http://www.shinagawa.biz/system/file...ND_50_REV1.pdf. It's a bit higher on the alumina than I thought, but I believe my firebricks are around 43% alumina in any case.

Cheers, Paul.