Dry stacking the dome, then mortar

[Harpist]

Howdy folks,

A friend of mine (a much better mason than I) who built an oven several years ago told me that, when he built his oven using half cut bricks, he dry stacked most of the dome using an inner form and shims on the outer gaps and then mortared the bricks afterwords. He then pulled the shims, did a bit of touch-up and was done. Only on the top couple of courses (that had custom cuts) did he mortar "as he went".

My plan was to mortar each course as I went. All my brick experience is with constant thickness gaps where this is the only way I know. But with a large outer gap for the half-cut bricks, this is another alternative.

His comment was that he felt that he could keep the inside of the dome a lot cleaner (less mortar squeezing through) and since he was using a form (and couldn't clean as easily as he went) this was important.

I would appreciate any and all feedback.

Good Roads

Harpist

[Tscarborough]

Re: Dry stacking the dome, then mortar

I do not think you will have a problem doing that, but remember that the role of mortar is holding bricks apart, not holding them together. That is to say, there is a tolerance in the actual dimensions of brick, and stacked dry your courses may wander a bit.

[Harpist]

Re: Dry stacking the dome, then mortar

I do not think you will have a problem doing that, but remember that the role of mortar is holding bricks apart, not holding them together. That is to say, there is a tolerance in the actual dimensions of brick, and stacked dry your courses may wander a bit.

Tscarborough,

When using a form I would have thought that the form itself would have the largest effect on whether the courses "wander". But as the gaps in dry stacked bricks are "chinked", it is probably pretty easy for the bottom edges to slip a little too causing vertical deviations in the course.

I hadn't thought about the role of gap in keeping expanding bricks from pushing together. Should direct brick-brick contact be minimized (i.e. always have a small layer of mortar)? If this were the case, the dry stack method would not be advisable.

Good Roads

Harpist

[Tscarborough]

Re: Dry stacking the dome, then mortar

As a rule in masonry design, the mortar has to be softer than the masonry units, and the joint is sized to allow for both the variation of size in the units (minimal for firebrick) and also for the expected expansion and contraction of the system through it's expected thermal cycle (also minimal for firebrick) and long term expansion of clay masonry/shrinkage of concrete masonry). This allows for any movement to take place in the joints and not in the units themselves. Most mortars have a property called called autogenous healing, especially lime based mortars. This means that they will self-heal minor cracking and settling, while brick/CMU alone can not.

What all of this means for a brick oven is that it doesn't really matter, if the FB plans are followed, they are sufficiently over engineered that you will be fine doing it dry laid. Just be sure and make sure the joints are as close to 100% filled as is practical.

I would say, however, that a modicum of care when wet laying the brick will take care of most of the mortar on the face, even when laying against falsework, and it will be faster and easier.

[Bama]

Re: Dry stacking the dome, then mortar

Why a chimney for your grill? Does it draw smoke when cooking meat?? Seems smoke would go straight up. Interesting. Very good looking set up. Congratulations...