First Layer Newbie Forum Discuss First Layer in the Good Background Information forums; Does the first layer of bricks need to be cemented to the base or do they just sit on it?...

[rob_jenny]

Does the first layer of bricks need to be cemented to the base or do they just sit on it?

[Neil2]

Set them on a thin layer of mortar.

One thing to keep in mind with masonry work. The mortar does not "cement" the bricks together. Mortar has near zero adhesive qualities.
The purpose of the mortar is to evenly transfer compressive forces between adjacent bricks.

[Rodneyf]

Originally Posted by Neil2

Set them on a thin layer of mortar.

One thing to keep in mind with masonry work. The mortar does not "cement" the bricks together. Mortar has near zero adhesive qualities.
The purpose of the mortar is to evenly transfer compressive forces between adjacent bricks.

You learn something new every day! I did not know that and it helps me understand a little better.
Thanks

[ThisOldGarageNJ]

Mortar makes up 7 to 15 percent of a wall's total area. Although thats a small percentage, the role it plays is not minor. It holds the unit masonry together so it forms a stable structure. But it also does a lot more. It protects masonry from water damage and weathering, so it lasts longer. It gives stone, brick or block work a clean, finished, uniform look. The key properties you need in it are workability, water retention, bond strength and durability. Since each of these depends on the others, you cant change just one. If, for example, you add more water to improve workability, you'll decrease it's strength.

Neil, This is from masonrytoolworks.com, If I am reading it correctly they are saying that BOND strength is important, But you are saying it doesnt bond and fills the space to keep pressure on the other bricks ? I'm still learning so help me out here please ?
Thanks Mark

[dmun]

The heat-stop mortar bonds like epoxy. I mortared firebrick pieces to whole firebricks to cut my triangles, and within a week they were able to withstand full tilt whole brick angled diamond cutting. Sliver-like fragments remained bonded together on the cut-offs. Heat-stop certainly bonds brick to brick.

I find ordinary mortar mix much less adhesive, I had several bricks in my outer structure come loose from small bumps, and had to be redone.

I can't speak to other refractory mortars, or the homebrew mix, which I haven't used.

[Neil2]

From a structural engineering point of view, I would try to design and build so that everything is in compression - i.e. held together by gravity alone. Do not rely on the mortar to hold it together. There will be a lot of thermal expansion and contraction.

If you do get any long term "adhesive" effect that will be a bonus. If you don't, your oven will continue to function indefinitely - like the ones the Romans built.

[bernerdog]

Back to the original question, there was a recent thread discussing mortaring the bottoms of the first course and the consensus seemed to be not to, with some assurances to those who already had that they would survive. I`m in that group and pressing forward but now wish I had set them w/o mortar. Plenty of room for personal views, I guess, but one poster mentioned that the FB plans do not do it (I haven`t gone back to check because at this point I`m trying to convince myself it doesn`t matter!). John

[RTflorida]

I think the reasoning behind not mortaring the soldier course is two fold - 1) no mortar allows the dome (including the soldier course) to expand independently from the hearth, they DO heat up at different rates. 2) Much like dry stacking your block stand, you want to get that first course of bricks as straight and true as possible. For the novice brick layer that is easier said than done.
Personally, I used a very thin layer of Heatstop 50 to set my soldier course. Yes, it does have great bond strength...it held very much like a good epoxy. My reasoning was to keep my soldier course in place; I figured tapping and setting rows 2-3 in place could knock things out of alignment in the soldier course. The thin layer did exactly what i wanted and I see no down side to doing so. Anything more than a quick smear (like buttering toast) could probably lead to problems, then again, anything more than a quick smear is totally overkill.......you just want told hold them in place until you get the next couple of rows done, weight and gravity will take over from there.

RT

[Neil2]

Like a lot of topics on this site, there are at least two schools of thought on this.

People have built them both ways with no ill consequences. I think this just goes to show how flexible the overall concept is and that we should not "sweat the details".

[RTflorida]

Agreed!!!

Rt