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ubarch 06-26-2010 12:16 PM

Problems with foundation
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So I've had to take a few steps backwards...

I've never done this sort of masonry work before, so when I read in the instructions that I should "use mortar to level the cinderblocks" I figured that the cinderblocks I had would never be level, and therefore mortar was not needed. I'm told that mortar is actually essential before I pour concrete into the cinderblock voids, so I disassembled my entire dry-stacked stand. We numbered each brick with a sharpie so that we can put them back together quickly (I had to chisel material off of certain blocks to make the structure fit together properly, so order matters now).

In the process, I discovered that the slab in my back yard is not level. See the attached picture; it's a couple of degrees off. I'm wondering if this will be a problem. I can level the hearth when I pour it, but unless I do something else before I start mortaring cinderblocks together, the stand walls will be at a slight angle.

If you look at the pictures from my earlier threat, you can see that the oven stand will be buttressed by the grill structure.

My question: Do I have to take action to level the stand, and if so, what do I do?

Older thread with pictures of dry-stacked stand and grill:

Thanks for any help.

Tscarborough 06-26-2010 12:48 PM

Re: Problems with foundation
Anything less than 1" can be fixed with the stucco finish coat. As a rule, when drystacking CMU you will have to shim the block to keep them level and plumb, as that is the primary purpose of mortar in normal masonry construction, i.e. to allow for the variation in individual units.

Tscarborough 06-26-2010 12:50 PM

Re: Problems with foundation
And as an aside, even when drystacking, the base course should always be laid in mortar to ensure that you least start plumb and level.

Neil2 06-26-2010 03:31 PM

Re: Problems with foundation
"it's a couple of degrees off. I'm wondering if this will be a problem."

If it slopes toward the proposed oven opening that would be ideal. I always suggest that ovens be built with a slight (0.5 to 1.0 %) slope to facilitate drainage if water does get in.

ubarch 06-26-2010 03:37 PM

Re: Problems with foundation
I'm afraid I'm still a bit unclear... Is the appropriate action to re-stack my stand and use mortar to keep the blocks plumb and level, but take no action to make the stand sit precisely in-line with gravity, or are you suggesting that I should use something (mortar? stucco finish coat?) to level the first course of blocks to be in-line with gravity?

Unfortunately, no. The opening is transverse to the direction of tilt. It won't actively collect water, but if any gets in, it won't drain right out.

Neil2 06-26-2010 03:45 PM

Re: Problems with foundation
Get the first course level. From the photo that would appear to be an inch or so at the "low" end. Ordinary mortar will be fine for this amount, but you may have to shim the blocks up until the mortar sets.

Tscarborough 06-26-2010 04:33 PM

Re: Problems with foundation
You are overthinking it. What will the finish of the stand be? Stucco or something else? None of this is critical, and there was no real need to even re-stack it. The poured slab on top will tie it all together and that is where you need to take care on level, not in the stand.

ubarch 07-06-2010 04:14 PM

Re: Problems with foundation
Okay, so I figured I would ask before I take action and go buy things, especially since the last two pieces of advice appear to conflict.

I drove two posts into the ground across my slab, and tied a piece of level string across them. The low side of my slab is almost 3" below the high side. I didn't make this slab; it came with the house. It may have settled, or it may have always been tilted. Do you think there's danger that the slab could move?

Can you pile mortar up 3" tall? I figure that if I want to get the first course level, I should go buy some bricks of various thicknesses, and use them to "shim" them first course of cinder blocks. Is this a good idea? How thick should a layer of mortar get?

Neil2: Tscarborough seems to think that it doesn't matter that the structure is tilted. Are you advising me to level the first course for aesthetic reasons, or because the stand would otherwise be unsound?


Tscarborough 07-06-2010 04:49 PM

Re: Problems with foundation
Well 3" is a lot. Your choices are to level the slab by excavating it (probably not worth it), level it by topping it with a material made for that (expensive), or cutting the first layer of blocks to level it (normal practice, although usually only within an inch or 2). The maximum you want your initial bedding joint (any bed joint, for that matter) is 3/4".

fxpose 07-06-2010 05:24 PM

Re: Problems with foundation

Originally Posted by ubarch (Post 93903)
The low side of my slab is almost 3" below the high side.

Over what distance? Perhaps the slab was pitched over that distance for drainage.


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