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I am building an outdoor kitchen using standard 8"x8"x16" concrete blocks on a concrete patio which slopes away from the house. The length of kitchen is 120" and the slope of the patio is about 3" over the 120". In order to have a level kitchen, I will need to a leveling agent of some sort. I believe a 3" mortar bed would be a bad idea. Should I build a form and pour concrete leveler? Is there any other methods you would recommend?

Some additional information regarding replys below... Thank you for the quick replies. I am also a do it yourselfer and have rarely worked with mortar or CMUs. I should have been more precise in describing my plans. I was planning to lay a mortar bed for only the first row. Thereafter, I was planning to use landscape adhesive between blocks. There will only be five rows. I also plan to add a concrete countertop on both sides of the grill which will add to the stability.

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  • Your patio is sloped at 1/4" per foot which is ideal for drainage, not so much for keeping the tomatoes from rolling off the counter. I'm not a concrete expert by any means, thus a comment, not an answer: I'd think that you could thicken the mortar joints on the down hill side by that 1/4" per foot divided by the number of courses to slowly level out the block until the top one is dead even. i.e. if you need it 4 courses high, each mortar gap would be 3/4" thicker on the low end and you'd end up filling that gap. You'd need to draw a string line precisely measured for each course.
    – FreeMan
    Sep 3 at 12:27
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How about cutting the blocks in the base course? Use a full 8" high block at the low end and trim each successive block 5/16" more working your way to the high end of the project.

Trimming the blocks exactly to height isn't super critical; so long as they're within say 1/2" of the needed height the mortar bed beneath the block should fairly easily compensate.

The trimming can be accomplished in many ways. An angle grinder with a masonry grinding disc will work although it'll take some time and create a lot of dust. A dry "turbo blade" diamond disc on the angle grinder or on a circular saw will work well too. A rented gas-powered concrete saw about 14" diameter would make very quick work of the job, and with its water spray turned on will reduce dust substantially. There are blades offered for reciprocating saws to cut masonry too, though I've never tried one. The job could also be done just with such simple tools as a hammer and brick chisel.

As an additional benefit, if the height of the countertop based on 8" block increments isn't exactly what you'd like, you can adjust its height to perfection with no additional effort -- just cut that first block to something less than 8" and proceed with successively shorter blocks as before.

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