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I will be scraping a dirt/gravel driveway down two inches and laying flat stones of various sizes and thicknesses. Need to have the tops at the same level, so some will need to have something underneath to raise them.

All will need some thing to keep them from moving easily. Ground is more gravel than dirt, such that I’ll have to use a skid loader to grade it. (Shovel couldn’t penetrate and tiller took hours to get a quarter inch off!)

Which is better, mortar or cement?

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  • Why can't you use sand?
    – wallyk
    Nov 13, 2020 at 0:35
  • Sand alone is not appropriate for paving. For mixing, I didn't say I couldn't use sand, and judging by Ed's answer, I probably should do so.
    – WGroleau
    Nov 13, 2020 at 1:43
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    I’m voting to close this question because it's moot--cement is not a usable product on its own.
    – isherwood
    Dec 10, 2020 at 21:42

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I think this is more of an opinion question because the only real difference is the size of the aggregate in the concrete. Cement / Portland cement is the basic component in most mortar mixes and sand gravel and cement is what concrete is made of. In either case 2” is quite thin and won’t have much strength but if the base is solid after scraping either will hold the flat stones in place.

To make absolutely clear you would never use straight Portland cement or less known types of cement as they have no shear strength without the sand for mortar, and sand and aggregate for concrete so mortar would be the only choice based on the below comments from the OP.

I have spread cement on freshly packed rock driveways but these were fresh and had no dirt yet. With rock on the ground not fresh this method would be a waste because the dirt prevents the concrete from bonding to the rock.

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  • I said cement, not concrete. Although I have enough three-quarter minus that I could mix it, I wasn’t planning to go deep enough for that to be feasible.
    – WGroleau
    Nov 10, 2020 at 19:47
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    I know that’s not very strong, but the current mix is mostly gravel and we’ve been parking on it without making any visible impression.
    – WGroleau
    Nov 10, 2020 at 19:48
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    Do you understand what cement is? It has absolutely no strength please re read my answer. Cement is used to create mortar and concrete if you don’t believe me just look up Portland cement the most widely used binder for what you want to do but it IS NOT used alone it is mixed with sand for mortar and add aggregate for concrete I have poured thousands of yards of concrete, probably close to a hundred yards of mortar, and stucco. By itself cement has no strength it needs the other material for both strength and volume.
    – Ed Beal
    Nov 10, 2020 at 20:02
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    Note if you search this site you can find many questions and answers on overlays and similar , there won’t be one that recommends plain cement, depending on how much space between the flat stones Turkey grit aggregate can be used for additional strength and even though the aggregate is course sand to ~1/8” gravel it is still called concrete. In this case adding fiberglass reenforcement will do no good because the joint at the flat rock will be the fracture point.
    – Ed Beal
    Nov 10, 2020 at 20:14
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Consider stone dust with aggregate as a base.

See https://www.youtube.com/watch?v=t4oB87U5zAk for what you need to do.

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  • Not far from what I did. “Quarter-minus with fines” is basically that stone dust mixed in with gravel up to a quarter-inch in size. I only had to scrape down two to three inches because the dirt below is already hard-packed from years of visitors parking there. Did not even need a vibrating compacter. And I'm using flat stones of varying sizes instead of large ones like the video.
    – WGroleau
    Dec 10, 2020 at 22:47
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I put down “quarter-minus with fines,” and packed it by laying plywood on it and jumping on that. I weigh 85 kilograms and expected to have to pack further after laying the stones. I was surprised to find that it actually holds the weight of an SUV.

I tried to use the SUV to press in the cobblestones by driving over them, and it didn't work. I now have to dig a hole under each stone and re-pack to get it level!

Edit: error and inaccuracy in second paragraph. As the first paragraph states, it held the weight of the SUV just fine, without mortar or cement. It was a much heavier motor home that displaced some stones (not “each”). And after about four months, it has apparently packed tighter, because now, the motor home does not make a dent.

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