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How can I lay cobblestone type paving over a pre-existing concrete slab?? Answered

We have this ugly patio slab mid yard and thought to dress it and its ajoining pathways up with cobblestone style paving such as we saw in Spain. I'd use river rock or round stones from the home DIY stores but do I lay cement and set the stones in or some sort of outdoor thinset and grout? How should I prepare the slab surface (its plain old cement/concrete and too big to smash and remove)? Please advise.


  • First, clean the heck out of the existing slab to get rid of whatever dirt, oil, grime , etc. it's accumulated over the years. Power-wash it if possible.
  • You'll need to rough up/smash up the existing concrete as much as possible. This gives it a good "tooth" - lots of jagged surface areas for the new concrete to adhere to.
....Maybe invite all of your emotionally repressed friends over for a Sledgehammer Party?

  • Then clean the heck out of the existing slab again, to get rid of dust & debris from the roughing/smashing up.

Do not skimp on the above steps - good surface preparation is at least 85% of success or failure. It doesn't matter how well you try to stick the new pavement on if you don't give it a good, clean, "toothy" surface to stick to.

  • Unless you get the existing concrete smashed up to where it's no longer flat, I'd expect you to have much better luck with stones/pavers that are flat on their bottom sides. Laying round-bottomed stones on a flat slab would be a serious headache, and round-bottomed stones might tend to "float" up away from your existing slab when you pour the new concrete much more than flat-bottomed ones would.
  • Ask the advice of a knowledgeable DIY-store employee about exactly which concrete/cement/grout to use. You may need to use one type to mortar the stones into place, and then another to fill in the gaps between stones and hold them permanently.
  • Watch out for freeze/thaw. If the existing slab is more than about 10 feet in any dimension, you'll probably want to score the concrete where you want it to crack in the first freeze. Not that you really want it to crack, but it's better to have the crack where planned it rather than just where it happened.
  • Good luck with the project! :)

I have a mould I am using for stone pavers and I have a slab of cement I am going to put these on top of. Of course they are made of cement and after I will stain each a different shade gray and brown. do I need to break up the cement or can I just put a cement bonding glue?

I will poor the cement directly onto the mould and it will set on top of the existing cement however is it important that it sticks to the existing cement?

I have the same thing over a dirt area and I will fill in the gaps with a fine sand I guess after the staining is complete.

I just don't know if I need a cement bonding glue or do I really need to beat up that cement slab because it's a LARGE area to have to beat up. can I drill holes and put rebar randomly instead.? Please advise!

Oh, that's way too much work. What you need is a truckload of sand and some sort of perimeter/edge. Cover the concrete with 1" or more of sand. place stones on top. Add sand under each stone to give it a solid footing and make it level. If your stones are not flat on the bottom this may require a good bit of sand. Pound each stone down onto the sand with a rubber mallet. Pour more sand on top and brush it back & forth until the gaps are filled. For the edge you could use some timbers, a single row of stones set in mortar or even a concrete curb. Don't skip the edge. Without the edge the sand will drift and the perimeter stones will sink and spread out.

Thanks for the information Drunnels. This is very helpful. My wife and I have been thinking of projects that we can do this summer to make our home more beautiful, and we've been looking into making a nice path like this one. Would you suggest doing it on our own, or having a residential paving company help us?

You would be best to remove the concrete, but you've covered that. Since you will be laying on concrete - do as you suggest and lay cement to place the stones on. There's not much point in preparing the surface, as the paving will essentially be held in place by gravity either way. If you can find any local youths who would like to have a go at the concrete with pick-axes consider letting them try to get rid of it? L

. I don't know much about doing what you're talking about, but see if Googling cobblestone +overlay +concrete helps.
. I didn't find anything here on Ibles; when you figure it out, publish an iBle.