[natural12]

I have a project where the homeowner would like to put concrete pavers on an existing concrete slab. The height or grade of the new patio will change to about 6" above the current concrete slab. I am adding a step.
My question is what is the best material to use between the slab and the pavers. The pavers will be about 2.5 inches which leaves 3.5 inches for a base material. I cannot remove this slab so that is not an option.

If anyone has any experience with type of application any opinions would be appreciated.

Thanks,
Mike

[Stonehenge]

Why is slab removal not an option?

The thing I would worry about with this is figuring out how you're going to affix a border to the edge of the concrete that wouldn't move when compacting a base material between the slab and the pavers. Even masonry might crack right off when you run a compactor near it. You could just use sand, but at that thickness I'd have a real concern about it settling out unevenly.

My preference would be to remove the slab. Is it just that the client doesn't want to pay for removal?

[natural12]

Thanks for the reply. I am attaching a photo. As you can see the patio is bordered by the house and the brick wall. We are going to add brick extensions on each of the three corners matching the one on the upper right. These will support a pergola. The lower part of the slab will have a step up, which will help adjust the somewhat steep slope. So all sides will have a solid border.

The reason for not removing the slab is I am afraid of disturbing the brick wall and the other is cost. If we can do it without removing the concrete that would be ideal.

Mike

[zullo-design]

I dont see why compacting it would be a problem? I get your point but if you extend your material past the edges you shouldn't need anything to hold it in while compacting. WE do 95% of our patios on slabs, however 3.5" of sand is going to very hard to avoid uneven settling like stonehenge said in his post, you could do 3" of crushed stone with a half inch of sand on top of it I guess.

[Stonehenge]

I'm not sure I understand what brick extensions are, but from the look of the picture, you may be able to get by with mortaring a smaller retaining wall block or maybe a cut cmu at the two opposite ends to give you support on the two final sides. From the looks of it, you'll only have a thick base at one end of this pavement, right? You might try some geotextile fabric between a couple layers of sand to help give it strength. But I think my preference would still be to remove the slab. I don't like prepping beyond a slab, because in my experience there will be settling where the change in subgrade materials is, and it'll affect the look and usability of the pavement.