How much concrete slab shift?

[Tom]

Hi, I'm installing travertine tile over my existing concrete. It will go in the backyard where there is a pool. The concrete is pretty old, maybe as old as 30 years since the house is that old. The concrete looks very good. The cracks are very fine and every contractor that has come by said tiling over is ok. Between the slabs there are aluminum spacers. There are also many drains in the deck which results in each slab being sloped inward. So where the slabs meet there is kind of an inverted vee. My mason is concerned about over the years the slabs shifting and the stress causing the tiles to break. He wants to put a cut over the aluminum spacers so that if the slabs move the tiles will not crack. Is this overkill? It would obviously look a lot better without those cuts and I think that any slab shift would be done by now.

On a related note, since I'm not removing the existing concrete, the tiles will be higher by about an inch on the house. They will now abut the house near the lower wood edge of the sliding door. Will this cause problems with trapped moisture?

Thanks for your help.

[Joseph Meehan]

Do what he says. Us a flexible material to fill in the space.

[raven]

No, it is smart. Partt of the reason why your slab still looks good after all these years is that the original mason understood that you have to account for movement. It's not very much, but concrete and stone will not tolerate any.

No, things often move seasonally as well as long term settling. You could make good solid marks on the slab on either side of the joint, and then take accurate measurements several times a day on many days throughout the year to determine if there's any movement, where even a couple thousandths of an inch would be enough to send a crack through your stone....

But I simply wouldn't take the risk: IMHO, the thing about stonework that really looks best is knowing that it's going to last and last.

Yes, you quite likely will. Given that your mason seems to know his stuff, I'd ask him to make a reccomendation, you're likely going to have to reflash at a minimum.

John