QUESTIONThe gas company is putting a new line under the sidewalk in front of our house, and will be replacing the existing concrete walkway from the sidewalk to our porch. We want to improve the appearance by tiling the walkway.
Our questions are 1) how long to wait for the concrete to cure before tiling, 2) what kind of mortar to use, and 3) what if anything to put between the concrete and the tiles? A contractor we talked to suggested putting 1/4" concrete board in between, but we've heard that some sort of membrane is better.
For your recommended method, how thick will the resulting sandwich be assuming 1/4" thick porcelain tiles (we need this in order to tell the sidewalk guys how much to lower our walkway relative to the sidewalk). Many thanks for your answer - the concrete is scheduled to be laid any day now!
ANSWER - First of all you need to determine what kind of tile to install? It needs to be slip resistant, and it needs to provide a relatively flat surface so no one trips. If you are in a freeze thaw area then the tile needs to be freeze thaw stable.
There are some types of natural stones that can be used. You need to determine is the stone gauged so the thickness between each stone is consistent? If it is you can directly adhere it to the concrete sidewalk if that substrate surface is properly prepared. If it is ungauged then you have to install it in a fresh/wet mortar bed method that will add a lot of thickness +/- 1".
The general rule is to allow freshly poured concrete to cure for 28 days before installing over it as it will shrink a lot during that time. Installing a concrete backer board over the concrete makes no sense. If the concrete isn't flat enough you can grind high spots and fill-in low spots with a patching mortar. If the concrete is cracked prior to installation you can apply a crack isolation membrane over it before adhering the tile to the membrane.
If the substrate surface is flat and the stone is consistent in thickness, then the thickness of the thin-set mortar used to bond the tile to the substrate should not be thicker than 1/4" after the tile has been embedded. The thin-set mortar has to be at least about 3/32" thick after embedment.
We do have free installation guidelines on the www.CTaSC.com website that you can download to help you make decisions and that covers more details in the installation process. Click on the following link for those Free Tile and Stone Installation Guidelines.