Install Tile Over Cracked Concrete Floor – Use a Membrane
QUESTION: I’m about to install ceramic tile on a concrete floor of a 40-year-old house. The concrete floor has cracks in it. This is a DIY endeavor and I don’t have the extra money to install the expensive membrane that I should use. Are my new tiles going to crack? What would you do? What about grouting the tile? Sarah H., League City, TX
Sarah’s got spunk. I applaud her spirit and she can have success if she does a few simple things. There are different crack-isolation membranes that uncouple the tile from the actual concrete slab. She might price all of them to see if there is one she can afford. Here’s the industry standard, but it’s fairly pricey:
Crack Isolation Membranes – Consider Affordable Felt Paper
There’s not a doubt in my mind that the new tile will develop cracks directly on top of the cracked slab if no membrane is used. Since Sarah’s budget is tighter than a banjo string, she might take a chance using two layers of 30-pound felt paper. This is a very affordable material and while I’ve never used it as a tile crack-isolation membrane, I feel it’s got a fantastic chance of performing quite well.
What About Filling Wide Cracks?
If the cracks in the slab are wider than 3/16 inch, I’d first try to bond the concrete together using a high-strength epoxy you can inject into the crack. This will go a long way to prevent future cracked tile. Here’s a fantastic concrete-crack epoxy I’ve used with great success:
How Do You Install the Felt Paper?
I’d then install the felt paper just as you would one of the fancy membranes. This requires a bed of thinset adhesive that you then cover with the first layer of felt paper. Smooth the felt paper using a rented linoleum roller. Be sure to install the felt paper so it crosses the cracks at a 90-degree angle if possible.
I’d then install the second layer of felt paper over the first layer at a 90-degree angle. I’d not install any thinset between these two layers. The weight of the thinset under the tile and the tile itself will press this layer against the first layer.
Once the tile is installed, Sarah should go to my AsktheBuilder.com website and watch my four-part video series about how to grout ceramic floor tile. She’ll get professional results with a minimum of practice.