Q: My husband and I are installing new flooring. Flood damage ruined the carpet. We decided to install a combination of laminate flooring and ceramic tile. The tile work is much harder than I thought. We're installing the large tile directly on top of the concrete slab. I'm using plastic spacers to keep the grout lines straight, but I'm having great difficulty. I've never grouted before and am worried about messing that up. Help! I don't want to ruin this project.
A: I'm sorry about your recent disaster, but I'm happy that you've bounced back with a great DIY attitude. You're going to be very proud of your work once it's complete. It's beneficial to push the envelope and be slightly uncomfortable. That's how you improve your skills.
First, it is impossible for me, to convey all you need to know about a ceramic tile job. Many a book has been written about installing ceramic floor tile.
I'm going to try to cover the most important points and share a few secrets I've discovered. Ceramic tile has a high compressive strength. This means you can squeeze it and it won't crush. However, ceramic tile, concrete and natural stone have low tensile strength. This means if you try to bend a piece, it doesn't take much effort to crack or snap it.
To prevent cracked floor tile, you need to make sure there are no voids between the tile and the floor surface. The larger the tile you're installing, the more difficult this task becomes, as it's very hard to get a floor surface in the same plane. You can use pourable self-leveling floor compound to get a perfectly flat floor surface if you plan ahead.
Cracks in a concrete slab can, and often do, extend to the floor tile. Professionals often install crack-isolation membranes between tile and concrete slabs to help keep tile crack-free.
The plastic spacers used to keep grout lines straight don't always work as intended. It's not because of the spacers. If you have a variance of just 1/32 inch between tiles, that can create a 1/16-inch difference if two of those tiles are installed side-by-side. Pretty soon the grout lines will look more like a sinuous stream channel if you use the spacers.
I prefer to use a grid on the floor made with a chalk line. I lay the tile to the edges of the grid lines. The center tiles are installed by sight, making sure the grout lines are consistent.
When you get ready to grout, I recommend that you purchase some very inexpensive tiles and install them on a piece of cement board in your garage. Practice grouting on this test area until you perfect your skills.
Mix the grout so it's the consistency of bricklayer's mortar. If it pours like pancake batter, it's too wet. Too much water weakens the grout and causes it to crack.
Apply the grout with a hard-rubber float at a 30-degree to 45-degree angle to the grout lines, which ensures the grout is flush with the top of the tile. Do not rub the grout with a sponge until it firms up enough so you don't remove grout from the joints.
Only mix enough grout in a bucket that you can install and finish in one hour. You can always mix more. Don't add water to stiff grout in the bucket. Retempering the grout with water will weaken it.