Basement Tile Installation
Recently I tiled a couple of floors in a basement. I thought it would be a great opportunity to break down some of the techniques I use when setting tile. Most of these steps can be used when tiling over a wood sub floor. Prior to beginning your tile installation you must check your floor for flatness. A good length for a straightedge is 10′, however you can use shorter lengths with a little simple math. The minimum industry standards for setting tile requires the floor to be within 1/4″ in 10′, if you lay your straightedge down and there is more than a 1/4″ gap anywhere under it, you need to use a Self Leveling floor patch (also called Self Leveling Cement). As you will see in the pictures below, the floor I was working on required the outside edges to be filled with Self Leveling Cement as there was a high spot in the center of the room (right where the cabinets sit). To fix this I used the Self Leveling Cement on the outer sides of the room so that the cabinet would not have to be shimmed on the outside edges, thus leaving a gap between the cabinet side wall and the floor tile. When I tile a floor, I like the sub floor to be as flat as I can get it. Typically I don’t want to see any space between the straightedge and the sub floor, however in 10′ having a space up to 1/16th inch or so is acceptable for me. Remember when I said if you don’t have a 10′ straight edge you can fix that with simple math? If you can come up with a 5′ straight edge you would want your floor within an 1/8th of an inch, a 2.5′ straight edge would require no more than 1/16th of an inch, etc.. Use the longest straightedge you can for the room you are working in, if you can’t find a straight edge a string line or chalk line can also work (though a string line is much more difficult to work with without two people). Most floors feel straight when you walk on them, you will be surprised to find out that your floor could be out quite a bit and require leveling.
Prior to pouring your self leveler you must prime the surface to be leveled with the primer specified by the manufacturer of the Self Leveling Cement you are using. I also recommend to seal off any areas you don’t want the Self Leveling Cement to seep into by either caulking them (such as floor plates in the framing) or building a dam of some sort (such as at doorways or around heating and cooling ducts). Self Leveling Cement is very liquid (hence the fact it self levels) and is always looking for someplace to run, don’t let the leveler run into adjacent rooms unless you intend for it to! Be sure to properly mix your Self Leveling Cement according to the manufacturer. Unless you have a way to measure out smaller portions I recommend mixing full bags at a time. Be precise with your measuring, no guessing with Self Leveling Cement! Also be sure to mix the Self Leveling Cement as long as the manufacturer recommends, don’t just think it looks ok. Again, if you follow the directions on the bag, Self Leveling Cement is very easy to work with, albeit a little messy. If you are in the area and would like me to come by and look at your floor, just give me a call at (573) 289-1045 to set up an appointment.
After you get your sub floor flat you are ready for the tile installation, or are you? I prefer to not bond my tile directly to concrete, ever! In Columbia, Missouri (where I live and work) the ground moves too much and that causes the concrete to crack. We have all seen stress cracks in tile from direct bonding them to concrete and I don’t want to worry about cracked tiles in the future. Using a roll on membrane, such as Red Guard is an ok product to use and is the minimum I would recommend. The best solution, in my opinion, is to use Schluter Ditra. Ditra allows the substrate under your tile to move independently of the tile itself. This lets two different materials move at their own rate without affecting the other. I also recommend using Ditra over wood sub floors in place of traditional backer boards. The backer board installation again is trying to force different materials to act the same way and that never ends up being a good thing! To install Ditra you should review Schluter’s installation handbook, which is supplied with every roll of Ditra sold. In the case of the job I was on I set the Ditra with a 5/16 x 5/16 V notched trowel using non-modified thinset. Non modified thinset is generally less expensive than modified thinset and is sometimes harder to find. To install the Ditra, mix your thinset a little loose (but still within the manufacturer guidelines) and trowel the thinset on the floor. Lay your Ditra into the fresh thinset bed and force the Ditra down with a grout float or concrete magnesium float. I prefer the concrete float as it provides a wider working area and seems to go pretty fast. We offer the Schluter Ditra and all setting materials at our shop in Columbia, Missouri.
Now that the Ditra is down, we are ready to tile the floor (finally!). Over Ditra you always want to use a non-modified thinset mortar. Since I was able to get the floor flat prior to installing the Ditra (manufacturer required anyway), setting the tiles is a snap. As you can see in the picture I snap a reference line with a green chaulkline, and am careful not to cover it up while I lay that row of tile. If you are tiling over Ditra you must be certain that waffles in the Ditra are completely filled with thinset by using the straight edge of your trowel to “burn in” the thinset. Once the waffles are filled completely, turn your trowel over to the notch side and comb the thinset in one direction (it doesn’t matter which direction, only in one direction). Combing the thinset in one direction prevents air pockets from forming under your tile and leaving hollow spots. Once you have combed and set your first tile, pull it back up and make sure that you are achieving the desired coverage with your thinset. You should do this periodically throughout the job to make sure that you don’t have a job failure.
To grout the floor be sure that your joints are clean and free of debris. You also need to be sure that there is no thinset squished up between your tiles in the grout joint. If there is thinset in the grout joint, scrape it out (if it is the day after your tile installation the thinset should scrape out fairly easily), then clean the joint. When you are setting the tile it’s a good idea at that point to scrape out thinset as you see it. Follow your grouts mixing direction on the bag and be sure to let the grout slake (sit in the bucket for 5-10 minutes before using), then mix it again with your mixer. After your grout has slaked DO NOT ADD MORE WATER, mixing the grout up again will bring it back to the same consistency it was before it slaked. Slaking allows the grout to be more uniform and extends the pot life. You should also let your thinsets slake as well.
Finally, the tile installation is complete. I know I don’t have pictures for every step, I get into a job and forget to stop and take pictures. If you have any questions please contact me or post them here. Thank you for reading, I hope this will help you with your next tiling project!