I am installing a new marble tile floor (12×12) in the entryway of my home. The base is 1.5″ mortar over a 2X6″ T&G sub-floor with a proper vapor barrier.
After removing the old tile I needed to smooth out the mortar base and make up a little height so I am installing 1/4 inch Hardi-backer board before laying the tile.
I am installing the the backer-board with thinset mortar. Here’s where I made a rookie mistake. I mixed enough thinset (hopefully thoroughly) and started applying it to the floor. Of course this took longer than expected and by the time I was ready to install the fourth piece, the mortar was a little stiff but I forged ahead. Now the corners of the backer-board are popping up a little. Can I fix this with construction adhesive and a few screws? Also, I still need to install two more pieces of backer-board. I had not initially planned to use any screws because I did not want to have to screw into the concrete.
If necessary, I can correct this by ripping it all out and starting over. Obviously I would like to avoid this. However, I would rather sacrifice $50-worth of backer-board & a day’s labor than risk the tile I’ll be installing over it.
Thank you in advance for your advice.
Replies
Rip it up. Scrape the thinset off the mortar and re-install a Ditra membrane as your backer over the mortar bed. If you are slow at troweling the thineset for the Ditra (it's installed the same as a backerboard, only without the need for screws), use Mapei's Ultra-Flex...Pot time is 2-6 hours and set-up once troweled is 15-25 minutes. Use a 3/16" V-notched trowel to apply the thinset, then simply roll out the Ditra and press it in. It takes half the time backerboard does and Ditra runs only about $1.25/s.f. It's the best shyt in the world and your installation will never fail.