If you saw yesterday’s article on How to Even a Floor to Prepare for Tile, you know that I’ve been shadowing Jim from Diamond Tile, and the next step for tiling this kitchen is to install Schluter DITRA underlayment.
DITRA is an uncoupling membrane, and it allows the floor to move (in-plane), eliminating major causes for cracked and delaminated tile. It neutralizes more movement than any other underlayment, and DITRA is a good choice for tiling over cracked concrete because it is waterproof and helps manage vapors and moisture. DITRA has proven itself within the industry, and any experienced tile contractor knows that DITRA is a terrific product.
DITRA is composed of a polyethylene (plastic) grid of square cavities, each with angled, dovetail cut-backs, and an anchoring mesh laminated to the backside. It comes in long rolls (i.e. 1 m x 30 m), and it’s lightweight and easy to cut.
You won’t see DITRA used on every job because it’s not always necessary, and DITRA adds significant cost and time to a tile installation. It’s another layer of thinset and it adds (at least) 1/8″ height to the floor.
Pro-Tip: Self-leveling mortar (SLM) is a good option for leveling a floor in preparation for tile. However, if it’s not properly mixed, SLM will crack and spall so it’s not uncommon to see DITRA installed over SLM.
How to Install DITRA
Yesterday Jim flashed the floor to eliminate any peaks and valleys, and the result is a nice even (not necessarily level) subfloor.
Step 1: Remove any Excess Thinset
Jim made a quick pass with his trowel to knockdown any slight ridges and he chipped away excess thinset from underneath the drywall.
Step 2: Unroll the DITRA
DITRA comes in long rolls, and Jim started at one side of the kitchen and worked toward the other. There’s no concern for staggering joints with the subfloor or how the strips are oriented. The goal is to butt edges of the DITRA together and ensure they don’t overlap.
Pro-Tip: Precutting and laying out all the DITRA gives it a chance to flatten out.
Step 3: Measure and Cut DITRA
Jim measured the DITRA about 1/2″ away from the wall to allow for movement, and he cut it with a utility knife.
Pro-Tip: It’s easier to cut DITRA from the backside.
He also made a cutout for the floor vent.
Step 4: Mark Edges
Marking the approximate location of the DITRA joints gave Jim a spread line for the thinset.
Step 5: Mix Ditra-Set
Jim always lays DITRA over thinset specific for that purchase, and Ditra-Set is one of the products available.
Jim mixed the Ditra-Set with water using a mixing paddle, and he let it slake for 15 minutes before remixing. Schluter recommends mixing the thinset to a “fairly fluid consistency (but still able to hold a notch).”
Pro-Talk: Slaking is the process of leaving the thinset undisturbed to allow the water to completely penetrate the dry ingredients.
Step 6: Spread Ditra-Set
Next, Jim spread the Ditra-Set according to his spread lines using a 1/4″ notched trowel.
Pro-Tip: A small v-notch trowel is also acceptable.
Step 7: Unroll and Press DITRA in Place
After Jim positioned each piece, he used a rubber grout float to firmly press the DITRA down onto the thinset. It’s important that the mesh backing be in complete contact with the thinset.
Pro-Tip: Jim always began working the grout float in the middle of a section to stretch and press wrinkles outward.
Step 8: Continue Laying DITRA
Jim butted adjacent pieces of DITRA taking care that they did not overlap at all.
In this way Jim put down all the DITRA.
Pro-Tip: It’s fine to walk on DITRA immediately after installing it.
On a couple of instances, Jim made additional cuts around wires and metal plates while laying the DITRA.
Step 9: Fill Cavities
At this point, non-modified thinset can be spread to fill the cavities in the DITRA and set the tiles. However, Jim opted to fill the cavities with more Ditra-Set and lay the tiles the following day (using more thinset) because it’s difficult to snap chalk lines over DITRA. Jim (and every other installer he knows) always waits until the next day to begin laying tile over DITRA.
Pro-Tip: Spraying hairspray over chalk lines helps preserve the lines on the plastic while working.
Jim mixed up more Ditra-Set and he made it slightly thinner so it’s easier to work.
Starting at one corner, Jim filled all the cavities and worked to avoid leaving any ridges.
A couple of buckets later and Jim was finished for the day. Now the floor is ready for tile.
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