Once you’ve completed the tear out of the old floor, the next step is to prepare the area for the new tile floor. Among the most important things to do is to make sure the subfloor is solid and secure. It is vital that subflooring beneath granite tile does not flex. It must be “rock” solid. (Pun intended) A dense material like granite is difficult to scratch or cut, but the more dense a material is the more likely it is to be brittle. If a force is applied to granite it doesn’t bend, That energy has to go somewhere. Instead of bending granite will chip or crack. Granite is almost impervious to surface wear from normal use, but it is succeptible to breaking if it doesn’t have the right base beneath it. Once you’ve gotten down to the bare floor, take steps to make sure the foundation is solid and true.

Whether or not you can see it, wood and concrete are both materials that change over time. It is quite easy to picture your kitchen floor as a solid unmoving object. The reality is that as wood and concrete abosorb water they swell, and as they dry they shrink. The effects of this are almost invisible especially if the only water involved is the humidity in the surrounding air. Still these effects have to be accounted for because granite tile is not going to shrink and swell along with the subfloor beneath it. This brings up the possible need for a crack isolation fabric, commonly known as a “slip sheet.” The purpose of a crack isolation membrane is to allow the tile to move horizontally and transfer the energy of movement from the granite to the grout surrounding it. Grout is kind of like a sponge. It serves the same purpose as the styrofoam blocks you get in the corners of the box with a new tv. Grout has a bit of bounce to it so if the tile moves the grout absorbes the energy.

There are two basic types of crack isolation fabric installation. One is called an embedded system, the other is commonly referred to as a sheet system. With an embedded system you lay down a thin set adheasive over your subfloor. Then you lay down a fabric over the adheasive. After the first adheasive drys, you lay down the second layer of thin set adheasive and attach the tile to it.

With a sheet system the sheets have sticky edges which you attach together forming one. Whole floor sized, solid rubberized sheet. Both systems work equally as well. Keep in mind that niether system will prevent tile breakage if you have not prepared the subfloor adequately. They can transfer energy side to side between tiles, (horizontally) but if the floor moves up and down (vertical movement) nothing can prevent broken tiles. You need to make sure you have an adequate structure beneath the subfloor. It should be reinforced and leveled before putting down the underlayment. Sand down high spots and fill in low spots. Granite is really heavy stuff so make sure the floor is strong enough that it can handle the weight.

Once the subfloor is prepared you will want to concider the topic of the next article Radiant In Floor Heating