TILE SURFACE PREPARATION FOR TILE

CONCRETE  SLABS

You have a layout of your tile project on paper now it is time to prepare the surface to receive the tile.

CLEANING

If you are setting tile to a concrete slab, you will want to make sure that the surface is clean and dust free. In new construction concrete is seldom covered to protect it from drywall mud, paint, and other debris.  So, depending on where you are laying tile, this could be a fairly involved process. Most residues can be mostly removed with a floor scraper. To remove concrete residue such as small pieces or drips stuck to the slab use a cement brick, a coarse stone with a handle. Always mop the concrete before beginning to get as much fine dust up as you can.

FLOATING

Use at least a 4-foot straight edge to check for high and low spots.  Mark these spots. The low spots can be filled with self-leveling cement made for this purpose. Check the floors again.  If there are persistent high spots, a different cement will need to be used to float them out.

If there are cracks in the slab, a crack separation membrane can be put down.  This is a mesh material that helps prevent the tile from cracking. Tile is brittle and here in Bryan and College Station our clay soils move a great deal. So, no one can guarantee against tile cracking, but a crack separation membrane will help hedge the bet.

Wood Sub-floors

It is important to make sure that floor joists are spaced, at the most, 16” on center and that they are properly sized for the span that they are crossing. Deflection in your joist or subfloor will cause the tile to crack.    Wider spacing will require additional sub-floor or bracing.  As joists on 16”centers are most common, we will proceed with that assumption.  There will need to be a minimum of a 1 ¼”sub floor consisting of a layer of tongue and grove plywood and cement backer board.  If the area is to be wet there will also need to be a shower pan.  Plywood sub-floor should be both glued and screwed to the joists.

CLEAN FLOORS

All previous flooring and debris will need to be removed before putting down cement backer board.  The floor will need to be checked for high and low spots using a straight edge that is at least four foot long.  Floors can be straitened using a self-leveling compound or by carefully shimming the plywood sub-floor.

Backer Board

When putting down cement backer board, it is a good idea to dry fit the entire floor before beginning to set the backer board to the plywood. Leave a 1/8” gap at all edges.  Once everything is dry fit it is time to put the backer board down.  Start by spreading thin set and scratching it with a ¼” by ¼” notched trowel. Set the backer board into the thin set and screw it according to the recommended screw pattern using the recommended screws.  Use a straight edge as you go to insure that the backer board is going down smoothly. Using mesh tape and thin set, float all of the seams between pieces of backer board.

WALLS

DEMOLITION

In the Brazos Valley interior residential walls are almost always wood studs with 1/2 inch drywall. In homes built before 1960 tile will often have been set to what is called a mud bed.  A mud bed is a layer of cement over felt paper with mesh in it.  This layer was typically between ¾”and and 1” in thickness. Starting in the late 60s it became very common to set tile directly to drywall.  When demolishing old tile it is always a good idea to get all the way down to the studs.  Once the studs are exposed use an 8 foot straight edge placed on the surface of several studs at a time to check for straightness. If the studs are bowed, take the time to straighten them. It is also a good idea to check corners for square so that adjustments can be made prior to the tile going on.

BACKER BOARD

Once your framing is straight, you are ready to start preparing the substrate.  The first layer should be30 # felt paper attached to the studs working your way up from the bottom overlapping each subsequent row The concrete backer board should be put on with noncorrosive screws placed every 5” on the studs. Take your time to make sure the screw set neatly with no part protruding from the backer board.  Leave a 1/8”gap between boards.  Tape the boards with fiber tape and float with thin set. Also float over the screws.