Preparing a wood subfloor for tile installation requires careful steps to prevent tile cracking, movement, and moisture-related issues.

Here’s a detailed breakdown:

1. Assessing the Wood Subfloor

* Ensure the wood subfloor is structurally sound, clean, dry, and level.
* The subfloor should be at least 3/4-inch thick plywood or OSB for sufficient strength.
* Check for deflection (excessive movement when stepping on the floor); it should not exceed L/360      (span length divided by 360) for ceramic tile and L/720 for natural stone.
* Secure any loose floorboards with screws to eliminate squeaking and movement.

2. Installing an Underlayment

To prevent cracking and provide a stable base, you must install an underlayment before tiling. There are two main options: 

A. Cement Backer Board (CBU)
Material: Typically 1/4-inch or 1/2-inch cement board.
Installation:

* Spread thin-set mortar over the wood subfloor using a notched trowel.
* Lay cement backer board onto the mortar and press firmly.
* Secure with alkali-resistant screws every 6-8 inches.
* Tape and fill the joints with fiberglass mesh tape and thin-set mortar.

B. Uncoupling Membrane (e.g., Schluter® DITRA)
Material: A flexible membrane that separates the tile from wood movement.
Installation:

* Apply modified thin-set mortar using a V-notched trowel.
* Roll out the uncoupling membrane and press it into the thin-set.
* Use a float or roller to ensure full adhesion.
* Allow it to dry before tiling.

3. Ensuring Proper Expansion Joints

* Leave a 1/4-inch gap around walls, cabinets, and other fixed objects to allow for expansion.
* Use caulk or foam backer rod instead of grout in these expansion joints.

4. Final Surface Check

* Before tiling, ensure the surface is flat, firm, and properly bonded.
* Wipe off any dust or debris before applying tile adhesive.