Tile over wood deck

for tile to stay put there can be zero flex in the floor or the tiles will pop up and come loose.

keep that in mind

honestly, something that close only 6" off of the ground, i would just pull it up and pour a full slab for before tiling over it

also tile can be very dangerous and slippery, so it needs to be a rough surface type of tile so it will be safe

and lay down some thick plywood on the framing
---

I don't think the water would approve of this.

You definitely want to put down a Tile Underlayment Membrane to keep the movement from cracking all of the grout.

A) do not tile over treated wood. Too much movement.
B) do not tile over dimensional lumber. You must add plywood, and preferably a backerboard as well. Backerboard must be installed in a bed of mortar.
C) tile will be slippery. You would need a tile with a textured surface, or a small tile with a lot of grout lines.

Do one layer of 3/4" exterior rated T&G plywood on top of the deck. Screw this layer into the joists of the deck every 12 inches. Also, put down heavy duty construction adhesive underneath this layer. Next do another layer of 3/4" exterior rated T&G plywood with the grain perpendicular to the first layer. This one should be screwed into the first layer of plywood every 12 inches. Also, use construction adhesive underneith. Go buy a roll of schluter ditra membrane and lay it on top of the plywood (using thinset). After drying, seal the seams of the membrane with schluter kerdi band and fill all the waffle pockets with thinset. Let dry, then lay your tile. you should have no issues.

I would recommend removing the decking tbh and laying the first plywood on top of the joists, but you should be okay without doing that. Also, if I were you. I would install some flashing around the edge of the deck for further protection against water from getting to the wood. The Schluter membrane will allow movement without cracking and is 100% water proof. I do not recommend concrete board for this project.

The only answer is no. I’m sure the wood deck joists and stringers weren’t laid out to support the additional weight of more plywood, backer board, thin set and tile. That’s a recipe for disaster, joist will sag, tile will crack..

quote:

---

Second layer of plywood should run the same direction (across the joists) as the first. Just offset the seams.

---

Actually, the weakness of the plywood runs along the grain. Laying the two layers perpendicular helps to eliminate this issue.

quote:

---

I’m sure the wood deck joists and stringers weren’t laid out to support the additional weight of more plywood, backer board, thin set and tile. That’s a recipe for disaster, joist will sag, tile will crack..

---

Not necessarily. I would visit the John Bridge forum where they have a deflection calculator for exactly this project. It will tell you if you need additional footings or joists.

quote:

---

They also have many discussions about the second layer of plywood.
Should be run in same direction across the joists, and do not screw into the joists with the top layer. Use shorter screws.

---

You are correct, the top layer does not get screwed into the joists. However, the bottom layer should be laid with the grain perpendicular to the joists not in the same direction as the joists. The top layer should be in the same direction as the joists and perpendicular to the bottom layer.

Negative. Same direction (perpendicular) as the bottom. Just offset the seams.


John Bridge Forum
Liberry
Wood framed floors
Plywood underlayment direction (post # 15)