I am a "newbie" when it comes to laying ceramic tile and need some advice since I have been getting some confusing advice from a local retailer. I am going to be installing tile in a small washroom (sink and toilet) (30"x80") and currently there is 1/4" plywood on top of the subfloor. I removed 2 layers of vinyl flooring and there is still glue on the plywood.

I went to this retailer last night to buy all the supplies I need to install the ceramic tile and the person in the section where the supplies are said to just apply the thin set to the plywood (they said that's what the person installing the floor in their home did). I asked about backerboard and they looked at me as if I didn't know what I was talking about. When I went to get the thin set they said do I need mesh and I asked is this recommended and they sold this to me. Upon reading more about this mesh, it seems like I would need to do a mud bed.

Since the area I am working in is very small, that mudding is quite involved (for a beginner), and that the mud bed would add considerable height to the floor, should I look more seriously at using 1/4" backerboard?

Hi

First thing you should do, is remove the 1/4 plywood...it's probably Luan ply(Mahogany). If you look on a bag of thin set, it will be the first thing listed under unsuitable substrates. Besides, its covered in glue. If you could let us know what is under that ply, that would really help.

It is a chipboard subfloor.

The thin set is SuperTek One Step High Performance Polymer modified.

Can you tell us if there is more than one layer of subfloor and what the thickness is of each layer? Also, if you could tell us the size of the floor joists, the spacing between them, and how far the joists span between supporting beams or walls, that's a very important piece of info in determining if your floor is suitable for tile.

And you do need some type of CBU or tile underlayment. That's pretty much a given in any installation over a wood subfloor.

Kman is right. If your floor flexes, the stresses on the tile will cause it to fail within a few years (or sooner). You could rip out the plywood and install 3/8" halex board. Halex is a birch plywood specifically designed for tile and it's easy to work with for beginners.

I personally would use the backerboard over the mesh idea. I know its what everyone does in the area..but it's not a whole lot better than just going over the chipboard. The backerboard will at least give you a bit of strength. Not a lot..but better than the mesh and skimming it. Cut it to fit, and then spread your thin set and set the board into it. Then fasten the board down with screws or or hot dipped galvanized roofing nails. The thin set under the backerboard is there to fill any voids that might be under it...it's not meant to glue the board to the floor..so used enough fasteners..every 6 inches or so. Use some fiberglass tape on the seams and you are ready to tile.

very informative Brian

Thanks everyone...

Kman: The subfloor currently consists of 5/8 chipboard with a 1/4 ply on top; the joists are spaced at 16"

Brian: Since I don't want to make any assumptions; I should remove the current 1/4 ply and replace it with the 1/4 backerboard, correct?

The trouble with giving advice on these forums is....you need to tell people to do everything by the book. At least that way, if something goes wrong....you didn't get bad information. The 1/4 in ply should come out...because you just don't know how well it is down..if there is spring in it...there is spring in the cement board you just put on top too. That kind of movement in not good..it creates cracks in the grout joints. So, it's always best to get right down to the subfloor to see what you are working with. Will going on top work? Probably...but for the half hour it takes to remove it...I would. The thing is...we arent there to see your floor. It's really up to you to decide if the floor is sturdy enough to support tile. Go in jump around..see if the floor moves...check to see that it is screwed down tight. Make sure the seams between each sheet dont have any movement. Add extra screws if you do notice movement. If it still shows obvious movement...then maybe adding another thickness of plywood is the way to go...at least 3/8th inch. Everyone here is pretty much going to tell you to make it bullet proof. It's not our fault. If you look up the word anal in the dictionary...it shows a picture of a tile guy.