[diyer2009]

Thanks to all for looking.

I am redoing a master bath. I've removed 4x4 tiles that were set on top of a 1.5 inch mud job. I have several questions about the best way to proceed with prepping for new tile:

1. It seems like the original tiles came off OK but the white thinset is still mostly in place and where its not are several voids showing the old mud base. It seems to me that the old mud base is kind of gritty and easy to chip/break away. I don't know if that's normal or not. Do I need to remove all the white thinset that remains?

2. Do I get off as much loose stuff as possible and then level patch wherever voids are before applying new thinset and tile?

3. Would I be better off breaking up the old floor and screwing down durock or hardibacker to my subfloor (plywood)?

My main concern is the condition of the existing mud job. I just don't know how it will hold up to a new tile application...

Thanks for all your answers in advance.

Neal.

[ballengerb1]

I'll go with door #3. If the old mud has cracks and pieces coming loose its time to start over from scratch. It would take many layers of Hardibacker to fill the missing 1 1/2" of old mud so I'd suggest 3/4" plywood glued and screwed to raise your sub and then either 1/4" or 1/2" Hardibacker also glued and screwed. Use whatever combo of ply and Hardi to get the old void filled to the proper level.

[diyer2009]

Thanks for the reply. One more question: any idea if the weight of the additional plywood and hardibacker would be close to the same of the existing mud assuming 3/4 plywood and 1/2 hardibacker?

Thanks again.

PS I'm not sure of the joist spacing below until I remove the mud...

[ballengerb1]

It would be a bit lighter but no clue how much since I don't know the size of your room. Let's just say lighter and leave it at that.

[diyer2009]

Thanks. One last question: do I need any material like roofing felt between any of the layers?

[ballengerb1]

No tar paper but you do use a modified thinset to glue the plywood down and then screw it too. More mofified thinset to set the backer board and the another layer of thinset for the tile. All layer except the tile also has screws .

[diyer2009]

Thanks Ballengerb. I'm getting differing opinions on this that its driving me nuts :confused: Some people are telling me don't glue it to allow for movement and other say glue as you're saying. I realize everyone's trying to help and believe their way is the best. Let me ask another question: how do you lay out the second layer of plywood? Should it be a different pattern than the first so that the joints are staggered? Is there any need to screw into both sheets of ply and into the joist?

Thanks again.

[ballengerb1]

The folks who want to allow movement aren't folks who have laid a ceramic floor before. Ceramic does not move one spec but if the sub floor flexes more than a few millimeters you will have a crack. Try reading the Hardiebacker site installation info. They make the best stuff I have used. James Hardie: HardieBacker 500 backerboard

[diyer2009]

Ballengerb, I don't see anything in the Hardibacker instructions that talks about using thinset between plywood layers. Of course its used between the backerboard and plywood and then the tile and backerboard. In your answer to me you said to "No tar paper but yoiu do use a modified thinset to glue the plywood down and then screw it too." Perhaps I'm reading your explanation wrong?

[ballengerb1]

OK, I should have written it as two separate sentences. No tar paper should be used in the laying of a sub floor. When laying a sub floor on another sub or when laying tile on backer board always use a modified thinset. If you were paying your tile directly on concrete you'd use straight ordinary thinset that dries rock hard and brittle.

[diyer2009]

Wow! So yet another opinion on plywd to plywood. So far I've heard: use thinset, wood glue, construction adhesive or nothing at all. Interesting. Starting to think just roll the dice and pick one :) Anyway thanks for your responses. Hopefully whichever one I choose won't be issue until after I'm dead or at least until I sell the place :)

[GC27]

In reading your posting it sounds like you are replacing only the floor tile in the shower and are probably doing so because they had become loose. This typiclally happens when there is standing water in the shower pan. The most common mistake I see in the field is that the shower pan material is not prepitched to the drain which leads to water sitting in the one or more corners of the pan. This causes what looks like snow coming through the grout lines which is the lime in the cement coming out or so I have been told. If you have a shower pan and plan on screwing down plywood and Hardibacker in order to get to the correct height to reinstall the tile you will be back fixing this shower again because it will leak and leak soon if not immediately. If you do not want to replace the shower pan and correctly pitch under the pan and then pitch the pan I would suggest at least carefully removing the existing mud job and doing it over. Start by water testing the pan by pluging the drain with an expanding plug and doing a water test. If the water level drops overnight you need to replace it. When you drain the water look to see if any water remains in the pan. If so you have a pitch problem. If you pass these two tests you can proceed with doing a new mud job. It is not really difficult to do. I start by creating a 1/4 inch per foot pitch from the drain to the walls. Keep in mind to allow for the thickness of the installed tile and thinset. Most often the sub floor is not level so I cheat by cutting strips of wood which I lay at the perimiter walls of the shower to establish my wall high point and use a straigt edge between my drain and these pieces of wood. Once the mortar has dried a little bit I take them out and fill the voids. When you mix the mortar it should resemble damp sand. The biggest mistake I see is people adding too much water. The dryer the mix the easier it is to work with. I also like to drill several holes in the threaded portion of the drain cover (The section that allows for height adjustment). This will allow additional drain holes for the mud job in case the small weep holes get clogged over time. I hope this helps and respond if you need additional help.

[diyer2009]

No sir this is not the case at all. I have gutted the bathroom entirely as a renovation project not because I had leaks or problems with my shower. Im merely trying to find the best and proper way to install tile flooring outside the shower stall right now. That is what the discussion above has led to and the reason for my questions.

[GC27]

My bad. If the material is in really good shape other than a few bad spots I would grind off the remaining thinset and go over the old mud job with a crack isolation membrane and then install my new tile. I use Schluter Ditra. Good luck.