why backerboard...is it needed? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-27-2004, 07:49 AM
I'm looking for some perspective as I've only done 4 floors to date (in my home. I'm a DIY'er). In the past, I've laid them on plywood with thinset designed for use on plywood (I believe it was flexbond).

I'm currently building a master bath in which I'm going to lay marble tile (walls and floor)(joists are now sistered so deflection is fine). So now I'm looking at what to use on floor and shower walls.

For the floor - what are the pros and cons of using thinset for plywood versus backer board? I figure there must be a strong reason for backerboard or people would avoid the extra work and stack up in floor height associated with backerboard (1.25" of plywood + backerboard = high floor)? is the extra work and increased floor height that comes with backer board a necessary evil to disconnect the tiles from the natural movement/expansion of the wood subfloor?

For the shower walls - what's the best build up from the studs to tile? 30# roofing felt, 1/2 backer board then modified thinset and tile? Do you tuck the felt/vapor barrier into the shower pan (yes, I'm going with a composite/veritek shower pan for the floor)?

Thanks, in advance, for any and all assistance.

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08-27-2004, 09:31 AM
Good morning Mike. Welcome.

Re. tiling directly over plywood vs. backer board, looks to me like you have it all figured out. Yes, the backer board will help isolate/uncouple the tile from sub-floor movement that will take place. Some experienced professionals still tile directly to plywood using special installation techniques but we do not recommend this method to our general membership and readers here on the Forum.

If 1/4" backer board on the floor creates a height problem, there are isolation membranes, Schluter Ditra being one, which will only add an additional 1/8" or so of height.

And yes again, 1/2' backer board on a shower wall over a vapor barrior, 15# felt is good, using a good modified thinset is a good construction method. I'm not familiar with the pre-made shower pan you mention so really can't comment on how the vapor barrior shoud interface with it. But the pan installation instructions will cover this detail.

John Bridge
08-27-2004, 06:41 PM
Hi Mike, Welcome. :)

We have one professed plywood guy in our membership. There may be other closet dudes we don't know about. :D

The main guy is Bill Vincent, and that's his username. Look him up in the member list and shoot him an email. He'll be more than happy to talk about tiling directly to plywood. He's been doing it for years.

08-31-2004, 10:29 AM
Hi All:

I was going to start a new thread but my issue is also about the need for backer board -- but over radiant heat. Here's the set-up. 5/8" plywood is glued/nailed to 2 x 12's @ 16" o.c.; 3/4" sleepers are screwed to the plywood @ 12" o.c. and 1/2" pex tubing is laid between the sleepers; light-weight concrete was poured between the sleepers, and 3/8" plywood was screwed into the sleepers. The system is running and seems to work fine. The original thinking was to lay down a vinyle sheet good over the plywood after leveling out any uneveness with a self-leveling concrete. My wife nixed the sheet good idea, I nixed wood (too many accidents waiting to happen), and so tile is the compromise.

In looking at tile at Lowe's I was told that I had to put down backer board because there would be too much flex in the floor. The tile guy at HD said that it would be okay because in total I have 1" of plywood given the concrete between the two pieces of plywood. (The floor IS very solid when you walk on it.) A tile installer at a local tile store said that I would be taking a chance that the plywood would delaminate unless it is A/C; in fact it is B/C. He recommended backer board, which I suppose I could use if I am very careful to only screw it where the sleepers are. I truth, I am very reluctant to take the risk, becuase if I put a screw into the tubing that's not the only thing that's screwed. While at the tile store I saw a mock-up using a red/orange plactic mesh which I now believe to be Schulter's ditra. What I object to with ditra is the series of channels that act as insulators to impede the flow of heat. Hence, what I really want to do is place the tile on the plywood, but only if I gain enough confidence it will work long term. Maybe I am being too purest about using ditra. Why is it recommended, as Mike2 seems to suggest, to isolate/decouple the tile from sub-floor movement?

I will, as you advised Mike, seek advice from Bill Vincent, but would certainly welcome guidance from any of the other experts that frequent these pages.

Thanks! Sorry if this is an overly long post.

08-31-2004, 11:00 AM
I wouldn't worry about the thermal isolation from the Ditra. The waffles are filled with thinset, so there is mostly concrete in the heat path from the tubing to the air.

I'd worry about tiling directly to plywood, since you only have a single layer (I know about the one under the gypcrete) of 3/8" over the sleepers. If the gypcrete does not support the plywood perfectly, you could have movement. This would be an area where bedding the plywood in thinset over the gypcrete/sleepers would be beneficial.

08-31-2004, 02:34 PM
Thanks for the reply, Bob. The material between the sleepers is light-weight concrete, not gypcrete, and it is already in place and covered by the plywood -- so if there are any voids their is not much to be done about it now. When you say "bedding the plywood in thinset over the gypcrete/sleepers would be beneficial" did you think that the plywood was not in place as yet, or would the bedding be on top of the plywood?

07-14-2015, 02:44 PM
Here's my personal experience (I'm not a "pro".)

1) In most cases, it is unnecessary to cover existing surfaces with cement backer board before tiling.

2) For example, it's ok to tile over existing vinyl sheet flooring as long as the substrate (typ. plywood and/or particle board) under it is both flat & dry (not appreciably swollen) - first, galvanized-nail down any loose spots & along any cracks, roughen its surface with a belt sander, wash with ammonia water to remove dust & any old floor "wax", & dry it.

3) Modern polymer-modified sanded thinset (about $15/50# sack at Home Depot or Lowes - this stuff sticks to (and thereby seals) just about anything*) stirred up with just enough water to make a "stiff" mix works fine for both setting the tiles & then grouting them the next day

4) Make your straight tile cuts with a scratch/break-type cutter - for curved cuts or holes use a dry 4" diamond blade-equipped hand grinder

5) If the existing sheet flooring is "coved" upwards along the wall, appropriate-width pieces of your new ceramic tile can cover it too after its surface is prepared (sanded, cleaned etc.) the same way that the flatwork was. The same thinset used to stick those pieces of tile onto the existing coving can be troweled into a nice looking border along their top edges.

6) While it's handy to use the conventional plastic coated tile spacers for your flatwork (little pieces of uniformly thick wood are equally handy & possess the added advantage of coming in any thickness you choose to make), expect to shift your tiles a bit when using them. The reason for this is that "real" ceramic tiles vary somewhat in size (especially from box to box) which will produce bad-looking corner junctions otherwise.

7) Harbor freight is a good place (cheapest) to get the necessary tools/equipment

* I resided my house with 4' by 8' sheets of 2" thick beadboard plastered with a 3/16" layer of this stuff (the white-colored variety) ten years ago. It still hasn't cracked, flaked off, or otherwise failed.

07-14-2015, 03:01 PM
Welcome darryl,
I do not wish to contradict you, but you have some very bad advice in your post.
In most cases, it is unnecessary to cover existing surfaces with cement backer board This is a very broad statement, I would argue that tiling over the existing floor is the exception, not the rule.
For example, it's ok to tile over existing vinyl sheet flooring as long as the substrate (typ. plywood and/or particle board) Particle board has no place under tile, ever. Often sheet goods are installed over 1/4" ply/luan and that also has no place under tile.
this stuff sticks to (and thereby seals) just about anything*)Thinset is not waterproof and seals nothing, it is an adhesive.

Respectfully, Nate

07-14-2015, 04:19 PM
Welcome, darrylsiemer. Please change that permanent signature line to a first name for us to use. :)

I gotta agree with Nate on your comments on this 11 year old thread.

3) Modern polymer-modified sanded thinset (about $15/50# sack at Home Depot or Lowes - this stuff sticks to (and thereby seals) just about anything*) stirred up with just enough water to make a "stiff" mix works fine for both setting the tiles & then grouting them the next day I'll add to Nate's comment that thinset mortar is not designed to be used as grout, even if you do happen to like the color. Same with your comment #5.

And while I'm happy your use of thinset mortar as stucco worked well for you, that's also an application I don't believe the product manufacturer would support.

We're happy to have you join us here and help with our visitors' questions, but please help us in our mission to keep our advice in general conformance with manufacturer's recommendations, tile industry standards, and best building practices. We work pretty hard at that most of the time. :)

07-17-2015, 10:33 AM
I'm a retired PhD chemist/materials scientist who's done a good deal of experimental work with cementitious materials some of which resulted in peer-reviewed publications. However, I'm not a professional tile or stucco installer. I wrote my note to share my experiences with other home owners willing to tackle their own remodeling jobs and want advice that's not motivated by financial self interest and/or a compulsion to "support" similarly motivated (and therefore compulsively secretive) industry/trade/colleagues.

Standard (cheap) polymer modified thin set effectively "seals" tiles to lots of different substrate materials and when used as grout, tiles to other tiles (it's an excellent adhesive that retains a surprising degree of flexibility over time). Like any other cement based material including most of mysterious concoctions labeled/sold as "grout", it's not absolutely impermeable to water which means that gaps filled with it should be painted with a wax, acrylic, or silicone based sealant (e.g., a cheap floor wax).

Tiger Mountain Tile Inc
07-17-2015, 04:04 PM
Daryl, your entitled to your opinions and other homeowners that want to follow your way of thinking are free to do so. But we just can't let that advice stand on it's own. We have to come in and say that this kind of advice goes against every industry standard.

You may think our industry is a conspiracy. You may think it's driven by greed and self interest. That's ok. But many people come here looking for something better than standard internet advice and we don't want them to confuse your advice with proper industry standards.

07-17-2015, 05:53 PM
I came here looking for expert tile installation advice, I guess that a bonus now is that I know where to go for Phd Chemist advice :)