Ceramic Tile Entryway [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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Dave 99
09-12-2001, 03:32 PM
Hello All,

Been browsing this forum for a week or so and must say, I'm quite impressed with the breadth of knowledge that's shared and the flair it is done with. Since the wife & I are in the process of remodeling another home we plan to move into soon, I figure I'll expand my horizons and try some of the work myself. For tile advice I think this is the place go.

One of the first projects is ceramic tile in the entryway. Area is approximately 80 X 50 inches. I've already stripped the old flooring, linoleum over 1/8 in. plywood, over the original vinyl tile. Remaining subfloor is 5/8 in. plywood and appears pretty solid, installed over 2 X 8 joists spaced 16 in., some glue residue from original vinyl tile. Planning on 8 in. tiles installed diagonally. I don't think I have a lot of room to build up the floor due to the exterior entry door. I had initially intended to just put down 1/4 in. Hardiebacker or Wonderboard over the existing subfloor and let it rip. Just a little concerned that the subfloor is only the 5/8 in. plywood. I probably could build up the floor some, just not with another 5/8 in. or more of plywood. What are your thoughts?

Once this is licked, on to the remainder of the honey-do list (ceramic tile floor in 1/2 bath, ceramic tile floor and back splash in the full bath, etc., etc.).

Thanks in advance for your assistance!

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John Bridge
09-12-2001, 03:47 PM
Welcome aboard, Dave.

The pros are going to want to know what the span is of the 2x8 joists. Standard is 2x10, but yours will work if they are not too long between supports and if the floor is fairly stiff. Ceramic of any size can't stand deflection at all.

They'll also want you to beef up the subfloor, I think, before you install the backer.

Someone will be along. Please tell us about the joists.

Dave 99
09-12-2001, 04:10 PM

The span isn't much more than 80 inches, the width of the floor. Kinda tough to describe but the home is a bi-level with the first floor partially submerged. There is no other flooring in the home at the same level of the entryway, which has stairs leading up to the second floor and down to the first floor.

I think the most I could build up the subfloor is maybe about 1/4 inch max, which should still allow for the backer & tile. Would that be sufficient?

John Bridge
09-12-2001, 05:04 PM

That would just about get you to the minimum. I'm not the world's greatest authority on backer board installations (I've done two to date.) Better wait around for someone who does it all the time. They'll be around. Hang tight.

09-12-2001, 07:13 PM

you mention the span being 80". The guys will want to know the span between each floor joist rather than the overall span


Rob Z
09-12-2001, 08:13 PM

Any option of cutting the door to allow for extra subfloor?

More plywood would make everyone happy.


Bud Cline
09-12-2001, 10:20 PM
In the "for what it's worth department" and no bigger than what you are trying to do I would go for it with one change.

I would force myself to use 1/2" backer. The 8" joists are marginal true but they are 16" on center and that's good.

The minimum floor thickness required is 1-1/8" before tile, this would put you on mark in the thickness department. I really wouldn't expect any problems and there are ways to deal with the additional 1/4" of height you would have.

Use a quality modified thinset and latex additive in the grout. I'm comfortable with this one I think.

09-12-2001, 11:13 PM
I hesitate to speak up, because you guys know more about this than I ever hope to, but I called the folks at Hardie a few weeks ago with similar question and they were adamant that their board couldn’t be considered to be structural. It would take a bit more time, but seems like gluing and fastening the heck out of a 1/4” ply laid long-grain across the joists with 1/4” HB on top would be stronger.

No offense intended to anyone. I’m a novice DIY’er, so you know what my opinion is worth. Just had to pass on what I got from Hardie for your consideration.

Mike Fossum

Dave 99
09-13-2001, 02:39 AM

The joists are 16 in. on center.


I would prefer not to alter the door. Just how much plywood makes you happy?


I think using the 1/2 in. backer board will be fine height-wise. There is a slight amount of glue from the original vinyl tile installation (back in 1971), should that be removed? The tiles came up very easily and the glue does not appear to be very substantial, the surface is fairly smooth.

Thanks to all.

09-13-2001, 06:34 AM
Sorry Dave,

If I had read your original post completely I would have seen you specified 16in OC.


Bud Cline
09-13-2001, 07:32 AM

The need to remove more of the remaining adhesive is a judgement call on the part of the doer. Without being able to see what you have I can't say.

Just between me and you....when you use thinset to install the cement board and also use screws in the cement board I don't think you will have any worries about the remaining glue. The main thing is to be sure the subfloor is flat (plain).

Dave 99
09-13-2001, 03:52 PM

I think I like where you're going. I'm not so sure about the 1/4" underlayment before the backer, but I may be able to squeeze in 1/2" plywood below the backer & tile. I think I'll measure the door threshold again, remember that originally only had just less than 3/4" to work with but that was before stripping down to the subfloor (removed about 1/4"?).


No sweat, I could have stated the joist info better.


I think I'm pretty comfortable with going with the 1/2" backer and lettin' it rip. The floor is pretty soliid (suspect it's due to the short span of the joists?) and I definitlely plan to perform a solid installation of the backer. But do you think the additional 1/4" (1/2" backer vs. 1/2" plywood + 1/4" backer) may be beneficial? This question could also involve my bathroom (that thread to come.....).

You guys are good......

John Bridge
09-13-2001, 04:02 PM
I think you can actually stiffen the floor by bonding hardibacker to the subfloor, but I get shot down every time I mention it. It goes contrary to "industry" standards.

Rob Z
09-13-2001, 06:21 PM
Hi Dave

I see you already got to it...I was going to say that if it was my job, i'd want to go with 1/2" ply (glued and screwed)at a minimum with 1/4 " backer board over that.

I agree with John and have had many discussions with him over the stiffening affect of backer board. I notice that it sure does seem to make the lfoor stiffer, but everyone that is a big shot in the tile business says it isn't so.

I think you 're good to go with this as is.


09-13-2001, 06:54 PM
I'm with John on this one...I think the backerboard adds stiffness after it's down...if it didn't, then we'd need an inch of more of subfloor before the backerboard...which is great if you have the room..but not many do. Sorry to agree with you John..I think?


John Bridge
09-13-2001, 07:36 PM
It's okay, Bri. I'll try to agree with you on the next one just to get even. ;)

Bud Cline
09-13-2001, 10:23 PM
The question as to whether backerboard properly installed stiffens a floor is an absolute YES in my experience. But then what do I know? I don't sit on any rule-making boards.

Dave 99
09-14-2001, 04:55 PM
Measured the exterior door threshold again with the old flooring removed, only have around 3/4" to work with on top of the 5/8" subfloor (including tile). I'll either use 1/2" backer or I could use 1/4" plywood + 1/4" backer. Your recommendations?

Thanks for your input, it's much appreciated.

John Bridge
09-14-2001, 04:59 PM
Once again, I'll only cast a vote. I would go for the ply and backer board. Ply glued and nailed/screwed to the existing.

The tiles, though, are going to be a little more than a quarter-inch. And then the thin set (at least a thirty-second).

Dave 99
09-14-2001, 05:32 PM

Duly noted, I still think thickness-wise I'll be okay.

Now I want to make sure about the installation of the 1/4" plywood & backer. I figured I'd lay the 1/4" plywood and screw to the subfloor around the perimeter of each piece. Then apply adhesive, lay the backer and screw in place using 1 1/4" or 1 1/2" screws. Is it really necessary to apply adhesive between the subfloor and 1/4" underlayment (will definitely apply between underlayment & backer) and if so, how should it be screwed down?

09-14-2001, 06:13 PM

I usually try not to jump in on the advice side, but I can speak on this one.

The glue between the 1/4 inch ply - that John is correctly suggesting - and the existing subfloor is more important than the screws that you will fasten it with. What you are trying to make is a sheet of 7/8th inch plywood subfloor. Think of the screws as gluing clamps. Put plenty of'em in, and not just around the perimeter, but if you have glued well, you could take them out in the morning and never know (not recommending that, of course, unless you got nothing better to do).

My opinion; worth price charged.

Dave 99
09-15-2001, 03:02 AM

I guess the thought of applying adhesive & screwing down the plywood, then again applying adhesive & screwing down the backer seems like overkill.

But I'm here to get sound advice, probably should just take it once it is given. I guess it's now time to get to work on the floor........

09-15-2001, 08:12 AM
After several installs of the backer board, I would agree it reinforces the floor. In almost any case, when you add layers of a product atop each other, the aggregate is stronger. Plywood is a good example. The use of thinset definitely adds to the stiffness as well.

I'm sure the reason manufacturers don't support our opninons is litigation related. There are undoubtedly people who will try to use the backer board as a substitute for a solid floor. Can you imagine how many substandard floors are out there that will never be suited for tile unless they are gutted and replaced???

Just my opinion, but I would find it hard to believe that the backeboard didn't offer some rigidity, support, etc. Heck, even luan plywood would offer some strength. NOT THAT I'M SUGGESTED THE USE OF LUAN PLYWOOD, but there is strength in layers

Come and get me....


09-15-2001, 04:08 PM

The adhesive between the layers of plywood is perhaps one of the few things on this forum about which I would expect no argument. It will add both strength and stiffness to your floor - gaa-ron-teed!

The thinset under the CBU is an entirely different kind of thing and something I know nada about. I know it's different because my understanding is you actually want to use not-so-good thinset for this particular application.

Apples and oranges I guess. But glue the plywood. Take a look at the plywood you already have. Is thin sheets of wood what? Glued together. Strong as hell. You are making it thicker. And the cleaner you can get the existing subfloor before gluing, the better. I recommend something like "Titebond II", or similar exterior grade wood glue.

Them real tile guys will come on now and 'splain us some more about thinsetting that cee-ment board down. 'Specially John, he loves that stuff.

My opinion; worth price charged.

Dave 99
09-15-2001, 04:24 PM
Fly in the ointment. Or maybe not. Seems that after an initial discussion about a new exterior door, the wife went ahead and has one being installed Monday (I'm always the last to know, need to hide the checkbook more efficiently)! I will communicate to the installer that he needs to consider that a tile installation is forthcoming & to protect for the thickness of that floor. If things go right he'll install the door & I'll have more than enough to work with to install the 1/2" plywood, backer & tile with no worries. I think this would be a good thing.

John & CX,

And I will adhere whatever plywood I put down!

Thanks to everyone thus far for your input & advice, it is greatly appreciated.