Large Tiles - sloped floor = Dilemma [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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Porcelaine Guy
08-17-2006, 10:19 PM
I'll start from the bottom and work up. This is what I've got, ~500 sqft of tile to put down:
1st layer = basement concrete floor (dry, old, stable, no cracks, no heaves)
2nd layer = Delta FL (plastic dimpled membrane) corsella-dorken com high compressive strength
3rd layer = 5/8" Fir exterior grade plywood
4th layer = Custom Building Products - Mega Flex thinset. This is the product that has the best specs I could find for shear strength between porcelaine and plywood (680psi).
5th layer = Italian porcelaine tile 52.5cm (20.7") square

The seams of the Delta FL were sealed with a bead of silicon.
The T&G of the plywood was glued. Butt ends are gapped ~2mm as per manufacturer. I used about 5 times the normal # of anchors so the plywood is very solid - no give (well within the L/360 criteria)

I am not terribly worried about the plywood expanding or contracting. The room will be temperature and humidity controlled and once the thinset cures, there is no easy path for moisture to get to the wood. There is effectively a vapour barrier above and below it.

The floor is not perfectly flat. It slopes gradually. The highest point is about 32mm (1 1/4") higher than the lowest point. The maximum slope from one tile to the next is about 8.5mm (0.33") The average slope is about 2.5 mm (1/10th of an inch over a distance of 20.7")

My questions are:

What would the pros do and how? Do I follow the gradual slope or
do I level the floor first with some leveling system?

Can I build up the low areas enough with thinset to bring everything to the same level? What is the maximum thickness for thinset? Can I build up the thinset in layers? The manufacturer says that it will adhere to itself very well.

Do I use some sort of nylon mesh tape (like for drywall applications)
over the plywood seams (butt ends especially) I have some gaps that are about 1/4", most are 2mm or less.

Do I fill the gaps first with some kind of caulking?

Thanks in advance for any advice.

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08-17-2006, 10:49 PM
Welcome, Guy. Please give us a first name to use. :)

This the same floor from a year ago but without the heating system this time?What would the pros do and how?I think the first thing a pro is gonna do is axe you just why on earth you did what you've outlined here. Seriously. :shades:

My suggestion would be to tear out what you've installed thus far and start with a mud bed to level and flatten the floor since you've obviously got the vertical room to do that. And I know that's not what you wanna hear, so let's wait for some other responses. :)

My opinion; worth price charged.

08-17-2006, 11:28 PM
Now just :D why on earth did you do that? (Sorry I couldn't resist.)
:bang: :x: I'm not trying to beat up on ya or add injury to the matter..but honestly I think you've got a bit of a train wreck in progress here. I agree with CX. You should start over. Simply because the whole system doesn't really conform to anything conventional. It's only as good as the weakest link in the system and I see alot of unusual variables possible.

08-18-2006, 03:51 AM
I have a couple of questions.
#1 - What was your reasoning for using Plywood over the concrete??(insulative? Build up?? )

#2 - You mentioned vapor barrier above AND Below...Please expand on this some for me.

#3 - do you have a web page for the membrane you used so i can look at some specs?

I am not going to dismiss this system you have designed out of hand simply because it does not conform to known practices.

I do want to try to understand your reasonings for each step and also determine if we have additional height to work with. That is....... if it is deemed necessary.

I'll try to help you out, but youve got to help me first :)


Porcelaine Guy
08-21-2006, 09:47 PM
In Answer to your questions:
1. Reason for using plywood = insulative as well as recommended by Delta FL manufacturer
2. There is no actual 6mil vapour barrier, but because the Delta FL is impervious to moisture and the porcelaine tile is impervious to moisture, they both effectively act as vapour barriers.
3.I wasn't allowed to put in the web page for the Delta FL, but a quick Google using either "Delta FL" or "Corsella Dorken" will get you there.

Please don't beat up on me too much. You might hurt my feelings.
I really just want to make the best of a bad situation. Tearing out and starting over is not a real option. I don't really see the need for that kind of extreme measure.


08-21-2006, 10:01 PM
You missed one question above, Robert:This the same floor from a year ago but without the heating system this time?

You should be able to post your links now that you have three posts. We have an anti-spam measure that prevents link posting before that.

You seem to be mixing flat and level in your description of your floor. The tile installation doesn't give a rat's patootie if the floor is/is not level, it only cares about flat.

So, we understand that your floor is grossly unlevel, but is it flat within a 1/4-inch in ten feet and no more than 1/16th-inch difference in any given foot?

If it is sufficiently flat, do you care if it remains unlevel?

Do you understand that you must still install some sort of tiling substrate over your plywood and that you are limited to a sheet or trowel-on membrane for that purpose?

Show us a link to that stuff you pewt under the plywood. Did the manufacturer know that you intended to install tile over this floor?

My opinion; worth price charged.

08-22-2006, 12:21 AM
Robert and all,

You got talked into using a method that is NOT intended nor recommend for ceramic tile. Says so right in their installation instructions.

You are not by any means the first to want to install plywood over concrete, or build a false floor in order to make the basement floor more confortable. Yeck it might even work fairly well sometimes? :shrug: You're on your own!

I will bet next weeks pay check that you will be sorry in a year or so if you continue. Not only because of this Delta FL stuff and the method, but also because of the size of those monster tiles. :eek: Actually for tiles that large the floor should to be flat within 1/8" in 10' (for best results), especially if they have any kind of gloss or are rectified. (Square edges, not rounded like most ceramic tiles). Being a basement you probably also have some floor drains which means the floor is also dished, which makes it a nightmare to work with.


08-22-2006, 04:58 PM
The first webpage is a little lists tile. If you go to the installation instructions, it clarifies it to vinal tile (squares) ceramic listed anywhere.

08-22-2006, 05:32 PM
Let me heap on questions!

Why set directly on the plywood?

If your building a false floor, why not make it level when you build it?

08-22-2006, 08:30 PM

Robert is not building a false floor. I just mentioned that as one way others have tried to warmup a cold basement floor.

Yes, it is a little misleading to those of us that think of ceramic tile when we see the word tile? But they would say that the word 'tile' does not automaticaly mean 'ceramic tile', and they are technically right.

It's always up to the installer to determine the suitability of all products and methods for the intended purpose.


08-22-2006, 09:12 PM
I don't know diddly about the ramifications of using tile over that system as is, but why couldn't he just put 1/4" CBU down or a membrane over the plywood, using short screws on CBU, so as not to penetrate the delta product. I've used that delta floor system in the last house that I lived in to solve a cold basment floor and moisture problem. It is very tough and supportive, you could drive a car over it and get no flex. I however laid laminate flooring directly over it. The increase in comfort level in the room was dramatic as was moisture abatement. Of course, I don't live there any more, so I can't tell give you a long term report.

08-26-2006, 06:19 AM
OK, After returning from Vacation I looked over this situation, checked the website and must Say...Good Job Jaz!!!

So now the question is this, Can we make a silk purse out of a Sows ear??

Perhaps........Perhaps not.
I would go to the guy who sold you on this system and say you told me to do this after i said i was installing ceramic tile yet you were wrong...Now, what are you going to do for me.

Next, I would do 1 of 2 things
#1 - Start over.............Or...............
#2 - Begin Again!! ;)