Ceramic Tile over new and old construction

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Old 12-03-08, 11:21 AM
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Ceramic Tile over new and old construction

Howdy Experts! First, thanks for all the information on this board. I've done a bit of reading here (and likely need to do more) but thought I might ask a few questions if I may.

BACKGROUND: My house is 80 years old. We have torn down a section in the back and had that part of the (faulty) foundation removed (crawl space) and re-built. On top of that new crawl space we have built a new kitchen - or at least the majority of the new kitchen is new construction. The new section is 22ft by 15 ft. That new construction is built with 2x10 joists spaced 16" on center with a span between support walls of 13 feet. The floor joists run parallel to the 15 foot dimension and are attached to the house. There is a two foot cantilever over the outside foundation. I've installed under floor radiant heat using UltraFin. The subfloor in this section is 3/4-inch OSB.

The entire kitchen, however, is "L shaped", with the "L" part extending into the existing or old part of the house. That part is built over 2x10 joists, spaced 16 inches on center with a span between supports of 13ft 9in. The existing floor in the old section is 3/4-inch t&g oak attached directly to the joists (no subfloor).

We'd like to be able to run 18" tile throughtout. Of course the older floor has leveling issues. My framing contractor has done an excellent job of mating the old floor with new - the old floor runs flat right onto the new floor - at least at the seam between old and new, which sits directly over the existing house foundation - which is in good shape. Note that I also installed radiant underfloor heat under the older section - all of which is on the same zone. I mention the radiant heat just in case that makes any difference to the materials I might use. The only part of the install I'm doing myself is insulation in the floor for the heating system - and I'm being very careful to follow the manufacturer's instructions.

So, finally, the question is, what do I now do. My plan is to run cement board over all and put the tile on that. Is that going to be sufficient? What about the sag in the older section - do I tear out the flooring, sister board the joists and install new subfloor? A slight bit of sag is not really a problem to me (aesthetically) as long as the tiles that span the space from old to new are flat, and as long as it does not compromise the floor's ability to properly support the tile.

Thanks very much for any adivice!

Mike Potter
Baltimore, MD
 
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Old 12-03-08, 11:47 AM
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As long as there is no moisture under the floor your ok ,if you have moisture you would have to fix the problem, (plastic vapour barrier) Install your cementbord and you can start tiles
 
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Old 12-03-08, 02:23 PM
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Originally Posted by lakings11 View Post
As long as there is no moisture under the floor your ok ,if you have moisture you would have to fix the problem, (plastic vapour barrier) Install your cementbord and you can start tiles
Vapor barrier?


The cement backerboard needs to be thinsetted and screwed down per manufacturers instructions.

You cannot have any "sag" in the floor. The floor needs to be FLAT, especially for 18" tiles, and it needs to be sound.

We are talking ceramic or porcelain, correct?
 
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Old 12-03-08, 02:49 PM
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If the home-owner wants to save money it is not neccesary to have it 100% flat you can use a , floor patch product under the cement board where it sags, If there is no moisture under the floor, Sure its better to start new but you dont have to. also insted of a cement board home Depot also carries a Orange underlay.
 
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Old 12-03-08, 02:52 PM
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You cannot use any type of floor leveling compound underneith CBU. Since you have to screw the boards down as well as thinset them, the screws will crumble the SLC.

Homes with crawl spaces should have a barrier on the ground underneith the structure.
 
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Old 12-03-08, 03:23 PM
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Thats why home depot stocks the Orange Membrane this is a new product made for tiles, you can use it on concrete,or wood the great thing about it is you dont have to install cement board or wire mesh Check it out its a great product
 
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Old 12-03-08, 03:28 PM
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I used to sell the stuff, it's Schluter Ditra. It is more expensive, at $83 for 54sqft, but installs faster. It's not that new either, been out for many many years.
 
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Old 12-03-08, 03:39 PM
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The existing floor in the old section is 3/4-inch t&g oak attached directly to the joists (no subfloor).
You cannot install cement board or ditra over the t&g boards. You will need to install a layer of plywood over the t&g boards first, and it should be at least 1/2" (thicker would be better). Then you can install cement board or ditra. If the floor is out of plane, and you will be using cement board, you can use a cement based patching compound over the cement board. If using ditra you need to get the underlayment flat first, and then install the ditra.
 
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Old 12-03-08, 04:02 PM
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That would be to high, with the tile 3/4 inch why cant you install ditra on boards it has worked fine for me in many areas.
 
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Old 12-03-08, 04:05 PM
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Just because you have done it wrong in the past doesnt make it right. Go to the schluter website and read the instructions. They have lots of good info and a "Ditra Handbook" in pdf that details acceptable installations.
 
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Old 12-03-08, 05:38 PM
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Good catch Johnny! Didn't even see him mention the boards.

Installing any tile or backer unit over plank/strip flooring is a recipe for disaster.
 
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Old 12-03-08, 06:42 PM
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Lakings11,

Sorry but, the only thing I agree with you is when you were referring to the orange stuff, (Ditra), and said; Check it out its a great product How about an introduction and brief bio so our newbie visitors get an idea of your experience?

This floor needs a layer of plywood, some patching and at least one expansion joint in the field where the old and new converge. That crack has to be left independent from the other side.

Jaz
 
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Old 12-08-08, 07:28 AM
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Thanks everyone for the suggestions and comments. Here are a few points relevant to the posts on this thread:

1) the existing (old section) of the kitchen, which will sit on the 3/4-inch tongue&groove oak, is built over a heated basement - no moisture issues there. There will, however, be a vapor barrier installed as part of the in-floor heating. I'm using Produx foil-foam-foil insulation, stapled about 6" below floor to create the necessary convective cavity for the UltraFin heating system.

2) That section of the floor is pretty flat and is now fairly level after some remedial work in the basement last week - lifting the main beam that runs through the middle of the basement. The floor will be flat (and very close to level if not level) before proceeding with the tiles. Just walking on that older section it feels very sturdy and seems to have no "bounce".

3) The tiles are stone - 16x24" in size (my initial post was in error saying they were 18x18 ceramic).

So, once again, thank you all for your observations, comments, and suggestions. I believe my contractor is doing a great job, but I'm the sort to worry, perhaps too much, about those older floors, which are really in pretty good shape considering they're pretty old. No water damage and thankfully they have not been sanded. I guess the real issue just comes down to whether the 3/4-inch oak works as a subfloor comparable to OSB.


Mike
 
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Old 12-08-08, 09:42 AM
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1. You cannot tile or lay a cementboard over planked flooring, which you got. You WILL have to install at least a layer of 3/8" exterior grade plywood.

3. Stone requires a deflection of L720, according to your specs (2x10, 16OC, 13span) you only acheive a deflection of L458.

You are risking stone failure having it installed like this.

You claim this "contractor" is doing a good job, but if he plans on install a natural stone, cbu, etc over planked flooring, and has not done a deflection calculation, he is NOT doing a good job.
 
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Old 12-08-08, 01:58 PM
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Mike

The requirements for natural stone are different than ceramic. Your floor joist system will not support a natural stone installation as is. You'll need to shorten the 13' span or possibly sister the joists to make them stronger. Additionally, natural stone requires at a minimum 2 layers of plywood totalling 1 1/8" thick. Anything less than this is a gamble you dont want to take. The thickness required of this floor may make your hydronic heating system less efficient than you would like for it to be.
 
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Old 12-17-08, 12:43 PM
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Thanks again to all of you for your very helpful advice. My carpenter does really nice finish work but I think he's not as informed/skilled when it comes to major sutructural issues. But then he wasn't asked to draw up the original plans and has done everthing exactly as specified in the plans I had drawn up. I'll let y'all know how it turns out! I am my own "general contractor" on this job - sort of "on-the-job-training" and boy, those lessons can be costly!

Also - I was mistaken regarding the cement board - my carpenter's plan is to install 3/8-inch exterior ply over both the 3/4-inch OSB in the new section, and the 3/4-inch tongue and groove oak in the old section. Which, as mentioned, may render the hydronic floor heating less efficient than desired. It was, of course, installed exactly as I had asked....

Mike
 
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Old 12-17-08, 05:33 PM
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Mike,

As you know there are two factors in determining the suitability of a subfloor system for a particular rating. First the joists, second the subfloor sheets.

The joists resist the deflection through out their span. While the subfloor sheets resist deflection between the joists. They need to be evaluated separately.

Your joists system as is will do for ceramic or porcelain tiles, but not for natural stone tiles. As mentioned above you need to either shorten the span or sister the joists. So either build a supporting wall under the floor, or glue and bolt some more lumber to the sides of the joists. You do not have to use 2x10's or install them the entire length of the span. Even 2x6 or 4's will do, and install them at least in the middle 2/3 of the span.

Installing the 3/8" ply over both areas will be OK. I would like to see 1/2", but? Then you can install either your favorite cement backer, or a membrane such as Ditra or Noble's CIS. (I use Ditra). Be sure to make an expansion joint where new meets old. That means an open gap in the subfloors continuing to the new plywood and continuing to the cement backer, and then the tiles, UNLESS you decide to use CIS. CIS will bridge the expansion joints so you can shift the location a bit.

Again, the max deflection as recommended by the TCNA and most manufacturers is L360 for ceramic and porcelain, and L720 for natural stone. However, there's a few products whose manufacturer claim is guaranteed for natural stone even at L480. I would still try to improve your floor, but these would offer some added assurance.

Jaz
 
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Old 12-18-08, 06:28 AM
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Installing the 3/8" ply over both areas will be OK. I would like to see 1/2", but?
I think you should go 1/2" as well. Not only do you have a deflection issue that requires 2 layers of plywood, but you also have dimensional lumber that will see a lot of movement with the seasons and moisture conditions. This will be the case even though the boards are very old. Jaz's suggestion of ditra or cis will help with that, but thicker plywood will go a long way imo. Cis would give you more flexibility in dealing with the joint between old and new, as cis is also a crack isolation membrane. I'd use cis here but ditra will work also.
 
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Old 12-18-08, 06:53 AM
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I was mistaken regarding the cement board - my carpenter's plan is to install 3/8-inch exterior ply over both the 3/4-inch OSB in the new section, and the 3/4-inch tongue and groove oak in the old section.
Just to clarify this. You are not considering setting the tile directly to the 3/8" plywood, right. That would be the worst case scenario in my opinion. There is already enough of a difference in expansion contraction rates of stone and plywood to cause proplems. Your heating system will just make that worse. The membrane is absolutely required.
 
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Old 01-02-09, 08:03 AM
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Once again a huge "THANK YOU!!" to everyone. Here's my new plan.

1) I will sister 2x4s on either side of the bottom of each floor joist. I'll run most of the length of each joist - glue and clamp in place, then screws every 6" or so. My understanding is that this will improve stiffness by a factor of 1.6 - which would just get me over the L/720 deflection requirement.

2) Over the 3/4" OSB subfloor, which is butted at the joists, I will use 1/2" BC exterior grade 1 plywood underlayment, offset about 4" from the joists and staggered midway between OSB sheets in the other direction. 1/8" gap all around the underlayment joints, screwed to the OSB but not through to the joists.

3) Ditra over the 1/2" plywood.

4) Underlayment to have 1/4" gap at all exterior edges

5) Expansion joint where the old meets new.

Any recommendations for glue for sistering the joists as described? Or is liquid nails/construction adhesive okay? Are standard #8 2.5" deck screws sufficient?

Happy New Year - and thanks again for all the help

Mike
 
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Old 01-04-09, 04:48 AM
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Mike

Sounds like you have done your homework. 2x4's will work but 2x6's would be better. You can use construction adhesive or a full spread glue. Use 3" screws and plenty of them. All else sounds good.
 
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