Porcelain tile floor in 100-yr-old kitchen


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Old 02-02-09, 08:34 AM
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Porcelain tile floor in 100-yr-old kitchen

Hi,

We're remodeling the kitchen in our 100-yr-old twin home. Our plan is to use 12x12 porcelain tile over 1/2" hardibacker. The joists are not all the same size, but are on average 8.0"x2.5", and spaced on average 18" o.c. The unsupported span is about 15'.

The subfloor is actually the "only" floor -- appears to be Georgia pine. It's actually been finished/stained in the other rooms but was never finished in the kitchen.
It's 3/4" thick, T&G, directly on the joists. One of the joists has a 2" hole half an inch from the bottom for a drain pipe.

The floor toward the back wall of the room rises about 1" over the last 4 feet. The rest of the floor is relatively level. Also at the back wall is what looks like a concrete slab, about 4'x3'... perhaps for an old coal stove? It rises about 3/8" above the level of the subfloor.

A couple of questions:
1) Any issues on joist support underneath? There will be a small island. Countertops will be quartz.

2) What should we do about the 1" rise toward the back of the kitchen? (The rise is where a row of cabinets will be installed). Will this cause the tile to crack, etc?

3) Our plan is to not put hardibacker over the concrete slab, and to just level it with mortar. Is this reasonable?

This is my first flooring post -- please let me know if I've omitted anything.

Thank you!
 
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Old 02-02-09, 02:56 PM
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1) Any issues on joist support underneath? There will be a small island. Countertops will be quartz.
I'm showing a floor deflection of L/321, and a floor should have at least L360 for ceramic install. Anyway you can shorten that unsupported span? You need to install at least a 5/8" exterior grade plywood over your current subfloor first, then a cementboard (1/4" is fine) then tile.

2) What should we do about the 1" rise toward the back of the kitchen? (The rise is where a row of cabinets will be installed). Will this cause the tile to crack, etc?
1" is pretty off.......any way you can yank up that subfloor and fix the joists?

3) Our plan is to not put hardibacker over the concrete slab, and to just level it with mortar. Is this reasonable?
Cementboards do not go over slabs. Any cracking? Hairline crack is 'ok' if there they are flush. Too level it, I would use a self leveling compound then a membrane, like Schluter Ditra.
 
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Old 02-03-09, 12:03 PM
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Thanks for the answers! I should have posted earlier, as over the weekend we rented a truck and bought the 1/2" backerboard.

What are the consequences if we skip the plywood subfloor over the current subfloor? We plan to use modified thinset between the backerboard and existing subfloor... is this not sufficient?

As far as the joist span -- under the kitchen it's actually more like 12', not 15', since I forgot to subtract the basement stairs that descend between the kitchen and the party wall.

About the 1" rise... I don't know if fixing that is an option. The concrete slab is part of the 1" rise... also, the existing subfloor doesn't look easy to remove. And I'd have no idea how to fix the joists. If we leave this as is, will this severely impact the appearance/performance of the tile floor?

Thanks again for your help.
 
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Old 02-03-09, 01:53 PM
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Demolition Man - I remember that movie, Sylvester Stallone and Sandra Bullock.

You cannot install the cement board over the plank floor. The planks expand and contract independently and that movement will destroy your tile floor in no time. You need to install a layer of exterior glue plywood minimum 1/2" over the planks first. If height is an issue, you can install an isolation membrane over the plywood instead of cement board. Schulter Ditra will add only 1/8" in height and Noble CIS will add only 1/16" in height.

As for the joist span, what you need is the unsupported span, that is the distance between the supports for the joists from below(like exterior block wall to center beam that joists rest on). Im not sure if thats what you measured.

The cement slab presents a problem. You cannot span the wood subfloor and the slab with tile. The 2 surfaces move independently and the tile will not be able to handle that movement. You'll need to incorporate soft joints (caulked instead of grouted) into your tile design that honor the joints between the slab and wood framed floor.
 
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Old 02-04-09, 11:14 AM
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Thanks Johnny, that's very helpful. My name actually comes from the Police song... which I think Sting did a different version of for that movie.

We'll probably go with the hardibacker instead of the Ditra, mostly because we've already bought it, and also because of price.

Can you clarify for me (in layman's terms hopefully) why a layer of plywood over the plank floor will protect the tile from the floor's expansion/contraction/movement, but a layer of hardibacker won't? Is it a deflection issue or something else? I tried to do online research after reading your last reply but now I'm more confused than ever (especially after trying to understand when to use modified vs unmodified thinset... sooo much conflicting advice out there).

The unsupported span is actually 12' I think... one end of the joists rest on the stone at the outside of the house, and the other end (under the kitchen at least) rest on a perpendicular double joist on the near side of the basement steps, if that makes sense.

Also... what kind of caulk would I use for the soft joints between the concrete and wood?

Thanks again.
 
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Old 02-04-09, 12:02 PM
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Can you clarify for me (in layman's terms hopefully) why a layer of plywood over the plank floor will protect the tile from the floor's expansion/contraction/movement, but a layer of hardibacker won't?
The best reason I can give you here is that neither hardibacker, nor any other cement board I know of lists planks as a suitable subfloor for installing their product and therefore will not warranty such an installation. All cement boards I know of require that they be installed over either exterior glue plywood or osb. Both plywood and osb are more stable than plank flooring. Cement board is in no way structural like plywood. Whereas plywood will add strength, stiffness and stability to a floor, cement board will not. No cement board manufacturer makes any claims that their board is structural and will strenghten a floor. Cement boards function is to be a good bonding surface for thinset and tile and that is pretty much it. Since it is not structural, your floor needs to meet all criteria for a tile installation before cement board can be installed.

Even old plank flooring expands and contracts quite a bit with seasonal and different moisture conditions. There needs to be something more stable between the planking and the cement board to isolate that movement. Hope this helps.

The unsupported span is actually 12' I think... one end of the joists rest on the stone at the outside of the house, and the other end (under the kitchen at least) rest on a perpendicular double joist on the near side of the basement steps, if that makes sense.
What is supporting the doubled up joist on the side of the basement steps? Does the floor seem solid? Is it springy when you walk accross it?
 
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Old 02-05-09, 01:41 PM
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Ok, I see. Makes sense now.

The double joist by the basement steps is supported by the stone wall at the back of the house, and on the other side by a doubled-up floor joist. I hadn't noticed this before. So the floor joists are supported by a perpendicular joist which is itself supported by different floor joists... I can't imagine this is the best scenario.

Would it help if I put in a column below the end of the perpendicular joists?

To answer your other questions, the floor does seem solid, yes. It doesn't move when we walk across it, but it does "bounce" very briefly and slightly when we jump on it.

What do you think?

Thanks again.
 
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Old 02-05-09, 06:36 PM
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If you can install a column, your floor will be happy with you.

Plywood will remove the bounce you feel once the planks are refastened. It's not the plank movement you feel that will kill the floor, it's the movement you don't see that occurs seasonally as the moisture content of the planking fluctuates. That not only creates excessive horizontal movement but unchecked vertical movement as it cups and crowns. Your tile will feel that.
 
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Old 02-10-09, 10:34 AM
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Sounds good, I think we'll be installing a column in the basement. What is the best place to do this? Should we do it right in the center of the kitchen floor above, or at the corner of the kitchen where the perpendicular joist rests on the floor joists?

Also, about the 2" hole at the bottom of the joist... would it make sense to glue and nail a few feet of 2x4 to the top of that part of the joist? The hole is right under where one corner of the kitchen island will rest, so I'm a little worried about it.
 
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Old 03-13-09, 08:02 AM
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Attaching kitchen island to tile floor

We're finally putting in the new kitchen cabinets this weekend. After the wall and base cabinets are in, we're building an island in the middle of the room from two base cabinets.

My B&D book says to screw 2x4 cleats to the floor, then attach the island to the cleats using finishing nails.

Does this apply to porcelain tile floor? Should I drill through the tile and 1/2" hardibacker so I can screw the 2x4's into the subfloor? Or is there a better way to attach the 2x4's to the tile?
 
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Old 03-13-09, 08:15 AM
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Just answered a similar question on another thread.

http://forum.doityourself.com/design...-cabinets.html

I've seen some contractors use construction adhesive to secure the cabinets in place, but Im not crazy about that idea.

If you use finish nails to secure the cabinets to the blocks, use a pnuematic nail gun if possible to elimate unwanted movement of the cabinets while you are nailing. You can also use screws and hide them with trim.
 
 

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