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Old 09-29-2007, 06:19 PM   #1
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Install 12" X 12" tile on bathroom floor.


Well, this is the main reason that I joined the forum. I want the advice of someone who has installed this tile.

Here is the situation.

My home was built in the late 50's. It is built on what I call a "Post and Beam" sub-floor. The beams are 4" X 6" and run the length of the house. They rest on a concrete pier and 4" X 6" post about 15" long. The good thing is, I have plenty of room to work in the crawl space. The sub-floor on top of the beams is 2" X 6" tong and groove flooring; running the width of the house. In most rooms, there is hardwood flooring on top of this tong and groove, with carpet on top of it.

I repaired the floor where there was rot. Someone had repaired it previously, but as in most cases that I have found in remodeling, they did a half-way job. Just enough to get by. So, I removed the remaining rot and brought it up to code.

I am going to put 1/4" plywood over the top of the sub-floor and place the tub on it. This was recommended by the plumber. My question is, what should I do from there? I want to top it off with either 6" X 6" or 12" X 12" tile. We are leaning towards the 12" tile. I don't believe there is any problem with strength.

I have installed hundreds of ceramic tile on walls. I have installed, taped and finished many square feet of sheetrock. I have done allot of electrical and plumbing. However, I have never tiled a bathroom floor.

Your help will be greatly appreciated.


Last edited by Handyman50; 09-29-2007 at 06:21 PM.
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Old 09-30-2007, 08:36 AM   #2
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Install 12" X 12" tile on bathroom floor.


You don't mention how far apart the beams are or the span between the piers. In a traditionally framed house with 2x8" joists, 16" on center. The subfloor would need to be at least 1" thick. On top of that ,cement board(1/4"or 1/2"), then the tile.
You would need to put down 3/4" ply on the T&G subfloor and then a layer of cement board. This would be over a framing system properly set in place.
I don't understand the 1/4" ply install under the tub.
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Old 09-30-2007, 04:12 PM   #3
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Install 12" X 12" tile on bathroom floor.


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You don't mention how far apart the beams are or the span between the piers. In a traditionally framed house with 2x8" joists, 16" on center. The subfloor would need to be at least 1" thick. On top of that ,cement board(1/4"or 1/2"), then the tile.
You would need to put down 3/4" ply on the T&G subfloor and then a layer of cement board. This would be over a framing system properly set in place.
I don't understand the 1/4" ply install under the tub.
Ron
Ron, thanks for your reply.

The 4"X6" beams are 42" apart. This is definitely not a common building solution in today's market. It was very common in the 50's in the Pacific NW. My dad, who was a plasterer and carpenter, said he saw it all of the time in that era. It is one of the strongest sub-floors that you can build. It would cost a fortune today, if you could even get solid 4"X6" beams. As I said, the sub-floor on top of the beams is 2"X6" tongue and groove flooring. So, I already have 1-1/2 inches beneath the tile. This eliminates the need for 3/4" plywood.

The 1/4" plywood would cover the entire 2X6 sub-floor. The tub would go on top of the 1/4" plywood. Then, the 1/4" concrete board would go on top of it up to the tub. This would match the 1/2" hardwood floor in the hall next to the bathroom. On top of both would be the tile.

I hope this is more clear.

Is there a reason to put a bed of mortar on top of the concrete board if it is level?

Last edited by Handyman50; 09-30-2007 at 04:17 PM.
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Old 10-02-2007, 11:41 AM   #4
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Install 12" X 12" tile on bathroom floor.


Seems my post disappeared.
It's not only the thickness of the subfloor, but it's makeup. The issue you have is that there are too many seams in the floor and the support underneath is spread further apart. Movement will kill a tile floor. Your floor moves. Not enough to see, but maybe enough to effect the tile.
Minimally you should screw down all the 2x6's to the joist below.
Forget the 1/4" ply, it's not rigid enough.The height issue between rooms is also something that does not dictate floor support. In traditional 20 th century framing the tiled room always sits higher then the surrounding rooms due to the extra support tile needs.
Glue and screw the ply down and thinset and screw(or nail) the concrete board on top.
This is an educated guess as to a solution, as I don't know the deflection rate of the floor.
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Old 10-02-2007, 04:16 PM   #5
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Install 12" X 12" tile on bathroom floor.


I looked on the John Bridge forum and checked the "flexolater" for your floor. It only went to 24" centers, and not knowing how far apart your pileings/supports were (42"?), I could only put in 24" centers. With that and no consideration for the 2x6 t&g, it indicated your floor would not be suitable for tile. Sure seems the 2x6 t&g would count for something. I am also thinking of putting tile in my bath I am redoing. But I'm not quite sure it would hold up. I may run a beam across the joists and do it anyway, but I would sure hate to have to tear it out later.
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Old 10-02-2007, 06:39 PM   #6
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Install 12" X 12" tile on bathroom floor.


Thanks for the replies, guys.

I have a thread on another forum. It seems the folks on there agree with you that my floor, as it is designed, will not support tile.

I think option #2, laminated flooring or something bathroom proof, will have to suffice.

Last edited by Handyman50; 10-03-2007 at 09:39 PM.
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Old 11-09-2007, 02:25 PM   #7
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Install 12" X 12" tile on bathroom floor.


I have the same subfloor as Handyman50. The house was built in 1961 in California. As an architectural drafter, I've seen quite a few houses with 2x6 T&G on 4x6 girders at 4' o.c. around here.

I've been wondering the same thing. Handyman50, did you ever get a definitive answer as to whether you can successfully put in a tile floor with that subfloor? Or did you go with another option?
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Old 11-09-2007, 04:33 PM   #8
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Install 12" X 12" tile on bathroom floor.


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I have the same subfloor as Handyman50. The house was built in 1961 in California. As an architectural drafter, I've seen quite a few houses with 2x6 T&G on 4x6 girders at 4' o.c. around here.

I've been wondering the same thing. Handyman50, did you ever get a definitive answer as to whether you can successfully put in a tile floor with that subfloor? Or did you go with another option?
No, I actually didn't get a definitive answer. However, after much debate, we decided not to take a chance on having to replace tile and/or grout caused by structural incompatibility. So, we are going to use floating laminate flooring that looks like tile. It is far more forgiving and far easier to install. We used it (laminate boards) in our kitchen and it has been working great for over 3 years.
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Old 10-19-2009, 12:16 AM   #9
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Install 12" X 12" tile on bathroom floor.


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No, I actually didn't get a definitive answer. However, after much debate, we decided not to take a chance on having to replace tile and/or grout caused by structural incompatibility. So, we are going to use floating laminate flooring that looks like tile. It is far more forgiving and far easier to install. We used it (laminate boards) in our kitchen and it has been working great for over 3 years.
I purchased a home that was built in the 1960's with the same type of post and beam construction (2x6 tongue and groove spanning 4'-0" between 4x6 girders spanning 6'-0" on center - keep in mind the 4'-0" span and the 6'-0" span are very important - if you have any other spans exceeding these numbers, the spanning members will required retrofitting). If you assume you're using a tile that will not exceed 20 pounds per square foot sustained permenant load (also called "dead load"), the floor will only deflect around 0.062" under complete loading (called "total loading"). So to say that the floor cannot meet the deflection ratios is not really true. However, the problem with these floors (as I'm discovering myself), is that the carpentry was usually bad, and the foundation may not be properly founded in bedrock.

In my case, the 4x4 support posts supporting the 4x6 girders are merley supported on 12"x12" concrete blocks in a small bed of concrete just below the surface of the soil (basically supported directly on top of clay). The clay moves up and down during wet and dry seasons (see if you have any diagonal cracks in the sheet rock around your door and window openings (this is a tall tail sign that you have clay under your home - probably already obvious if you've tried digging in the yard : ). This movement can be detrimental to the tile because when the clay dries out, the ground contracts, and the floor can settle differentially - i.e. some of the floor can drop in height while the rest of the floor moves in a different direction. This movement creates tension stresses in the tile that can ultimately lead to cracking. If you have these types of soils around your home, you should install a vapor barrier under the floor to help stabilize the clay from getting dry (I installed a 15 mil Stego Vapor Barrier in a 1350 sf crawl space in one weekend with a helper). The vapor barrier makes it easier to move around under the home too.

Make sure to watch out for the HVAC vents and splices in the 2x6 tongue and groove flooring. Each splice that does not occur over a support is a weak point and allows for isolated deflection ("movement" of the floor). It appears these openings are generally not properly braced and require attention immediately prior to placing the new flooring. If you can expose the tongue and groove flooring, look at where the decking splices occur. You can add new framing under the center of these splices or edges of the HVAC vents. 2x6 douglas fir #2 joists are generally the easiest way to stiffen the floor. I installed a double 2x6 along the edge of my HVAC vent in the bathroom, and the floor was very stiff afterward.

So I think a tile floor is possible in these types of homes, but there are retrofits required to minimize the risk of the tile failing. I think a glued plywood layer under the thinset and hardiboard is definitely a must to ensure the 2x6 tongue and groove will be held together so they act together and are not relying 100% on the tongue and groove to transfer the loads.

Any thoughts? Hope this helps.
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Old 10-19-2009, 07:38 PM   #10
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Install 12" X 12" tile on bathroom floor.


Sounds to me you are descibing "car decking". (Yes, it was used quite a bit in the NW, including myself.) If it were me, I would lay some 3/4" a/c ply over it, (screwed into the planks only, not the beams) then a layer of Schluter Ditra over the top of that. I have only done one job like this with car decking. No call backs. Any time I think I "May" have a deflection issue, I've always used Ditra.

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