Stiffening floor for stone tile

Reply

  #1  
Old 06-20-13, 07:42 PM
Member
Thread Starter
Join Date: Jun 2013
Posts: 18
Question Stiffening floor for stone tile

What would provide greater stiffness as a base for stone tile: (a) tearing up plank subfloor, blocking the joists as close to mid-span as possible then laying down 3/4-inch plywood or (b) laying the 3/4-inch plywood down directly on top of the existing plank subfloor? Increased buildup is not a concern; existing bathroom floor is at least 3/4-inch lower that the adjoining floor.

I suppose I should acknowledge a third option: tearing up the plank subfloor, blocking the joists, then laying down 2 layers of 3/4-inch plywood.

Thoughts?
 
Sponsored Links
  #2  
Old 06-21-13, 06:03 AM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 17,756
Blocking the joists would help, or at least it can't hurt. I think it depends a lot on the condition of the floor planks. If they are solid and well attached they could be an asset to leave in place but if they are rotten or wiggly they need to go.

I prefer to use Advantech sheeting. I've found that it is stiffer than most plywoods and much more resistant to moisture damage. It's difficult to find at some big box home stores because it is a premium product but it's commonly stocked at most lumber yards and contractor supply places. I've had good luck with one layer of 3/4" and a layer of 1/2" cement board. I bought a couple sheets last week and it was about $35 a sheet but I think well worth the money. Oh, and bend with your knees. It's very heavy.
 
  #3  
Old 06-21-13, 07:59 AM
czizzi's Avatar
Forum Topic Moderator
Join Date: Jul 2007
Location: USA
Posts: 7,174
I believe it is more than just the top dressing on the floor system that makes it stiff.

First off, agree with the Advantech - If you watch videos on it you will see flex tests and how much stronger it is than regular OSB. In Big Orange Box store, they like to have proprietary items and they call theirs Home Advantage - but it is the same thing. Rarely shop big blue so don't know what they carry or if they name it differently.

Tell us a little about the floor system overall. What size are the floor joists? What is the spacing between? and how long of an unsupported span are we looking at? What kind of plank sub-flooring do you have and what was the floor originally composed of (tile, vinyl)?

It is the whole sandwich that makes for a stiff floor. And lastly, what size and type of stone tiles are you looking at installing?
 
  #4  
Old 06-21-13, 09:02 AM
Member
Thread Starter
Join Date: Jun 2013
Posts: 18
Sorry for the lack of details in my original post. I actually did provide them when I initially wrote my post, but I was timed-out while I was writing it so when I clicked "submit" the entire post was deleted from memory. I was tired and annoyed, so I entered an abbreviated version.

This is a very old house, so the lumber does not conform to current standards. The following are actual, not nominal, dimensions:

Joists are 6-7/8 inch x 3 inch and are spaced 16 o.c.. The span is approximately 10 feet (perhaps 2 or 3 inches more)

The subfloor is constructed of 7 in x 1-1/8 in tongue & groove planks running perpendicular (as opposed to diagonally) to the joists. The subfloor planks are in remarkably good condition; they are very old and very dry, but very little water damage around piping holes. I'm inclined to leave the subfloor in place because the wall studs (which still support a lathe and plaster wall on the other side) rest on top of the subfloor.

So, my current thought is to forego the blocking of the joists, leave the existing plank subfloor in place, lay 3/4-inch plywood over the existing subfloor, top that with 1/2 inch cement board (HardieBacker, actually) and then install the tiles. We are planning to go with 6x6 travertine tiles (with some 1x1 travertine accent tiles). If it is likely that they will crack, we have a second choice which is 6x6 porcelain tile (also with the 1x1 travertine accent tiles).

I wish I had posted this before I bought my materials. I like the suggestion of using the Advantech subflooring material. The cost of the Advantech is not that much more than the 3/4-inch OSB that I bought. But if I have to rent another truck to swap it out, the cost and inconvenience becomes noticeable.

I appreciate you help!!
 

Last edited by Tom McMahon; 06-21-13 at 09:17 AM.
  #5  
Old 06-21-13, 03:15 PM
Nashkat1's Avatar
Member
Join Date: Mar 2012
Location: USA
Posts: 8,470
I sounds like the existing subfloor is very solid and should stay. You could replace 95% of it without disturbing the walls framed on it, but I'm not sure what you'd gain.

If the OSB is T&G, it will probably serve you well when it's sandwiched between that subfloor and the HardiBacker. If not, you might be better off exchanging it.
 
  #6  
Old 06-21-13, 03:24 PM
czizzi's Avatar
Forum Topic Moderator
Join Date: Jul 2007
Location: USA
Posts: 7,174
Your sub-floor is pretty substantial to begin with, but your initial question indicates your concern for a "bouncy floor". Is it unstable as it sits? Usually, I try to shoot for 1 1/4" total thickness of the subfloor (1/2" + 3/4"). You already have 1 1/8" and it is T&G to boot.

Do a simple test....Take a glass of water 1/2 full and set it in the very center of the room on the floor. Walk around and watch the water. If your floor is stiff, you will see very little movement in the water in the glass. If you have bounce problems, the water will ripple in the glass and show you that you need to beef it up.

If the test proves positive, then the OSB you bought will probably be fine. It is T&G isn't it?
 
  #7  
Old 06-21-13, 09:19 PM
Member
Thread Starter
Join Date: Jun 2013
Posts: 18
First of all, thank you all for taking the time to provide me with your knowledgeable advice.

The plywood I bought for the subfloor is t&g. It is interesting that you raise that. I have read conflicting posts by self-projecting experts on this subject. The majority have advocated for t&g but I have seen a few posts strongly advocating for not using t&g and spacing the sheets of subflooring ¼ inch apart. That didn’t seem to make sense to me.

I have read repeatedly that it is important to nail the first layer of subfloor to the joists but to nail the second layer of subfloor to the first layer, avoiding the joints. I don’t understand this.

This old house has bouncy floors in general. The bathroom that I am remodeling is probably the only room (other than the basement…LOL) that does not have any noticeable bounce in the floor. But, the bounciness elsewhere in the house is indicative of the overall construction.

I did try the glass of water test (with the bathroom in its current state: torn down to wall studs and plank subfloor). I walked about the room and saw no ripples in the glass. BUT, I am not a big guy and the lighting was limited to one utility light hanging from a ceiling joist.

The floor specs (joist size, spacing and span) indicate that the floor is stiff enough for ceramic but not stone. Do you think that building up the subfloor with ½-inch cement board over 3/4 –inch t&g plywood over 1-1/8-inch t&g plank subfloor would stiffen the floor enough to tile with 6x6 travertine tile or should I play it safe and fall back to porcelain tile?
 
  #8  
Old 06-22-13, 09:17 AM
czizzi's Avatar
Forum Topic Moderator
Join Date: Jul 2007
Location: USA
Posts: 7,174
The fact that you are using 6x6 stone as opposed to say 16x16 lends me confidence that your floor will be sturdy enough for your installation as you have mapped out. If after you screw all the planks down and install T&G OSB and you still have movement (another water test), then look to add blocking. The blocking will make 3 joists act as one (as they are all tied together. If after blocking and you still have movement, I would look at sistering the center joists with a 2x10 or larger to add ridigity.
 
  #9  
Old 06-22-13, 10:25 AM
Member
Thread Starter
Join Date: Jun 2013
Posts: 18
First of all, I gave you some bad info. My 3/4-inch underlayment material is plywood, not OSB. Sorry. I don't know why I referred to it as such.

The bathroom I am remodeling is on the second floor, so sistering the joists (which would have been my first choice) is not an option. That is what drove me to consider blocking the joists. I have read that while blocking does provide some extra stiffness by transferring some joist load to neighboring joists, it is one of the least effective methods of floor stiffening.

Once I had ripped up the old finish flooring and saw the 1-1/8 inch t&g plank subflooring and the condition it is in, I started to have second thoughts. Would I be losing as much stiffness by replacing the 1-1/8 inch planks with 3/4 inch plywood as I was gaining with the blocking?

I really hate undoing things that I've already done. I know because I've experienced that many times. I know, it is a personality flaw . But I know that once I install the plywood, I am not going to want to pull it out (and the subfloor planking) to add joist blocking.

And, I really won't want to tear out a travertine tile floor because of cracking. That would make me So, I think I will proceed with installing the 3/4 inch plywood over the existing plank subfloor. Make a final assessment of the floor stiffness then make the final decision on porcelain vs. travertine. I'll repeat the water test as you recommend. But, if there is any doubt, I will opt for the porcelain. I'm not that brave.

I'll keep you posted on my progress.

And, once again, a BIG THANK YOU to all of you who have lent your informed observations and guidance. I hope I can repay the favor.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes