Subfloor/tile ploblem...Please help [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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11-07-2009, 09:17 PM
Hello and thank you in advance for your help. I have a late 50's ranch. We are doing a kitchen remodel. Our house is on a full basement. The problem we are having is with our tile installation and the subfloor. The joist are 2x10's, 16" on center. We have the 3/4"x10" wide planks set on a diagonal as the subfloor.

To the planks, our contractor layed a bed of thinset and then nailed 1/2" hardieboard every 4 inches. He did not screw the planks down, just the existing nails. I was worried about that and added nominal 1x2" cleats with screws and glue to the joist and subfloor in the basement.

The floor has some squeaks and pops, but is very solid overall. I am worried that the tile (20x20 ceramic) will fail. Should I rip out the whole thing and lay a new subfloor, or is there another way to correct this? Can we go over top of this with 5/8" plywood and then ditra? I just feel sick about this.

Thank you.


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11-07-2009, 09:47 PM
Welcome, Jimmy. :)
Should I rip out the whole thing and lay a new subfloor, No, actually you should have your tile installer do that if you contracted for a proper installation and have paid for any of it. Guy should know better. Or at least should have read the installation instructions for the CBU he installed.

But one way or another you need to get those subfloor boards fastened to the joists such that there is no squeaking or undetected movement and then get a minimum of half-inch plywood properly installed over them.

Then a tiling substrate of your choice and tile.

You should first determine the unsupported span of your floor joists to see that they are suitable for a tile installation.

Adding plywood over what you have now would not be a viable recovery plan to my thinking.

My opinion; worth price charged.

Tool Guy - Kg
11-07-2009, 09:50 PM
Your "sick feeling" will keep you out of trouble if you listen. Hardie is not to be installed directly over solid wood need a layer of plywood.

But I wouldn't keep building on top of what you sense in building over "squeaks and pops" unless you want a failed tile job down the road. Time to back up by removing the Hardi, fastening the planks securely, installing plywood, then installing the Hardi.

Is this contractor of yours a full time tile guy?


11-07-2009, 09:51 PM
Thank you for your quick response. The house was built in 1958 and is brick and block construction for the exterior walls. Can we remiove the plank subfloor without affecting the structure of the house? The unsupported span is just 11'6".

Tool Guy - Kg
11-07-2009, 10:01 PM
You're good to go with your joists only being spanned 11 1/2'. :tu2:

While you can remove the solid diagonal boards, realize that the joists are not likely aligned with the walls of the kitchen. If you remove the solid wood planks up to the closest joist and replace with 3/4" T&G plywood, you'll still have some solid planks from the joist to the wall. That means you'll still need another layer of ply over everything to avoid the very problem of installing Hardi directly over planks.

It's probably a good time to ask how much available floor thickness you have. If you are pinched for height, you may want to consider Ditra instead of the Hardi, as it's only 1/8" thick. But I'm hesitant to move forward with a suggestion like that because of the rather large error your contractor has already made. A contractor that doesn't follow directions like they did with the Hardi is unlikely to follow the directions of Schluter by using an unmodified thinset.

11-07-2009, 10:03 PM
you'll have to evaluate what that plank flooring may be holding up, in the way of partition walls. if walls fall over joists, you may be ok. if the wall stands between the joists, you'll need to add blocking to support the wall before you cut out the planks there.

11-07-2009, 10:06 PM
Can't see you house from here, Jim. Don't know how it is constructed as concerns removing the subfloor.

But so long as you replace the subflooring with 3/4" T&G plywood subflooring, I see little likelihood of structural failure during the replacement.

Might be the easiest option, but you'll hafta judge that.

I'd still want the second layer of plywood if it were to be my tile installation.

Your joist structure sounds fine so long as the joists are in good condition.

My opinion; worth price charged.

11-07-2009, 10:09 PM
Height is really not an issue. We had wanted the new tile to be roughly flush with the existing 3/4" hardwood, but don't really care about that.

Do you think we can remove the hardie and mortar without damaging the planks? He nailed it off every 4" or so with 1.5" roofing nails (smooth, not ring shanked). The planks were covered with a tar paper (now removed), so maybe the planks are a tad "slippery" as to aid mortar removal.

Do you think the cleats I added will be a problem if I just leave them there with the existing planks?

Thanks for all of the help and advice. My wife is in tears and I need to help her get through this...and me too!

11-07-2009, 10:11 PM
You know what thinset mortar he used, Jimmy?

11-07-2009, 10:12 PM
Yes, he used Flexbond

Tool Guy - Kg
11-07-2009, 10:24 PM
How long ago?


11-07-2009, 10:25 PM
It was set 3-4 weeks ago

Tool Guy - Kg
11-07-2009, 10:31 PM
Installing tile over what you have is a big gamble that I wouldn't be willing to take. I'd want the Hardi removed and reinstalled properly, per manufacturer's directions. If you want to do a test area of removing the Hardi from the planks, go ahead. That thinset is going to be rock hard and removing it is probably not going to be too pleasant.

But you may have an easier time simply cutting the Hardi and solid planks out in sections off the joists...then replacing the planks with 3/4" T&G plywood like we talked about earlier....followed by an additional layer over everything. :)

11-07-2009, 10:53 PM
Thanks to all that have helped us out. We now know what the problem is and the solution. Our contractor seems to do nice work, except for this, but he is not a professional tile guy.

11-07-2009, 11:16 PM
but he is not a professional tile guy.

Um, well, yea we kinda figured that one.:(

Keep checking in here w/questions as you go to help keep an eye on him, glad you found us before he got any farther.:)

11-09-2009, 06:17 AM
Our contractor is coming back today to remove the planks and hardie, everything down to the bare joist.

Once we are at that stage, what should I put down for a new subfloor, assuming all of the planks are removed. Can I use a T&G 23/32" OSB and then hardie right on top of that?

Also, do you nail or screw the subfloor to the joist?

Use liquid nails subfloor adhesive in addition?

Thanks again gor the help.

11-09-2009, 06:28 AM
Hadibacker can be used over 3/4" (nominal) OSB, according to James Hardie's website. If you have the extra room, another layer of 1/2" plywood or OSB cannot hurt, and will give you a much stiffer subfloor. Stiffer subfloors are good for tile.

Always glue the subfloor to the joists using a suitable construction adhesive (Liquid Nails is suitable). Use either ring-shanked nails or deck screws. Make sure the long direction of the OSB, or the face grain of plywood, runs across (perpendicular) the floor joists.

11-09-2009, 06:36 AM
Thank you, Bob. So, I can nail the nominal 3/4" down to the joist using ring shank nails and then nail 1/2" OSB to that using 1-1/4" nails? Should there be an adhesive securing the 3/4" OSB to the joist in addition to the nails?

11-09-2009, 06:52 AM
You can tell I haven't had my morning coffee yet. Didn't mean to re-ask about the subfloor adhesive.

11-09-2009, 08:10 AM

It's a good idea to add cross-blocking between the joists anywhere the new 3/4" ply/OSB edges come to rest. If you go with something like T&G Advantec, you can get away without it at the T's & G's, but like, around the edges - it's a Very Good Thing.

and do be mindful of any partition walls that may be relying on the plank flooring for support! Trying to lift a sagging partition wall and block up under it AFTER the planks are cut out is kinda a pain in the butt that you don't wanna hafta deal with!

11-09-2009, 08:18 AM
Thank you. I think we are ok, as one wall runs perpendicular to the joist and the other wall runs parallel and directly on top of another joist. The other walls are exterior and there is already blocking there.

11-09-2009, 08:27 AM
Good deal. only other caution is your doorways into the room. those can sag too... little easier to deal with however :)

the walls perpendicular to the joists are gonna wanna have that blocking added. Doesn't need to be full 2x10 - can cheat a little and drop to 2x8 or even 2x6 if it's what you got, need to clear a pipe or wire, etc. Just wanna have it hanging securely flush with the joist tops, to support the new 3/4" layer :)

11-09-2009, 08:35 AM
Thank you for your help. You guys are great!

11-09-2009, 08:42 AM
So, I can nail the nominal 3/4" down to the joist using ring shank nails and then nail 1/2" OSB to that using 1-1/4" nails? You can do all that.

I prefer screws and glue for all parts of a subflooring installation.

Liquid Nail makes a lot of different kinds of pookey. Be sure you get the right one for your application if you like that brand.

I also prefer plywood for the second layer of subflooring for tile installations. I have nothing at all against OSB but there are some thinset mortar manufacturers who don't like their product used over OSB. Is it a real problem installing substrate material rather than tile? I dunno. But I'd install plywood for the top layer if it were mine.

Here is a good article ( an effective method of installing that second layer. If you've convinced your installer that he shoulda read the Hardi installation instructions, perhaps you can encourage him to read this, too. :)

My opinion; worth price charged.

11-09-2009, 09:33 PM
Is it a real problem installing substrate material rather than tile? I dunno.
Thanks for your advice...what does that mean, though?

11-10-2009, 05:24 AM
Is it a real problem installing substrate material rather than tile? I dunno.
Thanks for your advice...what does that mean, though? It means that OSB has a lot of advocates and detractors and they will debate the merits of OSB long into the night if you'd let them. CX has apparently staked claim to both sides of the argument while stating a preference for plywood.

I'd say pick either material, so long as they meet their respective rating requirements: Exposure 1 OSB or Exterior rated plywood with face grade no less than C.

11-10-2009, 12:05 PM
Ok, here is an update...the 3/4" T&G is almost down. He used the proper adhesive and 2" (I think) screw shank nails. Seems real solid and a nice job was done.

Probably overkill, but I am going to have him put a nominal 5/8" Plytanium down over the T&G. No adhesive here, correct, but should I have him use 1-1/4" ring shank nails or 1-1/4" coated screws?

These nails/screws will not quite penetrate the bottom of the T&G, short by about .0625", is this ok?

He does not have a nail gun, it was stolen from him 2 nights ago out of his truck. Any issues with using a good old fashioned hammer if we go the nail route?

I know I am being a tad paranoid, but just want a nice floor.

11-10-2009, 01:02 PM
i would go 1 5/8" screws myself. if you gotta hammer in nails instead, i'd still opt for just a bit thru the bottom layer, as opposed to stopping short of going thru. thru is better. seeing as you already used nails, well, then nails again, one would suppose...

(2" sounds a little skimpy to hold the 3/4 down to the joists - that'd be the absolute shortest i'd wanna use)

11-10-2009, 01:34 PM
After looking closely, he used 2-1/2" screws on the T&G.

But, by using 1-5/8" wouldn't you risk hitting a joist? By my thinking, 5/8" nominal and 3/4" nominal is actually 19/32"+23/32"=1.3125" total thickness + or -

I figure I could use 1.25", 1.5", or 1-5/8" screws or nails, but what is best?

Sorry for overthinking this.

11-10-2009, 01:52 PM

You're not accounting for the unthreaded portion on the pointy end of those screws in those calculations.:)

Use 1-1/2" if you can find them or 1-5/8" and worry no more. These are deck screws, not drywall screws. If you hit a joist there will be little to no holding power in the end of those screws. It's more important to get full penetration on the screws than to come up short just on the chance you may hit a joist.:)

11-10-2009, 01:55 PM
What Dana said.

The 1 5/8ths" decking screws are a very common size, available even at your local Homer's.

My opinion; worth price charged.

11-10-2009, 02:06 PM
Thanks again. I will use 1-5/8" screws.