Beefing up the flooring before tiling.

HI all, a nice brisk frosty morning in my part of Canada. Wishing I was in in the Carolina's or Florida fishing.

My wife has mandated that I put down ceramic tile this November, and boxes of the stuff arrived a couple weeks ago. In my previous house we had a pretty good floor, and with the exception of one spot that I had to tear up and redo the rest was perfect. My brothers-in-law did most of the work. This time I want to do most of the work, and obviously I don't want to redo any of it. Not to brag but I'm pretty darn good at grouting and wet sanding as we call it up here.

My concern is around the flooring itself; in my current house the flooring seems to be a little soft, and there is one spot where I have a bit of a bump and squeak. I have no clue how thick the current sub-flooring is, but I have a furnace duct that I can pull out to measure that way. I was thinking of adding 1/4" to 1/2" of new high quality sub-flooring but I'm guessing the key to success is getting the new flooring secured to the beams under the flooring. So I guess my question is, what should I do, and how do I find those beams? Will a good quality stud finder find those floor beams? And I'm guessing I should use good ole chalk line or fancy smancy laser to ensure I put my screws (or nails) down right. I have no issue in spending the money to do the job right. For the spot where I have a bump I think I will cut a cross through it to relieve any expansion rising, and then nail/screw it again.

This discussion helps a bit.
Do I have correct materials and procedures installing tile over 3/4" plywood sub

Thanks again everyone. And if there is another discussion thread that outlines this, you can simply post the URL to it. I went back 100 days and did

 

What is your flooring?

What layers of your subflooring are soft?

Adding a new layer of sheeting on top of soft materials underneath is sure to cause problems in the future. You need to start from something solid and build from there. It may be as simple as screwing down your existing subfloor or you may need to remove a layer then install new.

 

I usually try to get at least a 1 1/4" thick subfloor. The first layer is attached to the joists, The second layer is attached to the first layer and not to the joists. This helps with expansion and contraction issues. Then you set 1/4" cement board in a troweled layer of thinset and tape all seams. Now you are ready for tile.

The above assumes your joist system is sufficient to meet minimum deflection guidelines.

 

Hi Bob_Plumb,

I'm wondering how wet sanding in incorporated in tile installations.......anyway.

I looked at the link you provided and you were given some good info, especially by HeresJohnny.

Soft subfloors do not work well in a tile installation, you gotta fix it.

Let's start with the basic info: size of the joists, (tell us their species and grade if possible) The spacing of the joists, (usually 16" oc) and the span of the joists. (ie. 11'9" or 12'3") Condition, age etc.

The floor needs to be flat, level would also be nice, but flat is more important.

Not to jump ahead.....but do not ever use 1/4" ply as an underlayment for a tile installation, 3/8" min. as required. BTW, the "joists" are not beams, and the second layer of ply is not the subfloor. The subfloor is on the joists.

Start with that for now.

Jaz

 

Not saying it would be a bad thing but I have never, ever, seen, had, or finished any floor tile work, and I've built like 15 houses, that ever had a sub floor with that thickness.

Good solid 3/4 subfloor firmly attached to sold floor joists is the min.

 

New Construction is different from remodeling older homes. Different set of rules used. So, I err on the side of overbuild so I don't have issues. Many older homes where the bathroom was a tiled floor over 1 1/2" mudbed requires you to build it back up so that the toilet flange works. 3/4"ply + 1/2" ply + 1/4" Cement Backer Board is usually a perfect fit. I try never to shoot for the bare minimums - I've seen too many failures as a result of insufficient prep on the subfloor.

 

I don't know yet, but I'm guessing there is only one layer of subflooring, and I'm guessing its soft in spots because they did a poor job of nailing it to the joists.

I don't know what you mean by "...meets minimum deflection guidelines", but I will look it up.

House is about 18 years old, the joists are 2x12, and yeah I think they are spaced about 16". Excellent condition - I have no issues with wetness, mold, etc, etc. So you are telling me the sub-floor is what actually sits on the joists, and the top layer we would call the underlayment? Around here the stuff nailed to the joists is called the flooring, and the layer on top is called the sub-floor. But I like the way you think. So using your lingo my sub-floor is 5/8" thick, and I am guessing the underlayment is 1/4" thick so if it is it sounds like I will have to lay something on that, but that sounds like asking for trouble. My house is pretty much bang on level everywhere, but I have this one spot that seems to have 'popped' up a bit. I have to determine what is going on there. In a previous house I had this issue so I cut a cross in it, and then retailed it. Worked perfectly.

Thanks for the info guys, I'll do some more reading and thinking about what you fellows said here. Feel free to chime in some more.

 

Hey Bob, didn't realize it was your thread till just now. Here is a span calculator for you, you should be fine with 2x12 joists, but always best to check. The Amazing John Bridge Forums Deflect-O-Lator :-)

5/8" subfloor is not enough for tile. If you have 1/4" on top, that does nothing for structural integrity. To be safe, remove the 1/4" and replace with another layer of 5/8" and then your 1/4" cement board in a mortar bed. Should be good to go.

 

Bob,

If the joists are 2x12" (1.5x11.25"), that's good as long as they are not overspanned. Since the house is relatively new, and in Canada, I'm sure the floor meets min. specs, but, min specs for regular flooring, not necessarily for ceramic. So, I bet the joists meet L360 deflection. L360 is also the min. for ceramic IF everything is done perfectly. I like to go a bit better than the worst it can be. So how about you answer the questions I axed you in #4?

As for the subfloor.....5/8" t&g "subfloor grade" subfloor is what I consider cheapass when at 16" oc or more. But again, it meets min specs. Yes, you need more ply, probably another 5/8". But you wanna take the 1/4" to the curb first.

Jaz

 

Sorry JazzMan I thought I had. I'll go through them again though. Been meaning to write sooner but double shifts (day and midnight) have a tendency to make a fellow tired. I'll try to respond this weekend.

I do know my joists are actually 2x10 (which means they are actually 1.5x9; never did understand this imperial system). I will try to determine how long they are.

Thanks again guys.

 

2x10 makes more sense, they're 1.5x9.25" Has nothing to do with Imperial system.

Jaz

 

Its more than just 2x10's, it is how long the span is that the 2x10's carry that is unsupported. Plug the numbers into the span calculator I provided to you and see where you fall. JAZ goes even a step further to want to know the species and grade of lumber.

 

Yes I do cuz the species and grade makes a BIG difference on how stiff they are.

ie:

Southern Pine 2x10 #2 @16" oc to meet L360 @ 40/10 live/dead loads max span =16'1"
Change above grade ONLY to #3 = 12'2"
Hem-Fir #2 = 15'2"
Douglas Fir #2 14'11"
Spruce-Pine-Fir #2 14'6"

The standard grade used for joists seems to be #2 although some species come in and many as 35 grade classifications, most come in as little as 5 grades.

Jaz

 

Sorry for the delay in responding guys. I haven't been able to find out much more because my house is completely finished so I don't know how long the joists spans are. All I know is they are 2'x10', 16oc, with 5/8" subfloor and 1/4" underlayment. My brother-in-law who has built and sold quite a few houses (without any issues) told me "you got nothing to worry about, their doing a lot more with a lot less around here". So it seems he has a lot of confidence in our code, and the way my floor is built. I still might rip up the 1/4" and put down 1/2".

I'm really out of my element here, I'm a computer networking geek, so thankfully brother-in-law is getting involved. But I did want to say thanks a bunch again guys for your guidance. I'll be back again soon enough I'm sure regarding something else.

 

Without answering jazmans questions we don’t know if the floor structure is adequate. One thing for sure though is that the quarter-inch underlayment has to go. It would be a good idea to replace it with half-inch plywood. Then quarter inch cement board or a membrane like Ditra.

 

So, we didn't do the flooring project yet, Christmas and its preparations came fast, we should have known better. So, this is back on the wife's radar now. And now that I have told various folks what you guys are saying I am hearing it all; that are floor is fine the way it is, to its not and we have got to beef it up. And now Ditra has entered the conversation, will all sorts of various opinions.

I have done a little reading and YouTubing on this Ditra stuff. They do a great job in showing how its great stuff, but not so much on addressing flooring strength integrity. Most of them do seem to be saying to put the Ditra directly on top of the subfloor. However since my subfloor is only 5/8" thick I am not sure this applies to me. So my question(s) is:

In other words; does Ditra add the necessary strength, and is a substitute for sub-flooring? Or is it really just a substitute for concrete backerboard (and other type of subflooring) that is harder to work with, with the requirement of approx 1 1/8" total wood flooring assuming 2x10 16" o.c.? See what I mean?

...and yep I know I have to do the two layers of differing mortar/thinset with the Ditra.

Thanks again guys.

 

First, need to understand there are a couple of Ditra/Prova products, the membrane material is used in showers for a completely waterproof installation, The other is the uncoupling membrane which isolates any movement in the sub floor from reaching the tile and causing cracks.

Neither is a structural component!

 

Yep, knew that, and was looking at the uncoupling type. But that still leaves me with questions. If the purpose of beefing up the flooring is to eliminate movement, and if the purpose of the uncoupling type is to isolate any movement in the subfloor, then will me laying the Ditra on top of the existing 5/8" subfloor (1/4" underlay removed) as is be fine and good to go? But there seems to be this 'standard' of 1 1/8" minimum of total wood flooring based on the typical 2x10 16" o.c. flooring.

EDIT - According to this document:
https://sccpublic.s3-external-1.amaz...20Handbook.pdf

In section/method D-W16-T-18 (on page 4) it would seem that I can get away with my 5/8" subfloor. I think I will leave the 1/4" underlay on, and add in additional screwing (spaced 4" apart) if required. The document also mentions that there should be 1/8" gaps in the flooring. If I don't have that I will have to consider my options. Maybe cut that in, using a circular saw; don't know yet, will need to research that.

Thanks again everyone.

 

If everything is done perfectly and all components are in excellent condition, ⅝" subfloor grade at 16" oc should meet minimum specs for ceramic tiles. (If your goal is to build it to the minimum specs). This of course does not include the factors of the framing members. As always the fine print says that the entire system must meet L360 deflection. So even if on print your subfloor is thick enough, if you develop grout cracks or worse, then the system does not meet L360 deflection and your floor has failed.

As for the ¼" underlayment, you've been told it belongs at the curb on rubbish day.

There is no standard of 1 ⅛" minimum subfloor thickness, that's some people's preference, and that's ok cuz the more the better.

Jaz

 

Thanks Jazman; there are lots of web sites that suggest the subfloor should be a minimum of 3/4, 1 1/18, etc. Actually, its shocking how there can be so many different opinions on how thick a floor should be for ceramic tile.

The goal is to do it right. But of course I have to work within some existing paramters; i.e height of other floors, and a kitchen already installed. So I have to make some compromises yet try to exceed minimum 'by enough'. Getting consistent information has been a struggle to say the least. I find too some web sites don't do a good job of quantifying the current situation and so you are left wondering.

And I appreciate your firm advice on tearing up the 1/4. I'll take that into consideration. Maybe I will take it up and put down 1/2" cement board, and be done with it.

 

You shouldn't be shocked at the differing opinions and long as they are better than minimum industry standards. Me, I say ¾" subfloor grade ply or OSB is a good standard for ceramic tiles installed over CBU or a membrane such as Ditra. If you have the height or want a stiffer floor, add another layer of ply over the sub, but never ¼" and never.....never luan. The minimum thickness of the second sheet should be a true ⅜ or thicker. And not just any ⅜", but a good quality made with glues that are exterior rated.

You can use ½" CBU instead of ¼" if you feel the subfloor is good enough and/or if you just want a thicker floor to match an adjacent room, but ½" is no better than ¼" for this purpose. Me, I'd got with Ditra.

Jaz

 

That's just it. Seems every author is stating a different minimum 'standard', but no one is actually quoting any sort of industry code standard. I'd love to read on 5 web sites that USA or CDN code '23eg56-da2017-p3' details flooring design.

Anyway thanks again everyone; you have been a great 'sanity' check. I'll be back again someday soon I'm sure regarding something else.

 

First, sorry for posting again, but I have learned a valuable lesson. It's seems I need to upgrade my glasses, invest in a nice little flashlight, and a few small handheld rulers (instead of using a measuring tape) with great visibility and clear markings no matter the lighting conditions. It turns out the underlayment is 3/8" not 1/4". But picking at it a bit with my fingers and a screwdriver it does seem to be a softer material, and minimally attached to the 5/8" plyboard subfloor. So as of today I am thinking I am going to rip it up and replace it with top quality plyboard that is truly 3/8". I am not planning on using any type of backerboard or Diatra. So 5/8" + 3/8" + mortar + 1/4" ceramic tile. And I will glue between the layers of plyboard.

So now I am not sure if new 3/8" is considered a part of the sub-floor or is consider underlyament. Thus my question is regarding screwing:

• Should I screwing be such that the screws go through both the 3/8" and 5/8" into the joists?
• Or should I screw the 5/8 into the joist, and then screw the 3/8" into the 5/8" but not through it into the joists?

I'd love to add on cement backerboard or Ditra membrane, but that will cause too much of a height difference with existing flooring, and other existing structures I have to work with.

Thanks again.

 

You need a bonding membrane and I recommend against trying to set tile directly on plywood, and 3/8" at that. This is why cement backer or ditra is used. They are set in a bed of mortar strictly to fill any voids in the underlayment. The cement board then acts as a great bonding agent for the tile. It also provides a cushion against the seasonal expansion and contraction that happens with wood subfloors. As I have said many times before - tile requires certain criteria be met and height of the surrounding floor is not one of those.

I would feel happier if you simply removed everything down to the joists, added back 3/4" Advantech T&G, then mortar, then 1/4" cement backer, then mortar then your tile. You will end up with the same height.

 

I've seen lots of tile jobs where backer board or membrane was not used. And with all due respect I am not tearing up half the house just to lay down the tile; I'd sooner sell the house than do that. My wife is about ready to get rid of the tiles anyway; she is irked to say the least. Frankly I think its a sore state of affairs that code allows such a minimalist floor to be built, but that is modern North Americian capitalism these days; cheap and instant gratification now followed by issues and pain later.

 

Well, all the wrong reasons to proceed with your project. These considerations should have been taken into consideration prior to starting your tile project. Then again, I have to provide a warranty with any job I install, so I never recommend or install to industry minimum standards. Jazman has been installing tile his whole life and I think he would be hard pressed to recommend tile directly on plywood. I believe he also helped set some of the industry standards that are recommended by he Tile Council of America.

Wood expands and contracts, tile and mortar doesn't to the same extent. The difference in these two causes a loss of bond between the mortar and the plywood. The practice of creating slip membranes where these two forces don't transfer to the tile is a key element in the installation of tile.

The fact that you have seen others do it does not make it a best practice. I have also seen a lot of failed installations that required tear out and redo as a result. BTW, they are among the easiest demo jobs out there.

 

I am not a flooring guy, this is only food for thought. I have seen sheet flooring where I could have swore it was ceramic tile until I inspected it further. I remodel kitchens and the difference was not obvious.
I don't know the brand name but it was about as realistic as it gets and would be naturally warmer than tile and easier to install.

 

Thanks Brian, yes we have discussed that too. We have discussed that, but the ceramic tile is already sitting in the garage. I'll get it done, and done right, it just won't be 2x or 3x army tank grade flooring.

 

Sorry I missed this. Well, I have not started the project yet. I have started my due diligence; and really the original intent was to address one spot that seemed a bit soft. Being an IT guy this is an alien world to me, but I can learn, and have learned lots already thanks to you folks. I was hoping to get a consistent answer as to what the flooring code requirements are for ceramic tile, and instead I have gotten all sorts of contradictory opinions. (You folks are not the only ones I have asked.) And my wife said she wants it done. Happy wife happy life right? You do know that woman thinks differently than a man right?

Frankly I wish I could win the lotto and be set for life. Seeing all this contradictory 'standards', opinions, and seeing general sloppiness and corner cutting done by lots of builders (all you got to do is watch TV and read the news) I have found a respect for the true professional (most if not all of you in this forum) where being a 'do it better than right' craftsman is a part of your genuine essence. I would love to have the opportunity to switch careers and build the 'perfectly made' house, with "perfectly made" meaning the sweet spot balance between well thought out and implemented building, and keeping the costs reasonable. I would love the opportunity to build my own house, and being able to win any sound mind 'challenge' from a fellow craftsman. Sorry didn't intend on sounding all corny.

Thanks again guys. Yeah I think I'm done with this discussion. ( Might be back tomorrow though....who knows. )

 

There are several types of deflection that you need to consider. One is the span of your floor joist. An over spanned section will create movement from the bounce of the joists. The second issue is deflection between the joists as a result of a sub-standard subfloor. In the past, they dealt with these by installing a thick concrete slab that floated on a bed of tar paper which both separated it from the subfloor but also was strong enough to stand on its own. Absent that thick slab, we now use cement backer board and try to recreate what once was in a different way. Thus the beefy build up of the subfloor and the slip membrane action that the cement underlayment provides. I'm sure I am over simplifying things, but the previous recommended procedures are the correct mix to make your install one that I would stand by.

 

Righto, thanks again everyone.

 

Not to resurrect an old discussion post, but I did want to give you guys a ton of thanks. Due to life getting in the way of life, we never did do the tile job until this past Feb.

Right or wrong, good or bad here is what I did:
Left the 5/8 + 3/8 in place, and screw it down to the joists.
Put down 1/4 cement backerboard, with mortar underneath, and then screwed it to the flooring, between the joists.
Then laid the tile on top of that, with mortar also backbuttered to the tile.

Time will tell, but I did want to thank you fellows for all the advice you gave me.