AboutChris Expertise 20+ years flooring installation ...carpet,wood,tile and vinyl. Residential and commercial. I do not sell the products , just install what ever the shop / customer has purchased. I actually love seeing the finished project completed and it gives me great satisfaction to help others acheive that goal. If I don't know the answer I will say so, and then I will recommend another expert for you. I may even research the subject and answer to the best of my ability ...including links to my sources.
I wish you all success
Chris
Experience 20 years as an independant contractor
Education/Credentials H.S. diploma
A.S. agriculture Mt San Antonio JR. College
Past/Present Clients Gene Bonas and Kevin Churnock Inc.
Sheward&Son&Sons
Century 21
Forte Const.
Famous Footwear
BOSE Corporation
Homebodies General Contractor
Perry Floors, Tri Cord Flooring
T.J.'S Supplies
I asked a while ago about refinishing hardwood which had been badly damaged by an improper install of tile over it. My wife has decided she wants tile in place of the hardwood and I am getting the stuff together to do the job.
I ran into a question, though, because I have only ever put tile down over concrete and this will be over a wooden subfloor. I want to make sure I get a strong enough and flat enough floor to allow for the tile to work.
Could you take a quick look at what my plan is for the floor and let me know if you think it would be enough...?
Top layer - 12" square porcelain tile
1/4" Hardibacker (set in thinset)
1/2" CDX ply (added new)
1/2" CDX ply
The area is about 9 feet deep by around 10 feet wide. The joists below are 2x8's which were 16" on center. As part of the floor leveling and strengthening, they will be sistered with equivalent 2x8 stock making them about 14.5" OC.
Could you just tell me if this sounds like a decent floor to put the tile down on?
I hope I've provided enough detail, but if not, please let me know.
Thanks again!
Mark
ANSWER: Hello Mark,
Welcome back. that truly sounds good. More than adequate !
When you mention the 2 layers of 1/2" ply, why two? And what is your reasoning to add sister joists. Is the floor really going to be leveled by adding that extra lumber? Let me steer you to a deflection calculator that I use for tile...to determine if the underlying floor is strong enough.
This handy calculator will take into consideration the joists ... the length and span and type of material ... so far it doesn't look like it considers double plywood.
Even without the joist sistering your floor is strong enough for ceramic tile.
Chris
---------- FOLLOW-UP ----------
QUESTION: Hi Chris,
Wow... That calculator is a lot easier than doing the math on paper (which is what I was doing before) to figure the deflection.
I wanted to follow up quickly on your questions. 2 layers of ply at 1/2" gives me a solid inch of flooring plus 1/4" hardibacker totals at 1.25" combined floor strength. I've heard that I should have at minimum 1.25" for tile - is that not true?
I was going to sister them to make SURE they can handle the load of the tile without exceeding the L/360 calculation. In addition, the floor is not perfectly flat so I was hoping to fix some of that while sistering them up. Also, it isn't perfectly flat, so I am concerned that I may have to use floor leveling compound (SLC) to fill in some low spots.
If I were just going to put SLC in some low spots (not a full pour), over which layer should it go? The stuff I looked at is rated for OSB, plywood, cementious backer and lots of other material.
Thanks again for your help! I really appreciate it.
-Mark
ANSWER: Hello again Mark,
I never have a problem with an over engineered floor...I just thought that you might want to save a little in these lean times.I would feel comfortable with the layers of plywood and required prep.
But don't allow me to change your mind , that's not my intention. I am not telling you one way or another what to do ... just allowing you to see the calculations. It's a quick and handy way to be sure you are within spec.
The SLC or even manually troweled products are done last. Once again , allow me to interject some thoughts, based on the next answer I may receive from you.
How much deviation is there..and here is what I would do to save on material. For tile ..SLC is overkill. If I were to finish all the sub layers and find my floor running out 1/2" in 10 feet or so, I would mix a batch of thin set mortar and screed the product into the low areas and allow that to dry overnight. Making sure it is actually a bit low ever so slightly so as not to cause an issue the next day. There are at least 2 ways to do this. Trowel with tooth side and allow to firm up (4 hrs) and back fill all the grooves. let set over night. Or use an 8 foot Metal framing stud to screed with..about 5.00 at Lowes / Home depot ...this method may be short cut with the aide of a 6/4 ft level acting as a straight edge only
The next day as you tile this area you can spread the thinset and back butter the tile to achieve flat / non lipping installation ...level is a good goal ...but smooth and flat is most desirable and easily attained. I actually try to leave the word level out of my vocabulary when speaking of flooring. Flat is the key word I use.
Manually applying thin set or trowelable fast set products will save you the expense of SLC and all the difficult instructions they contain.
I can give you 3 or 4 other types of manually applied , suitable compounds if you like and you could call around for availability.
Here is a video in YOU tube in the area of floor prep to demonstrate some screeding techniques with manually applied products ... they are much more cost efficient...the same principles would apply with thinset mortars and speed set mortars,
Thanks again for the quick and informational response. So here's the deal...
The floor isn't very far out of "level" going from one edge to the other. The joists have sagged a bit though and created a low spot in the center. If I put a long straightedge across the floor, it looks like the deepest low spot is about 1/2" out of flat.
As far as level goes, I don't think it is far enough out to worry about - just the low spot in the center could be an issue.
Since I am sistering the joists from the unfinished basement below, I will be using lally columns and a stretch of 2x6's to press upwards. After the sisters are in place, I'll take out the lallys and 2x6's. Anyway, I think that'll help with the flatness quite a bit, but it still won't be perfect.
I am really glad to hear that there are some alternatives to SLC because of the expense of the stuff. If you don't mind, please let me know the names or types and I'll go searching around here (Pennsylvania).
For these alternatives, would you trowel/screed it over the backerboard and below the tile in the bed between the subfloor and the backerboard?
You mentioned earlier that you though 2 layers of ply at 1/2" is more than enough - do you think I could/should drop down to 1/2" plus a 3/8" layer?
Like I said I've never put tile over a wood floor before, so I am not sure on how much floor has to be there to make sure things work out.
BTW, I don't think allexperts will allow another post to this question, but if I have to, I'll just ask another. :-)
Thanks again!
Mark
Answer Mark,
As the wood floor is not suitable due to the nature and the size of each plank I think a layer of 3/4 ply and 1/4 cement board will be perfect along with the added support from the underside of the unfinished basement.
The products I will list here:
Durabond ...now owned by Bostick
Webcrete95...and see the additional products here too.
Mapei: a bit harder to navigate ..from the home page clik tile and stone ...then search for the preparation products ...or better yet call the contact # ..ask for technical service and proper product for your application.
Personal preferences from my experience and product availability..
C-Cure , Durabond , Mapei and Laticrete.
I use them all, just depends on what is available and where. They all do the same thing basically...price is a factor too.
I would always screed to / on top of the cement board ... allowing for a best scenario bond ... cement board ...cement products... tile and cement again ... Wood and cement are the weak link. Not to say you need to fear the cement board , that's why they use screws....
