I just fininshed sistering 2X10 joists (16 oc) under a remodeled 6X9 bathroom that will be finished with ceramic 12 inch tiles. Becuase the 5/8 ply subfloor was out of level, I ended up using 3 bags of leveling compound and now have a 1/2 inch thick base (tapers to less than 1/8 at the center parallel with joists). I was considering applying 1/4 inch hardiback above the concrete levelor, but this now seems overkill. Do you think I really need to put down the hardi or not before going ahead with the tiles? My concern is that I am adding more and more weight. And with a clawfoot going in, that will add up.
THanks
Replies
I wouldn't think the 5/8's subfloor is enough. You won't get any structural help from the cement board.
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What is the span of the new joists?
"Put your creed in your deed." Emerson
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FastEddie
The span is about 14 feet, although I sistered 16 footers to the original 14 footers so I have about 2 feet of overlap above the beam. The 2 feet of overlap sisters to the 14's on the othere side of beam.
Thanks
2x10 @16" spanning 14' gives a deflection of L/462. Minimum for ceramic tile is L/360 so your joists are fine. The ply is a little thin, and the leveling compound does not add any appreciable strength. The hardie backer does not add any strength either, all it does is provide a good bonding surface for the thinset. I would forego the hardie and add a layer of ditra instead."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
I vote for the 1/4" hardibacker over the leveling compound before adding the 12" tiles. Those tiles can handle a little give in the floor better than they can handle the levelling compound cracking due to the flimsey 5/8 plywood subfloor. The Hardibacker will keep the leveling compound from coming back to haunt you in my opinion and not really add that much more weight.
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"You cannot work hard enough to make up for a sloppy estimate."
Everyone will probably yell at me, but I say size up the Hardibacker to 1/2 inch.
I'm one of those "by the book" guys, and all my tile books say that a long lasting subfloor should be a minimum of one and one eighth of an inch in thickness.
So if you add everything up that you plan on using, it's not thick enough to me;
5/8 plywood subfloor + 1/8 (at it's thinnest) of leveling compound + 1/4 inch Hardibacker = 1 inch....... not enough.
............alright guys......... fire away (hiding behind chair)
Mike
I'm with you mike. If something happens it's much easier to say it was done to a published standard than not, especially in this day and age where clients can look online for standards.
Beer was created so carpenters wouldn't rule the world.
dang Mike, after that post you deserve what you got coming to you! Roar!
every court needs a jester
In my area , the rule of thumb is 1" of wood under your tile. I would have been inclined to put down 3/8" spruce ply before the leveler. Cementboard products would also do the trick here. Other methods wood inlcude using metal lathe with thinset, then level. There are also a number of fabricated tile bases available.
Sistering 2 x 10's underneath will certainly help alot, but what it comes down to is how much deflection there is in the floor, and only you can tell that. The more deflection in the floor, the greater the chance of the tiles "popping". My gut is telling me that with what you have done so far you will probably be fine.
Dave
Since the deflection of the joists are within specs, you should be concerned about the deflecton of the subfloor between the joists.
A couple of solutions:
1 - Install an additional floor joist between each of the existing joists.
2 - Install a layer of plywood to the bottom of the subfloor, glued and screwed.
Since you are putting in a clawfoot tub, plus the added weight of a tub filled with water, I would be especially concerned about the point loads of the tub. Solid blocking substantially supported in those four locations would seem to be a must.
Bryan
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Klakamp Construction, Findlay, Ohio
In my area if it's in the TCNA Manual it's OK - if it's not, it's NOT OK.
Jeff