I have a customer who has about 16 broken tiles all in the high traffic section of her kitchen: in front of the refrigerator, sink and pretty much all the base cabinets. After observing the structure from below as my helper walked around in the infected areas I noticed substantial deflection in the plywood subfloor: The joist are actually steel framing material with 3/4 OSB glued and screwed. Joists are appropriately sized and spaced for the span. I am thinking about installing blocking in the high traffic areas. Maybe every 12″ o.c. screwed to the joists and glued to the subfloor. Any other ideas? Will notching the blocking around the metal joist flanges still be effective? Should I drive short screw up into the subfloor alone to hold it while the glue sets up? Any ideas for stiffening this floor would be greatly appreciated. Or if you think there may be other reasons for the tile failure I’m all ears. Thanks.
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Replies
too much deflection.... i'd
too much deflection.... i'd add a layer of 1/2" plywood underlayment on top of the subfloor... yeah , i know ... hard to do...
but i don't think your blocking is going to do the trick
I don't think blocking will
I don't think blocking will do much good with metal joists.
Tile should have more than 3/4" OSB under it.
Might work out OK if he adds new joists in between every existing... break the span of the OSB in half... emphasis on might.
Also worth knowing how the tile was installed.
>>>Joists are appropriately sized and spaced for the span
You don't say what "appropriately" is, but nonetheless I'm with Mike on this one....too much deflection between joists.
Thicken the subfloor with ply, glue, and screws. If in doubt add Ditra.
Check out this site for massive amounts of info:
http://www.johnbridge.com/
I definitely agree with the additional plywood idea and that would be ideal but the customer really wants to just spot treat this. Replace only the broken tiles instead of tearing up an entire 200sq ft kitchen so I was looking for a solution from below.
So below my only option would be to add an additional joist and half the existing span of the plywood?
If you've got to solve it
If you've got to solve it from below, cut pieces of 3/4" ply to fit between the joists, glue and tack screw in place (the screws won't have enough purchase to be structural), then position blocking at intervals between the joists, tight against the plywood, especially at the joints between sections.
>>If in doubt add Ditra.
Will ditra help deflection problems?
It helps, because it creates a slip plane between the tile and the subfloor. Asking 3/4" osb to support a heavily used tile floor is asking for trouble though. I'd add a second layer of 3/4" plywood or Advantech from below.
I haven't used Ditra, but
I haven't used Ditra, but from what I've read it's not a magic bullet for a floor frame with too much deflection... mostly intended as waterproofing and protection against cracks telegraphing thru from a slab below.
They needed 1 1/4" of ply under the tile or 3/4" ply and 1/4" Ditra.
I'm doing a 450 sq ft tile job today. The floor was so wavy that we had a mud job done on top of the 1/2" subfloor to level it out and today we're thinsetting down 1/8" ditra on top of the concrete b/4 we tile.
Ditra will handle the cracking. It's a crack isolation membrane. Thats what it's for in iffy areas.