Replies

1. 
   gary_ | Aug 20, 1999 08:17am | #2

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   please don't use plywood it stinks it's to flexible especially in the laundryroom try using backerboards there great easy to use and last for ever.

2. 
   Guest_ | Aug 20, 1999 07:44pm | #3

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   Backer board will only be as stiff as the floor underrneath.

1. 
   Guest_ | Aug 21, 1999 03:28am | #4

   *Cross bridging will help each joist share a bit of its load with its neighbors, but it won't do anything for flexing of the sub-floor between the joists.Adding the extra joists would probably do the most good to prevent sub-floor flex. On top of that, going to 3/4 plywood, installed with plenty of screws, should give you a pretty stiff floor. Don't count on the backerboard for any resistance to flexing. It will mainly isolate the tiles from lateral expansion and contraction of the sub-floor with changes in humidity. If height build-up is a big constraint, go for thinner backerboard and thicker plywood. If you could live with the height, two layers of plywood glued together would give you a remarkably stiff floor under the backerboard. Add the extra joists and you could invite the whole neighborhood in for a foot-stmpin' square dance.

1. 
   Guest_ | Aug 21, 1999 08:26am | #6

   *D, go with the ply underlay and add the joists, as suggested,yes there is a thinset for ply it's called flex-i-bond, can't think of the maker right now, but you should be able to find, one thing DON"T use an additive with the flex-i-bond , it's already there, Good Luck! Geoff

3. 
   Guest_ | Aug 21, 1999 08:26am | #5

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   Retrofitting ceramic tile in a 5x5 laundry room. After pulling up vinyl tile and underlayment I find that sub floor is only 1/2 ply. MIGHT be able to add 1/4 underlayment on top of that and match level of adjoining floor. Lowering joists is not an option. I have access below from crawl space.

   QUESTIONS: Will cross bridging between joists below be sufficient to stop flex or should I also put a layer of 3/4 ply under there?

   Are there modified thinsets that have some degre of flex to them?

   TIA

1. 
   Guest_ | Aug 12, 1999 11:12pm | #1

   *If you have access to the subfloor below, consider adding joists to cut the spacing in half. ie from 16 to 8 inch centers etc. This will reduce the load on each joist by half and cut the plywood span to half. 1/2" plywood spaning 8" should be fine. How are the plywood edges handled. I have never seen 1/2" t&g, so are they blocked. If the plywood is not t&g the edges will need to be blocked.