I’m getting ready to install ceramic tile in a remodel over inconsistent thickness subfloor planks with pretty wide gaps between boards. Planning on laying healthy layer of mortar on subfloor then 1/2″ Hardibacker screwed down. Question: Can I put some 6mil poly on subfloor to prevent mortar from squeezing through and falling into basement? Cleanup isn’t quite as much an issue as losing all the mortar and gap-filling benefit.
Thanks for all advice in advance.
Bob
Add a strap for easy carrying and pouring when working with 5-gal. buckets.
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Replies
If this is not a full mud bed, you need to put down at least 3/4 inch plywood first, perhaps more. Some would say 3/4" plus 3/8" before the backerboard. How big are the joists, spacing, and span? You need to get at least L/360 for tile, L/720 for stone.
If the subfloor is really uneven then you may be better off pulling it up and working off the joists.
You can calculate your floor deflection here:
http://johnbridge.com/vbulletin/deflecto.pl
Billy
Edited 5/13/2004 11:53 am ET by Billy
Edited 5/13/2004 11:53 am ET by Billy
Billy,
Thanks for the cool defelction calculator link, it confirmed what I thought already: deflection isn't the concern. This floor feels rock steady, and the calculator indicated L/897. Also, the subfloor isn't skimpy, just a little uneven from board to board, but averages about 7/8" thick and good condition. Thanks all for the input.
Bob
If that's your deflection, a mud bed is not needed. Instead thinset ( 1/4" x 3/8" trowel) and screw (every 6" - 8") CBU's down. The thinset will adhere the CBU's while filling the voids. I don't think there will be enough thinset to create a problem with the gaps......... depending on gap size and how you trowel.
F.
What Andy Said..............
Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Listen to Boris. Andy's way is best, Jon's is second best but just fine.
A mud bed does NOT take care of inadequate deflection, but it's not an issue in your case.
Never, never install CBU without full support underneath, so DO NOT thinset CBU directly to your subfloor slats. CBU has no structural value and it will crack over the openings between the slats.
Billy
Edited 5/13/2004 2:58 pm ET by Billy
ReBob,
If it were me, and the thickness of the floor were an issue, I'd rip up the old subfloor, level the joists (a few ways to do that), lay down new 3/4" plywood, then thinset, CBU. thinset, tile etc.
Not what you wanted to hear probably.
If thickness is not an issue, you can level the floor, and lay down a new 3/4" ply subfloor over that......
IMO, do it right. It IS easier.
Jon
Do a mud job.
the mud should be mixed approx 5:1 and mix with the liquid pretty dry.
In which case I dont see a problem in floor cracks unless they're reallyyyyy large.
Also before you mud you will be laying down 30# felt and wire lathe.
I dont see how any mud would get through that.
Be well
andy
My life is my passion!
http://CLIFFORDRENOVATIONS.COM
If your floor is otherwise stiff enough you can level it with a pourable leveling compound, such as from Tec. It can be placed feather-thin and is self leveling. You apply it as a liquid, so it will find every little crack if the floor is not sealed. It would be used instead of backer board.
"Listen to Boris. Andy's way is best, Jon's is second best but just fine. "
ReBob,
Andy and Boris are the Pro's here when it comes to stuff like that, not me.......
Jon