I need some advice on how to best prepare our subfloor for ceramic tile. We are remodeling kitchen- complete redo. We ripped out the worn out oak hard wood flooring in the kitchen (it was beyond repair). After removing oak strips, we got a good look at subfloor. It is made up of various width, 3/4″ thick planks nailed (not ring shank) to the floor joists (which are timber 3×8’s). The planks run perpendicular to the joists and are spaced about 1/2″ apart. The joists are spaced 24″ o.c. and the span is 14′.
In some spots, the planks have some give to them when you walk on them- slight bowing in between joists and there is some squeaking due to loose nails. The planks are not rotten although a few are split or cracked. In general they “look” in pretty good shape. The floor is not quite level, but it
My plan was to tighten up the planks to the joists by hammering all the nails firmly down and adding some wood screws to help keep the planks tight and quiet. Then I would go over the planks with 3/4″ t&g plywood pts, using constr. adhesive and wood screws to hold in place.
My questions: Do you think that the planks really offer any benefit to the situation; ie extra support for the plywood? Do they significantly increase the risk of a noisy subfloor? Also, if I do go over the planks with the plywood, is there a better direction to lay them down- parrallel or perpendicular to planks?
Any help would be appreciated.
Replies
The planks do provide a very significant benefit especially with the added screws. A single layer of 3/4" plywood would be marginal with the 24" oc joists. It will be fine with the planks underneath. I would run the plywood in the same direction as the planks, perpendicular to the joists. If the plywood is not t&g, the joint should break on a plank.
Sawzall around the edges of the planks, then rip them out. They arn't helping anything and they will make your bathroom floor finish out too high. Use at least 3/4 t&g glued and screwed. Last add a layer of durrock.
I missed that little bit about 24" oc. If possable I'd add more joists, if not, leave the planks in.
First I would use new ring shanks to secure the existing sub-floor planking to the existing joist. 2--8d nails per joist. 3 x 8 are probably sufficient to carry the span of 14 feet @ 24" centers. Unless there is some obvious defects in the original sub-floor, the boards are strong enough to span, especially if you fiqure they are spanning only 21". However your deflection between joists is a bit much as you noted. I would use 1/2" cdx nailed over the original subfloor using 6d ring shank. I would use rosin paper between the two subfloors instead of any construction adhesive. Run your plywood the same as the original sub-floor and joints on joists.
For the tile, you will want to secure your tile backer to the sub-floor. I like using DURAROCK (1/2") with a thinset bed and screwed down. Any reasonable leveling you need to do can be done with the mud and with the tile mud.
I would think, though, you could delete the plywood step and go right to the DUROROCK. End the sheets on the joists. Instead of rosin paper, use mason lath with your thinset to stiffen the floor. Also be sure to screw into the sub floor between the joists.
I say I think, because of the uncertainty on my part of exactly what deflection you are experiencing. It would be worthwhile to try one or two sheets of DURAROCK in the worst place of deflection and see what it looks like. Do a dry fit first, just screw it down.
If the additional floor heigth is not a problem, then the plywood would be the sure bet, although maybe unnecessary. If it is a problem, then try the DURAROCK, this should give you about 1" finished heigth. If more support is needed, then your recourse may be to pull all the sub-floor or add som additional joists.
david