k...@attt.bizz;3055713 Wrote:
>
> Don't even need wonderboard. Plywood or even OSB (cheaper) is good
> enough.
I understand and agree. It's just that as soon as you start telling
someone to practice tiling on cheap wood paneling (or whatever), then
you also have to explain that while using wood is fine for practice,
it's never a good idea to tile directly over wood in your home
renovations. Wood swells and shrinks with changes in it's moisture
content, and ceramic tiling just doesn't have the elasticity to
accomodate that movement. The result is cracks in grout joints and
tiles popping lose as a result of the wood substrate swelling and
shrinking moving more than the ceramic tiling can accomodate.
(Plywood swells and shrinks less than lumber because the swelling and
shrinkage in the direction of the grain is very small, and so the
alternating direction of the plys help to constrain expansion and
contraction in plywood. Still, it's never a good idea to tile directly
over any wood, including plywood.)
PS: Most experienced tilers already know the rest.
That's the entire reason for using a tile backer board like Wonderboard
between wood (like plywood) and the tiling. The Wonderboard is
dimensionally stable. Like all ceramic materials, it's got very low
thermal expansion or contraction and it doesn't swell or shrink with
changes in it's moisture content or the amount of humidity in the
surrounding air. While the wood the Wonderboard is screwed to may be
wanting to swell or shrink, as long as the Wonderboard itself isn't
swelling or shrinking, then the tiling stuck to it doesn't have an
excuse to crack.
The effect is similar to standing on the fault line the day before the
quake. There can be tremendous stress in the bedrock a mile under your
feet (in the plane between the plywood and the Wonderboard), but as long
as the ground you're standing on is stable and motionless, you're
completely unaware of any such stresses, so you have no reason to
crack.
And, that's also why you can tile over ceramic tiling. If you already
have a dimensionally stable substrate, like a concrete slab or old
ceramic tiling, you don't need to install a tile backer over it. You
can just go ahead and tile over any dimensionally stable substrate
(provided it's strong enough that flexing of the substrate isn't going
to be an issue either).
--
nestork