Typical kitchen floor, but only 1/2" plywood subfloor instead of
5/8". The subfloor is kind of springy, I think. I suppose the best
way would be to pull up everything and replace it with 3/4" tongue
and groove, but I'd have to remove cabinets, etc. So what I plan
on is adding 1/4" plywood for a bit of strength to the existing 1/2",
using staples and glue (liquid nails), and then adding 1/2
hardibacker. The height then matches the old floor and I think
it'd be pretty strong for ceramic tile.
Another thing is that the hardibacker half-inch stuff is labeled
for "walls", but was sold to me as being for floors. I'm told it's
the same stuff. And the website for Hardie says the hardibacker
500 is primarily used for walls, while the quarter-inch stuff is
Why? Am I making a mistake, or will I just have a level, stronger
floor? (thinset mortar on top of the half-inch HB, for 12x12
Still sound good?
On 17 Nov 2003 11:03:45 -0800, email@example.com (G. Mark Stewart) wrote:
Maybe. From what I have read, the concrete or hardibacker substrate is
NOT considered to add ANY structural integrity to the floor. As an
engineer, I'm not sure that I fully buy it, but hey, my background is
aerospace, not construction materials.
Perhaps a better solution would involve gluing and screwing 1/2" AB or
AC exterior ply to your existing sub and using 1/4" backer. Your end
buildup would be identical.
Might want to check in at John Bridge forums, or at a proper
tile/stone purveyor, for a more professional read on this. I do know
that the thinset adhesives are rated by deflection. If it feels
springy, it likely isn't ready for tile.
In the design of concrete structures concrete is assumed to have ZERO
strength in tension. Concrete is riddled with microcracks that make it
unreliable in tension. Therefore, bending stresses in concrete
structures must be carried 100% by the reinforcing medium. If the
hardibacker does not have steel (or other) reinforcement to withstand
the tension forces in bending, don't use it for flooring.
I hear you, but Liam may have had a point about my post. If the OP to
whom I was responding didn't intend the Hardibacker to span between
joists, but only to sit on a suitably stiff sub-floor, it is probably
OK. My guess is that Liam could probably be pretty helpful if he wanted
On Tue, 18 Nov 2003 22:19:46 GMT, Java Man (Espressopithecus)
Yep, he's right about the deflection issue. That's the real concern.
Point is that he doesn't have a good day unless he gets to flame
three posters in ahr. If he gets to show off his tiling knowledge
at the same time, even better for him. Too bad he can't provide
the tile knowledge without the acid remarks.
I'm a little lost here -- what else could it be? Surely no one uses the
backer board without a decent sub-floor under it, right? Like I said, if
there's some detail you need that I've left out, I'll do my best.
All I have is a first impression that he, as well, should seek out the
help of a pro.
But tantrums aside, I'm curious about a couple things. Firstly, I didn't
see anything on the Hardie website to indicate that 1/2 was weaker than
1/4. In fact, the brochure in the store stated that 1/2 was dimensioned to
replace 1/2 sheetrock, and 1/4 was dimensioned to minimize the rise of the
floor surface, no other indications.
Secondly, it seems to me that adding the 1/4" to 1/2" and gluing is less
strong than a single 3/4" layer. But that this is assuming that the glue
used is weaker (more sparsely applied) than the bond between layers of
plywood. Am I right or wrong, here?
Hey I did give useful advice (namely thicker plywood, thinner backer),
and did it in my usual self-deprecating way. For that, you called me
an idiot that had no clue. My advice was based on his original post
which indicated his floor was "springy". Obviously a highly subjective
term, but suggestive of a floor that needs a little structural help
before laying tile.
If I remember correctly ;-) maximum substrate deflection for latex
modified thinset is L/360 for tile and L/720 for natural stone.
According to their manufacturers, and the tile council literature I
have read, concrete backer board and Hardibacker are not considered to
structurally reinforce the floor. On the other hand AB and AC exterior
plywood is considered a structural improvement.
And yes, I have laid both tile and natural stone floors, and done it
right; namely, proper substrate reinforcement, backerboard selection,
and thinset use.
Java Man reared up on his hind legs and bellowed in agony:
My advice was already given. In your haste to 'impress' the other big
mouth you must have missed it. What you call 'advice' is mere chatter.
Borrowed from a book or a website and better suited to a chat group
where you don't need to be specific.
Hardibacker underlayments add density and that's what you need.
However, you give no detail as to how your floor is built. Hard to get
specific help without giving specific detail. Also, contact Hardi with
your primary question.
Your first concern should be the following.
Oh, coupla' things I forgot to mention in reference to some of the
exchanges. First, thanks for all the help and input. Secondly, in
reference to the structure of hardibacker board, I noticed one of
the sheets I rejected from the pile at Home Depot had been
damaged, apparently, but something really heavy and round. The
Hardibacker did NOT crack (it's supposed to be score-and-snap
cuttable, so this was a surprise), but deformed around the impact
with four visible layers somewhat separated and "stretched"
around the blow. Not clear what it's made of -- take it for what
it's worth. And, contrary to what one of the salemen told me, it
does seem much cleaner and stronger than wonderboard.
What else do you need? By typical floor, I mean 16" centers, 2x8 joists.
Not sure what details I left out of the fist post. The span of the 2x8s
is about 10 feet.The joists themselves are in fine condition.
First off zipperhead, we don't know what you mean. And there's no such
thing as 'typical'. Case in point; it's NOT typical to use 1/2" plywood
for subflooring. Unless you have a mobile home. Case in point; you
haven't told us if it's a mobile home. you haven't told us shit. We're
supposed to guess what you have, and what the conditons are, etc.?
You're asking for help in a usenet group that's worldwide. Okay, for
the most part nationwide, but the point is we can't see what you have.
We don't know the age of your house. We don't know the area you live in
and what may be 'typical' for that area, those builders, those
inspectors, nada. We don't know anything until you tell us.
Use the L/360. And bottom line, that subfloor you have is crap. I
recommend no less than 3/4" subfloor with 1" mortar. or at the very
least, 1" plywood subfloor with 1/4" Hardi.
Your 1/2" crap and 1/2" Hardi over it (which if you'd bother to take the
time and look at the specs on their website, actually has less strength
than the 1/4") is substandard for ceramic tile installation. Good luck.
Hire a pro.
This does pretty much sum it up and is good advice. A minumum thickness is
required. Just getting that thickness is not enough alone, the L/360 formula
is to determine the overall flex. Too thin a substrate = failure. Too much
flex = failure.
My advice (way back in the thread) was probably too brief... it's OK to use
Hardie 1/2" inststead of other 1/2" products as long as _all_ requirements are
If someone can't figure out to apply L/360 or determine flex and stability...
they should hire a reputable, professional tile setter.
Just adding a 1/4" sheet of plywood and 1/2" of some backer board to gain
minimum thickness has all the signs of a job headed for failure due to not
understanding the overall picture.
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