1/2 Hardibacker Floor?

[G. Mark Stewart]

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.

Sound good?

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 for floors.

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 ceramic tiles)

Still sound good?

TIA!

Mark

[TinMan1332]

It'll be fine on the floor.

[DLGlos]

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.

David Glos

[Java Man (Espressopithecus)]

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.

Rick

[Liam McConn]

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.

[Liam McConn]

So typical for ahr these days. 2 idiots discussing a product that neither knows anything about.

[Java Man (Espressopithecus)]

If you don't agree, why not do something constructive and tell us why? Are you afraid someone will find fault with your advice?

Rick

[Jimmy]

Liam is a lot like another guy who used to post here. Lots of advice about the posters, little advice about the OP's questions.

[Liam McConn]

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.

[Java Man (Espressopithecus)]

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 to.

Rick

[Liam McConn]

Fuck you and the other guy both big mouth. Let's hear some specific advice that will assist the op. Otherwise f*ck off and die cockroach.

[Jimmy]

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.

[user]

At least he has knowledge to impart. Quit acting like a whiney wuss and take from it what you can.

[G. Mark Stewart]

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.

Mark

[G. Mark Stewart]

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.

Mark

[Liam McConn]

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.

[DLGlos]

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.

DLGlos

[TinMan1332]

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 met.

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.

J.P.

[Bill]

From the Hardibacker site:

------------------------------------------------------------------ For all floors:

Use minimum 5/8" exterior grade plywood or 23/32" exterior grade OSB, complying with Local Building Codes and ANSI A108.11, over joists. Joists' spacing not to exceed a maximum of 16" on center.

Deflection must not exceed L/360 of the span, including live and dead design loads.

Do not use glue between grooves of tongue-and-groove subfloor to allow for expansion and contraction of subfloor."

-----------------------------------------------------------------

Now that said, The key is the L/360 deflection rule. Also, the OSB grade is important, especially with the marginal floor thickness. The thicker

1/2" backer over 1/4" plywood won't help that.

My advice? saw out the subfloor as close to the cabnets as you can and replace the 3/4" OSB (screw & glue). Shim the remaining floor with

1/2" plywood fillers (screw & glue). Use thinset under the 1/4" backer and attach with recommended screws or nails (lots of debate on attaching...).

You are then ready for tiling. Anything less...is a gamble.

-- Bill (who recently replaced a bathroom floor with 1-1/8" OSB...just to make sure)

[DLGlos]

Liam,

The original post said he had a 1/2" ply sub, which I think everyone can agree is totally sub-standard. Then the OP talked about ADDING

1/4" ply and then 1/2" Hardibacker; still likely not up to snuff.

My response was to ADD 1/2" ply, for a TOTAL ply thickness of 1", then use 1/4" Hardi. That said, he should still look at the quality of the

1/2" ply currently in place. Considering the original builder used such a inadequate subfloor, it may not even be AB or AC exterior.

Your are correct that a professional consult may be appropriate. But, if he can get the substrate up to L/360 specs there is a chance the final install will work.

DLG