Tiling kitchen and underlayment support

The wife and I recently had an accident with the washing machine that flooded our kitchen. This required the vinyl to be pulled up along with the plywood underlayment exposing the subfloor, which is Engineered Wood. We felt this was a great time to upgrade to a tile floor and felt that we would be able to tackle the task ourselves. After speaking to people from Lowe's and Home Depot, they suggested that we use the 1/4" Hardibacker EZ Grid product as an underlayment to the tiles as it is lighter, easier to cut and compable in durability, water resistance and strength. We purchased it, began the install and were about half done when I ran into the guy that built my house. He said that we should have used 1/2" Durock and that we will experience problems with the Hardibacker. After this dicussion I called one other Contractor who said the same thing. Has anybody else had the same problem? Has anyone had problems with the Hardibacker in general? If I truely need to use the 1/2" Durock how do I remove the Hardibacker I just laid down? Any help would be greatly appreciated.
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Other than the thickness, what's the problem or projected problems? If you have a sturdy subfloor, and installed the Hardibacker according to directions, I don't see a problem. I just used Hardibacker on my new kitchen countertops. 1/4" was OK, I installed over 3/4" CDX plywood. Hardibacker is set in thinset AND screwed to plywood. I felt 1/4" was good, we're not walking on the countertops! BTW also installed ceramic tile over Hboard. and sealed grout.
-- Best Regards, Dennis J Sunday Home Inspection Systems Www.homeinspectionsystems.com

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The issue is how much deflection will the floor have under use. This determines if your floor will crack. If the deflection is better than 1:480 you're probably ok.
Bear in mind that for the same material properties (modulus), doubling the thickness reduces the deflection by a factor of 8. This makes 1/2" material 8x stiffer than 1/4". I don't have data but my sense is that Durock is stiffer (higher modulus) than Hardibacker.
My own preference is 1/2" Durock over the plywood underlayment.
RB
vbreck wrote:

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I was just concerned that two professionals suggested the Durock while the two retailers recommended the Hardibacker. Normally I would trust the professionals because their livlihood is at stake and if it turn bad then the retailers just say 'Oh well'. Wanted to see if anybody else went the route I did and what if any problems they had.
On deflection, I know the formula is l/360 or something similar to that but how do you measure it?
BTW. Thanks for the replies.
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Measure it with as tiny ruler.;-)
Actually the easiest way to get an idea of how much movement you have is to stretch a taught line over the floor that is secured to the wall on either side of the room (perhaps a 12 ft or greater span.) If you then hang a light weight in the center that just touches the floor and walk over the floor while someone monitors the gap between the weight and the floor you'll see if there is any movement. What you want is less than 0.03 inches (1/32") movement up and down.
If you have a laser pointer and can mount it so that it doesn't move then point it at an angle at a small mirror on the floor. Locate the laser pointer close to the mirror and reflect the spot on a wall distant from the mirror. Using simple geometry the reflection of this spot on an adjacent wall will permit you to determine the floor movement.
My preferred approach though is to calculate the floor deflection from the structure.
RB
vbreck wrote:

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I tiled my kitchen last spring...I went with the Durock as an underlayment....it is messier than the Hardibacker but I thought that it was more durable and better able to handle any water (hopefully none..ever) better than that hardibacker. as far as deflection I installed the 3/8" Durock right on top of a 3/4" t&g subfloor. Glued and screwed it down. The tile has held up perfectly...no cracks etc...I've been very happy with it.
hth Doug

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