Hardie backer boards

[charlie1]

Having recieved conflicting fitting guidlines from hardies tech dept i decided to call them up again. There answer re fitting 6 mm boards to timber subfloor, Should be glued and screwed, but IF excessive bounce in floor then this has to be addressed first! I asked him to define excessive bounce but he could not. Can any of you guys give me the definative answer to an excesively bouncy floor because in my experience there is always movement in a timber floor!

 

[DHTiling]

Only the installer can decide is deflection is excessive, this IMO is moving floor boards or floors that deflect when waled across etc etc... some peeps do the glass of water test but experience tells you what you can and cannot tile.

 

[beanz]

I'm not convinced that the glass of water test actually works. I've yet to see a timber floor you could jump on, and not get movement in the water!?!

 

[The D]

My stance on it is if there are loos boards or if the boards are fixed with only nails. if the floor creaks when you walk on it or if you can make the water spill over the edge of a glass when you walk on the floor then there is to much bounce.

 

[charlie1]

Lets face it, all timber floors have slight movement, what im trying to get at is, this seems to be a total get out for hardie. What if a floor fails, they can just say must have been too much movement in the floor! Must admit, i like using the boards but this does concern me!

 

[Dougs Third Go]

but hardie don't claim to eradicate deflection, it's just a substrate to tile onto, so it's not their concern tbh. If there's too much deflection in a timber floor it needs sorting before you put the hardie down.

 

[Rookery]

Yes all manufacturers will find a get-out and in their eyes its usually fixer error. Trouble is, it usually is fixer error by those who dont know or dont care enough to get it right first time.
Its difficult to measure bounce. To justify me over-boarding with Hardie, I show the customer how much bounce there is by putting my pendulum laser on the floor and walking (Not jumping) around and they can see the beam bouncing up n down. Most customers can understand that a rigid tile glued down wont bend and therefore thats why they're paying the extra to get the job done right.
I think there is a calculation for measuring the deflection, its something like: joist span divided by 360 equals allowable deflection. So therefore a joist span of 450mm will have an allowable deflection of 1.25mm. Christ knows how you'd measure it though. It may not even be true, I might have imagined it. At the end of the day the fixer has to make the call.

 

[The D]

I am loosing the will to live ( You do not fit hardi to solve a bounce problem you sort the problem then fit the hardi )

 

[Andy Allen]

why would hardie need a get out clause...? they provide a decent surface to tile to, its up to the experience of the fixer to prep the floor, if you dont know whats suitable to tile to, then imo you shouldn't be doing the job, as it will be nothing but guess work...

 

[Peter]

If a floor isn't too bad to start with, I find that the Hardie will stiffen it up nicely, even though it's not meant to be for that purpose. Agree that a bad floor needs sorting first though.