Why Adhesive Back Of Hardiebacker Type Boards Over Chipboard?

[sg86]

Hi all,

I've researched and researched on the best thing to do when tiling my bathroom floor. The floor is T&G chipboard, the green stuff (property about 18yr old), and is pretty sound in my opinion.

I was going to ditra matt over it but some tilers i've had over some said thats fine, some said to put down 12mm ply, another 6mm ply, another tile straight on.

I've decided to put down 6mm hardie backer, and then ditra matting. My question is why do i have to put adhesive on the underside of the boards and then screw down, instead of just screwing them down? I thought the whole point of overboarding like this was so that no wet addy would touch the chipboard, if i'm going to put adhesive on the chipboard why would i not just put the membrane straight on top?

Thanks in advance!

 

[Old Mod]

What's your final floor covering? (Tile)
If it's anything other than stone Ditra isn't necessary.
Unless of course u we're going to use the Ditra as a waterproof membrane as well.
The Hardie will act as a decoupler.
The reason for the adhesive is merely to take out any unevenness in the substrate, it's function is not to stick it down, the mechanical fixings do that job.
Given the other options ur were told, u've chosen the best one imo.
You could just use a decoupling membrane but the Hardie will also firm up the floor as well, although it's not designed for that, but it's a useful side effect.
Just remember to stagger joints and tape them after its installed.

 

[sg86]

Hey thanks for the quick reply.

I really thought the whole point was to not get the chipboard wet though? Maybe water from the adhesive won't soak into it fast enough, but i'm dubious about that.

If the floor is level and flat (i'll double check but i think its pretty much spot on), can i just screw down the hardie? I read somewhere you can just use a bit of Silicon or something on the back of the boards for the purpose of leveling any small unevenness?

 

[Old Mod]

Honestly, u've no need to worry about moisture from adhesive,
Prime the chipboard as per adhesive manufacturers recommendations, and use a rapid adhesive if ur still worried, but it'll be fine.
U don't need a massive bed, 6-8mm trowel will normally be ample, as long as u get good overall coverage.
If u choose to stray from Hardie's fitting procedure that's up to you, but that's how anyone on here who uses Hardie, will fix it!
Bagged powder adhesive only requires time to set, it's a chemical reaction, unlike tubbed adhesive.

 

[sg86]

So, in this regard if the floor is currently solid, i've no need for ditra or hardie board :S. If i'm putting the same adhesive onto the chipboard i don't see the point.

Also i've been told and read elsewhere that adhesive onto chipboard is a nono.

On a sidenote, can one use normal drywall screws for hardie? The ones they sell are 32mm and these would fly right through potentially into pipes, i need 20-25's with the 6mm board

 

[Italy]

Hey thanks for the quick reply.

I really thought the whole point was to not get the chipboard wet though? Maybe water from the adhesive won't soak into it fast enough, but i'm dubious about that.

If the floor is level and flat (i'll double check but i think its pretty much spot on), can i just screw down the hardie? I read somewhere you can just use a bit of Silicon or something on the back of the boards for the purpose of leveling any small unevenness?

@3_fall ,earns flower of sterling, just to quickly answer forum!!!
is the master of tile!!! is the n1 🙂

 

[Old Mod]

Ok, yes u need to isolate chipboard!
DO NOT TILE CHIPBOARD! 🙂
The Hardie does NOT rely on the adhesive!
Just use a good quality, self countersinking, non rusting 25mm screw!
Screw in the predetermined positions on the Hardie, and u'll have a good solid substrate as long as your original floor is secure, flat with no deflection, and sufficiently load bearing.
That's all there is to it, nothing complicated, just straight forward.

 

[sg86]

Perfect thanks 😀. I have some single-part flexible adhesive (bal), so if this stuff is ok i may as well trowel some on before the boards, i bought it a year ago and it says it has 12 months shelf life, how would i know if its "off"? lol

BAL - Single part flex GREY - Single Bags - bulk discounts available from 24.99

 

[Old Mod]

As long as it's been stored correctly it may be ok.
If it's at all lumpy in the bag, it's prob not.
When u mix it up u'll know if it's no good, it'll just be different.

 

[sg86]

As long as it's been stored correctly it may be ok.
If it's at all lumpy in the bag, it's prob not.
When u mix it up u'll know if it's no good, it'll just be different.

Hehe, that's difficult when you don't know what normal is in the first place 🙂. As you say i'll take a look and see if its lumpy. For this purpose from what i'm told its only meant to be a filler really, so may as well use it and save wasting 30quid.

Its probably not wise to admit i ripped the bathroom out over a year ago is it? 😀

Just one last thing 3_fall before i leave the thread, i asked about screws but the question got lost it seems. Can i just use drywall screws with this boarding? i want to use something shorter than the hardie 32mm ones