Overboarding Karndean floor - Tile Advice

[burncross]

Got a job coming up.
A new kitchen has been fitted over the top of the original Karndean flooring. So it would be very difficult to remove the Karndean.
Its a timber floor (floor boards) with Plywood poss 3 or 5 mm, then the Karndean.
So I am thinking instead of trying to spend hours if not days trying to remove, simply overboarding with 6mm Hardiebacker, screwed down with 30mm screws. Then install the small format tiles using a good quality adhesive (Weber rapid set flexible).
Is this the way to go?

 

[Andy Allen]

Can you not just lift the ply.?

 

[Time's Ran Out]

Stick the hardibacker and careful not to use too long a screw!

 

[burncross]

I reckon it would be difficult to lift the ply, could be screwed down? and kitchen units and kitchen island are fitted directly on top

 

[White Room]

As Timeless recommends, glue and screw.

 

[JMC tiling]

What you glueing the Hardi down with on karndean chaps? I'd go with no-more-ply glued and screwed using there 25mm screws. That glue sticks like nothing else I know but don't get it on your hands.

 

[LM]

I reckon it would be difficult to lift the ply, could be screwed down? and kitchen units and kitchen island are fitted directly on top

Speaking with absolute confidence from experience as a time served LVT installer there is no way the underlayment is screwed down, in fact I'd wager that it's hardboard and it'll have been twist nailed or even stapled down. I would screw right through to the subfloor along with sticking down my preferred over board. The LVT won't come away from the hardboard but the hardboard coukd come away from the ply or chipboard sub base.

 

[Bill]

Speaking with absolute confidence from experience as a time served LVT installer there is no way the underlayment is screwed down, in fact I'd wager that it's hardboard and it'll have been twist nailed or even stapled down. I would screw right through to the subfloor along with sticking down my preferred over board. The LVT won't come away from the hardboard but the hardboard coukd come away from the ply or chipboard sub base.

I have Karndean in my house and the plywood substrate was definitely screwed down and then the screw heads were covered by an Ardex compo...........

 

[LM]

Your lucky you had a competent floor layer. The Ardex compound was Feather finish. For soft flooring hardboard is acceptable and not many installers would spend the money or go to the effort of having to use a saw to cut a board when you can use a knife on a much cheaper board that's quicker to install and will do the job. Never mind the time involved to screw down all the boards. Vinyl floors don't "suck" the board off the substrate the same way as tile adhesive does.

 

[peteablard]

I used 9mm ply in my house and screwed it down before fitting Karndean but normally you'll find its 6mm max and stapled as Lee said. I'd try and lift the lot as you've no idea how secure the original floor is underneath

 

[Time's Ran Out]

Screwed at 150mm centres through the Hardie , the adhesive, the vinyl, the plywood and into the floorboards - it isn't going anywhere!

 

[peteablard]

IMO You're still relying on the floor layer to have secured all floor boards before over boarding. Chances are it will be OK but I'd still rather try and get a pry bar under it in the door way to make sure

 

[Kyle Knowles]

Your lucky you had a competent floor layer. The Ardex compound was Feather finish. For soft flooring hardboard is acceptable and not many installers would spend the money or go to the effort of having to use a saw to cut a board when you can use a knife on a much cheaper board that's quicker to install and will do the job. Never mind the time involved to screw down all the boards. Vinyl floors don't "suck" the board off the substrate the same way as tile adhesive does.

I know a couple of kahndean fitters who use 3mm ply cut with a knife and nailed down and u really wouldn't wanna tile over that

 

[Dumbo]

I have Karndean in my house and the plywood substrate was definitely screwed down and then the screw heads were covered by an Ardex compo...........

When ever I do karndean on timber that is what I do . But I wear a belt to work and don't just rely on my braces.