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I have to put some hardie backer boards down in my bathroom and my question is can i leave the existing Lino down on the floor that is laid on top of 3mm hardboard (by Lino fitter) and this is on my wooden floor or do i have to take up lino etc and just put a layer of adhesive on the wooden floor and then put backer boards on top any advice would be grateful

Take up the lino and hardboard - they are not suitable under hardibacker

Cheers Darrenba i will do but what is the reason just for an extra piece of knowledge for myself.

Darrenba,
Also after putting the boards down on the adhesive -also how thick/thin does this have to be- and then screwed down how long before i can walk on it, is it straight away or 24hrs

If I was doing it then I get all the panels cut and fitted in place dry and then use a rapid set adhesive with my normal floor trowel (12mm curved notch) then screw down. Leave for a few hours (or overnight) then tile.

Your floor would only be as strong as the fixings in the hardboard and the bond between the lino and hardboard if you laid the tiles on top. I think 6mm is recommended to lay backers into (that's what I use.) If you've bedded them properly you can probably walk on them straight away but 3 hrs to be safe

Haveagohero are you agreeing with darrenba about the time of leaving for a few hours after laying them before tiling with rapid set adhesive or normal adhesive

I have heard that the screws for the backer boards are not very good and need to be countersunk and pre-drilled before installing, can someone confirm this or tell me what type of screws they used also heard that the cutter you can buy from them is not very good but i dont have a grinder and dont want to buy one just for this job

Lift Lino/hardboard...
Cut your hardie boards to size and fix in brick pattern....cut your boards outside,..and you can use a Stanley,but you will need to score a good few times...
Lift boards and use a....single part flex with a 6mm notch lay boards onto this and use the hardie screws(they will just screw right through..the boards are marked for screws)...

No need to wait for any length off time..just tile away...

I always use an old hand saw to cut the 6mm boards

I'm only laying 2.5 boards would I still need to lay them brickwork style hardly seems worth it for 2 full boards and just about half a board

Should be ok if it's only that amount off boards mate...

Cheers tictic
My only other question is the screws that are sold with the backerboards are 30mm long but my wooden floor is 19mm board I'd 6mm which means I'm gonna have to put at least 5mm bed of adhesive or screws will go through the wooden floor and I didn't want to chance that so should I use some wood screws 25mm

if the screws will go through then use some shorter ones, you don't want to be hitting any pipes!