Best 6mm backing options

[Slippery]

I priced for a bathroom install in a timber house (timber cladded, timber frame, softboard/hardboard internal walls)
The customer rang me and asked if I could match another price (£1930) as my price was higher (£2135) as I had done work for him before and was happy with me.
The bathroom has tiles already and I imagine that it would be easier to remove the backing (mdf or ply) and re-line it. In Hardy backer it would be £135, the other guy said he would use 6mm MDF, this accounts for most of the saving already!
There will be a freestanding bath close to one wall, I said I wouldn't chance using MDF as if it started popping behind the bath it would mean taking out the washbasin, bath and possibly even the toilet to get access to repair.
If I use Hardy backer behing the bath where it could get wet, would MDF or ply be ok in the drier areas?
I'm also considering contract board but I would maybe have to battern out the walls to fit them.
The tiles are Metros and I think he has bought ready mixed addy already.
Whats the best option?

 

[Qwerty]

Walk away

 

[Qwerty]

@Slippery .... walking away really is your best option with this job. If the customer is set on penny pinching as they clearly are, then not only will the work fail using those materials buy you will hate working there and ultimately live to regret it.

 

[Andy Allen]

No one in there right mind would suggest tiling onto mdf...

 

[One Day]

Your immediate response should have been:
"The reason you want me to do the job rather than the cheaper guy? - That's the reason for the £205 difference"

I would now lose all interest...

 

[Slippery]

Ok, cheers, but what would you use?

 

[Qwerty]

Either plasterboard (tanked where required), or 10/12mm backerboard depending on stud spacing (wedi, marmox, jackoboard, schluter etc)

 

[One Day]

Ok, cheers, but what would you use?

I'd never use mdf or wood in a bathroom, or anywhere else for tiles for that matter. Plasterboard, tanked if necessary would be a budget option, or Kerdiboard if the budget allows.
My way - or no way. Stick to your guns on prep, after all - it's your reputation at stake for the next several years after you complete the job.

 

[Dumbo]

Could let the other guy do it then do properly when it fails , and it will .

 

[Flintstone]

Mdf are you joking!

 

[Slippery]

Mdf are you joking!

Thats what I said, then I said this

I'd never use mdf or wood in a bathroom ob.

, verbatim!

 

[Slippery]

I think I will go the plasterboard route, I already have a tub of mapei tanking fluid left over from my wetroom repair.

Thanks for the answers

 

[LM]

Make sure you use powdered adhesive on top of the tanking, do not use tubbed addy.