How to fix into cob? - Prep this wall for tiling

[StephenStephen]

So I want to tile this wall which will be part of a wetroom.
The sequence I've got here is, I think:
-cob
-lime render
-cement render
cement render with pebbles
-external paint
-cement render
-plaster

It's a little hollow, a couple of small cracks, but I think is stable enough not to justify pulling everything out and starting from cob
It's pretty wonky
I'm thinking that I'll:
-fix the hole (bodged for a previous pipe) with NHL lime and Stone
-batten and fix hardiebacker

I'd like to screw the battens in in such a way that they help to tie the various layers back to the cob, but can't think how to fix screws into cob - do I drill out a core and put in lime render, or resin, or use bolts?

 

[StephenStephen]

Hi all - wondering why I'm getting no replies - Am I talking nonsense, is it in the wrong forum, or does no-one know the answer?

cheers, Stephen

 

[Keithmac]

I'm not a professional by any means but would you not be best off using shower wall panels rather than tiling?.

You need someone who's experienced working with Cob walls to chime in really.

 

[bobasd]

the plaster you mention is gypsum skim finish plaster - the wrong stuff an way to thick.
doin a wet room in a cobb building sounds wrong.
why not think about a one piece shower enclosure?

 

[StephenStephen]

the plaster you mention is gypsum skim finish plaster - the wrong stuff an way to thick.
doin a wet room in a cobb building sounds wrong.
why not think about a one piece shower enclosure?

Yes indeed, the wrong plaster, and the wrong render, all five layers over the lime are wrong.
In principle, having a cob base shouldn't make a difference to the shower design - whatever is behind the tiles needs to stop water going through it, whatever the underlying structure, though admittedly if it it fails on a cob wall the implications are potentially worse. I'm not a big fan of separate enclosures, too many joints and meetings that can leak, fail or crack, and I'd have to make the shower the size available, rather than the size I want.
Anyway, whatever I'm doing with the shower, I still want to tie these layers together without ripping the whole lot out and disturbing the cob, so I'm still looking for fixing methods between cement board, through these layers and into the cob.

 

[bobasd]

one piece shower enclosures are just that - one piece, no joints.

anything else, as suggested above, get a cobb experienced plumber or whatever trade.

 

[StephenStephen]

It's an interesting idea, and thank you, but if it is one piece, then it simply won't fit through the room door - the shower space I want is (off the top of my head) about 900mm by 1.5m - I can't see how I'd get that through the door. it's also, for various other reasons, not what I want, and would still leave me with the original question of how to fix through these layers into the cob to hold it all together.

 

[algas]

Fixing anything to cob we always pre drilled approx 2/300mm with say a 20mm drill then bought 25/30 mm broomhandles cut them approx 150mm longer than the hole sharpened the ends and hammered them in, cut left over to length to get square/ vertical edge then screw on battens and cement backer board then tile, good quality adhesive and grout, job done, if you need to fill a large hole you can buy cob blocks or celcon will do. don't use concrete blocks unless at bottom of wall where stone footing is as they are a lot different in density and can cause cracking.

 

[StephenStephen]

Fixing anything to cob we always pre drilled approx 2/300mm with say a 20mm drill then bought 25/30 mm broomhandles cut them approx 150mm longer than the hole sharpened the ends and hammered them in, cut left over to length to get square/ vertical edge then screw on battens and cement backer board then tile, good quality adhesive and grout, job done, if you need to fill a large hole you can buy cob blocks or celcon will do. don't use concrete blocks unless at bottom of wall where stone footing is as they are a lot different in density and can cause cracking.

Thank you - very much appreciated, Stephen