Hardiebacker 500 12mm\6mm No More Ply questions

[jond500]

Hi All,

Firstly this is a DIY question, not a for reward question. I'm re-fitting my bathroom but like to do things right

I have already finished the electrics and boarded the head of the bath where the shower and screen will mount with Hardibacker 500 and fixed at 150 mm intervals with 45mm Stainless screws and countersunk etc. The problem I have is the wall along the back of the bath (1700mm) is way out of true due to years of moisture ingress and bowed and will be trued but have just left it open to fully dry out for the last few weeks.

Now for problem 1, originally I was going to dot\dab moisture proof 12mm plasterboard onto the far wall which will only get occasionally splashed but have now bought more Hardibacker 500 after reading threads on here. I'm not a tiler by any stretch of the imagination but am aware if the prep is rubbish the end result will be also.

The wall is question is concrete airiated blocks which are soft as anything and that's what I have to attach the Hardibacker to. I have Dri-Wall adhesive and also stainless screws but am looking for your advice on how you would fix it. In an ideal world I would batten the wall but really don't have the space to do so so need to fix it somehow. I'm thinking of using either the Dri-Wall adhesive or Pink Grip in conjunction with long window type fixings and using a gauging rod or the hardibacker itself to mark the wall and level it then leave to go off... your input would be really appreciated. Do I PVA the wall before or seal it with something else?

Problem 2 is simpler, I have bonded 6mm no more ply to the floor which has 18mm waterproof chipboard underneath, I sanded off all the high spots, vacumed, brushed and made sure ir was spotless before bonding the floor. I have a tiny bit of movement in a 3-4" area where 2 boards meet, I'm just thinking of putting some more screws in to make it solid. The floor will have UFH, then SLC applied before tiling. I have the Porc tiles and a cement based flexible adhesive as supplied by Topps.

The Hardibacker will be sealed with a Mapei waterproofing along the joins and corners, does it need priming before tilling?

Sorry for all the questions but appreciate the help.

Cheers,

Jon.

 

[DHTiling]

I got as far as already done the electrics..:yikes:.. you did that..?

- - - Updated - - -

 

[jond500]

I got as far as already done the electrics..:yikes:.. you did that..?

- - - Updated - - -

Fair enough response, forgot to mention that I qualified as an electrical engineer 20 years ago so competent and all work I have done has been passed, tested and certified by an electrician to 17th Edition.

 

[DHTiling]

Phew!!!!!!!!!!!

 

[Ollie02948]

Hi Jon. Why don't you just use plasterboard along the bath? Or is weight an issue. Hardbacker is a better substrate to tile to but if you can't frame it then plasterboard might be the easier option if you dot and dab it and then tank it all. You don't have to prime hardbacker just make sure it's dust free. The issue with the floor should really of been sorted before you installed no more ply. Am I right in thinking you have used the mega strength adhesive as well? Screws may work by pulling it down tight but if you have got movement in the original floor it will always be there unless rectified.

 

[jond500]

Hi Jon. Why don't you just use plasterboard along the bath? Or is weight an issue. Hardbacker is a better substrate to tile to but if you can't frame it then plasterboard might be the easier option if you dot and dab it and then tank it all. You don't have to prime hardbacker just make sure it's dust free. The issue with the floor should really of been sorted before you installed no more ply. Am I right in thinking you have used the mega strength adhesive as well? Screws may work by pulling it down tight but if you have got movement in the original floor it will always be there unless rectified.

Thanks Ollie for your response, I will try to answer your questions below:

I am using Hardibacker as opposed to plasterboard due to the fact it's fully waterproof, all the issues left from the previous installation cost me money (before I lived here) due to moisture ingress and latterly as I have found bowed timbers etc and rotten plasterboard hence why I have ripped it all out . It will be used as a shower a few times a day and the HB areas will get wet or just get splashed, the back wall is a stud wall hence the HB and not dot\dab.

The floor was solid before fixing, yes, I used the mega strength adhesive and wiped the back of the NMP as advised with water before fixing it, the movement is only about 1-1.5mm in a very small area so will just put some more screws in. Personally I found their self drilling, self countersinking screws lacking.

Cheers,

Jon.

 

[Rookery]

Just to clarify, Hardiebacker is moisture resistant not waterproof. Good stuff though.

 

[Ollie02948]

Surely though the reason why it had moisture ingress was because the materials weren't installed correctly in the first place. Hardbacker is a great product I just can't see a easy way of you being able to install it without building a frame. Plasterboard tanked correctly would be fine depending on tile weight etc. when you screw down the no more ply just make sure it is fine as once the ufh is installed and slc on top yo don't want any problems as that will be costly

 

[jond500]

Cheers Rookery for the clarification,

The original installation is from when the house was built ~20 years ago and only became apparent once I had started the strip out.

The head of the bath and the back wall are stud walls so I have plenty to fix the HB to and the outside wall is where the blockwork is so will use moisture resistant plasterboard if I can't fix HB to that wall without framing.

I added a few more screws to the floor and it's now completely solid in the area that was moving.

Cheers,

Jon.

 

[andy8758]

Hi JondD - A little alarm bell sounded about the "bowed out wall" due to Moisture Ingress. If the top layer of plaster is insecure - remove it. It wont take long, creates a lot of mess, but the sub strata will make a better surface to fix Hardibacker. As someone else said - Hardibacker is not waterproof, it is very strong and water resistant but if you have a shower over the bath - paint some tanking solution on the Hardibacker. I think your problem 2 has already been well answered above. Good luck with your project and let us see some pics. I suspect you will make make an outstanding finish with the attention to detail that you have expressed here already. Regards Andy.

 

[jond500]

Hi All,

Many thanks for all the advice, this project is still going but for several reasons has taken much longer than I would have liked.

The back wall was sorted by laminating new joists to the existing ones which corrected the run out. I then fixed Hardibacker to them and then tanked with the Mapei Shower Kit ready to tile.

The floor is completely solid now with no bounce due to the addition of more screws

Cheers,

Jon.