Hardiebacker onto terracotta hollow tile wall

[adibell]

Hello,

I’ll start by saying I’m not a pro. Im a DIYer but value doing things the right way.

I’m doing our bathroom, removing all the blown plaster and cleaning up the walls before using [insert appropriate tile backer board here], tanking the joints and tiling onto these.

I was going to use Hardiebacker 6mm boards, using gripfill adhesive, plus mechanical fixings, as shown on the hardiebacker install guides for masonry. However, the two internal walls are terracotta hollow tile block walls rather than brick. SEE HERE FOR EXACTLY WHAT I MEAN, it’s the only place I’ve found info on what the heck they are: Structural Terra Cotta - Structural Clay Tile - http://historicbldgs.com/terra_cotta.htm
They are one chamber thick (see diagram on that page), though the ribbed-for-your pleasure surface runs horizontally, rather than vertically shown in that picture.

I’m concerned that unless I go purely into the mortar joints with the fixings, I won’t get a proper fix onto the walls. Hardiebacker install video states the mech. fixings must go a minimum of 50mm into the masonry. Additionally, the uneven surface of the blocks makes me think the grab adhesive won’t get anywhere near enough contact with the blocks.

Does anyone have any experience with this situation, or could offer any advice please? Battening onto the wall is not an option as the bath would no longer fit between the end walls!!

 

[Tile Fix Direct]

Hello Adibell
I cannot give recommendations for Hardibacker but an alternative would be to use Orbry long boards with dot and dab fixing (possibly with additional fixings using Orbry Spankers);
https://www.tilefixdirect.com/pdf/orbry-solid-wall-fixing-guide.pdf
The advantage would be you would be able to create a flat wall (the Hardibacker fixing would follow the contours of your solid wall), and the Orbry boards are insulated so it would reduce condensation from the cold external walls which in turn would reduce the risk of mould growth. Don't forget to install a fan in the room to remove excess moisture!
Orbry Board - https://www.tilefixdirect.com/product/Orbry-Insulated-Backer-Board

 

[Bill]

Why not remove all the plaster and render the walls in sand and cement then use a tanking system for render........ no need for boards then.

 

[Waluigi]

To give a third option and provided the Tiles don’t exceed the weight limit of 32kg PSM inc Adhesive and Grout, I’d Dot and Dab Plasterboard onto the wall. There’s no need to add mechanical fixings to plasterboard (with the exception of insulated plasterboard) so no need to worry about drilling into your hollow blocks. Wet areas would be tanked as normal.

If the walls do exceed the weight limit then I’d agree with Julian and install the Orbrey system. With a little careful planning you will easily hit the mortar joints where necessary.

 

[WetSaw]

This sort of thing is what most internal ( and some external..) walls are made of over here in Spain. Even ones with a single row of holes take fixings OK. Use decent plugs ( I use Fischer) designed for hollow walls and you'll have no problem.

 

[adibell]

Hi all,

Thank you! Great to see a really helpful community on a forum! There’s a lot of other forums I’ve been on before where things descend into trolling and lectures on just getting someone in to do it for me!

I think using the dot and dab technique is probably best with some tile backer boards. I hadn’t heard of Orbrey before but if anyone who isn’t the sole supplier of the suggested product weigh in on this please? Would Hardiebacker work in the same way; dot and dab, with fixings into the mortar? Is Orbrey actually any better?

I didn’t really want to use plasterboard, it just gives me a bad feeling in wet areas. I was planning on using Hardiebacker boards for the whole tiled area of the room (we’re also having an area of plaster on the opposite walls to the wet area), but is this really necessary? Its quite hard going on the wallet.

 

[adibell]

View attachment 103974

This sort of thing is what most internal ( and some external..) walls are made of over here in Spain. Even ones with a single row of holes take fixings OK. Use decent plugs ( I use Fischer) designed for hollow walls and you'll have no problem.

Here’s a photo of our wall. I was concerned that the walls were too thin, and they’re super brittle. I’ll have a look into the plugs you mention.

 

[Balloo]

To give a third option and provided the Tiles don’t exceed the weight limit of 32kg PSM inc Adhesive and Grout, I’d Dot and Dab Plasterboard onto the wall. There’s no need to add mechanical fixings to plasterboard (with the exception of insulated plasterboard) so no need to worry about drilling into your hollow blocks. Wet areas would be tanked as normal.

If the walls do exceed the weight limit then I’d agree with Julian and install the Orbrey system. With a little careful planning you will easily hit the mortar joints where necessary.

 

[Balloo]

I concur

 

[Boggs]

Plasterboard will be fine in wet areas, you can get 12.5mm moisture resistant plasterboard and then apply a paint on tanking liquid to make it waterproof.

Remember the Hardie boards will still need to be tanked as they are only moisture resistant and not waterproof.

 

[Waluigi]

Hi all,

I hadn’t heard of Orbrey before but if anyone who isn’t the sole supplier of the suggested product weigh in on this please? Would Hardiebacker work in the same way; dot and dab, with fixings into the mortar? Is Orbrey actually any better?

Two very different boards. Personally and completely irrelevant to the forum sponsor being on this thread, I’d still opt for Orbrey. It’s far easier to work with, to manoeuvre and to cut plus the actual board itself is waterproof so would only require tanking at the joints, screw holes and abutments. Hardiebacker is not waterproof, it requires fully tanking and despite what I have heard the reps say, it allows moisture to pass through it. Hardiebacker on a floor area is very good but on walls less so.

There are however some disadvantages with Orbrey and in fact all lightweight foam boards- they require a tighter spacing between timber studs on stud partition walls, mainly on boards 12mm. The thicker boards less so.

In terms of using Plasterboard, it’s absolutoey fine. I’ve been using it in wet areas for a very long time with either a paint on or sheet tanking membrane on top within wet areas. No need to tank in areas outside of the shower/bathing areas.

Just to add- bare plaster in a Bathroom is absolutely fine. Prime the wall with a primer or watered down paint.

 

[adibell]

Great, thanks for more replies. So with regards to using plasterboard, would I face difficulties if my tiles on their own are 20kg/m2? Why would anyone pay a fortune for tile backer boards over the MR plasterboard? Should I still use mechanical fixing with the MR plasterboards?

Additionally, because I hate the void behind plasterboard when using dot and dab, I taught myself to plaster, and use Hardwall plus skim. Would I be better just to use bonding (seeing as the clay tiles will be low suction?) and tank it, then tile onto that? For the plaster only areas, I won’t be dot-dabbing, so should I just brown the whole room? Should I also skim before tiling if that’s the case, or is the basecoat plaster ok to tile onto. I’ve gotten myself confused with so many options now!

 

[WetSaw]

Wedi board or similar foam cored boards are lighter and only need sealing on the seams and screws. Plasterboard is a lot cheaper!

 

[Waluigi]

Are you tiling the bare plaster walls? I assumed these were being painted.

I would always try to tile onto a board rather than plaster, With the exception of smaller, lighter tiles.

 

[adibell]

So I’m tiling up to a waistline all the way around the room, then full height above the shower bath, like the attached image (the bare painted plaster bit in white obviously).

So I’d have to plasterboard/tile backer board most of the room, but then I’ll do browning plaster for the bare plaster bit. I’ve looked at Fischer plugs and would be happy using these as mechanical fixings in the hollow clay bricks, now I just need to decide whether I use tile backer boards, or WR plasterboard...plasterboard is cheaper, but additionally, I lose 12.5mm+ dotdabs, which I can’t then actually fit between the ends of the bath and the end walls....the bath is 1700mm, and the opposing walls are 1720 apart!

 

[Waluigi]

The single only reason I would ever use MR plasterboard in a Bathroom is if I was using TE boards and filling the joints.

For all areas outside of the shower area I would tile directly on to bare standard plasterboard.

Keep in mind that if you do skim MR Board, you’d need to use Thistle bond it. MR board isn’t designed to be skimmed bare. It has a coating.

 

[adibell]

Using the MR plasterboard in the wet areas and tanking, would there be a difficulty tiling onto the surface of them because of the coating? Does a tanking system offer a good adhesion surface, or would I also want to use something like Gripcoat to give a mechanically grippy surface? Would I also potentially see an issue tiling onto the standard plasterboard with the weight of my tiles (20kg/m2)?

I feel like plasterboard is the best option cost-wise, I’m just concerned the bath won’t fit if I add 2x 12.5mm + the dabs at each end of the bath. But I guess I’ll find out when I strip the plaster off later today.

 

[Waluigi]

Get everything stripped out and see what you have.

The depth of a dot and dabbed plasterboard might be governed by how Plumb your wall is either side of the Bath.

As a general rule- tanking doesn’t reduce the weight you can hang off PB but each tanking products is different. You would never usually need to prep the tanking before tiling.

 

[adibell]

But would the surface coating that prevents you from skimming onto MR plasterboard also mean that your tiling adhesion isn’t great?

 

[Waluigi]

..... it’s absolutely fine to tile direct on to MR plasterboard.

 

[adibell]

Cool, fingers crossed for they fit the !

 

[adibell]

Ok so I could just about fit 2x 12.5mm if I squeeze the bath into place, but assuming dot and dabs will add a cm or two onto this, I can’t fit anything 12.5mm in place, unless I only board down to the top edge of the bath. I assume this is a terrible idea and opens up to water ingress significantly.

Would 6mm tile backer boards suffice on the walls to hold tiles, or are these a bit too flexible?

I’m getting a distinct feeling I’m going to have to take out one end wall and build a stud one instead, just for the sake of a couple of cm!

 

[Waluigi]

Lose the Bath in the wall if the rim on the Bath is big enough. Both ends if you want it even.

If you have to dot and dab one end in after the Bath is in then no problem at all. Keep in mind that you should be installing batten/CLS on the underside of the Bath to support it.

 

[Boggs]

How big is your bath?
Some 1700mm baths actually only measure at 1675mm. This might help you a bit

 

[adibell]

Hi so the bath is 1690, but the walls are 1710 apart. So realistically there’s not actually enough room for the bath plus the boards. Have decided I’ll have my first go at buildjng a stud wall as it doesn’t seem too hard, plus I can put in some recesses for shower gels etc anyway. Will simplify the process, I can use MR plasterboard and tank it, plus I won’t have to plaster the hallway wall on the reverse side, which is a bonus.

Any recommendations for tanking systems?

 

[Waluigi]

Only if you say thanks

 

[Boggs]

Tilemaster.

 

[adibell]

Of course sorry! Thank you all for the advice, it’s been really helpful! I’ve took the wall out now, so will be removing the rest of the plaster tomorrow, building the new wall and getting the plasterboard on hopefully!

Thanks again!

 

[Waluigi]

Might be the best way forward. At least you can decide exactly where your new wall is.

 

[Raccus]

provided the Tiles don’t exceed the weight limit of 32kg PSM inc Adhesive and Grout, I’d Dot and Dab Plasterboard onto the wall. There’s no need to add mechanical fixings to plasterboard

A query about your comment..... the thought i have, is if normal plaster finish walls can only hold about 20kg psm, how can a dot and dabbed only boards hold more? For arguments sake, say the dot dabs made contact with 20% of the area of the boards, that implies that the dot/dab adhesive is over 5 times stronger than plaster, as its covering only a fifth of the area but holding more weight. Is my logic correct?