Best subfloor for bathrooms

Gavin83

Hi all. We recently bought a project house and we’re now turning our gaze towards the bathrooms. From what I can tell having lifted up a bit the subfloor throughout is currently 18mm chipboard. I’m considering increasing/replacing this up to 25mm to provide a really solid subfloor.

However I’m wondering what to do in the bathrooms. At the moment we’ve got carpet (yes it’s gross!) but I’m intending on tiling. Ideally I’d want it the same height as the rest of the floor. Would I be best off going with 18mm plywood + 6mm backer board, thinner plywood + thicker backer board or using something like nomoreply?

Making the subfloor as solid as possible to prevent any movement is the priority, plus it obviously needs to be waterproof!

andyhop

For the last 15 plus years , I’ve stripped out every bathroom we do , back to brick and joists and every time replaced the floor with 25mm marine plywood . Impact gunned with 80mm screws and all
edges fully supported 

We’ve never had any movement , cracked tiles/g rout or any split silicone on the perimeter joint 

Prime back and edges and you can tile straight to it . No large step etc 

Always a good solid base to build everything off . Hardibacker is OK but you often just over boarding a problem substrate . Wedi or Jackoboards - cement topped foam boards compress under traffic, ripped out many a wet floor with there trays 

grumbler

andyhop said:

For the last 15 plus years , I’ve stripped out every bathroom we do , back to brick and joists and every time replaced the floor with 25mm marine plywood .

Personally, I wouldn't tile plywood directly. That's what hardibacker exists for, but if you add it on the top of 25mm plywood, this will be thicker than the OP wants.

I never tried 'no more ply', but 22mm t&g looks perfect for the OP's requirements and can be tiled directly.

danrv

I’m currently renovating my bathroom which originally had carpet.
The 18mm chipboard subfloor was water damaged in places and had swollen over the years.
I’ve replaced it with moisture resistant 18mm P5 green grade chipboard and it’s solid on 400mm joist centres.
Went for this as it’s T&G whereas plywood isn’t.
I was going to fit Lino/PVC sheet for top floor as it’s waterproof but I may go for something like Aquastep click flooring or similar.

Gavin83

Thanks for the responses so far!

grumbler said:

andyhop said:

For the last 15 plus years , I’ve stripped out every bathroom we do , back to brick and joists and every time replaced the floor with 25mm marine plywood .

Personally, I wouldn't tile plywood directly. That's what hardibacker exists for, but if you add it on the top of 25mm plywood, this will be thicker than the OP wants.

I never tried 'no more ply', but 22mm t&g looks perfect for the OP's requirements and can be tiled directly.

Have you used hardibacker before? What have you put it over?

andyhop

danrv said:

I’m currently renovating my bathroom which originally had carpet.
The 18mm chipboard subfloor was water damaged in places and had swollen over the years.
I’ve replaced it with moisture resistant 18mm P5 green grade chipboard and it’s solid on 400mm joist centres.
Went for this as it’s T&G whereas plywood isn’t.
I was going to fit Lino/PVC sheet for top floor as it’s waterproof but I may go for something like Aquastep click flooring or similar.

Chipboard has no place in a bathroom . You have no idea of what makes a strong bathroom if you believe what you have fitted is of a good standard 

andyhop

grumbler said:

andyhop said:

For the last 15 plus years , I’ve stripped out every bathroom we do , back to brick and joists and every time replaced the floor with 25mm marine plywood .

Personally, I wouldn't tile plywood directly. That's what hardibacker exists for, but if you add it on the top of 25mm plywood, this will be thicker than the OP wants.

I never tried 'no more ply', but 22mm t&g looks perfect for the OP's requirements and can be tiled directly.

1000+ bathrooms without a failure , what do I know 

I don’t offer bathrooms with huge steps 

I don’t offer bathrooms with any PVC cladding 

I don’t offer value for money over a few years 

22mm T&G tiled directly to substrate 😂 

Hardibacker exists as people want quick fixes , as long as it lasts a few years , it’s good enough . It’s for the untrained , the unknowledgeable and those that want to to the minimal amount of prep for the most amount of money

If your floor flexes , adding endless amounts of overlay still isn’t going to solve the issue 

Doozergirl

andyhop said:

danrv said:

I’m currently renovating my bathroom which originally had carpet.
The 18mm chipboard subfloor was water damaged in places and had swollen over the years.
I’ve replaced it with moisture resistant 18mm P5 green grade chipboard and it’s solid on 400mm joist centres.
Went for this as it’s T&G whereas plywood isn’t.
I was going to fit Lino/PVC sheet for top floor as it’s waterproof but I may go for something like Aquastep click flooring or similar.

Chipboard has no place in a bathroom . You have no idea of what makes a strong bathroom if you believe what you have fitted is of a good standard 

To be fair, the base of my bathroom is what seems to be a laminate faced moisture resistant Egger board that was actually outside for several weeks at this time of year as it went up before the first floor walls. It's had less water on it since it's become a bathroom.  

Not sure that I'd use it for tile, but it's perfect for LVT.  

Doozergirl

andyhop said:

grumbler said:

andyhop said:

For the last 15 plus years , I’ve stripped out every bathroom we do , back to brick and joists and every time replaced the floor with 25mm marine plywood .

Personally, I wouldn't tile plywood directly. That's what hardibacker exists for, but if you add it on the top of 25mm plywood, this will be thicker than the OP wants.

I never tried 'no more ply', but 22mm t&g looks perfect for the OP's requirements and can be tiled directly.

1000+ bathrooms without a failure , what do I know 

I don’t offer bathrooms with huge steps 

I don’t offer bathrooms with any PVC cladding 

I don’t offer value for money over a few years 

22mm T&G tiled directly to substrate 😂 

Hardibacker exists as people want quick fixes , as long as it lasts a few years , it’s good enough . It’s for the untrained , the unknowledgeable and those that want to to the minimal amount of prep for the most amount of money

If your floor flexes , adding endless amounts of overlay still isn’t going to solve the issue 

I don't see anyone else laughing?  

If you have superior knowledge, it's fine to share it without laughing or taking the proverbial.  People ask because they want to know what their options are, people answer because they think they might have something valuable to add.   Sometimes people say thank you and it feels great! 

I think the right answer is to suggest that people ensure that they have a stable base.    I've replaced floors with ply and put hardiebacker over it many times because adhesive keys better to the concrete and the concrete is moving even less than the boards.  Hell, I've even replaced joists, then ply, then hardiebacker. 

Every room is different, every person is different.   If I judge that someone doesn't have the budget for what I'd do, I just don't say anything at all because it isn't helpful.  

Gavin83

Doozergirl said:

andyhop said:

grumbler said:

andyhop said:

For the last 15 plus years , I’ve stripped out every bathroom we do , back to brick and joists and every time replaced the floor with 25mm marine plywood .

Personally, I wouldn't tile plywood directly. That's what hardibacker exists for, but if you add it on the top of 25mm plywood, this will be thicker than the OP wants.

I never tried 'no more ply', but 22mm t&g looks perfect for the OP's requirements and can be tiled directly.

1000+ bathrooms without a failure , what do I know 

I don’t offer bathrooms with huge steps 

I don’t offer bathrooms with any PVC cladding 

I don’t offer value for money over a few years 

22mm T&G tiled directly to substrate 😂 

Hardibacker exists as people want quick fixes , as long as it lasts a few years , it’s good enough . It’s for the untrained , the unknowledgeable and those that want to to the minimal amount of prep for the most amount of money

If your floor flexes , adding endless amounts of overlay still isn’t going to solve the issue 

I don't see anyone else laughing?  

If you have superior knowledge, it's fine to share it without laughing or taking the proverbial.  People ask because they want to know what their options are, people answer because they think they might have something valuable to add.   Sometimes people say thank you and it feels great! 

I think the right answer is to suggest that people ensure that they have a stable base.    I've replaced floors with ply and put hardiebacker over it many times because adhesive keys better to the concrete and the concrete is moving even less than the boards.  Hell, I've even replaced joists, then ply, then hardiebacker. 

Every room is different, every person is different.   If I judge that someone doesn't have the budget for what I'd do, I just don't say anything at all because it isn't helpful.  

I’m certainly appreciative of any answers I get. I’ve been a member of these forums long enough to know how annoying it is when you give advice only for the OP to never return!

Doozergirl, what would you do in my position? While I wouldn’t go as far as to say my budget is limitless it certainly isn’t my primary concern here. I want it done properly.

It’s certainly a good job budget isn’t my primary concern, 25mm plywood sheets are far from cheap!

It’s also worth noting I’m making assumptions what the current subfloor is as I haven’t yet lifted the carpet in the bathrooms. However in several other rooms 18mm chipboard is used and I’ve no reason to assume they haven’t used the same. While I wouldn’t exactly describe the subfloor in the bathrooms as weak it’s certainly springy and creaky enough I wouldn’t feel comfortable tiling on it.

grumbler

Gavin83 said:

Thanks for the responses so far!

grumbler said:

andyhop said:

For the last 15 plus years , I’ve stripped out every bathroom we do , back to brick and joists and every time replaced the floor with 25mm marine plywood .

Personally, I wouldn't tile plywood directly. That's what hardibacker exists for, but if you add it on the top of 25mm plywood, this will be thicker than the OP wants.

I never tried 'no more ply', but 22mm t&g looks perfect for the OP's requirements and can be tiled directly.

Have you used hardibacker before? What have you put it over?

I used it once for thick timber floorboards, and would use again for any sort of timber, including plywood.

Not sure about the actual trademark and thickness I used. It's just fibre-cement board that you screw reliably to timber for tiling.