How to ensure floor grading for bathroom renovation?

[diyaaron]

I am renovating our bathroom and am at a loss about the floor grading. I understand that the floor  outside the shower needs to be graded to a floor waste. Our bathroom floor is James Hardie Scyon/Secura floor, installed on the joists over a brick pier foundation in a 1980's cut and fill home, with the floor surface equal height to the adjacent hallway floorboards. I'm wondering how to grade the floor to the floor waste. I'm also worried about floor movement.

I've seen lots of people talk about tiling over floor leveler. If the floor leveler does it's job then where does the grade come from? I assume you shouldn't create the grade with the tile adhesive?

The installation guide for the floor suggests that tiles can be installed either directly to the flooring, or over a sand-cement mortar bed on the sheets (obviously with waterproofing in there too). If you were going directly onto the floor (with waterproofing and adhesive), then that would mean you would need to grade the floor itself by either flexing or sloping the floor. The installation guide suggests a frame tolerance of 3-4mm over 3m, which is approx. 0.1% difference. The NCC 2022 part 10.2.12 speaks to a minimum continuous fall of a floor plane to the waste being 1:80, which would be 60mm over 3m or 20x over tolerance, so i don't understand how the tiles could be installed on the flooring without a screed bed.

As such, I assume the grade will have to come from a sand-cement mortar bed. I know there's lots of complexities with screeds - bonded vs unbonded, location of membranes, movement considerations etc. I'm concerned about the potential for the screed cracking given my substructure, especially if the screed is thin (<40mm), and am worried about large floor height differences with the adjacent flooring if the screed is very thick.

I'm not sure where to go from here. Am I overthinking something? Have I already got myself too deep?

Can I just do a thin screed over the floor to create a grade, get it waterproofed, then tile over the top? Not sure about bonded vs unbonded screed in such a scenario, and if any product would be needed between this and the floor for movement considerations. 

[Jason]

Hi @diyaaron, 

Please note that a couple of our resident Bunnings D.I.Y. experts are taking a well-earned break at the moment, so there might be a bit of a delay before one can get back to you. Sorry about that.

Let me see if some other helpful members with bathroom renovation experience might be able to share their experience: 

@Nailbag, @Renowayoflife, @homeinmelbourne   

Thanks,

Jason

[diyaaron]

I've had a chat to James hardie about the scyon flooring, some waterproofing manufacturers and also Sika about some screeds and applicatinos to this floor. Out of all that it looks like i'm probably going to go with some Sika Eco Screed as a bonded application over some Davco Primex as a primer over the scyon, with some crommelin waterproofing over the top. 

[MitchellMc]

It's great to hear you've received expert advice @diyaaron.

I have 1:100 in 2.3.3 of the code, which is 10mm per metre. Over 3m, that would be 30mm, not 60mm. Or, if it were 1:80 that would be 37.5mm:3000mm. Regardless, I wouldn't be trying to alter the sheet pitch (as it's outside their guidelines), and I'd go with what you have discussed with the supplier, which is a screed. I thought I'd just mention that for when you do screed. 

Remember also that unless you have a 6000mm bathroom and the drain is in the middle then that height also wouldn't be correct. I presume you have a 3000mm wide bathroom and the drain is in the centre. That means you only have distance of 1500mm as we are sloping from each wall down to the drain in the middle. So, that would be 15:1500. From each wall over the 1500mm to the drain, it will need to drop 15mm. 

It might be worth having a professional come in and provide a quote. That would allow you the opportunity to ask some questions on how they would go about doing the grade. If it's a reasonable price you could have them do the screed and then work on the waterproofing and tiling.

Please let us know if you have any questions.

Mitchell

[Nailbag]

Hi @diyaaron 

I can't offer anything further at this stage to the excellent advice @MitchellMc has provided. I've done a lot of bathrooms myself. But there are some areas which I have always got in my very experienced tiler to assist with. So, I would be definitely leaning towards getting a professional quote as getting the floor correctly and accurately done is vital. It also sets you up correctly for the wall cladding.

Nailbag

[diyaaron]

Thanks guys. 

Just to clarify something though:

2.3.1 of AS3740 requires a 1:100 min fall to the floor waste for any substrate a waterproofing membrane is laid on.

2.3.3 also requires 1:100 for falls in wet area falls.

However NCC 10.2.12 requires a minimum continuous grade of 1:80, unless you don't have a floor waste (not having a floor waste seems like a bad idea)

I believe the NCC supersedes 3740 in this respect through Part A2 of the NCC, in that it is mandating a minimum requirement higher than the standards. 

[JacobZ]

Hi @diyaaron,

I'd definitely use the 1:80 ratio as specified in NCC 10.2.12.

As you've said, these are minimum fall requirements so by going with a 1:80 fall you are in line with the recommendations of both AS3740 and NCC 10.2.12.

Let me know if you have any further questions.

Jacob