How to ensure bathroom concrete floor falls to the drain?

[JSLawrence]

Hi team,

Seeking advice for our bathroom renovation. We currently have a thick screed floor 5cm deep which had tile on it so the shower and floor drains sit around 5cm above the bathroom concrete slab, and around 0.5cm above the house concrete slab. We have removed the bathroom tile and will be removing the screed layer and then filling the whole bathroom floor with concrete to sit below the house slab level. We will then waterproof the concrete and use it as our bathroom and shower floor. Seeking recommendations for the best way to get the sloping of the concrete right for the drains and the best concrete for the job. We live rural so really difficult to get tradies in to do the work, hence the DIY. Thanks so much.

[EricL]

Hello @JSLawrence 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your bathroom renovation.

For your bathroom renovation, you'll want to ensure that the new concrete floor has a proper slope toward the drains to prevent water pooling. Since you're working on this yourself and aiming for a professional finish, here’s a step-by-step plan and some extra tips:

First, consider using Dingo Concrete or similar from the store. This pre-mixed product is easy to work with and provides durable results suitable for wet areas like bathrooms. To ensure the slope is correct, you’ll need to set up a guide system before pouring the concrete. Use metal screed rails, which you can find in the building section, to outline the slope to the drains. For the angle, the standard fall for a bathroom is 1:80 to 1:100, meaning the floor should slope 1 cm for every 80-100 cm of floor length.

Mark the desired height of the finished floor on the walls, starting slightly higher at the edges and sloping toward the drains. A laser level or spirit level is perfect for this task to ensure consistent alignment. You can find affordable laser levels at the store, such as the Ozito 10m Range Cross Line Laser, to simplify this step.

Before pouring the concrete, prepare the base by cleaning the existing surface thoroughly and applying a concrete bonding agent, such as Dunlop Multipurpose Primer. This will help the new concrete adhere to the slab and create a robust base.

When you're ready to pour, work in small sections and use a straightedge to level the concrete while following your guides. A steel trowel or a magnesium float will help smooth the surface but be careful not to overwork the concrete as this could weaken it.

After the concrete cures, which typically takes about 28 days to fully set, apply a waterproofing membrane. Products like Dunlop Undertile Waterproofing from Bunnings are excellent options for DIYers. Make sure to follow the manufacturer’s instructions carefully, including applying multiple coats and extending the membrane up the walls. Please note that you'll need to engage the services of a certified waterproofing specialist as it needs to be signed off. 

A handy trick for checking the slope is to pour a small amount of water near the edges of the floor once the concrete sets slightly. Watch the flow to ensure it moves toward the drains. If adjustments are needed, this is easiest to address while the concrete is still wet.

Finally, as a rural DIYer, it’s worth investing in a good quality trowel and float set to achieve a smooth finish. Take your time with the prep and curing processes for the best results, and good luck with your renovation!

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you have any other questions we can help with, please let us know.

Eric

[Dave-1]

Good Evening @JSLawrence 

Wow, must say the instructions @EricL has given are far better then what I would have thought of. I fully admit I have only the theory side in my head as havnt done any sloping of concrete for a bathroom yet  

The only thing I can think of adding is have you sorted your tiles out as in the height of them? Just in case you are wanting thicker tiles. Oh and make sure you have the type of drain fitting for the room and also for showers ect (depth and width wise) you want before you concrete as thats another thing I have seen people run into after they have done their concreting.

I will be filing these instructions away for future use for sure.

Dave

[Nailbag]

Hi @JSLawrence 

I think following the great advice by @EricL is the way to go. Just be aware that Dingo product goes off in an hour, so you need to have your act together with everything ready as that time will soak up quickly if you haven't done this type of job before.

Nailbag

[JSLawrence]

Thanks so much Eric. That’s so helpful. I will see if I can get a waterproofer in to do that part but I feel better about having a go at the concreting myself now. Really appreciate your advice.

[JSLawrence]

Hi Dave, we will be sealing the concrete as the floor, so no tile. The drains will need to be reduced to the level of the concrete which I’m thinking the laser level will be absolutely needed for. That’s a great point about the drains too. I will need to source them beforehand. Thanks for your advice and thoughts 👌

[JSLawrence]

Thanks Nailbag, 

That’s great advice. The concept of concrete ‘going off’ is something I’ve only recently become aware of so I’ll be doing some more research on that beforehand.