How much bathroom floor demolition/restoration is required for new screed?

[SensibleHill]

I'm hoping for some advice on the scale of floor demolition/restoration we have to embark on. Basically - if I am expecting to have to re-screed for different falls across the whole floor, does that mean I have to chip out all the existing floor back to the concrete? In addition, because I have to remove some of the concrete to get new drain pipes laid, how do I restore the concrete in those parts afterward?

We have made good progress demolishing the bathroom we are renovating. The bath, vanity and shower hob are out. As per our other posts, we are rearranging the bathroom so that the shower is where the bath was and the vanity is where the shower was, and there will be no bath. I am still deciding on how the fall should go, but obviously a good portion of the room needs the fall changed, if not all.

The plumber has advised how he will need to alter the drainage and has said we can save money on his labour by removing a line of concrete so he can lay the new drainage pipes (basically, a line of concrete to be removed from near the corner diagonally opposite this one, to this one). So now I have to get a grasp on the scale of what to remove next, what extent to go to, and then how to restore it so it can be screeded and tiled on etc.

The picture below is where the bath was, basically now where the shower will go, showing the concrete, sand below that, the broken brick bath hob, and the tiled edge of the rest of the floor.

Previous bath location showing concrete slab and floor tiles to right

(We are in Perth, brick and tile construction all the way through, no wood or fibreboard present.)

[EricL]

Hello @SensibleHill

Thank you very much for sharing your question about demolishing and screeding your bathroom floor. Your plumber was very considerate by requesting that you do the concrete cutting. Having the plumber do this usually means a great deal of expense and poor use of his time.

I suggest getting more details from the plumber. How wide does he want the cut channel to be? How deep does it need to be? Does he want a large box cut at the end of the run so that he has room to install a waste and flange? You might also want to consider if you want to install a modern Mondella 100 x 100mm Stainless Steel Rumba Tile Insert Floor Grate. You can then make provisions for it by having the pipework at the correct level.

Floor preparation is quite involved, removing the old tiles is prudent because you can't tell which part of the old tile floor has been compromised. Re-levelling your floor is a given as the cement base of your bathroom must be re-established. The cut channel will have to be filled in and then the shower base's fall will have to be established. 

I propose speaking to your plumber about the sequence of events and which parts of the floor they will be actually doing. Seek clarification on how far you can go as far as screeding is involved. Parts of the floor prep will need to be done by the plumber as it will need to be signed off. 

Here are a few handy step-by-step guides:  

• How to tile a shower base
   
• How to screed a shower base

If you need further assistance, please let us know.

Eric

[SensibleHill]

Thanks Eric,

The plumber has been very helpful and invited us to send pictures etc as we go so we get the site prepared for them as they need. He gave guidance on the size and placement of the channels and areas to clear, it is basically just sufficient enough to create space to work in for installing the drainage.

I am anticipating to have to fill the channel, but not sure what concrete mix I use for that, can you advise?

What I'm expecting to end up doing is chipping out the entirety of the screed that's on the concrete, channel out the concrete for the plumber, then once they are done, fill in the channel, then use a self levelling mix across the whole floor to smooth it out, then re-screed the whole floor for the correct falls.

I'm just a bit apprehensive about the task of lifting all the screed because I'm expecting it to be a fair challenge, and wondered if there is any way around it or any process to make it easier.

Thanks,

Ben

[EricL]

Hi @SensibleHill

To fill in the channel, I suggest using Bastion 20kg Concrete Mix or similar. This is pre-mixed and you just need to add water, just keep in mind to mix only what you need to fill in the gap. I suggest hiring a pneumatic air hammer to make short work of the tiles in the room. Manually removing it with a hammer and chisel will take too much time.

My number one tip for your project is to use a builder's line to create guides for the fall. With a visual guide in place, you can be confident that the fall of the floor is correct.

Please keep us updated with your progress, we look forward to seeing the start of your bathroom renovation.

If you need further assistance, please let us know.

Eric

[SensibleHill]

Hi @EricL thanks for the previous advice. I managed to lift all the tiles and most of the screed (have to go back over that), but I left the concrete channeling to the plumbers as I ran out of time. They've been and gone and now I have the bathroom in this state:

Bathroom floor showing channel to showerBathroom floor showing channel to floor wasteBathroom floor showing shower wasteClose up of concrete edge and underlying sand, in channel

Now I need to concrete in the channel. Is this appropriate to use? The concrete you linked is not available near me:

https://www.bunnings.com.au/swan-cement-20kg-general-purpose-concrete_p0760097

How should I prepare the site? I have to remove the sand of course. The last image shows the edge of the channel, and underneath is of course sand because it's the foundation slab. You can see there was some wire mesh rebar present. I assume I should compact the sand, but do I need to prime the sides of the concrete with anything? Do I tie it into the existing concrete in any way? Should I add any rebar to it? It's a channel that's about 30cm wide and 1.5m long in an S shape. Slab is about 8cm thick. 

Thanks!

[EricL]

Hi @SensibleHill

It's great that you're making progress with your bathroom renovation. My apologies if the Bastion Cement link did not work. In reference to the Swan Cement, it is alright to use that for your flooring. Once you've removed the sand and compacted the rest, I suggest using the Dunlop 4L Multipurpose Primer on all exposed cement surfaces. It is ideal to use on new and old concrete, particleboard, marine plywood and fibre-cement sheets. Please make sure to prime the sides of the wall as well. 

It will not be necessary to put rebar into the floor area as it will not be carrying a significant amount of weight. However, you do have that option if you wish to add more strength to the floor. My number one recommendation is to try and control the drying time of the cement floor. In extreme heat, I suggest spraying the cement floor with your garden gun in mist mode. This will slow down the drying time and prevent the floor from cracking.  

Please make sure to give your cement floor enough time to fully cure. Applying waterproofing and tiling too early will result in the moisture inside the cement being trapped and anything put on top of the cement surface will peel off. 

If you need further assistance, please let us know.

Eric

[SensibleHill]

Hi @EricL ,

Just following up, I also asked the manufacturer of the concrete for advice and they advised to compact and wet the sand, and also that a primer and rebar would not be necessary, and to vibrate/tamp it to remove bubbles, and to cover it with plastic to retain moisture so it wouldn't dry to fast as you noted. I did it a few weeks ago, ended up needing 20 bags, I think it worked out ok so thanks for the advice.

Compacted sand before concretingFinished concrete

[MitchellMc]

Great results @SensibleHill.

Please keep us updated on your project and reach out again if you need further assistance.

Mitchell