How to install a new inset bath in a pre-existing frame?

Hello @crisis

Thanks for sharing your question about your bath. Your idea of removing the front section of the bath frame I believe is a sound idea. I Propose removing just the two front support pieces and the top section of the bath frame. Predrill the position of the support screws so that it can quickly be remounted without taking so much time. My best advice is to have the plumbing fittings ready as well to make sure that when you place the bath into position the plug and wate can be installed as well.

Another thing you can do is to use ordinary concrete and not quick drying so that you have time to adjust the bath and re-install the frame.

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 Afternoon @crisis

Yeah I like your suggestion about removing the front and dropping the bath in. @EricL's suggestions for the steps to go through sound like a good way forward.

That Jbox under the bath. Mmmm I dont know the rulings about if its allowed or not but it may be worthwhile to have a look into it before the bath gets put in place. Just in case it needs to be modified.

Dave

Hi @crisis

Those tap fittings are only temporary caps. If you turn the mains water off and unscrew them, you will find the actual tap thread will be about 1/3rd the length of the caps which may give you enough to drop the tub in from the top. Otherwise removing the front timbers and sliding it in will work.

I would also double up the rear and right support timbers as this will give you more play to position the tub Currently it would sit under the render which would be too deep when you allow for tile adhesive and tile thickness. This may then mean relocating the front frame forward.

Nailbag

Thanks @EricL I hadn’t thought about actually placing the same frame back again but I probably can.

In terms of fixing that back into place do you think it would work if I used brackets on the sides and the back of the vertical supports and a connector on the front? I can screw the left and right edges into the edge of the rest of the frame.

Thanks again, it’s great being able to test my ideas

Thanks @Dave-1 . I’ve had the Jbox checked. It’s not ideal but there is no alternative.

Thanks @Nailbag , unfortunately the faucet under the taps doesn’t allow enough space to get the bath in. It’s also what meant I had to cut the old bath out instead of lifting it.
Thanks for the advice

Hello @crisis

Using brackets is a sound idea, I propose pre-testing the fitting to make sure everything is in place, and test fitting the bath. I would just like to remind you that @Nailbag raises a very good point in regards to the position of the render. For more perspective, imagine the render, adhesive and tile installed into the small space at the side of the bath. You must provide more space for installation otherwise it will be too close and there will no space to adjust.

If you need further assistance, please let us know.

Eric

@EricL @Nailbag Thanks I have taken the advice on the frame on board and it was something I hadn’t thought of or considered. I have removed the front of the frame and am now waiting on the bathtub to arrive before building up the frame.

Is H3 pine ok to use for the frame?
Thanks

Hello @crisis

H3 treated pine can be used to frame your bath. My best advice is to do a dry fit and to bring some of your tiles to fit as well to make sure you've provided enough space for everything that you'll be putting in.

If you need further assistance, please let us know.

Eric

Hi @crisis standard structural M10 is fine. It should be getting exposed to moisture.

Nailbag

Hello,

Still progressing my bath tub install. I have removed the frame front in the way you suggested and have everything pre-drilled ready for a a quick install once the tub is in. I have also levelled the walls and ensured the frame and bath will allow for render and tile. I am now attaching villaboard on the top of the frame front and the left side where the render and tile won’t overlap the bath flange. I will attach to the front of the frame once installed. I have a few question about attaching the villaboard.

1. I know that for a timber frame I can use galvanised fibre cement nails - is there any problem if I use galvanised fibre cement screws? I already have some of these and don’t want to buy nails if the screws will do the job.

2. I know I need to silicon the screw heads to not compromise the waterproofing. Do I need to cover the screw heads with anything else so that when the waterproofing membrane is applied it won’t be compromised by the screw heads/nail heads? I have read I can use joint compound..? Will that work?

3. When joining the villaboard at a right angle (front of bath frame (vertical) and top of bath frame (horizontal) should the two sheets of villaboard meet flush? I.e one doesn’t overlap the other?

Cheers

Hello @crisis

As much as I would like to say yes to the use of galvanized fibre cement screws, I can only suggest what the manufacturer has recommended and that it is to use fibre cement nails. Their big flat heads provide superior holding power. I'm not aware of any extra compound you should use on the nail heads and therefore recommend not using any unless specifically instructed by the installation manual. The Villaboard panels must not meet flush but be left with a 2mm to 3mm gap.

Let me call on our experienced members @Nailbag and @AlanM52 for their recommendations.

Here is a link to the Villaboard installation manual: Villaboard Lining Installation Guide

Here are some handy step-by-step guides:

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

Eric

Hi @crisis

1. It's recommended you use cement sheet nails as this will sit flush without the need to countersink the heads which will compromise each fastening point. Otherwise there is a specific gal screw for cement sheet that drives in flush.

2. No need to apply any silicone over each nail head. The waterproofing process of tapes, and compounds will do this.

3. I have always (possibly right or wrongly) stopped the two intersecting sheets to their inside corner edge so not overlapping but also not leaving a specific gap there than the edge not being perfectly straight. Basically the same as when hanging plasterboard to external corners. But @EricL has mentioned they shouldn't and a gap of 2-3mm should remain. I couldn't find that information in the document he linked. But if @EricL can direct us to that section then thats definitely how it should be done It. Metal external edging covers the corners before waterproofing

Nailbag

Screenshot 2025-10-06 at 7.09.23 am.png

Thank you @Nailbag and @EricL ,

I understand leaving a gap when fixing cement sheeting to the same surface/in the same plane but wasn’t sure when it came to corners. Thanks for the diagram Nailbag.

@Nailbag I assume the tape you are talking about is reinforcing fabric?
Cheers

Yes thats correct @crisis

Hello friends @Nailbag @EricL @and whoever else may be reading this. An

update and another question on my bath install. I have successfully added cement sheeting to the top of the frame and happy to say everything is level. I put the bath in as a dry run to check everything and the bath is not resting flush on the frame. It is resting at the ends but not in the middle and it seems the edge of the tub bows upward I.e it is the tub not the frame. I removed the bath and put a level on the underside of the flanges and sure enough it isn’t level.

Any idea if this is normal or a fault with manufacturing and I need to change the tub?

Hi @crisis

Different manufactures and price-points will determine this type of error, but it's likely this is within tolerance. Just remember there will be a silicone sealant to go around once in its final position resting on the tiles. Give the manufacturer a call and get their opinion to make the call. Worse case just put a thin packer underneath.

Nailbag

Thanks @Nailbag I did wonder about tolerance i will give the manufacturer a call . Is it not an issue that the tubs weight isn’t fully supported by the frame? I was worried about tub movement and impact on tiling.

Hello @crisis,

I'm in total agreement with @Nailbag. Give the bath manufacturer a call to find out about the tolerances and if the bath needs to be swapped over.

Eric

Once its plumbed in and siliconed its not going anywhere @crisis

Nailbag

Hello, thought I’d reply with an update to help future readers looking for advice. I shimmed and siliconed but before this I also lifted bath a smidge and put a layer of silicone between bath and mortar bed. This stopped any slight movement. Included a pic not that it shows you much. The walls and frame have also been prepped for waterproofing

JacobZ

Hi @crisis,

Things look to be coming along nicely.

I can't wait to see everything once it has been completed.

Thanks for the update.

Jacob

pollywog

Hi Crisis,

Just wondering how this went for tiling as I’m in the middle of a similar project. Did you leave a gap for the tiling to run under the bath lip on the dwarf wall and if so did it have to be exact allowing for tile thickness and adhesive?

Any update would be appreciated.