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How to remove cement mortar bed under bathtub?

Hello friends,

I removed the old standard size spa bath tub in my bathroom with the plan to replace it with a regular bath. I now need to remove the mortar bed it was sitting on to install the new bath. I am wondering what my options are for removing it other than taking to it with a sledge hammer. I am reluctant to use a sledge hammer because I don't want to accidentally damage the slab underneath. What other options do I have? I have read I can use a reciprocating saw with a diamond blade? Is there an option to leave it there and bond a fresh layer of mortar to support the new bath? Have included photo to show size and thickness. And yes that is an electrical wire set in the mortar.

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Tim_Engineer

The smallest and lightest electric breaker you can find is the ideal tool for this job. Buninngs have the Ozito 900W 3.5J Rotary Hammer Drill Kit for about $90, it will have a point and a chisel attachement with it too. Go carefully and slowly and Use the hammer setting only (not the rotary drill setting). You'll need a dust pan and broom to remove rubble, a bucket to carry the rubbish outside. Clean it out regularly so you can clearly see the leading edge of the work and help you avoid damaging the surrounds. Something comfortable to kneel on while you work and ear and eye protection is a must for a job like that. Have fun!

AlanM52

Re: Options for removing the cement mortar bed under a bathtub

You could also try breaking it up using a drill (corded or cordless) set to hammer with masonry bit.

Then pick at the holes with something like the Trojan Fibreglass Handle Pick Hoe (0101389) and also tap with the hoe end.

Cheers

EricL

Hello @crisis

It's fantastic that you've received excellent advice from @Tim_Engineer and @AlanM52. I totally agree with the suggestion of keeping it clean so that you can keep an eye on the leading edge of the mortar bed. This will prevent you from accidentally digging into the slab underneath. It might be possible to just trim the surface of the old mortar, but it will require you to do a test fitting to make sure that the new bath will fit. As to the new mortar bed you just need to make sure that you have enough space for it when you push the new bath in.

Please remember to wear personal protection such as gloves, goggles a mask and ear protection when using the hammer drill. Make sure that there is adequate ventilation so that the dust can get out of the room.

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

If you need further assistance, please let us know.

Eric

Dave-1

Good Evening @crisis

Ive never had to replace a bathtub tho expect I will be doing the same when I redo my bathroom sometime 🙂 I have removed mortar from a varity of bricks, rocks and generally it has sheered off with a bit of force. Mortar has no re-enforcing in it so I would actually go old school with a pound hammer and a cold chisel. I would work from the edge of the mortar (where it meets the slab) and then inwards. Have the cold chisel at a 30 deg angle and use a pound hammer (you can get them with a rubber cowl around the top to help protect the hand)

Once the mortar cracks it should be easy to remove.

Dave

Nailbag

Hi @crisis

I would be tackling it as @Tim_Engineer has suggested with a Pneumatic hammer with a both a narrow and wide angled chisel. As good as that Ozito model is that he suggested, its going to be very slow going as it doesn't have a heavy enough impact/Joel rating. I would recommend hiring a small to medium hammer specific (non-drilling). From several first hand-experiences it's well worth going down this track. Even a compact model like this will still be relatively heavy. The trick is to not apply too much downward pressure, just let the tool do the work. You just concentrate on steering and adjusting the angle. It won't take long to get the hand of it.

You ideally should be wearing an N95 rated respirator and being very noisey, good hearing protection is required and I would also be wearing gloves and eye protection. @Tim_Engineer also make a good point to regularly clear away the debris as you go so you can see what you're doing. And think about masking up cupboards and doors for dust control.

Nailbag

crisis

Thanks. I have received lots of great advice. Can I clarify, are you saying there is no need to remove all of the mortar if the new bath fits with enough space for a fresh mortar bed? Does this mean so long as the new bath is supported properly with fresh mortar it is ok to sit the new mortar on top of old mortar? I will wear an N95, hearing protection, gloves and goggles.

crisis

Thanks Tim - I already have this tool. It has been very useful for removing tiles and I will also use it to drill some holes to put in my kitchen. Thanks for the tip about making sure I can see the leading edge.

crisis

Great idea. Thanks

crisis

Thanks Dave. I had to google what a pound hammer is, but was pleased to realise that I already own one 🙂 I will try this first and see how I go. Good point about the lack of reinforcement.

crisis

Thanks for the tips. I will definitely be wearing an N95, goggles, hearing protection and gloves. I feel reassured that maybe it isn't going to be as hard a task as I thought it may be.

AlanM52

Reminds me of my younger days in the eighties when I laid thousands of bricks around our new house using wire cut 3 hole.

Later on I wanted to do alterations and would be out there on one of the kids stools with club hammer and brick bolster (purchased from Bunnings) trying to get the mortar off because it had of course seeped into the holes.

AlanM52

EricL

Hello @crisis

I would like to amend my suggestion. It would be better to remove all of the old mortar so you can put in a fresh batch.

Eric

Nailbag

Just be aware @crisis a pound hammer "compresses" what it strikes before it will break it away making it more difficult and a slower process to remove concrete. You need to be chiselling the mortar/concrete away.

Nailbag

crisis

The mortar bed has been successfully and relatively easily removed. I ended up using the Ozito 900w hammer drill as I already had this tool. I used a combination of the chisel and pointy (don't know what that's called) attachments and just used which one made sense. The pointy one was good for shearing off pieces close to the leading edge and the chisel for getting underneath. The concrete naturally separated from the underlying slab as it broke so avoiding damage was easy. It was good to have two drill bits because inevitably I would occasionally get them stuck and need to use one to free the other. I have attached some photos. When I got to the point in the second photo that entire block lifted from the slab as one piece. I can't remove it though until I get an electrician to deal with the small matter of the electrical cord that is embedded in it. @Nailbag @EricL @AlanM52 @Dave-1 @Tim_Engineer Half way

Nailbag

Nice work @crisis and thanks for the update and photos. 👌

Nailbag

EricL

Hi @crisis

Thank you very much for sharing those photos, it's good to see that you've managed to remove the mortar without damaging the base floor.

Please keep us updated with your progress, we look forward to seeing your new bath installed.

Eric

Dave-1

Cheering @crisis

😀 Woohooo and my first thought was "More stone for gabion walls!" hahahhaha

Tick one part of the project off!

Dave

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