I have a slab floor throughout my house including the bathroom underneath the bath tub. I want to remove the bath tub and create a curb less / flat / no trip walk in shower.

Problem is, the floor under the tub is also flat so I think water would/could drain out into the bathroom. I do not want to install a fiberglass shower floor that we'd have to step up and over. There will not be a sliding shower door assembly, as we'd have to step over that too. I want to "slide" into my shower, so to speak.

Do you know if I can grind the flat concrete floor under the tub to create enough slope to drain properly? Is this possible to do?

Or, is there another method?

I'm hopeful I can make this work, but I need some advice, please!

How thick is the slab? What is "IN" the slab? In theory you could mill out a basin provided there is enough room to do so without striking re-enforcement or hydronic tubes, both of which are notorious for migrating during a pour...

I think the slab is 4". Probably rebar but no hydronic tubes.
How would I "mill out" a basin?

Well you could do it with a hand grinder and a diamond wheel but I would contact someone who does CC Cutting/grinding/polishing and consult with them as they will have tools better suited to this job. Your also going to need a plan for controlling the dust and airflow...

I'll look around for a guy that could grind it. Dust will be an issue, I know. Thanks for the tip. If anybody else is knowledgeable about how to do this, I'd love to hear from you.

I agree with romar. You could do it with a diamond cup wheel on an angle grinder. I would take likely one wheel and likely over 3 hours of constant labor and lots and lots of dust as romar said.

http://www.homedepot.com/s/diamond+cup+wheel?NCNI-5

The bigger the wheel you use the gentler the slope you will likely get and the nicer the job in the end. The wheel is held flat so all side are always hitting and just apply more pressure on the side you want to cut more. A slight amount of pressure will cut a lot. You limiting factor will be the angle grinder getting hot from the load of running.

Good Luck.

There is likely a 12" square void under the tub where the drain is. During construction it is hard for one trade to pour a full slab that meets the needs of the plumber, so they leave a void in the concrete which the plumber may fill with mortar or cement to keep vermin out. The drain is fitted to the tub bottom, not the concrete. So, while you might be able to carve out a slope for the shower floor, you will have to see what the drain area looks like before finishing your design. If you have to fill in concrete anyway, then you have the option of breaking out the whole shower area and repouring the whole thing with a slope to the drain....and the drain cast right into the concrete. I will leave it to more experienced concrete specialists here to fill you in on the methods for making sure any new pours are sealed so the water doesn't run between pours.

Yea, you are probably right about the drain void under the tub. With the sealing of a CC surface being a possibly iffy proposition, easilly overridden by any crack(and concrete cracks), I don't know that I would wand a CC shower that was part of the rest of the floor for water to migrate thru. Myself personally I would cut out a recess and grout in a shower pan and either tile or CC that. That would more positively insure all the water goes down the drain...

I installed a basement bathroom shower on a cement floor. I rented a 10" diamond saw and cut a hole in the cement slab. Then I had a plumber add a T joint and drain to the existing plumbing. Then I added the cement back. I used a plastic shower insert to speed assembly.

Due to the hazard of silicosis you will need a full face mask as well as a vacuum with the exhaust going outside and the suction hose near the diamond blade. A different method would be to spray water on the are before and during the sanding. This will help keep the air clean, but will coat everything around the area, so you might cover everything with plastic first.

I installed a basement bathroom shower on a cement floor. I rented a 10" diamond saw and cut a hole in the cement slab. Then I had a plumber add a T joint and drain to the existing plumbing. Then I added the cement back. I used a plastic shower insert to speed assembly.

Due to the hazard of silicosis you will need a full face mask as well as a vacuum with the exhaust going outside and the suction hose near the diamond blade. A different method would be to spray water on the are before and during the sanding. This will help keep the air clean, but will coat everything around the area, so you might cover everything with plastic first.

Posted By GaryO on 26 Feb 2017 09:32 AM
I installed a basement bathroom shower on a cement floor. I used a plastic shower insert to speed assembly.
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Gary, I know cutting concrete is a messy deal, I'm not really looking forward to it. Did you sink your plastic pan so it it is level with your floor? If yes, can you please explain what you did to make it stable (added concrete under it? How thick, rebar, wire, etc?)

I didn't sink the pan. The shower "kit" was 4 pieces (3 walls + the pan). The pan has a 4" lip and is about 2" below the top of the lip. Beneath the pan was a foam liner to keep the pan flat.

I replaced the concrete that I removed for the plumber's access. I did not add rebar or fibers (PVA or Basalt).

If you are worried about the strength of the concrete, I suggest either PVA (polyvinyl alcohol) or Basalt fibers, not the other fibers because these bond chemically with the cement and make a much stronger concrete. I did mix my own recipe rather than the "Quickrete" type mixes at the big box stores, but they would be okay.

I've looked for a grinder guy in my area with no luck - so now I am debating either cutting the slab out that is under the tub and making a new concrete pan that is level with the floor, or, just leaving the slab alone and installing a fiberglass pan on top of the slab.

I like the curbless showers, but setting a pre made pan on the slab is a lot easier! I'm not sure what pan to buy, as there are sooo many on the market. I'd like to last a lifetime, so quality is important.