The chisel isn't cutting it. No, seriously, it's not cutting at all.
August 1, 2012 6:19 PM   Subscribe

How do I remove a small concrete shower pan lip without losing my sanity in the process? Special snowflake details inside.

Mr. Muirne81 and I are renovating a 70+ year old utility shower in the basement. The original pan is made of a super-hard concrete. We gutted the stall and waterproofed everything, then installed concrete board to the studs, anticipating that we would just tile up and over the pan edge that juts out from the base of the wall. (A small expansion gap was left between the board + the pan.)

Unfortunately we were naive, and didn't think about the fact that this edge only exists on three of the walls, nor the fact that the edge is uneven. In some places, it only extends 1/2" from the base of the concrete board. (Face palm)

Because the pan extends completely behind the depth of the concrete board, it was decided to chisel just the protruding portion flush with the concrete board so that floor tile & wall tile could be installed more easily. Great theory, but in reality, it's taking me forever to chisel the edge. (Only 4" in an hour. Yikes.)

Does anyone have any ideas for speeding up the process? Is there a concrete saw that's small enough to be used in a tight shower stall? Would a reciprocating saw w/masonry blade be able to chew through the concrete? I know the fastest way to solve the problem would be to hire a pro, but as much as we'd like to, it's just not something we can afford at this time.

Thanks in advance for your thoughts!
posted by muirne81 to Home & Garden (6 answers total)
Two options:

You can fit large hammer drills with chisels. I've used a Hilti ATE 70-ATC with a chisel to make holes in concrete walls and you should be able to rent a similiar tool.

You can get concrete grinding disks for angle grinders. This option will create a crazy amount of dust and is really hard on the angle grinder (count on destroying it). A wet dry vac and misting spray bottle will help alot plus taping off the shower stall as much as possible with the DHS favourites plastic sheeting and duct tape.

However how deep is your lip. It looks not much deeper than the tile thick. If that is the case and assuming no other factors (like you are trying to preserve the existing tile) if it was me I'd just just screed a new mortar base flush with the lip. Way easier and cheap.
posted by Mitheral at 6:37 PM on August 1, 2012 [1 favorite]

You can get concrete grinding disks for angle grinders.

You can also buy dry-cut diamond saw blades for angle grinders. Still a lot of dust, but depending on exactly the situation you might get a better cut that way. Angle grinders are cheap, so don't worry about hurting the tool itself.

I also have a Dremel-like tool that has a 90-degree, flush-cut head that I am pretty sure could accept a diamond blade. Some creative mixing and matching in the tool aisle at Home Depot or Harbor Freight might get you an option that would work.
posted by Forktine at 6:53 PM on August 1, 2012

Might be worth swinging by your local tool rental place and explain your problem to them- I can't tell if it's big enough, but a one day jackhammer rental won't be too much cash, and may solve the issue in 15 minutes.
posted by jenkinsEar at 7:54 PM on August 1, 2012

Hmmm...we live in a very wonky house, and have often had problems like this. My suggestion would be to leave the lip, but find a rail angle trim or a type of edging or bullnose tile that covers it, or find a bent tile; or, even if you have to cut two longer, thinner pieces to make it fit, and find a way to fool the eye to make it look even. I'd rather cut tile than cut concrete.
posted by peagood at 8:22 PM on August 1, 2012

I think you should avoid doing anything such as grinding or sawing, wet or dry, which generates dust or fine droplets because concrete of that vintage very often contains significant asbestos:
In the early 1900s, asbestos fibers were used in concrete, and in the 1950s the concept of composite materials came into being and fiber-reinforced concrete was one of the topics of interest. There was a need to find a replacement for the asbestos used in concrete and other building materials once the health risks associated with the substance were discovered. By the 1960s, steel, glass (GFRC), and synthetic fibers such as polypropylene fibers were used in concrete, and research into new fiber-reinforced concretes continues today.
As the imprecise and somewhat mealy-mouthed Wikipedia article puts it.
posted by jamjam at 11:21 PM on August 1, 2012

If it were me, I'd go to the local tool-rental place and rent a pneumatic air chisel and compressor, or if you already own a compressor it's probably about the same price to buy a cheap chisel from Harbor Freight. (Normally I would say avoid HF at all costs, but this is probably a one-time thing.)

Basically, the air chisel is like a small jackhammer. You put a chisel into the front of it and it goes back and forth. Wear heavy gloves, ear, and eye protection! And take turns doing it. I think it will make short work of that lip.

The only downside is that I suspect it will leave a rough edge, compared to using a diamond saw or a grinder. But since you are tiling over it, that shouldn't be a big deal.
posted by Kadin2048 at 7:55 AM on August 2, 2012

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