Do I have to remove the old thinset before installing new tile?

Question

I will be installing some new 12x12 tiles in two bathrooms approx 25 sq/ft each. When I pulled up the old tiles, there was no thin set that had made contact with them so the removal was very easy. Now, the thin set on the floor is a different story. I have been chipping away at it by hand in one bathroom to get to the cement floor below and it has been a bugger to get off. Before I attempt to continue this process in the second bathroom, I would like to know if it is absolutely required to do so if it is well adhered to the cement underneath?

(It's my hope, obviously, that I can tile over the old thin set as long as it is level and firmly attached.)

EDIT: My subfloor is a concrete slab with the thin set on it. It must be chipped away to remove vs. cut and replace sub floor.

Answer 1

Like Greebo says, you want to get back down to the concrete, but I'd suggest that more to have a flat surface to build on top of. To make the job go faster, you can use a power tool. Several would get the job done:

Power Chisel (best fit for the job):

Air Hammer (you'd need a high capacity air compressor):

Demo Hammer (more power than you need, but it could be useful for other jobs in the future):

MC Hammer (don't touch this):

Answer 2

Having done this exact thing recently, I found that using the hard metal brush attachment for the angle grinder worked very well to remove thinset without affecting the concrete beneath it. I'd lean towards the stiffer bristles.

Be sure to wet the thinset before starting, and as needed. The thinset comes off like mud, leaving clean concrete. Once finished, scoop up the mud and sweep.

Done.

Answer 3

The answer is, "if you want to do it properly, yes". You're going to find it near impossible to get a good base to lay tile on if you try to apply thinset overtop of old thinset.

You may find it actually easier to remove the subfloor completely (cut it out with a circ saw set to the depth of the subfloor) and replace it to give yourself a clean surface on which to work.

Answer 4

After calling the rental places and comparing what I have done (using a cold chisle and hammer) to the results I would anticipate with a power chisle, I opted for the cheaper (and now added tool to the tool chest) of a $39 Royobi 4.5" angle grinder. I attached a two row Dimond cutting cup about $40. At Matthew PK's suggestion to water the floor down, it did eat it up and make mud. In three hours I finished the bathroom I started by hand and finished the second bathroom! Floors are smooth as glass and I was able to tile both rooms the next day.

All suggestions/Answeres were most appreciated.

Answer 5

You can put tile over old thinset. Make sure it not loose, vacuum to remove any debris, check for cracks, apply membrane if needed. I've done it hundreds of times for fifteen years including my own five houses. Remove the old thinset to get a flat surface for wood or laminate installation.

Answer 6

You easily can go over old thin set with no problem,as long as it is down good....I have done whole house on top of strong bonded oldthinset....it is actually a benefit to the instsllation of the new tile....only a pro can understand what I mean....but trust me ,it is okay

Answer 7

Just finished removing tile and thin set from a small (5'x5') bathroom floor an hour ago. I use a wide cold chisel and hammer to remove the tile. I found it was much more productive to cut through the grout lines first with an angle grinder and diamond blade. You could use a circ. saw but I didn't have one on hand. I used my shop vac to collect the dust as I ran along the grout with the blade. You don't really need to go all the way through the grout to the subfloor, just a decent groove. The tile still broke up in pieces with the grout lines cut but the pieces were much larger making the job faster.

I found a wide chisel / scraper type attachment at Lowes which fit directly into a recip. saw and that made pretty short work of the thin set ridges. Going perpendicular to the ridges is much more effective. Altogether the job took about 4 hours and left the new surface pretty smooth. I may just hit any high spots with the grinder again to make sure. It's a little late to do it once you start laying tile.

Answer 8

well, chipped all the tile up in my home OMG. So now the thinset, I found a rental tool at homedepot .Its a floor buffer and you put this round buffer with teeth and it removes thinset.DUST but fast. and yes you can go over thinset just make sure it not loose. have fun ;)

Answer 9

thinset removal bit $25 on amazon hooks up to an air compressor. .. gives you more control than a roto hammer. Been doing tile for 10 years and so far best bang for your buck

Answer 10

wet the thinset with a generous amount of water before attempting to remove. It will soften most thinsets up a bit but the biggest gain is in dust mitigation. Let it soak as long as you can, I try to let it set for at least an hour. You will have a tremendous amount of dust EVERYWHERE if you don't. There will still be dust but it will be manageable when wet. I just scaled 150 square feet today and although it was a back breaker it wasn't nearly as bad as it could've been. Used a Bosch rotary hammer with a 1.5" scaling bit. Couldn't find a wider bit but this actually worked well. I use a 4" manual scrapper to ensure everything is flush and this really cleans any remaining thinset. Good luck, it isn't for the faint of heart !!!