Take the 2-minute tour ×
Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It's 100% free, no registration required.

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.

share|improve this question
1  
Is there a mechanical device that I can use to speed up the process? So far I have had two days with a cold chisle, screwdriver and hammer in my removal attempt in bathroom one and still have some to left on the floor. –  Carl B Sep 8 '12 at 12:55
2  
You can use a power chisel, air hammer, or demo hammer. –  BMitch Sep 8 '12 at 13:29
    
@BMitch - Thanks for the suggestion. Could you put that as an answer so I may consider accepting it along with other potentential solutions. –  Carl B Sep 8 '12 at 13:34

4 Answers 4

up vote 12 down vote accepted

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):

power chisel

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

air hammer

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

demo hammer

MC Hammer (don't touch this):

mc hammer

share|improve this answer
    
Since it's thinset on slab, I agree - get yourself a power chisel - rent from Home Depot for the day. –  The Evil Greebo Sep 8 '12 at 15:55
1  
I will rent the power chisle to get the thin set off. The MC hammer was an option I didn't even think about....Hmmm Can't touch this....Could be handy if I go far with the power chisle and he could warn me that I have gone to far into the concrete. lol. Nice touch! –  Carl B Sep 8 '12 at 16:02
1  
MC Hammer might not be useful, but Vanilla Ice might be able to help. –  Tester101 Sep 10 '12 at 12:02
2  
Extra upvote for MC Hammer. –  Karl Katzke Sep 11 '12 at 18:46

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.

enter image description here

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.

share|improve this answer
1  
up vote for your comment - The walls have just been painted in the bathrooms. Will this fling the "mud" all over the place? Can it be done with misting water to keep the dust down? I like this idea as well. –  Carl B Sep 9 '12 at 16:39
2  
The mud flings laterally. I did it by taping a six inch cardboard "curb" around my work area. It couldn't hurt to put up some plastic but I found it unnecessary. I kept it wet with a brush in a bucket of water. You will know when It's too dry. If there is dust add water. Thinset will readily absorb. –  Matthew Sep 9 '12 at 17:58
1  
I have GOT to get me one of THESE! –  The Evil Greebo Sep 10 '12 at 18:11
    
Also, you will know if you're brushing concrete because you'll likely see small sparks as the concrete reacts to the steel brush differently than the thinset. Brushing the concrete will wear the brushhead out, the thinset shouldn't affect it much. I used two of these brushheads to do about 100 sqft. –  Matthew Sep 14 '12 at 15:02
1  
Wow I wish we had read about that when we were chipping up thinset after breaking up tile! We used an air hammer with a high capacity air compressor, but it probably took close to 20 hours to do a small bathroom plus 6x6 hallway and 3x3 closet. I think the thin-set used was some heavy duty stuff too. IT WAS HORRIBLE. We have one more area to go so maybe the grinder option would be the way to go for the next part. Would that also work for linoleum glue? I think our glue is water soluble. –  Angela L. May 11 '13 at 15:31

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.

share|improve this answer
    
+1 for your reply.The thin set is applied directly to the concrete slab. There is no way I can cut, remove replace the sub floor. –  Carl B Sep 8 '12 at 12:59
    
Fair enough - go with BMitch then –  The Evil Greebo Sep 8 '12 at 15:56
    
If I could choose both answers I would. Your input was most helpful and I wish I could give you some of my rep for taking the time to answer. TY. –  Carl B Sep 8 '12 at 19:15
    
Not necessary. :) –  The Evil Greebo Sep 9 '12 at 2:55

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.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.