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Which grinder to use to remove paint on concrete slab prior to applying thinset

Which grinder to use to remove paint on concrete slab prior to applying thinset

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  #1  
Old 12-13-07, 02:15 PM
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Which grinder to use to remove paint on concrete slab prior to applying thinset

What is the best tool to use to grind paint off a concrete slab?

Here's the background:

In a previous post, I was advised to remove the paint on my concrete slab prior to applying thinset--

http://forum.doityourself.com/showth...47#post1271947


I have a 5" Makita angle grinder similar to this one--

http://www.absolutehome.com/web/cata...A3627B3B53E062


I have a grinding wheel like the one below that I used to grind down some small bumps in the floor, but I'm not sure how to best use it to work on a large flat surface (the room is 13'X8')--

http://www.northerntool.com/webapp/w...Product%20Page


It seems like what I really need is a wheel that I can place flush on the floor, or it will take me a very long time to scuff up the floor in the room with just the edge of the grinding wheel I have.

Any suggestions on the best way to proceed?

Thanks.
 
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  #2  
Old 12-13-07, 07:41 PM
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In the previous post you indicate that it is a blue hue on the floor that may be old paint. It sounds as if there is not much paint on the floor.

If you can take a new single edge razor blade (small window scraper) and get any paint residue to peel up, you will need to address the paint issue. Many times paint does not adhere very well and can be scraped up with a 4 inch razor blade scraper (floor covering supply).

If you cannot scrape any residue with the single edge razor blade, wet the floor and check to see if water beads up or is absorbed by the concrete.

I would test a 12"x12" area with some very high quality "flex" type thinset, if it is extremely difficult to remove after 24 hours you can install over what you have.
 
  #3  
Old 12-14-07, 06:48 AM
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You can rent a floor scrifier from a tool renatl place if need be. It will make faster work of the paint removal.
 
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Old 12-14-07, 08:25 PM
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Originally Posted by erkleboy View Post
In the previous post you indicate that it is a blue hue on the floor that may be old paint. It sounds as if there is not much paint on the floor.
The color is so faint that I even thought that maybe the concrete was dyed. If it is paint, it was applied 33 years ago when the house was built, and the paint was never re-applied. The previous owners did remarkably little maintainace to the house and, while they were here for almost 30 years, I very much doubt that they would have cared for the floor in an unfinished basement when there were important things in the living space that they ignored.

I will try the scraper first before I go with a rental.

I know that surface water does not bead up.
 
  #5  
Old 12-15-07, 08:45 AM
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Does the slab absorb the water?
 
  #6  
Old 12-15-07, 09:46 AM
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Originally Posted by HeresJohnny View Post
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Does the slab absorb the water?
I poured a 1/2 cup of water onto one spot on the slab. The water slowly spread out to an amoeba shape. The edges feathered quickly, appearing that the edges of water were absorbed. I poured in an area where I know there is a small dip, so the water pooled there a bit initially (no pbeading). After ~ 30 minutes, the water was pretty much all absorbed; now just a wet spot is left.
 

Last edited by GaetanoL; 12-15-07 at 09:48 AM. Reason: added detail
  #7  
Old 12-15-07, 05:24 PM
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OK, so I've finally goot the surface dirt off the floor in my laundry room. And, in good light and on my hands-and-knees I can definately see the remnants of an old paint job.

I'd say there is less than 50% coverage, which perhps helps explain why the slab is able to absorb so much water so quickly.

I bought a 4 1/2" coarse abrasive wheel (Norton Rapid Strip) with a 5/8 threaded hole. I am able to screw it direclty into the spindle of my angle grinder, without using the grinders retaining nut. The abrasive wheel's center hole is sufficiently deep that I can place the wheel flush with the slab. Despite the floor being pretty clean, I'm kicking up a lot of dust. I've got the Shop Vac running right near by to minimize that. I'll post back to say how it all turned out.

Any comments in the meantime are appreciated.
 
  #8  
Old 12-18-07, 11:14 AM
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So, I got the paint off the floor. The abrasive pad that I used was OK for the relatively small are in which I was working, but I don't think my technique would work well for a large area. I went through 3 pads @ $9 each. Took a couple of hours to get do ~ 150 sq ft.
 
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