Sealing a semi-painted concrete floor?

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Hello and thank you for any help you all can give us.

My wife and have taken up some laminate "wood" planks in our closet to investigate the possibility of going with a concrete floor. After removing the planks and rolling back the blue plastic barrier the slab looks to be painted with a white paint, perhaps a moisture barrier / primer. Looks deliberately painted and not just over spray from the walls.

I easily scraped some up with a water based stripper if that lends any insight to what it might be.

So just for grins I took out the big grinder and a 50 grit diamond pad and sanded a larger portion of the painted floor to see what it would do. It made the floor very smooth and removed about 60% - %70 of the paint.

We stood back after wiping it with a wet cloth and thought the mottled / distressed look might be very attractive.

My question is does anyone see any potential problems with sealing it like that? Sealer adhesion issues?

I have had concrete floors in the past and am familiar with regular waxing etc to keep them looking good.

Please see photo, thanks!
 

havasu

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Looks like that is just overspray from when they painted the walls and ceiling before the carpeting went in. How would you deal with those glue lines from the rubber padding?
 
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Thanks havasu, I think your right about the over spray as the paint is much thinner towards the middle of the floor. I'm not sure about the glue, I touched it a bit harder with the diamond pad and it looks to be coming off, I could try a little acetone maybe?
 
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floor after sanding (2).jpg I decided to run my 50 grit pad a little more on the rest of the closet floor to see get a better idea of what the paint will do and I think we'll just take it all down to bare concrete. We are fortunate (so far) to have what looks to be a nice slab.

A little off topic but I hoped maybe havasu could advise:
The 50 grit pad get things pretty smooth, I wonder how high of a grit you typically go up to for a residential floor?
We're not looking for a mirror polish but want furniture to slide easily :)

Thanks!
Here is a updated photo after going over it with a wet mop:
 
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havasu

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Honestly, I've seen this done a few times, and they look awesome. The problem with your floor is the small nail holes along your entire perimeter from the old tack strip, which held down your carpeting. You can fill them in, but will always stand out. What is your remedy there?
 
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In a previous home I used mapei concrete patch to fill in holes and it worked very well and sanded smooth. You are right though, the patches are somewhat visible depending on the tone of the adjacent concrete.
 

havasu

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How about a skim coat of self leveling compound around the entire floor, give a light sand, stain and coat with a poly coating?
 
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That would give the best results but I have an entire house to do and that might be too much work for us I think. I'll know more when more flooring is taken up and the full slab condition is revealed.
I hate tack strips! :)

Do you have experience with grit levels that these types of floors are brought up to?
 

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A smaller grit will allow a good binding surface, provided you are coating with a poly type coating. If left raw, 200 grit would be minimum.
 

havasu

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Keep in mind if you are dealing with a full slab flooring, expose the entire floor to see if you have a stress fracture somewhere in the floor. I found a huge fracture running down my hallway, which made me forget about a concrete floor treatment, and opted to run wall to wall porcelain plank tile instead, using "Redgard" 4' wide near the crack to allow for expansion/contraction.
 
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I really like the look of those porcelain planks. Redguard is interesting stuff, I would like to learn more about it.
We have now exposed the entire master bedroom floor and so far the slab is looking good, flat and no cracks. I have decided to dry polish with my 7" inch variable speed grinder using grits 50, 100, 200, 400, then apply a lithium silicate densifyer, then 800 grit and see what we get before going higher.
I have a great dust shroud attachment for my grinder that attaches to the shop vac for nearly dust free sanding, very cool.
I'll be back with pictures soon.
 
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Ok, time for an update on our project. We tried a few different methods to remove all the paint from this floor.
First we rented a buffing machine from Home Depot and a 17" heavy plastic disc that had these metal blades attached to it, I think it's called a floor prep disc. It worked ok, I got to stand the whole time which was nice, but since our floor is not perfectly flat a lot of paint was left in the low spots.
Then we tried paint stripper and scrapers, yuck. Very time consuming and labor intensive ans still the floors would need a sanding to remove all the traces of paint.
So I found this 4" Scotch Brite disc that mounts to a handheld drill and tried for a while, worked very well with little effort but very slow as each pass removed 1/4" at a time.
I thought if I could only have a huge one of these mounted to a buffer I'd be done in no time. Well after searching I found to my amazement there is no such thing. But I did find a 7" one with a velcro back that I could use on my big grinder. Sold!
I got it and used it today for a few hours and it was magic! It ate paint with such little effort and took big swipes. I was still sitting/kneeling on the floor to do it but it went fairly quick. I really like it because it takes the paint and doesn't remove any of the surface of the concrete, just polishes it a little.
Here is a photo showing the floor halfway done with paint removal:
20200201_160933.jpg

Here is a photo of the 7" Scotch Brite pad that saved the day:
20200201_161026.jpg

And here is a photo of what the floor looks like wet from mopping
20200201_172743.jpg
 
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Now I have a new question I wonder if anyone might have some insight into:
I originally intended to polish the floor with 7" diamond resin pads using my grinder but have learned that crawling around on the floor sucks.
I found a product that might be what I have wanted all along called Twister Diamond Floor Pads. https://americomfg.com/product/twister-floor-pads/
They look like big Scotch Brite pads and they come in a set of 4. A 400 grit, 800 grit, 1500 and 3000.
They are meant to be used wet and with a slow speed floor buffer. A set of these pads is around $200 and they last a long time.
I wonder if they would work for my project since this product looks to be more of a restoration/cleaning tool, but my my slab is pretty smooth as is so maybe they would shine up my floor?
 

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Those are interesting. I would call the company and tell them exactly what you are doing and how much you have already done. A buffer could be rented.
 
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I will call the manufacturer Monday and see what they say and post back. I'm hoping it will work because I think the relative softness of the pad (compared to a diamond grinding wheel) will allow it to flow with the subtle dips in the floor surface, and no more dust.

I found this video on YouTube of some guys demonstrating the process, a lot of folks are critical of it in the comments but I'm not looking for a mirror shine, I'm willing to settle for what might be considered an "ok" floor compared to what most hard core professionals produce... also I think I'll skip the burnishing step and just slow wet polish the 3000 and get what I get. I'll probably wax my floor anyway.

I'd like to know what some of you guys think of what is done in that video, thanks a lot, this thread is helping me along.
 
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I agree with you on that, but here the burnishing step is the final one for that high, no finish required kind of polish, and since we are doing this one room at a time I'm going to see what we get with this first room. Who knows, if we don't like the end result we could always go for the burnish.

I watched that video again and it's worth noting the two 40 pound horseshoe weights they have on their machine. Plus the weight of a 5 or so gallon water tank.
 

highup

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This is an interesting project. Do keep us updated.
Perfection is a brand new slab, with polishing being an intended part of the plan. So far what you have done looks pretty good. Once furnishings are in place, a lot of the floor won't be seen anyway.
 
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