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anyone have experience concrete floor grinding?

mark thomas

Titanium
Joined
Dec 15, 2004
Location
SF Bay Area
After considering epoxy and cement-based leveling for my shop floor, I'm now thinking maybe all I need is to grind it and seal it. I can rent an Edco 2-wheel grinder locally for $150/day. I figure I'd need to remove about 1/8" on average over the 400 square feet to get it as smooth and level as I'd like. The manufacturer says this grinder can remove 1/32" over 350-500 feet per hour. Four-plus hours of grinding sounds like a bit of a slog, but if it turned out well, probably worth it. I got 'resurfacing' (grind, level, epoxy coat) estimates from $4.50 to $7.50 per square foot.

Anyone have experience and advice about grinding concrete floors?
 

4GSR

Diamond
Joined
Jan 25, 2005
Location
Victoria, Texas, USA
In one of my past lives, we had a company out of the Dallas/Forth Worth Metroplex come down to our facility and refinish the floors. They shot peen the concret and removed about 3/16" to get below the oil stained concret. Once this was done, they floated the peened area with the epoxy grout and let dry about three days to harden before moving machines on it. We did sections of the shop at a time, took about two months to do the entire shop. Seem like it was much higher than $7.50 sf. Of course we had about 20K s/f done. BTW the surface held up darn good, easy to clean up/ contain spills. The surface was easly damaged by heavy parts dropped on the surface, damaged area was easly fixed with repair kits provided.

Ken S.
 

Timw

Stainless
Joined
Nov 8, 2005
Location
N E Florida
I would ask for a reference for someone who already used the machine and get their opinion and hopefully see their results. The grinding option sounds like a possible can of worms to me.
I would also ask about consumables with the machine. There has to be blades or teeth that wear. And how much mess does it create?
 

IdahoJim

Cast Iron
Joined
Apr 10, 2007
Location
Blackfoot, Idaho
After considering epoxy and cement-based leveling for my shop floor, I'm now thinking maybe all I need is to grind it and seal it. I can rent an Edco 2-wheel grinder locally for $150/day. I figure I'd need to remove about 1/8" on average over the 400 square feet to get it as smooth and level as I'd like. The manufacturer says this grinder can remove 1/32" over 350-500 feet per hour. Four-plus hours of grinding sounds like a bit of a slog, but if it turned out well, probably worth it. I got 'resurfacing' (grind, level, epoxy coat) estimates from $4.50 to $7.50 per square foot.

Anyone have experience and advice about grinding concrete floors?

Mark, the amount removed per hour will vary widely depending on the hardness of the surface. Some concrete floor surfaces are fairly soft, and others are very hard. You can geta bit of an idea by rubbing the clean surface with your hand...if your hand comes up with a lot of concrete dust on it you can assume the surface is fairly soft and will grind pretty quickly. I assume the Edco grinder is using non-diamond grinding stones? If that's the case, you want to buy a few bags of silica sand to use while grinding. you broadcast the sand on the floor before grinding....it helps keep the stones clean (much like chalking a file keeps the swarf buildup down) The sand also acts like an additional grinding agent. Just run the grinder back and forth like a floor buffer and check your results every few minutes, by sweeping things clean and seeing what you have. If you want a really slick finish, you'll probably have to go to diamonds at some point, but you can get a decent finish with just the carborundum stones. Once you have the finish you're happy with, apply an acid hardener to the floor....that will harden and densify the surface, and is a one-time application. Some people harden before diamond-grinding...it helps get a very slick finish. If you decide to stop with just a satin-type finish, and then harden, you can apply a sealer to the hardened surface which will give more gloss, and will fill some of the pores and minor pits left in the finish. The sealer will go farther on the hardened surface, as the hardening tends to seal the pores and prevent the sealer from soaking into the surface. If you want to forego using the sealer...no problem....the hardened surface alone is resistant to the penetration of spilled chemicals like oil, and they can usually be simply wiped up. You can also get acid hardeners that are colored, if you'd like to permanently color the floor. A few years ago, I had a customer that runs a Jaguar car shop. He decided to go with an acid hardener, but he wanted a Jag-Green floor, too. That was before acid-coloring had come along, so he tried adding Rit clothing dye to the acid. It worked very well, but he didn't use enough dye, so it's a faint green. He may be one of the very first people to use color with the acid hardener.
Be sure and use a dust mask if it starts getting dusty in your shop.....there is silica in the concrete, and you're also using silica sand in the girnding process.....silica dust is a good thing to keep out of your lungs, if possible.
The non-color hardener I've used the most is "Lapidolith" by Sonneborn. Any good concrete accessory-supply business should be able to order it for you, or know of a comparable substitute.
Jim
 

swarf_rat

Titanium
Joined
Feb 24, 2004
Location
Napa, CA
Would acid hardener be a good choice on a concrete floor in otherwise good condition? I have a steel trowel finished floor, always meant to paint it but never got around to it. Now I am getting oil stains from the inevitable spills, would like a more stain resistant surface but I'm a little skeptical about how well paint will stand up. The floor gets stuff dragged over it, driven on by my forklift, etc.
 

IdahoJim

Cast Iron
Joined
Apr 10, 2007
Location
Blackfoot, Idaho
Would acid hardener be a good choice on a concrete floor in otherwise good condition? I have a steel trowel finished floor, always meant to paint it but never got around to it. Now I am getting oil stains from the inevitable spills, would like a more stain resistant surface but I'm a little skeptical about how well paint will stand up. The floor gets stuff dragged over it, driven on by my forklift, etc.

Yup...the acid hardener will help, but won't eliminate the stains you already have. I'd clean the oily areas of the floor really well with TSP (trisodiumphosphate) before using the hardener. Let the floor dry after cleaning before using the hardener as you want the hardener solution to penetrate into the surface. The hardener makes the floor much more resisitant to damge from abrasion (like dragging heavy machinery over it). If the floor has had any sort of sealer applied, that sealer should be removed before using the hardener.
 

kustomizingkid

Titanium
Joined
Aug 2, 2010
Location
Minnesota
I just did my home garage 26x32', concrete was in excellent shape but very tightly power trowelled so I just needed to break the top layer to help the epoxy bond. Took 6 hours of straight grinding.
 

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
I know the process is much slower then wood but... I have read that wood floor sanding can quickly make thing less flat with dips and humps. that is why I used agiant random orbit sander not a belt sander when i did my floors. I have seen refinished wood floors with gouges from letting the drum sander stop moving.
Hardest part is getting into the corners and along edges
Bill D
 
Joined
Nov 19, 2007
Location
marysville ohio
After considering epoxy and cement-based leveling for my shop floor, I'm now thinking maybe all I need is to grind it and seal it. I can rent an Edco 2-wheel grinder locally for $150/day. I figure I'd need to remove about 1/8" on average over the 400 square feet to get it as smooth and level as I'd like. The manufacturer says this grinder can remove 1/32" over 350-500 feet per hour. Four-plus hours of grinding sounds like a bit of a slog, but if it turned out well, probably worth it. I got 'resurfacing' (grind, level, epoxy coat) estimates from $4.50 to $7.50 per square foot.

Anyone have experience and advice about grinding concrete floors?
My friend had a new floor poured and they did a lousy job finishing it. they said we can fix it by grinding it. Not so much. now he has a badly finished floor with big old grooves in it. Not really like waves. more like swells!
 

jscpm

Titanium
Joined
May 4, 2010
Location
Cambridge, MA
Just to emphasize what moonlight says above, you cannot get a floor level by doing what you propose.

I had an epoxy floor installed and after the "professionals" were done, there were serious differences in level and the boss came with a machine and verified that his workers had basically screwed up and not done things correctly, and they had to regrind the whole floor, then install these special studs that establish the level plane and regrind again and pour again and they got it more or less level the second time.

Basically, unless you are skilled, you will not get a level floor. Also, it is a lot of work. Grinding is no joke. Those guys were working on my floor for like two weeks and there were 2 of them and it was only about 750 SF.
 

BoxcarPete

Stainless
Joined
Nov 30, 2018
Location
Michigan, USA
It might depend on the grinder you get. I did about 1600 ft² a couple years ago, took me 8-10 hours with the big boy propane powered triple-orbiting disc diamond grinder. It was self-driving and I had no trouble keeping everything level to the limit of observable perception. Maybe if I started laying levels out they would show some dips, but mostly it was just like mowing the lawn with a double-wide walk behind mower on its slowest speed (but maybe even a little slower). If I remember correctly I spent more time vacuuming up dust and changing bags than I did actually grinding anything.
 

MaxPrairie

Hot Rolled
Joined
Jul 9, 2015
I know a guy who does epoxy floors, business moved from Minnesota to Florida. He says the concrete down there is very soft compared to up here. So depending on the area and aggregate used, you may have it easy or hard. Typically, the grinding is done to prep a good surface for the epoxy to bite into. You may be better off grinding a lick off, using a concrete binder, then use a self leveling mix over top. He also says grinding is better than blasting, I don't know enough to dispute that. You do need to get that dust off after grinding also. If you want more info, I can find out...I think he only charges 50 cents/sf for advice. :codger:
 

doug8cat

Titanium
Joined
Jul 10, 2008
Location
Philadelphia
IMHO unless you REALLY know what you are doing, leave it to a proffesional, especially if you are planning on coating or sealing it. A couple of decades ago I built an ~400 Sq foot kennel. Had the concrete floor sanded and epoxy coated . The proffessional (Came highly recommended.) Something went arwry and it had had to done all over again, contractor covered it but I had to deal with the 3 week delay while trying run a Vet practice.
 

mike44

Aluminum
Joined
Mar 21, 2020
I have seen concrete floors that cement finishers have grinded. I would leave this job to professionals. Probably have seen this 15+ times. If a slab is rained on when the concrete has not begun to dry , then pock marks appear from the drops. The finishers would power trowel the slab til the floor was without pock marks when the concrete begins to turn white. Even if the rain continued, they could still trowel the slab if it turns white.
Also have seen old floors ground to remove bad finish or oil stain marks.
 

Ivan Vegvary

Plastic
Joined
Sep 23, 2017
After considering epoxy and cement-based leveling for my shop floor, I'm now thinking maybe all I need is to grind it and seal it. I can rent an Edco 2-wheel grinder locally for $150/day. I figure I'd need to remove about 1/8" on average over the 400 square feet to get it as smooth and level as I'd like. The manufacturer says this grinder can remove 1/32" over 350-500 feet per hour. Four-plus hours of grinding sounds like a bit of a slog, but if it turned out well, probably worth it. I got 'resurfacing' (grind, level, epoxy coat) estimates from $4.50 to $7.50 per square foot.

Anyone have experience and advice about grinding concrete floors?
Only did this once. Poured a raised circular concrete platform. Wife wanted to "marbize" stain it. Rented a floor belt sander. Did a marvelous job, only cost me 2 belts. Kept the machine in constant arc-like motion. Easy.
 








 
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