Floor Grinder - Help

[mustangman]

I rented an EDCO floor grinder today - the one with two heads with diamond inserts. I am preping my garage floor for epoxy paint. The floor is 1200SF and after almost 6 hours, I have only done about 200SF. Not exactly what I was expecting. This is a 1 year old steel trowelled floor with no coatings or sealers and it is relatively flat. Do I have the right grit or am I doing something wrong? I tried grinding it wet and dry, with no significant difference. Also, the finish is still very smooth, not much different than the original and definitely not the 100 grit that I was wanting for the epoxy. Any thoughts or recommendations? I really did not want to acid etch, but I may have to.

Todd

 

[Bad Idea]

100 grit is not very aggressive, it is usually used for smoothing or polishing. If possible, get some diamonds that are more coarse. I usually use 30 grit for cutting. You can use a 60 grit and get a decent profile, 30 grit is good for prep but may leave some scratch marks that show through thin coatings.

 

[iceman536]

I spent maybe 6 hours grinding my 500 sq ft floor, and half of that had remnants of a previous epoxy coating. Did you tell the rental place what you were going to do? Sounds like they didn't set you up properly.

Also, your floor won't be noticeably "rough" after grinding. If you're creating dust then you're removing something, and that should result in a good profile for your epoxy.

 

[mustangman]

Thanks for the replies. I did tell the rental guys what I was going to do, but I don't think they were all that knowlegeable about epoxy floor prep. The grinder I got was the EDCO with the Dyma Sert diamond inserts. I do not know what grit they were. The EDCO website indicates that there are three different models available, but does not list the grit. I could not find any identifying marks on them. Anyway, after about 14 hours of grinding I am finally finished. The grinder did make a decent amount of dust so I am sure I was removing material albeit slowly. I ground away until the majority of the original finish was gone. There are still some small patches (low spots) where the original finish remains. Should I just hit these with the hand grinder? The surface where I ground still feels smooth. Definitely not a sandpaper like finish. Is this good enough for the epoxy to adhere to? Should I follow this up with acid etching. I plan on pressure washing the floor tomorrow the remove all of the dust and will let it sit about a week before applying the epoxy. I plan to use the PPG aquapon 35 product and will thin the first coat about 10%.

 

[iceman536]

My opinion is to not introduce water into the equation at all. Vacuum well then leaf blow the dust. I see no need to etch the floor (ever if you grind). Moisture will cause you much more problems than the 2 grains of dust you miss cleaning up.

I would guess your floor is rougher from grinding then you would get it by acid etching.

 

[jocool1585]

I work in rental and have rented those machines out for years. Ask them for the black grinding stones shown on this page: http://www.edcoinc.com/accessories-floor-grinder.html (right side). Those should leave a rougher finish than the diamond inserts. Those machines are really designed to cut down and smooth concrete, so you're never going to end up with a super rough surface with one. I've prepped several stores with the stones and have had good results.

 

[Black Moon]

I've used a 'shot grinder'. I'm not sure of the technical term but it uses little pieces of steel like ball bearings and blasts the floor. I does an awesome job but makes a bit of a mess. You have to stop every several minutes, sweep up the shot and refill the machine. Call some of the rental places and see if they have one.

Back up. Is there paint already on the floor or grease or sealer? If not just acid wash it. It's not hard to do, doesn't make a mess (no dust) if you're just trying to etch the concrete.

Good luck