Floor grinding not going well.

[roger55]

I started the floor with a test in a place where I will have cabinets.

After I ground about a 3 ft2 section, I found that the section is not smooth at all. The cement areas around the pebbles are ground out 1/16 to 1/8 of an inch lower than the exposed pebbles. And in a few places, there are pockets even deeper than that. I am also finding it very difficult to grind it evenly without small mounds or gouges.


And btw, dust is flying everywhere! The shopvac is a 5.5 hp model with a clean filter and it can't even come close to sucking up everything out of the dustless hood.

What the heck am I doing wrong??? Would it make any difference to try do it wet?
No way I can do anymore of the floor like this. I am frustrated and thinking about stopping here and going to an acid etch instead.

This is the diamond cup wheel I am using:
http://www.toolplanet.com/product/910527

 

[PAToyota]

I really doubt that you are going to get results that you're pleased with using a handheld grinder.

 

[rsanter]

not sure who it is but someone makes a device that will hold a grinder like that for doing floor grinding. it is really for finishing the edges where the large grinder cannot get up to.

you can try one but I think renting a full sized grinder would be better

bob

 

[Brickout]

It almost looks as if you're taking too much off.

 

[tojan19]

That's the same grinder set up I used but different wheel. I didn't have a problem with my pebbles not grinding down. I did only have a few strips of floor where I hit pebbles. You will open up some sub-surface voids but the should be small. The epoxy will fill these. My vac was a 6hp and I also used the clean stream filter. It's going to clog up pretty quick but not every 3sq ft. All it takes is a little banging to get the stuff out. Don't try washing it unless you have 2 days to let it dry. Try putting a little water in the bottom of the vac. not so much it hits the filter. If you have a vac where the inlet tube is exposed in the tank as I'm pretty sure all shop vac brand vacs do, go get a drywall dust bag. It helps. I replaced my Craftsman with a new Ridgid in the middle of my project (Stupid filter holder broke and I needed and excuse for a new one) and was able to switch to using bags. Keep the filter in there also. I still had a good bit of dust escape and had to sweep up / vac occasionally. It's probably going to take you more than 3sq ft to get the hang of how to move and hold the grinder. You'll get it. I'm sure you'll get a few spots where the edge catches and you put a nice gouge in the floor. I had about 6 over 300sf. After the epoxy and flakes are down I can't even find them. The epoxy probably filled the spots.
I really suggest knee pads or a foam cushion. I had a cushion from hunting. You still need a dust mask or respirator, wear gloves and long sleeves because the concrete dust ***** the moisture out of your skin.

 

[Kevin54]

Roger.......check this thread to see if it may help http://www.garagejournal.com/forum/showthread.php?t=20542

 

[JohnReynolds]

FYI, be sure to check the condition of the grinding wheel. They wear down REAL fast and when they do wear down, it will feel like using a jack-hammer the way that grinder will bounce around.

John

 

[roger55]

That's the same grinder set up I used but different wheel. I didn't have a problem with my pebbles not grinding down. I did only have a few strips of floor where I hit pebbles. You will open up some sub-surface voids but the should be small. The epoxy will fill these. My vac was a 6hp and I also used the clean stream filter. It's going to clog up pretty quick but not every 3sq ft. All it takes is a little banging to get the stuff out. Don't try washing it unless you have 2 days to let it dry. Try putting a little water in the bottom of the vac. not so much it hits the filter. If you have a vac where the inlet tube is exposed in the tank as I'm pretty sure all shop vac brand vacs do, go get a drywall dust bag. It helps. I replaced my Craftsman with a new Ridgid in the middle of my project (Stupid filter holder broke and I needed and excuse for a new one) and was able to switch to using bags. Keep the filter in there also. I still had a good bit of dust escape and had to sweep up / vac occasionally. It's probably going to take you more than 3sq ft to get the hang of how to move and hold the grinder. You'll get it. I'm sure you'll get a few spots where the edge catches and you put a nice gouge in the floor. I had about 6 over 300sf. After the epoxy and flakes are down I can't even find them. The epoxy probably filled the spots.
I really suggest knee pads or a foam cushion. I had a cushion from hunting. You still need a dust mask or respirator, wear gloves and long sleeves because the concrete dust ***** the moisture out of your skin.

It's not that the gravel in the concrete doesn't grind down. It's that the cement between the gravel pebbles seems to be pulled out down lower. It is leaving a really rough surface.
The grinder is removing so much material that the shop vac can't even begin to **** it in at all. So, it's not a matter of the type of filter. Material and dust flies all over the place. No way I can continue to grind like that. I am really at a loss as to why I am not getting results like yours. Could my concrete be that much different? It was poured 4 months ago. Could it be the wheel difference?

Since 25 mils is only about 1/40 of an inch, I don't see how the entire rough floor could ever be smoothed out with epoxy. I am not going to use chips and I want a nice smooth surface.

I think I am done trying to grind and I think I'll have to go the acid etch route. Too bad I just spent $300 on the grinder, hood and wheel. I am pretty frustrated.

 

[AlphaGarage]

It does look like you're taking that down way too much. The aggregate is much tougher than the cement, so understandably the grind will remove the cement leaving tiny stone islands.

The purpose of grinding before coating is primarily to remove material the may inhibit adhesion, to expose more surface area for the coating to mechanically grab onto, and, with the better epoxies, to open pores giving the coating more area to chemically interact with.

On some floors there is the added benefit of smoothing an irregular surface, but that's not usually the necessary, and if it is needed floor wide, then a hand grinder is the wrong approach, or at least not a quick one.

When the fresh concrete cures, certain components migrate to the surface, these can be hard and slick, grinding removes those very thin layers. If the concrete is overworked to get it smooth, that condition is exacerbated.

To accomplish those goals usually the grind doesn't need to reach down very deep, literally it just needs to go down a few mils, the thickness of a couple of sheets of copy paper.

 

[roger55]

It does look like you're taking that down way too much. The aggregate is much tougher than the cement, so understandably the grind will remove the cement leaving tiny stone islands.

The purpose of grinding before coating is primarily to remove material the may inhibit adhesion, to expose more surface area for the coating to mechanically grab onto, and, with the better epoxies, to open pores giving the coating more area to chemically interact with.

On some floors there is the added benefit of smoothing an irregular surface, but that's not usually the necessary, and if it is needed floor wide, then a hand grinder is the wrong approach, or at least not a quick one.

When the fresh concrete cures, certain components migrate to the surface, these can be hard and slick, grinding removes those very thin layers. If the concrete is overworked to get it smooth, that condition is exacerbated.

To accomplish those goals usually the grind doesn't need to reach down very deep, literally it just needs to go down a few mils, the thickness of a couple of sheets of copy paper.

That's good to know.
Maybe my wheel is just too aggressive. It cuts very, very fast. I'm not sure if I can move the grinder fast enough just to take off a few mils. Plus, I'm pretty sure I couldn't get it even. Do you think the acid etching is a better thing to do in my case? My floor is pretty smooth overall except for a few small divots that could be filled prior to using epoxy.

 

[AGBill]

I have tried to hand grind my concrete floor with the same results you have experienced. I used up 6 carbide discs grinding an area about 2 feet by 3 feet. It is not possible to do this task with a hand grinder, period.....

To see what equipment is required to grind a floor, take a look at this thread:

http://www.garagejournal.com/forum/showthread.php?t=15731

Unfortunately, very few rental places have the proper equipment for rental, and none were available in my area. Acid etching is probably your only option.....

Bill

 

[AlphaGarage]

The wheel could be very tough, your cement could be a bit soft, the reason is probably somewhere in between.

People have had good results with muriatic etching and our epoxies, specifically BonTite 1101 when used as a primer coat. When you put down the muriatic acid the substrate should fizz a bit, if it doesn't you need a stronger concentration, if it smokes you need to dilute it. But concentrations differ supplier to supplier, so be sure to read and follow all instructions and warnings carefully.

Keep in mind that muriatic acid is a caustic and nasty chemical, but it is cheap and easily sourced. We carry a organic "green' etcher that does the same job, OrganiPrep 921. We sell it to zoos, patient care facilities, clean rooms, places that can't take the dust from grinding, or the harsh side effects of muriatic acid.

OrganiPrep 921 is a concrete etch compound specially designed to provide a surface profile on green and mature concrete. The depth of the etching achieved with this product is the same as hydrochloric or muriatic acid with 80% less odor and a more uniform etch than liquid etch materials. Safer for use than hydrochloric or muriatic acid. The residue is easily removed by rinsing with water. The gelled form of OrganiPrep 921 provides easier neutralization and rinsing than liquid products since it does not highly penetrate into the concrete. The downside? It costs more than muriatic acid.

 

[roger55]

Update

I decided to give grinding another shot today.

After trying the new Hitachi grinder again, I decided that it still was just cutting to fast for me to control. It only has one speed (6000 rpm) and I thought if I could just slow it down, it might be controllable.

I checked an old 7 inch polisher/sander that I had stuffed in a drawer and found that it had the same 5/8 - 11 threaded shaft. It is a variable speed with a max rpm of 3000. I put the 7 inch diamond cup on it and gave it a try.

Well, I found that it is easy to control and cuts just fine. I used it full speed with a little downward pressure in a circular motion. I am able to keep the cup really flat on the the concrete and am getting a very even surface with a nice sandpaper texture.
After about an hour and a half, the sander (Harborfreight cheapie) died. I went over to Autozone and picked up a new polisher/sander for $75 that was also a 3000 rpm maximum with the right threads. I told them that I was going to give the thing hard use. They said if it breaks within 90 days, they would give me a refund. I would have bought a good name brand unit but I could not find one in San Angelo and I wanted to continue my grinding today. So Autozone was my only choice.

I did a little over 300 square feet this afternoon. It is probably going at a rate of about 100 square feet per hour.

I need to grind 1050 square feet total (4 different rooms), so it is going to take me several more hours and it is pretty hard work.
However, I think I will have a better profile for the epoxy using the grinder versus the acid.

I still haven't decided on the epoxy to use yet. I am leaning towards the Wolverine.

Here's my workshop build thread:
http://www.garagejournal.com/forum/showthread.php?t=8044

 

[Buckled]

If you have more trouble you might want to try renting one of these and the vac that goes with it. The vac is made for commercial grinding and tuck pointing and can handle the concrete dust. It works pretty well.

http://www.us.hilti.com/holus/modules/prcat/prca_navigation.jsp?OID=-17659