concrete for grinding / polishing

[LD1]

I poured the floor in the new garage this weekend, and overall it ain't bad. But a number of things didn't go as planned.

The rain showed up about 2 hours early. Concrete was placed and set just ready to be troweled, and it rained. If rain held off as forecast it would have been done and covered.

Second thing I think was a combination of rookie driver and bad batch. I ordered 5 slump and this stuff was dry gravel with a little sand stuck to it. Well he watered it too much and we has soup. And the guy just wanted to sit in the truck where he could see us giving directions when to unlock chute, wheel to lock, when to stop, etc.

But all that aside, what's done is done. I am actually kinda happy with the finish. Look and feels like a floor that has been painted with that sandy paint. But not sure I will like that for a garage. On one hand, I want smooth for cleanup, but don't want to bust my Azz when wet. There are also a few high spots, bit not bad.

So...I am considering renting a grinder. They did some grinding/polishing in the break room at work and I really like it, but know nothing about it. Anyone care to shed some light? Best method or machine? Single head or double? Is there one wheel I can use for removing high spots that will also leave a good finish? Or am I gonna have to use half a dozen different grits getting finer each pass?

 

[davesl708]

Congrats on the new garage.

How about an epoxy coat? Will stick very well to fresh rough concrete.

I would be concerned about the very wet mix of the concrete. Will large machinery be sitting on it?
Might not be bad insurance to notify the concrete company about the wet mix.

 

[RDrancher]

It sounds like you were shorted on the cement content.

You can rent a single head floor sander and use sanding screens to straighten things up and then abrasive pads to add a little polish. If memory serves me, the white pad is the finest. We used to use a floor sander for acid stain prep. I'd let the concrete set up for at least three weeks before sanding. Be sure to use a good penetrating sealer. Forget the big box sealers. Make a visit to a decorative concrete store and get some good roll-on sealer.

 

[LD1]

I don't want to spend a ton on sealer or epoxy. Its just a garage floor. I am not fond of epoxy as my experience, it don't like heat. Like the abuses from torching and welding. Then it peels. And the result sucks. I like just natural concrete. Oil stained concrete looks good too. Again, working garage, not a museum. Just needs to be functional.

I do like the looks of the exposed aggregate after bringing. With that, and the few high spots I'd like to knock down, just wondering how well a grinder would do. Or if I am gonna make more of a mess trying to shave a few high spots and and up with lots of ridges?

And it seems there are a ton of options for heads. Different grit, diamond, etc. Would be nice if I only need 1 that will do a nice job of removal, yet still leave a food finish.

Not sure what the concrete company can do. Gonna be a "he said she said" thing and I am sure the driver will say I told him to keep adding.

And even if I have issues down the road with heavy equip, there is no way to prove that was the issue. But I don't for see any issues. 4" a 4000psi +wire, 4" stone, and solid clay under that. Heaviest I have is my BH @18k but big tires. Next to that is a drw pickup

 

[SPIKER]

LD1 good to see it coming along, I would keep it wet for next week or two even so it hydrates in this heat/cold well. I closed up my barn and flooded it for weeks and it is very hard! I used box store stain and it would not even penetrate even after using double strength acid etching & mops on it. the Rustolium Stain was - is GARBAGE get something better for sure. If you have not yet sealed it might as well wait as it is already late. Sealing it now is not going to help, using sealer after if hydrates & drys & prior to moving everything in.

M

 

[LD1]

Here are pics of 30-40 year old concrete that has been living under vinyl tile tile just last month. All I know is they went to 800 grit and then sealed. Have no idea beyond that. I really like the look, though I don't want it quite that slick.

 

[Streetcar]

With a wet load and rain during the set, you could be in for constant dusting of the floor if you do not seal it

 

[LD1]

When I say a wet load I may be exaggerating. It was wetter than I would have liked. But have poured and seen poured even wetter. This was maybe a 6-7 slump. And the concrete was pretty well set when the rain hit. Then it was off and on. I am no expert, but I dont think I hurt the floor any, just the finish. Which is why I am inquiring about grinding. I did some calling this morning. But am only left with more questions.

How long before I can grind? If more than 5 days, I may wait and proceed with building first.

Not sure what grinder I need, and what wheel. What grit? Flapper or diamond? Dual or single head? This is 40x40. I want something that wont take forever to remove the few high spots, but also leave a good finish. But will get different grits if need be. And would like to get this done in a day. And with never doing this, I dont want something that is gonna leave ridges where I remove high spots and try to taper back out to the rest of the floor. So what would be easier to NOT leave ridges, a single head or double?

 

[kevin37b]

LD you are obviously a handy person , enjoy your post's . As John said you got a bad batch , cement wise . As they say the cream comes to the top . Not so in your case . I would let normal traffic , wear / tear polish it up . You start grinding you may rip the top clean off of that floor . Just a thought from a dummy .

 

[EddieWalker]

Go to your local rental yard and see what they have. I've rented the ones with 3 stones that you put in with wood wedges. You have to buy the stones and they come in different grits like sandpaper. One type for removing a bunch of material, another for smoothing and another for making it shiny smooth. You just stand there and hole the machine while it spins and grinds down the concrete. It's real simple to use, but you do have to make sure you keep moving along so you don't wear down one spot more then another. With a fairly fresh pour, the concrete is still pretty soft and the sooner you get on it, the easier it's going to be.

Eddie

 

[LD1]

Well, I think I have made my descision after consulting everyone on my call list.

I called the people that did the grinding and polishing in the earlier picture. For a garage floor, his advise was a 40 grit finish. He said you will still be able to see some scratch marks, but you would have to really get down in the light just right. So it sounds not too smooth and not too rough. And that if I needed to hog a bunch off high spots to get 16 grit, but the 40 will do it all, just be a little slower.

Since the stones cost extra to rent, I think I am gonna shoot for a saturday rental that way I have all weekend to put 8 hrs on the machine if its a metered rate, and can get more "free" time if it isnt a metered rate. That will give me a full week of cure.

 

[s219]

How high are the high spots if you had to estimate, and how wide? Are we talking trip hazards or just something that would affect rolling carts? At a minimum, I'd wait 5-6 days until it has an initial cure and then look at it again to re-evaluate (I assume its under plastic right now). It may look better than you think, then again, it could be worse . But past experience has shown me it's good to step back for a bit and then think over the options rather than foam at the mouth right away (not always easy). When we troweled my barn floor there were a couple areas where it wasn't quite perfect, but I don't even notice/care anymore, especially after a year of use, dirt, grime, oil spots, etc.

We had a concrete floor ground down and sealed where I work, and it looks awesome -- looks classy. But it's in the foyer of a building. Not sure how well it would do in a shop. Especially the sealer. I don't have a feel for how a ground floor would hold up in a shop environment with or without sealer.

 

[EddieWalker]

When renting, I've always picked up a lot more of the disposables then I figure I needed and I also find that going with the most aggressive ones first seems to be what I use the most. If you do not use it, you get your money back when you return the machine. If you think you will need 3 sets of stones, bring home at least 6 and return what you don't use.

Eddie

 

[LD1]

How high are the high spots if you had to estimate, and how wide? Are we talking trip hazards or just something that would affect rolling carts? At a minimum, I'd wait 5-6 days until it has an initial cure and then look at it again to re-evaluate (I assume its under plastic right now). It may look better than you think, then again, it could be worse . But past experience has shown me it's good to step back for a bit and then think over the options rather than foam at the mouth right away (not always easy). When we troweled my barn floor there were a couple areas where it wasn't quite perfect, but I don't even notice/care anymore, especially after a year of use, dirt, grime, oil spots, etc.

We had a concrete floor ground down and sealed where I work, and it looks awesome -- looks classy. But it's in the foyer of a building. Not sure how well it would do in a shop. Especially the sealer. I don't have a feel for how a ground floor would hold up in a shop environment with or without sealer.

the high spots arent bad. Just enough that water dont make it to the drain in certain areas. Certainly nothing that would be a trip hazard or effect rolling a cart. Maybe 1/2" over a 5-10 sq ft area.

No its not under plastic. Continuous rain in the forecast and I am keeping it hosed down in between rains though.

When renting, I've always picked up a lot more of the disposables then I figure I needed and I also find that going with the most aggressive ones first seems to be what I use the most. If you do not use it, you get your money back when you return the machine. If you think you will need 3 sets of stones, bring home at least 6 and return what you don't use.

Eddie

No stones. Everywhere I am calling has dymaserts or diamond wheels. And they are super expensive to buy, and almost equally expensive to rent for the day. I just reserved a single 17" head electric grinder for the weekend for $125. Worth a try.

 

[EddieWalker]

Post pics, I'm not familiar with that and I'm interested in your results

Eddie

 

[Streetcar]

When I say a wet load I may be exaggerating. It was wetter than I would have liked. But have poured and seen poured even wetter. This was maybe a 6-7 slump. And the concrete was pretty well set when the rain hit. Then it was off and on. I am no expert, but I dont think I hurt the floor any, just the finish. Which is why I am inquiring about grinding. I did some calling this morning. But am only left with more questions.

How long before I can grind? If more than 5 days, I may wait and proceed with building first.

Not sure what grinder I need, and what wheel. What grit? Flapper or diamond? Dual or single head? This is 40x40. I want something that wont take forever to remove the few high spots, but also leave a good finish. But will get different grits if need be. And would like to get this done in a day. And with never doing this, I dont want something that is gonna leave ridges where I remove high spots and try to taper back out to the rest of the floor. So what would be easier to NOT leave ridges, a single head or double?

LD1
I had similar issue of rain hitting as concrete achieved its initial set. The top 1/8" of the slab was compromised.
My slab is outside storage so flaking and dust is not an issue. In a garage it would be another story.

 

[s219]

the high spots arent bad. Just enough that water dont make it to the drain in certain areas. Certainly nothing that would be a trip hazard or effect rolling a cart. Maybe 1/2" over a 5-10 sq ft area.

So that's not so bad other than maybe for drainage. But I guess one advantage of grinding is that you can get the surface down to a uniform hardness if there was any concern about the rain affecting the top surface durability.

 

[mjcountrybumpkin]

I really hope you got a grinding wheel and not the dima-serts( not spelled right). We ground 40,000 sq ft. With several machines a few years ago. After about 3 days, we stopped using the dima- sett heads all together.

If you grind any grind it all. Make the entire surface have a same finish then epoxy coat (after 30 day cure)and you'll be really happy.

 

[LD1]

I really hope you got a grinding wheel and not the dima-serts( not spelled right). We ground 40,000 sq ft. With several machines a few years ago. After about 3 days, we stopped using the dima- sett heads all together.

If you grind any grind it all. Make the entire surface have a same finish then epoxy coat (after 30 day cure)and you'll be really happy.

The one that I am renting, the way the guy describes it is one big 17" diamond wheel. I am gonna look at it friday night and if I like it, I will take it for the weekend.

Still no plans on epoxy though.

 

[mjcountrybumpkin]

The single grinding wheel design works excellent.
If you grind the surface of the concrete and do not want an epoxy, look at a densifier. The grinding of the surface will "soften" it a lot. A Densifier will fill in the microscopic voids and strengthen it.