Grinding uneven/ not flat concrete floor?

[ianagos]

Well I was asking before about a good contractor and never was able to get someone good. first guy I hired delayed for 2 months until I hired a large industrial firm to finish the pour. This firm does alot of the huge industrial and commercial pours through Atlanta so I figured they wouldn't have a problem with a easy 1280sqft. Turns out the industrial firm thought it would be a walk in the park and they ended up screwing it up. Not terribly but the floor is definitely not flat as promised and they were not able to slope for my drain or put in the anchor bolts. They are not really willing to remedy the situation but have somewhat considered giving me a credit with their company for other services?

The question is has anyone ever ground a floor to achieve a better degree of flatness?

I was planning on renting a Blastrac BMG-555 as it is available locally. All in all it would come out to about $3200 for everything I need all the way to a 400 grit polish.
With that machine Does anyone think it would be possible to remedy the situation? i will attach pictures of the worst area and the rest is mostly fine only slight humps.

I also have a company that said they could come out and polish for $6500 but they make no guarantees to flatness but did say he would see what his guys could do? They include a sealer which I'm not sure I want as I was planning on going with the ballistix coating?

I already purchased the densifier as I was planning on using it on the power troweled concrete.

Here are some pictures
In this first one you can see the low spot. it is such that rain on the garage door would flow to the middle of the shop.

From my measuring all the edges are also 1/8-1/4 high so just taking those own would help significantly


Here is the low spot

Floor drain they also left the bathroom area very rough as they did not hand trowel in and the power trowel couldn't reach


There is a lot of pine straw in the surface. It was storming during the pour so heavy winds and rain.
I was picking it out but the concrete guy said to stop as it wont affect the final floor.


And a few more of the cuts they did.
I though they would use a walk behind or sof cut saw but nope i was gone 15 min and came out to see them cutting with a demo saw... is this normal?

 

[ianagos]

I should also mention a repour is mostly out of the question due to time and cost. This is a 8" thick slab with 24" footer and 4k fiber concrete. Rebar is on 12" centers and since I cut out some of the old slab that was here 6-8" fiber concrete with no rebar I do not want to cut out this one.

Close friends and family have told me that if I leave this in there knowing the type of person I am it will bother me indefinitely so I don't mind biting the bullet on this grinding now.

 

[ConCretin]

Definitely not a professional job on several levels. The hand work around the drain is awful. The saw cuts should ideally be done immediately after the concrete is set using an early entry saw. In addition, the cuts should be 1/4 the slab depth and need I mention, straight. Two fails right there.

The overall flatness might not be as bad as the string line indicates since slab edges tend to rise up with power troweling. The traditional way to assess flatness is using a 10' straightedge. 1/4" gaps underneath aren't unusual for a standard floor.

The biggest concern might be the stormy weather. If they didn't remove the surface water before finishing, you are likely to have a very dusty floor.

Not sure I can offer much in the way of repairs. Grinding can help with rough areas but it's harder improve levelness with a grinder than you might think and it's obviously not going to fix those crappy saw cuts. Sorry for your troubles.

 

[ianagos]

Definitely not a professional job on several levels. The hand work around the drain is awful. The saw cuts should ideally be done immediately after the concrete is set using an early entry saw. In addition, the cuts should be 1/4 the slab depth and need I mention, straight. Two fails right there.

The overall flatness might not be as bad as the string line indicates since slab edges tend to rise up with power troweling. The traditional way to assess flatness is using a 10' straightedge. 1/4" gaps underneath aren't unusual for a standard floor.

The biggest concern might be the stormy weather. If they didn't remove the surface water before finishing, you are likely to have a very dusty floor.

Not sure I can offer much in the way of repairs. Grinding can help with rough areas but it's harder improve levelness with a grinder than you might think and it's obviously not going to fix those crappy saw cuts. Sorry for your troubles.

Well pretty much what I figured.

The rebar and base compaction was all done by me so I know that was correct.

The rain let up just after the last truck poured and they covered the slab in plastic for an hour or so and came back with the power trowel.

I’m still water curing it’s been about 2 weeks since the pour.

The edges are definitely high and that’s why I was thinking grinding there should help the situation a good amount

 

[Armorpoxy]

As the former owner of a large surface prep company we can tell you that attempting to grind a floor to 'make flatter' is almost impossible as the grinder will just follow the current floor pattern flow. What a grinder will do is grind down and smooth small irregular high spots and remove material or smooth out the areas it is grinding on but it is very hard to use the grinder to grind large areas to lower heights.

 

[ianagos]

As the former owner of a large surface prep company we can tell you that attempting to grind a floor to 'make flatter' is almost impossible as the grinder will just follow the current floor pattern flow. What a grinder will do is grind down and smooth small irregular high spots and remove material or smooth out the areas it is grinding on but it is very hard to use the grinder to grind large areas to lower heights.

Since the floor is majority flat except for the one low spot and the high edges do you think it will be feasible to grind down the edges some and then just work on the majority of the floor avoiding the low area?

There is no getting away from grinding as I have to do something the get the slope from the garage door to not flow In but I know that could be corrected with a 7” hand grinder vs renting a planetary grinder

 

[Armorpoxy]

In our opinion you would have better control to make these corrections with a hand grinder since a large planetary is much harder to control to make corrections on smaller areas. Make sure to wear a mask and good full face respirator and that your grinder has a shroud with vacuum hookup as the amount of concrete dust this process can create is enormous and not to be inhaled.

 

[ianagos]

In our opinion you would have better control to make these corrections with a hand grinder since a large planetary is much harder to control to make corrections on smaller areas. Make sure to wear a mask and good full face respirator and that your grinder has a shroud with vacuum hookup as the amount of concrete dust this process can create is enormous and not to be inhaled.

Ok will that sounds like something I can do try to correct the worst stuff with a hand grinder then just run the planetary over to get uniform surface finish. I know I may get exposed aggregate in some locations and I don’t care. The apearance is not critical to me more so the flatness and good surface finish.

The area is 1280sqft that will be a cnc machine shop.

I have lithi-tech 4500 I plan on densifing after the 80 grit metal bond diamonds. Then I would run a 100/120 grit then start at 100 resin bond all the way to 400.

Now I also already have ghost sheild 8510 on hand do you think I should apply that or something else as a sealer to go under your ballistix product? I have another project to use it on if not on this só it’s not big deal to buy something else. I just want to make sure the ballistix has a very good bond. Really choosing ballistix as it was listed to be able to go on polished concrete and be area patchable.

 

[Armorpoxy]

Hi, do NOT use Ghostshield 8510 under Ballistix, they are not compatible. The densifier should be fine though.

Most water based sealers should work fine. Our ARM8400X is what we pair it with with excellent results.

 

[ianagos]

Hi, do NOT use Ghostshield 8510 under Ballistix, they are not compatible. The densifier should be fine though.

Most water based sealers should work fine. Our ARM8400X is what we pair it with with excellent results.

Ok will do thank you for your help so far.

Any tips on the grinding? Do you think it’s possible a beginner?

 

[Denwood]

I ground my floor with the HD diambrush deal which worked ok for paint prep, but is not nearly as aggressive as you'd want. I helped my neighbour out with a 240 volt (commercial) floor grinder and it turned out extremely well, and did not take long. For sure you can do this DIY, but like others have said, I would not try and re profile the existing slab as ya, the grinder will follow the slab level.

$3200 sounds crazy expensive for what you need.

 

[ianagos]

I ground my floor with the HD diambrush deal which worked ok for paint prep, but is not nearly as aggressive as you'd want. I helped my neighbour out with a 240 volt (commercial) floor grinder and it turned out extremely well, and did not take long. For sure you can do this DIY, but like others have said, I would not try and re profile the existing slab as ya, the grinder will follow the slab level.

$3200 sounds crazy expensive for what you need.

It’s $800 for the grinder then the rest of for all the consumables like the diamonds.

The concrete company is fighting me said they did a fine job and trying to say they did this as a favor etc etc why should I expect a commercial grade job blah blah when that’s why I hired a more expensive industrial company at all…

 

[Armorpoxy]

Honestly it can be done. Give yourself a lot of time and a good vacuum. Make sure you take measurements with a laser and a measuring method to mark your progress.

When we grinded floors flat we used sophisticated lasers and such and it was very difficult and time consuming and expensive.

If you really want to do it right pour a new self leveling topping, that’s what we did very often.

 

[ianagos]

Honestly it can be done. Give yourself a lot of time and a good vacuum. Make sure you take measurements with a laser and a measuring method to mark your progress.

When we grinded floors flat we used sophisticated lasers and such and it was very difficult and time consuming and expensive.

If you really want to do it right pour a new self leveling topping, that’s what we did very often.

I have a decent rotary laser As well as a plane laser level. Family used to do some grading work.

Forms where checked before they poured to be within 1/8" but that didn't help the floor....

 

[mepstein]

It’s $800 for the grinder then the rest of for all the consumables like the diamonds.

The concrete company is fighting me said they did a fine job and trying to say they did this as a favor etc etc why should I expect a commercial grade job blah blah when that’s why I hired a more expensive industrial company at all…

Did you have a contract that specified what was promised or expected? Did you pay them in full? Once they have their money, it's done, at least in their mind.
I think trying to grind it yourself will result in more money with minimal results.

 

[ianagos]

Did you have a contract that specified what was promised or expected? Did you pay them in full? Once they have their money, it's done, at least in their mind.
I think trying to grind it yourself will result in more money with minimal results.

The contract was verbal and the wanted payment in full which I was thinking this is a big company why should I worry.
I told him and he agreed it would be within 1/4". the anchor bolts was also very clearly part of the job but they didn't do that either.

I'm going to drive out to them tomorrow he basically got to the point of insulting me via text message today. Basically saying that my expectations are ludicrous. Funny that wasn't the case when I stated it all out before they did the work....

They are just going hard into the blaming me saying this is just residential why should I expect it to be done to such a high standard.

How many residential slabs with 8" of concrete and rebar on 1ft centers do you see?

 

[Sumboodie]

Possible to overpour a self levelling "grout" if you need the floor to be really flat?

The floor in the warehouse is lumpy enough that the forklift scrapes on a couple spots. And this was a several million dollar aircraft hangar when it was built in 2003

 

[ianagos]

Possible to overpour a self levelling "grout" if you need the floor to be really flat?

The floor in the warehouse is lumpy enough that the forklift scrapes on a couple spots. And this was a several million dollar aircraft hangar when it was built in 2003

well everyone I've talked to said it would probably chip out at the edges. This shop will be for heavy equipment. ill be putting a 36klbs machine on one side and a 15k lbs in the middle and a bunch of smaller lighter equipment in the 2-5klbs range. that equipment usually comes in on machinery skates etc. and have very high point loads.

I want a nice flat floor because if I do welding layout or even just carrying heavy stuff on a pallet jack it makes life easier. also would really like water to not pool in there...

I have considered a patch there and epoxy but id still have to grind for epoxy. i had epoxy in the last shop as well and it chipped up in a few places and you cant just patch that up.

 

[Sumboodie]

Heavy equipment usually has wheels or tracks. What kind of equipment uses skates to move around?

 

[ianagos]

Heavy equipment usually has wheels or tracks. What kind of equipment uses skates to move around?

They just come in on skates then they set them and drill foundation etc. Planned machine is a Mazak Integrex I200ST

 

[Sumboodie]

Oh, milling machines. Not heavy equipment. I mean, sure it's heavy, and I guess equipment, but heavy equipment is construction, forestry, farming type stuff is what heavy equipment is.

 

[Sumboodie]

You don't need pads for those machines to sit on? My brother is an manufacturing engineer at a big gun outfit. They have 4ft+ thick slabs under some of their machines.

 

[ianagos]

You don't need pads for those machines to sit on? My brother is an manufacturing engineer at a big gun outfit. They have 4ft+ thick slabs under some of their machines.

I think Mazak specs out a 2ft thick foundation for them to garuntee their .0002” accuracy over the machine but that’s not needed for me. My last integrex was on worse concrete and held .0002” for me once warmed up.

I also have a 22klbs forklift and my skid steer they will live outside but will come in the door for moving equipment.

 

[benwah]

I have lithi-tech 4500 I plan on densifing after the 80 grit metal bond diamonds. Then I would run a 100/120 grit then start at 100 resin bond all the way to 400.

If you densify after 80s, you'll almost guaranteed cut the densifier off with the 100's.

My suggestion would be to density after 200 grit resin bonds, that way you finish with the 400's and the densifier is still in tact.

 

[ianagos]

If you densify after 80s, you'll almost guaranteed cut the densifier off with the 100's.

My suggestion would be to density after 200 grit resin bonds, that way you finish with the 400's and the densifier is still in tact.

Good to know thank you

 

[ianagos]

As an update the current plan is to grind the high edges down with a 7" makita grinder and then start putting up the walls the by the time that is done it will be over 30 days and the concrete will be cured enough. at the moment the surface of the concrete is still very soft. scratched by my 3 mohs hardness pick. and it has been over 14 days

 

[ianagos]

Well I rented a larger 900lb propane grinder and things went ok. The grinder rental shop gave me the wrong diamond hardness even after I told them the hardness and I spent days grinding nothing because the diamonds kept glazing over. (they also told me what speeds to run the grinder and it was way too fast also causing issues) the rental place did make it right eventually though by exchanging the diamonds and giving me another weekend of grinder rental. I used a lavina grinder and used buttons for the grinding starting with a grey 30/40 ad moving all the way to an 800. Now that I know way too much about concrete grinding if you need more material removal id recommend starting with 30/40 grit bars then moving to the 30/40 buttons then stepping down to the 70 buttons and so on. By the way I am about 145lbs wet and you got to be a big boy to handle those grinders I had to swing like a monkey to tip that bad boy for diamond change outs.

Then I densified with lithi tek 4500 I used 1 gallon for about 1200sqft and it basically was not accepting any more and i was warned several times about putting too much on. I had 3 gallons on hand as I expected it to tale much more but it didn't. this came back to bite me later with my balistix install Also I actually did this after the 200grit resin bond diamonds

Lastly after the grinding and densification I sealed with ballistix counterattack. this may not have been the correct product for my application and I ran short even though I ordered extra. but it is beautiful where I had enough and it didn't soak in too much. I have some ballistix single component for after I finish the drywall and whatnot to make the floor hopefully get back to looking like it did after that 800 grit polish (it was beautiful)

I used rs-88 polyurea joint filler before I started grinding to fill the expansion cuts and it took forever to clean them out properly..
I did alot of my edging with the 7" makita and a name brand wheel but later gut a 4" wheel from harbor freight and it removed material much faster actually. I had to slope about 3/4" from the main slab to the front slab. you can see that in the picture of the inspector looking around

Inspector on the scene


Grinder and vacuum I used




After the 800 grit resin bond diamonds


You can see some of the waviness in the floor here. due to not great cutting diamonds and a real crazy floor so I had to settle.



Here is immediately after the ballistix and it did look better as I used the remainder I had to touch up but it had a 6 hour recoat window and it would be a day or 2 before I could get more so I will have to run a black stripping pad and try again if I want it to be perfect and i do after the approx. 40 hours of grinding I put into it yes at least 40 hours... 6-10 hours a day for 6 days.... I had another guy working for me taking some shifts on that thing.... as at first after I had issues with the diamonds the grinding company just kept saying keep trying those diamonds will probably work... they did not.

If you look at the back that's where I started a little heavy and it came out looking very good. some arras looked fine as I as applying but it soaked in as we were finishing. I was also able to see a lot of spider cracking in the concrete. I do believe the counterattack was not quite as viscous of a product as I was hoping for. It was not rated as a penetrating sealant but ill tell you it seriously soaked in and I like that as I really wanted a hybrid product that would be topical and stop all oil penetration As well as soak in so it would maintain water and oil repellency even if scratched off.

 

[haugy]

Well I rented a larger 900lb propane grinder and things went ok. The grinder rental shop gave me the wrong diamond hardness even after I told them the hardness and I spent days grinding nothing because the diamonds kept glazing over. (they also told me what speeds to run the grinder and it was way too fast also causing issues) the rental place did make it right eventually though by exchanging the diamonds and giving me another weekend of grinder rental. I used a lavina grinder and used buttons for the grinding starting with a grey 30/40 ad moving all the way to an 800. Now that I know way too much about concrete grinding if you need more material removal id recommend starting with 30/40 grit bars then moving to the 30/40 buttons then stepping down to the 70 buttons and so on. By the way I am about 145lbs wet and you got to be a big boy to handle those grinders I had to swing like a monkey to tip that bad boy for diamond change outs.

Grinder and vacuum I used

Hey man, I'm about to rent one of those Lavina's and use 70 grit on my floor to level out where it wasn't troweled dead flat and to put a profile on it. How did it do when you went from 30/40 to 70/80? I don't need to 30/40 mine, but am curious about the finish and overall look? Sounds like me at 175lbs will also be throwing my weight around haha

 

[ianagos]

Hey man, I'm about to rent one of those Lavina's and use 70 grit on my floor to level out where it wasn't troweled dead flat and to put a profile on it. How did it do when you went from 30/40 to 70/80? I don't need to 30/40 mine, but am curious about the finish and overall look? Sounds like me at 175lbs will also be throwing my weight around haha

Honestly with 30/40 buttons it’s already decently smooth. Going to the 70 didn’t visually look too much different actually except for a few spots that must have gotten a rock in there or something during the 30/40 and got more scratched.

I ran about 20 passes with the 30/40 and barely have exposed aggregate but that was really due to the wrong diamonds

Are you just profiling for epoxy?

The 30/40 and 70 take the longest and cost the most due to being metal bond diamonds after that it’s much cheaper and I’d say go ahead and take it higher if you don’t plan on doing epoxy since the added cost is almost nothing in comparison to the grinder rental.

 

[haugy]

Honestly with 30/40 buttons it’s already decently smooth. Going to the 70 didn’t visually look too much different actually except for a few spots that must have gotten a rock in there or something during the 30/40 and got more scratched.

I ran about 20 passes with the 30/40 and barely have exposed aggregate but that was really due to the wrong diamonds

Are you just profiling for epoxy?

The 30/40 and 70 take the longest and cost the most due to being metal bond diamonds after that it’s much cheaper and I’d say go ahead and take it higher if you don’t plan on doing epoxy since the added cost is almost nothing in comparison to the grinder rental.

Yeah, I'm just putting a CSP1 profile for Polyurea coating.

I've got a few rough spots where the finisher didn't smooth it out real good. (I told them I didn't want it polished).
I figured the 70 will easily knock down what I have (120 was doing it), but also enough to profile it. (120 was too smooth)

Mainly I'm debating the big Lavina. The cost is 3 times as much as the Edco. But I'm also doing 2,000sq/ft. I should have the same setup as you, Lavina and dust collector from Sunbelt.

 

[ianagos]

Yeah, I'm just putting a CSP1 profile for Polyurea coating.

I've got a few rough spots where the finisher didn't smooth it out real good. (I told them I didn't want it polished).
I figured the 70 will easily knock down what I have (120 was doing it), but also enough to profile it. (120 was too smooth)

Mainly I'm debating the big Lavina. The cost is 3 times as much as the Edco. But I'm also doing 2,000sq/ft. I should have the same setup as you, Lavina and dust collector from Sunbelt.

I don’t think you need the lavina for what your are doing. It’s gonna cost 3k or so for the setup.