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Floor grinding woes

ctfortner

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Dec 7, 2009
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193
Location
TN
Well add me to the long list of those who said grinding a floor for epoxy, *****. 10 plus hours of grinding and it's still not right. Here is how my weekend went. I have read and searched on here until I am blue in the face and thought I had a good plan to get this done.

Pickup an Edco 10" grinder and dustless vacuum from home depot at noon Saturday and after talking to the guy, actually convinced him to swap the disc out with a brand new one. This one uses a disc/blade, not inserts. Maybe that was part of the issue???

Get home and a friend joins me for what we assume to be many hours of grinding and sweeping...and it was. We picked a square, about 150 sq ft, and grinded and moved and grinded and moved...It just wasn't doing that much and he tried, I tried, we added 100 lbs worth of dumbbells, which helped but not much. After about 2 hours of grinding on that one square, we moved on.

I know the dang thing would cut because when you hit a high spot, it just ate it up. This concrete seems to be VERY hard, which I expected. I think the blade is having a hell of a time getting through the hard power troweled surface.

So of course I have read about the diamabrush...some good some bad. We were very frustrated in the edco so while he grinded (well attempted too), I ran to home depot and got a diamabrush. They did not have floor machine with vac attachment so he said use a buffer that has one. So I rented that. Let me tell you, this thing was laughable. We ran this thing on a square in the same spot for about 10 minutes and it hadn't even scratched the smooth concrete. I am sure it could have used some extra weight but since HD said get it back within 2 hours and I will give your money back, we just took it back.

So, back to the Edco. It never got any better, we did the entire floor this way, spending about an hour on each square going forward, taking turns. The end result is the entire floor still needs more work to be porous and/or have a sandpaper feel.

My dilemma is what to do next. I am $250 in to this point on rentals. I have the Nohr-S system sitting in the house waiting. Temps are steadily getting lower at night (in West TN). My initial thought is to get the 7" grinder and dust deputy and do a few squares a day (1600 sq ft total). I would be willing to rent another machine if there was one that would finish the job, but I have zero faith in the Edco, at least using the blade that I had on it. There are other rental places around here that you buy your own inserts. There is a place here that has the Husq P280 dual head, again i have to buy the inserts. It will cost me another $400 for that and inserts for 24 hours.

here are some pics of the concrete and what it looks like. You can even see rocks in some spots, but it still doesnt feel very rough, and it is not porous. I put some water on a couple spots, 2 hours later its still there.

The blade it had

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LegacyIndustrial

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deerfield, IL

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Shea

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Sep 19, 2012
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California
You most likely need softer bonded diamond inserts for the grinder. If the concrete is extremely hard at the surface as you state, then the bonding needs to wear away quicker to expose more of the diamonds for cutting (grinding). If it doesn't wear away fast enough the segments get clogged and tend to produce a finer finish and do not cut as well. They can even get hot enough to glaze over and put more of a polished finish on the concrete.
 

PureLeaf

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Jul 25, 2014
Messages
1,417
I've used the exact Edco grinder you rented but to grind old thin set off a floor after we removed the tile as we were trying to get it as smooth as possible to be covered with a floating floor of vinyl laminate. It worked great... it was slow, but I'd say it took about a day to do 1200 sq ft, and when the Edco would catch a high spot, it'd really try to twist your wrist and take off in a direction.
 
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ctfortner

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Dec 7, 2009
Messages
193
Location
TN
Got another machine rented for the weekend and soft (red) dyma dots made for hard concrete. Hopefully it will get the job done. I was going to rent the Husq. 280 or 450 but no one had the segments for hard concrete in stock and I couldnt get them in time for the weekend.
 
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ctfortner

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Dec 7, 2009
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TN
Alright, somethings going down this weekend, one way or another. I couldn't get the Husq. unit since no one had the inserts I needed for hard concrete. So I just picked up a newer model dual head edco unit, one that adjusts up and down to make level on your workspace. I did not plan to use this one since it requires 6 dyma dot inserts, 3 per side, at the tune of $60 each (at this rental place anyway).

Then the great folks there offered them to me at basically their cost, $40 each. So now I was looking at $105 for the grinder, and $240 for the double dot inserts. Oh, but wait...I needed the red ones (soft bond) for my crazy hard concrete, and they didn't have them in stock. Didn't have enough grey ones either, which is for Medium hard concrete. I am thinking the odds are against me with this and then he says hang on, let me check something. While on the phone he goes to their warehouse and rummages through bins and boxes and says wait, we may have something here. He was able to locate 6 used red (30 grit) soft bond double dyma dots for me, and even found a set of grey ones that are 18 grit as a spare. He said these were some people have bought and left on the machines in the past, you can just have them! I owe this guy a Thanksgiving turkey! SO, I have the dual head machine with 2 sets of serts, all the way till Monday since they are closed on the weekend, for $130 out the door.
I also recently met a super nice person that had an awesome vacuum setup they let me borrow, and I am very grateful for that as well. Things are looking up I think, let's just hope they get the job done!

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ctfortner

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TN
Haven't posted an update because it has been depressing... I must have the hardest concrete known to man.

So I got home with the Edco dual head and went to town with the soft 30 grit diamond dots and while they helped a little on the areas that I had almost done, they wouldn't do much of anything on the hard slick power troweled surface though, which really sucked. I gave it 4 or 5 hours of run anyway, swapping out the 30 grit with the 18 grit, no difference. I had the machine all weekend but didn't even use it Sunday as it was pointless.

I was off yesterday so I took the machine back and they offered me another one as a swap out since it didn't work for me, the Husq. PG 450. This is the one I wanted originally but it was in need of some work. We looked into that one and they changed out some things on it and it was good to go. All they had on hand were the pink 60 grit diamonds so I took them and tried it out. Well guess what? Yea, sucked too. I used it on a square that was pretty splotchy (as the pics in first post) and made 2 very slow passes in the same direction, then a slow pass in the opposite direction. About an hour total on that square, 150 sq ft or so. It is better, but there are still many smooth troweled spots left that it just will NOT touch, even if you focus on it.

So a recap:

I have used 3 different big grinders now with soft diamonds and hard diamonds, 18 grit, 30 grit and 60 grit.

I have an Edco machine (borrowed) to use all I want with a 7" diamond wheel cup. This does NOTHING on the the smooth troweled surface, wet or dry.

I tried a dymabrush from home depot on a buffer machine. The concrete literally laughed when we turned it on. It wouldn't make a scratch on it.

Let me know if you cannot see this video. I only filmed this for 2 minutes of it, but I ran the PG450 on the same spot for 5 minutes and it basically did nothing. It weighs 300 lbs! I added to 30 lb dumbells to it later and still nothing. I had my son stand on it, nothing. I want you to see how ineffective this is on my concrete. I am spent with this thing. I am going to try a test spot of etching and see if that will eat the crust off this mess. If it doesn't, I am at a loss. Maybe shot blast, or maybe just get a wrecking ball

https://photos.app.goo.gl/n5SKwSfeQieSFgXe6

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ctfortner

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TN

LegacyIndustrial

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Break out the etch.
BTW... if you still have the grinder, add weight and wet that surface.

In order for the grind process to work, you actually need the concrete to help you.
You need paste to form and get between the diamonds and the floor, the paste helps to wear down the steel that the diamonds are encapsulated in. No paste and you start to glaze the diamonds. If you think they are glazed, refresh them on some softer concrete, then go back to the hard stuff. I know it ***** but we do this every day and it is possible.
 
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ctfortner

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TN
I do not have the grinder anymore, but I used weights, up to 120lbs, and added my son once to ride on it, and used water in a spray bottle with all grinders. I have tried it all. I do believe it is possible, and I do believe I still may not have had the best/correct diamonds for my job. I am sure yall have big beastly machines with the correct diamonds and years of experience. Even if I could make what I have rented work, it would take days to do 1600 ft that way. I have more hours and pain of loading and hauling grinders that I care to get into at this point. Every pro I have spoken to locally says they generally shot blasts. I also talked to the guy that did my concrete and he chuckled a bit and said he wished he had known I was going to do this because he knew it was a shop that was going to be used (not just pretty) and they weighted their trowel machine to give it a nice hard top. To go along with the fact that it is 4000 psi limestone with fiber as well.


Break out the etch.
BTW... if you still have the grinder, add weight and wet that surface.

In order for the grind process to work, you actually need the concrete to help you.
You need paste to form and get between the diamonds and the floor, the paste helps to wear down the steel that the diamonds are encapsulated in. No paste and you start to glaze the diamonds. If you think they are glazed, refresh them on some softer concrete, then go back to the hard stuff. I know it ***** but we do this every day and it is possible.
 
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shadycrew31

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Jun 23, 2017
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Burbs of Philly
I get that you really want epoxy but it might be time to consider other options. Sounds like you've done a ton of work though, I would have thrown the towel in after the first hour.
 
Joined
Dec 24, 2018
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Location
Renton, WA
Hey CT. What's the latest? I've been grinding my garage floor (475 sq/ft) and had some of the same issues. I really wanted to get all the way down to the base concrete but, I can't get through most of it. I only tried the single disc EDCO grinder.

Anyway, would love to hear if you had any success since your last post.
 
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ctfortner

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Dec 7, 2009
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TN
Sorry, haven't been on here in a bit. The short story is that I am waiting on spring to finish this up. The weather got to where it we don't see many days above 50, other than random days here and there, and even then the humidity is 80% or more when that happens. Decided to wait and play it safe and also give me time to regenerate because I was ready to say screw it.

So, it is still not ground all the way and I will be looking to do this again around March. I am going to buy the softest diamonds I can find to hopefully cut the concrete better.
 

dcg9381

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Jun 20, 2018
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Austin, TX
So I had a similar floor. And same deal - hours and couldn't get the damn tire marks out.
What I didn't try was a "wet" grinder (home depot) - nor can I guarantee that using it would work.

I was going to ask if you'd considered polyurea, but note that you already have it. Our polyurea went down fine and has not even showed a hint of lifting. Consider a solid color if you've got those tire marks..
 

LegacyIndustrial

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deerfield, IL
A grind can help with surface anomalies but will not pull out waves in the concrete.
Sunbelt does have some decent equipment available.
Good luck with your project.
 

Armorpoxy

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NJ
A grinder will follow the pattern or waves of the floor to a great extent and most likely will not ‘level it out’. It will smooth out irregularities and properly open up the pores to accept a coating or resurfacer. The only way to really flatten out a floor without the use of sophisticated lasers to guide grinding is to pour a self leveling topping.
 

fredmatic

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Jun 18, 2023
Messages
2
I’m having the same issue. To the point the floor starts to give back this metal look makes no sense. The edco grinder I’m using is the brick inserts. Using a c10 coarseness. Nothing absolutely nothing. I’m lost at this point. I was looking for a blaster but no rental in this area has one. Severely delayed my project time. Any ideas would be appreciated.
 

benwah

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May 21, 2014
Messages
980
Location
Crested Butte, Colorado
I’m having the same issue. To the point the floor starts to give back this metal look makes no sense. The edco grinder I’m using is the brick inserts. Using a c10 coarseness. Nothing absolutely nothing. I’m lost at this point. I was looking for a blaster but no rental in this area has one. Severely delayed my project time. Any ideas would be appreciated.
Mist some water in front of your grinding path. Like Shea and Legacy mentioned, you most likely have the incorrect bond. If your concrete it extremely hard, you need a soft bond Diamond. If your concrete is extremely soft, you need a hard bond Diamond. I wouldn't expect the guys at Home Depot, or Lowe's or whatever to know this. Maybe you have a Sunbelt around you? If not, grab a pump sprayer and wet out the area in front of your grinding path and see how that works. We typically charge $1-$1.50/SF for surface prep depending on hardness. I perform a Mohs Hardness Test on every slab so I know which Diamonds to use
 

fredmatic

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Joined
Jun 18, 2023
Messages
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Unfortunately no sunbelt near me. I would have to go 40 miles out. I tried to water the path earlier I swear it started looking like metal like a shiny metal. And this is just a 280 sq ft one car garage lol
 

SolarColumbia

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May 7, 2019
Messages
211
Location
Wisconsin
I feel your pain. My past garage was 840 sq ft if hard troweled nastiness and the dual head Edco removed concrete but didn't profile well with the medium bond diamonds, which was all they had.
 

Hnines

Active member
Joined
May 13, 2017
Messages
26
I have 2 questions regarding this…..
1) In a situation like this, if you were to etch the floor first, would it possibly make the grinding process easier after the concrete had been etched?
2) In cases like this where you might not be able to get the pad grinded to the correct coarseness, are there some options that will bind to the floor better than others, like say polyurea for instance?
 

HaiKarate

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Oct 20, 2020
Messages
314
Location
Seattle
I kind of skimmed this so I may have missed it, but how are/were you powering this thing?

I only ask because I ran into similar issues with my machine. I didn't have power to the shop yet so was using a generator. "Seemed" to work fine - machine spun up and would 'grind' but very poor performance. Took me longer than I admit to figure out, but the generator I was using wasn't up to snuff (An OLD 5500w portable). Finally tried out a new 8000W+ unit and the grinder finally worked like it should.

TLDR; Ensure your power source is adequate
 

James-W

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Feb 3, 2013
Messages
12,432
Location
Southeastern Wisconsin
I may be out of line here, and if i am then I apologize. But I am thinking if I were you I would hire it done. You have spent a lot of time on this project and it seems to be a project that is not going quite the way you had planned it to go. At this late stage, I think I would bite the bullet and just hire a reputable company to come in and finish the job. I suspect it would be a little cheaper since you have a lot of the work already done. I know many people do it themselves, they do a really good job, and it saves them a lot of money. But sometimes doing it yourself is not the best way of doing something.
 

DaleCarter

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Feb 22, 2020
Messages
3
Location
Alabama
Dear Concrete Finishing Gurus,

I have 3800 sq ft of brand new slab that was floated blue by the finisher. There haven’t been any oils or contaminated on the slab. There is some localized dirt and black tire marks on the slab.
What prep do I need for a two-part epoxy coating? Acid etch? Or just a thorough pressure washing with a surface cleaner attachment and plenty of drying time?
 
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