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Old 11-03-2009, 11:16 AM   #1
pattenp
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Default Grind down a hump in concrete.

My garage floor is not level at the door. It has at least a 5/8” hump at the center of the door so when the door closes it leaves a gap on each end that the weather skirt can not totally seal. Is it possible or should I say worth while to try to grind down the hump. It would take grinding a spot about 48” long by about 12” wide. It would need to be taken down at least 5/8” for 30” of the 48” length with the rest of the length for feathering it out. The concrete it over 5 years old so it’s good and hard. What is the best way to do this?

I thought about scribing a piece of something on the door bottom to conform to the hump and reattaching the weather skirt to it, but the door is 18’ long and I can’t think of what to use that won't look mickey mouse. Any thoughts on that solution?

Thanks in advance for your suggestions.
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Old 11-03-2009, 11:27 AM   #2
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Default Re: Grind down a hump in concrete.

Are you sure it is the floor and not the door?
A door that wide can develop a sag in the center.

Either way, I would go with the idea of scribing a wedge for the bottom of the door.
It doesn’t have to go all the way across.
Just taper it from the edge of the door to where it will be about a Ό inch thick.
A new rubber bottom of door seal will make up the difference.

I just used a 2x4 painted to match the door.
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Old 11-03-2009, 01:50 PM   #3
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Default Re: Grind down a hump in concrete.

rental place has concrete grinders or you can buy a cup grinder for your hand held grinder at Lowes. Just wear a mask while grinding
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Old 11-03-2009, 04:08 PM   #4
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Default Re: Grind down a hump in concrete.

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rental place has concrete grinders or you can buy a cup grinder for your hand held grinder at Lowes. Just wear a mask while grinding
I was thinking of a hand grinder but didn't know if it would take a month of Sundays to grind down 5/8". Plus not sure what I'll end up with... a really rough looking spot with the aggregate showing.
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Old 11-03-2009, 04:12 PM   #5
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Default Re: Grind down a hump in concrete.

What about filling in the low spots as opposed to griding the high spot?
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Old 11-03-2009, 04:54 PM   #6
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Default Re: Grind down a hump in concrete.

Tapers made out of Azak plastic board would do it. It's white, it's plastic. Glue it on with phenoseal, drill and screw right through it. It should be very clean looking.
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Old 11-03-2009, 05:31 PM   #7
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Default Re: Grind down a hump in concrete.

Definetly grind it with diamond impregnated cup brush. It will go surprisingly quickly. Concrete is very soft when it comes to diamond cutoff saws/grinders.
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Old 11-03-2009, 08:21 PM   #8
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Default Re: Grind down a hump in concrete.

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What about filling in the low spots as opposed to griding the high spot?
To fill the low ends to either side of the high spot would take a lot of leveling cement and would cause other issues with the drainage slope of the floor towards the door.
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Old 11-03-2009, 08:27 PM   #9
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Default Re: Grind down a hump in concrete.

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Definetly grind it with diamond impregnated cup brush. It will go surprisingly quickly. Concrete is very soft when it comes to diamond cutoff saws/grinders.
Will a cup grinder produce a smooth surface or is the final outcome more of a matter how good the operator is in using it? It seems to me with using a hand grinder it would be difficult to get a decent flat and smooth surface.
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Old 11-04-2009, 02:03 PM   #10
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Default Re: Grind down a hump in concrete.

You could try attacking it like a hump in the yard - use a 4' level and grind a 2" or so path across the door side or inside down the the level required. Then work the rest of the hump back to that level line.
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Old 11-04-2009, 03:14 PM   #11
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Default Re: Grind down a hump in concrete.

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You could try attacking it like a hump in the yard - use a 4' level and grind a 2" or so path across the door side or inside down the the level required. Then work the rest of the hump back to that level line.
I was thinking of setting up some type of guide using a level to aid in making level passes with a hand grinder.

I looked at a couple of different cup grinding wheels and am not sure which is the best to use. Attached are pictures of two kinds, is one better than the other?
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Old 11-05-2009, 08:36 AM   #12
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Default Re: Grind down a hump in concrete.

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To fill the low ends to either side of the high spot would take a lot of leveling cement and would cause other issues with the drainage slope of the floor towards the door.
For some reason I thought we were dealing with a channel the door sat in... I'm with you now.

As far as the grinders, the silver one is designed like the bobcat driven units we use on dragstrips after trying a few different placements for the heads.

Maybe a method like used in bodywork: spray something non-permanent over the whole area, measure what needs to come down and as you work through that area you will grind through the mark keeping you in the right area. My mind is going for temporary spray "chalk."
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Old 11-05-2009, 08:46 AM   #13
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Default Re: Grind down a hump in concrete.

What hump?

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Old 11-05-2009, 10:37 AM   #14
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Default Re: Grind down a hump in concrete.

Call Penhall - they'll get your humps out
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Old 11-05-2009, 11:08 AM   #15
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Default Re: Grind down a hump in concrete.

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What hump?

That's a good one.

Actually he looks like the guy who did the concrete.

Last edited by pattenp; 11-05-2009 at 11:10 AM.
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Old 11-05-2009, 11:19 AM   #16
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Default Re: Grind down a hump in concrete.

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Originally Posted by pattenp View Post
It would take grinding a spot about 48” long by about 12” wide. It would need to be taken down at least 5/8” for 30” of the 48” length with the rest of the length for feathering it out.
I think it would be difficult to grind that big an area level without a reference. I would build a simple 60" bridge that spans the hump (couple of angle-iron rails screwed to 2x4s at each end. Set the bridge over the hump and cut a series of slots with a diamond blade in a cheap circular saw (gonna get lots of dust in it). Don't even need a gauge -- just set the blade at the depth of the flat area you want to level to. You can turn the bridge 90 degrees, shim it and repeat the process. Then grind off the checkerboard squares to the depth of the slots. Lots of slots means less grinding.
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Old 11-05-2009, 11:25 AM   #17
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Default Re: Grind down a hump in concrete.

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I think it would be difficult to grind that big an area level without a reference. I would build a simple 60" bridge that spans the hump (couple of angle-iron rails screwed to 2x4s at each end. Set the bridge over the hump and cut a series of slots with a diamond blade in a cheap circular saw (gonna get lots of dust in it). Don't even need a gauge -- just set the blade at the depth of the flat area you want to level to. You can turn the bridge 90 degrees, shim it and repeat the process. Then grind off the checkerboard squares to the depth of the slots. Lots of slots means less grinding.
That's exactly what I was thinking to do. Now I just have to get up the nerve to do it. The cure may be worst than the disease.
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Old 11-05-2009, 06:10 PM   #18
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Default Re: Grind down a hump in concrete.

What type of construction is the door?
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Old 11-05-2009, 06:15 PM   #19
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Default Re: Grind down a hump in concrete.

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What type of construction is the door?
Wayne Dalton 18' steel raised panel door.

Want to try to fix the floor instead of fudging the bottom of the door if that's want you're thinking. I'm hoping to epoxy the floor and want take care of the high spot.

Last edited by pattenp; 11-05-2009 at 06:18 PM.
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Old 11-05-2009, 08:09 PM   #20
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Default Re: Grind down a hump in concrete.

I don't know if anyone answered the smoothness question. Yes, quite smooth, with aggregate showing. I did it near the garage door in my shop due to the slope transition being in the wrong place and getting water under the door. It will likely take a couple hours, and you may want a capable helper if you want to keep the grinder going all the time. Eventually your arms will need a rest. Plus, it is nice to have someone checking your progress as you work. Dust will be everywhere in the garage just so you know. Not a terrible job, but wear a mask and eye protection. The most important part is to keep referencing your progress.
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Old 11-07-2009, 07:27 PM   #21
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Default Re: Grind down a hump in concrete.

Yeah scribing the door is what I was thinking but not with a steel door...it was just a thought.
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Old 11-10-2009, 03:23 PM   #22
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Default Re: Grind down a hump in concrete.

I'm in the same boat with my shop. My 12' door opening has a dip in the center about 1/2" low for about 8 ' . My door is built by Overhead Door , it has a some great weather stripping , but I still get some water when we have a hard blowing rain. I was going to try to grind the ends down, but the door frames would need to be removed to do it properly, and I'm not wanting to remove the door because it weighs about 1500lbs and I don't have the proper equipment to handle such a task . . I thought about adding a threshold and trying to build up the center with some type of epoxy, I just don't know which way to go.
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Old 11-10-2009, 08:04 PM   #23
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Default Re: Grind down a hump in concrete.

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and I'm not wanting to remove the door because it weighs about 1500lbs and I don't have the proper equipment to handle such a task
Wow! What kind of door do you have that weighs 1500 LBS? A standard, insulated 16' door section is something like 75 to 125 Lbs. But, that is not to say that removing and installing one is a fun task!
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Old 11-10-2009, 08:15 PM   #24
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Default Re: Grind down a hump in concrete.

have you thought about cutting the problem area out and repouring?
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Old 11-11-2009, 05:16 PM   #25
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Default Re: Grind down a hump in concrete.

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Wow! What kind of door do you have that weighs 1500 LBS? A standard, insulated 16' door section is something like 75 to 125 Lbs. But, that is not to say that removing and installing one is a fun task!
I have a Overhead Door model 620 12' wide x 14' tall rolling steel commercial door, the guy from Overhead told me it was that heavy, and if it doesn't weigh 1500lbs it can't be far from it.
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Old 11-11-2009, 08:31 PM   #26
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Default Re: Grind down a hump in concrete.

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have you thought about cutting the problem area out and repouring?
Sure have... it's just one of those jobs I just dread taking on. At this point I'm just going to living with it. I may just take the easy route by doing something on the bottom of the door to fill the gap.
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Old 11-11-2009, 09:21 PM   #27
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Default Re: Grind down a hump in concrete.

I went through that early this summer. My concrete floor lifted 1/2" up dead center to the 16' door (bentonite - hate that stuff). I purchased a DeWalt 4.5" grinder and a diamond cup grinder, a silica dust mask, a plastic drop cloth, duct tape, 2' level, work gloves, knee pads and went to work. I planned to install a sunami-type threshold when done.

I marked off the inside edge with masking tape, taped a full length drop cloth to the bottom of the door, opened the door and went at it. Once the grinder cuts the hard top 1/8" it cuts like a warm knife through butter. Start at the center, work out 2' in each direction, check with the level, finess, then work out 4' each direction, check level, finess...took a little over an hour to feather down from 1/2" high center out 6' in each direction (12' total).

Cleaned the cut out real well (vac and compressed air) then glued down a nice threshold. Problems solved.

It wasn't hard, not too expensive, but really dusty - you need that silica mask!

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Old 11-11-2009, 09:43 PM   #28
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Default Re: Grind down a hump in concrete.

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rental place has concrete grinders or you can buy a cup grinder for your hand held grinder at Lowes. Just wear a mask while grinding

+1 to this. A grinder and a cup stone will take that 5/8" down in no time. Wear a real respirator, the dust mask will not keep it out of your lungs.
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Old 11-12-2009, 10:42 AM   #29
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Default Re: Grind down a hump in concrete.

Thanks for the reassuring comments. You just boosted my nerve to try to do this.
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Old 11-12-2009, 12:54 PM   #30
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Default Re: Grind down a hump in concrete.

you`ll both those wheels. The double row is for quick stock removal and the single is for smooth finish. Might also want to look into high grit diamond polishing pads
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