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Removing high spot in concrete

86242 Views 9 Replies 8 Participants Last post by  BINOVC
The high spot covers a 1'X4' area. The flooring is about 1/4" to 1/2" too high in this area. How can I level the floor? Can I use an angle grinder?

Also, do you have any tips on leveling the floor? I'm just using a straight 2x4 right now. I was planning on grinding the floor and checking it as I go.
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This is a very confusing post. You say you want to level the concrete, then you say the floor is too high. Is the floor made of concrete, or do you have a floor covering over the concrete, which you plan to remove in order to get at the concrete beneath the floor covering?

Then you mention that you are using a 2x4 to level the concrete, which sounds like you are placing concrete, and not quite getting it level, so you plan to grind it down to level later. At least I think that is what you are saying.

Grinding concrete down to level is about the least efficient method of leveling concrete, the best way is to place forms at the correct elevation, then screed with a screed board, which can be a 2x4 (make sure it is dead straight), or a steel angle. If the forms are level, you should be able to get the concrete level within 1/16 of an inch this way, which is good enough for most applications.

If your concrete is already out of level by too much, you can grind it down, but be sure you use a high quality dust mask since concrete dust is very bad news for your lungs. An angle grinder works, or you can chip it using a jack hammer, then place new concrete to the correct level.

But I may have totally misunderstood what you are doing, a little clarification would be good.
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I guess I should have said I wanted to flatten the floor and not level it. It is a concrete slab that I'm running laminate flooring over. I'm using a 2x4 to see if there are any low or high points. I would like to flatten the high spot so there isn't a hump. It looks like I would have to grind the 1x4 foot section 3/8" to get the floor flat. What type of wheel and size angle grinder do you recommend?
Any help would be appreciated. I looked into small 5" concrete grinders, but they are out of my price range. Is there anything else I can use? Possibly something I can purchase as a one time tool at harbor freight.
DIYer here, not an expert. This sounds like a job for self leveler—except that stuff sucks.


The idea is that you poor it out and it will seek it's own level like water to raise the floor to the level of the hump, rather than trying to ground down the hump.

1. It doesn't level as glass smooth as the marketing suggests, at least not for larger areas. If it is a small bathroom or similar, it may work well for you, but I would use it as a last resort.

2. One bag will yield one large bucket full and cover around 50 sf. depending on how high the hump is. If you have to mix more than one bucket, you have to mix the second bucket long enough to mix properly. That amount of time makes it difficult to poor the second batch quick enough. The first poor may begin to thicken fast enough that the second (or more) poor may not blend smoothly and you may get a ridge where the two separate bucket fulls meet.

3. It is very hard to get a perfectly smooth level finish for larger areas.

4. If the floor is "L" shaped, or any shape other than rectangular, an even poor becomes harder to achieve.

5. If the height difference of the bump is a lot, you may exceed the acceptable amount of thickness for the self leveler, it will have to cover the "island" of concrete as well as the "sea" of concrete to be level.

In short, the self leveler may be the answer to your problem, but it requires more finesse and luck than the product marketing admits to, and may cause you more problems than it solves.


Possible solution:

Take your level, put one end on the hump, the other on the lower part of the floor. Use a ruler and measure the hight of the gap between the floor and the level created by bridging the two different heights in your floor with the level. Read the installation instructions with your particular flooring to see what the grade should be. It should tell you some information about the acceptable hight difference over a particular length from the high spot to the low spot (grade is akin to the angle of a line in a line graph).

Use the level or other straight edge that is long enough to create the proper grade according to the instructions, use a pencil or something to start making marks where the level touches the edge of the high spot and at the other end of where it touches the low spot. Do this radiating around the high spot until you've mapped out the radius of where the low spot has to be filled in to meet the high spot with the appropriate grade according to the installation instructions.

Identify the appropriate concrete patch or other material you can use to connect the high spot to the low spot to fill in the gap. (someone here can tell you or maybe you'll get lucky and find a big box employee who actually knows what they're talking about to recommend the right product). You will apply this with a large trowel to bridge the gap between the "island" and the "sea" in your concrete to the places you've measured.

Use the level or strait edge as a screed, placing one end on the high spot and one end on the low spot and scrape across the filler/patch compound so that you get a straight line across the filled in gap in a radius around the high spot to the low spot with no gap under the straight edge. You may have to feather and smooth again with a trowel by hand. You may have to repeat this process for other isolated high/low spots elsewhere on the floor.


The goal here is not to have your entire floor resemble a frozen sea where it is perfectly flat and level across the entire floor. Instead, you're shooting for having the high and low spots "bridged" to the amount that the "waves" in your "sea" of concrete are shallow enough that they do not exceed your particular floorings accepted tolerance. It will not be perfect, but the rise and fall of the floor will be shallow enough that the flooring can follow it along the surface without having gaps between the flooring and the concrete, flex enough to break, crack, snap the tongues in the tongue and groove that joins them, or be compromised too much in general.

This may take longer than pouring self leveler, but you have much more control. It's far easier to gradually add just enough material to accomplish a "level enough" floor than it is to end up with too much material and/or simply adding another layer of uneven, rippled self leveler. If you find you can't get it level enough this way. You can always still use the self leveler (if the patch material and leveler are compatible and can bond). In theory, the self leveler should work a little better at this point because it will have less of an extreme height difference to flow over if you hadn't done the "spot" leveling previously.



Again, I'm a DIYer myself, not an expert, so you might want to wait till you hear from an expert. I do have experience trying to solve your particular situation myself, and I know the self leveler is not as easy to use as one might think. I also know you will not be able (or want) to remove material from your existing floor, rather you want to add just enough to the low spot to bridge the gap far enough away to create the appropriate grade.
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I understand your problem I'm having the same problem. Removed laminate and planning on tile but have a high spot to lower to the rest of the floor. Was planning on an angle grinder or to bust it up and re pour the spot up to the level of the rest of the floor. Will be checking back here for any responses you might get
I understand your problem I'm having the same problem. Removed laminate and planning on tile but have a high spot to lower to the rest of the floor. Was planning on an angle grinder or to bust it up and re pour the spot up to the level of the rest of the floor. Will be checking back here for any responses you might get
Rent (or buy) a 7'' grinder and a 7'' diamonf cup wheel.

As it is one job, you're probably better just renting the cup wheel...a new one, ok quality is 75$ or so,

Do put a mask and a exhaust fan on the's messy but easy.

I know this is an old post, but, in case anyone comes across this... the cup wheel absolutely worked for me. I had an area of about 1+ foot by 4 feet that sat up about 1/2" higher than another part of concrete (from a previous pour). A 4" Dewalt cup wheel (cost me $39 at Lowes) on a cheap little grinder from Harbor Freight, got the job done in less than an hour. It started out REALLY dusty, so I brought in a water hose and held it along side the grinder. I left the water on at a trickle. It made a wet, soupy mess, but, hardly any dust. The concrete soup can be scraped up after it dries. The wheel cup ground the concrete down like a charm - nice and smooth! Super easy to do.
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Thank you for posting solution.
Will be buying cupwheel and grinding high spot in my basement. will use water too. Probably will build splash guard around it to protect walls.
Thanks again.
I also used my 4" grinder with a dewalt diamond cup wheel. Although it seemed to grind the concrete easily, once I got down into concrete and aggregate (small pebbles), it was a different story. Did you encounter this, or was your concrete fairly rock-free?
I'm thinking I need to rent the home depot 10" grinder. Looks to have the similar style of grinding wheel, but bigger and alot heavier.
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