How to Laser Level a Floor


Nobody ever forgets their first rodeo with installing flooring. Something always goes wrong, always. One of the most common things that go wrong is you get done laying your flooring, check for flatness, and find out that… it isn’t flat.

Let’s just get your mistake out of the way right now.

You checked the finished installation if it was level when you should have checked to see if the subfloor was level before you laid the flooring. If you use a laser level, not only is checking the final product quick, but checking the subfloor is both fast and precise.

Why Level the Subfloor?

Does it really matter if a surface you can’t see is level? Yes, because as anyone who has ever done flooring will tell you, if the sub-floor is level, the actual surface flooring will be level. However, if your sub-floor isn’t level or has imperfections then that will wreak havoc for years to come.

Some people might think an uneven floor isn’t the end of the work, but you know when the sub-flooring isn’t level or has warped because it will manifest on the surface. For tile, you will start to see tiles crack, and on wood floors, your wood will begin to squeak. If you ever notice these little details in the flooring in a house, it is likely because the sub-floor has warped or wasn’t properly level in the first place.

How to Laser Level a Floor

By placing your rotary laser level on the floor, it can help you identify highs and lows in the subfloor. For this job, ideally, you want a surface laser level, but even a single line laser level can be used, it just means more work.

With a surface laser level, you simply need to set it at the benchmark high spot you are trying to recreate throughout the floor. Where you see one laser line, it means that the area is the same elevation as the benchmark, but if you see two lines, then the floor is lower or higher. From there, you need to rotate a few degrees marking out high or low spots until you reach the full 360-degree circle. It is moments like this where a rotary laser comes in handy, especially one with a remote so you can do it without constantly having to walk back and forth, an act that can get exhausting in larger rooms.

After you have found the high or low spots, it is important that you work with a strong filler, one that won’t bend or break down over time. This means you won’t be right back where you started in just a few years when the low or high spots begin to warp enough that it affects the actual surface of the flooring.

Of course, after doing all that, you do still want to use your laser level to do a final surface check. It is better to discover if any mistakes were made early so you can redo them quickly.

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8 Things to Keep in Mind When Leveling a Floor

Pinpoint low and high areas

Well, there are awesome rotary laser levels to find the uneven areas but when all else fails, go back to the basics.  Drop a marble.

If you drop a handful of marbles and they consistently roll to the same areas, then you know those are low areas.  If they roll to one side, then you know that the side is lower.

  • Heaves:  High areas on the floor
  • Dips: Low areas on the floor

If no marbles or rotary laser level, then use an 8-foot carpenter’s level by placing the level on different areas of the floor and notice for dips and heaves.  But you don’t need the bubbe!  If there’s a gap under the level, then those are dips.  If the level rocks, then you’re on a heave.

Determine the Basic Issues

There’s a lot more after checking for heaves and dips.  You need to find out what the underlying issues that are causing the floor to be unlevel.

Depending on the issues, this is either going to be a DIY job or you’re going to need a professional.

Sometimes the problem is just age-related settling. However, there are large issues that can cause an uneven floor such as foundation problems, cracked joist(s), rotted wood or sill plates, or a delaminated subfloor.

The only true way to check is to actually get underfloor and check the joists and beams.  If you find insect damage (termites), rotted, cracked or broken joists, then you should hire a structural engineer (professional) take a look at it.

Understand what Self-Leveling Underlayment is

Good news!  If your professional engineer didn’t find a structural damage then you could possibly fix the issue with a cement base, self-leveling floor product.  Such as this one:

You can also get this product at a Home Depot or Lowes.

This self-leveling product is mixed with water to form a slurry or paste, which you then spread over the floor with a gauge rake.

You can also get a full self-leveling kit:

These types of products can be used on:

  • wood subfloors that are uneven but still in pretty good condition
  • concrete floors
  • ceramic tile floors (yes!)

At around $1.50 per square foot, this is an affordable and practical leveling solution depending on the area size of the floor.

Deal with the Subfloor

We talked about the subfloor near the top of this article and we mentioned it again lower.  It’s important and can be a nasty culprit to a floor that isn’t level.

When subfloors become delaminated or warped, it can’t be level or structurally sound.  The best bet here is to replace the subfloor panels that are damaged or in bad shape.  The most common subfloor material is OSB (orient strand board) and plywood.

These are durable materials but after prolonged, current moisture they DO eventually delaminate and ruin.

Plane a Heaving Joist

Occasionally, a floor joist will start to bow and bend upward. This is actually a pretty problem to solve.

All you need to do is remove the panel over the bowed joist (indicated by heaves with the marble test) and planing the high part of the joist to make it level across the top.  If you can get your hands on a power planer, then this makes quick work of a heaved joist.

Use Shims to Correct Joist Issues that Remain

If you have warped joists as the culprit, then you can easily level a floor using shims to correct some joist issues.

Shimming involves attaching wedge-shaped, thin wood on top of the low areas to make the top of the joists level.

You’ll need your rotary laser level to pin-point low area and putting the shims on by gluing and securing to the joists.

Sister the Joist System if Current System is Inadequate

This is a job for the pros and should only be undertaken by the properly trained and experienced.

Sistering joists involve new joists being attached to the old joist to strengthen the floor.  Again, this is a large project and could involve plumbing and electrical work in order to not damage pipes and wiring.

Determine the Foundation Factors Involved

While everything that we listed above are common issues when you find your floor needs leveling, there are many other structural issues that can cause an uneven floor.

Foundation, for instance, moves.  This causes splits, cracks, uneven floors, wall damage, and even doors that won’t close!

If it’s a foundation problem, this should definitely be looked into by structural engineers.

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Howze it? I'm Raf. Been living and working construction in Hawaii for about 10 years. Just recently started doing some handy man work around my neighborhood and then got the itch to review equipment that makes my life easier and hopefully yours too.


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