How to Patch and Level a Concrete Subfloor

We are well on our way to putting Humpty Dumpty back together when it comes to our mudroom and laundry room. The kitchen, it’s still a blank canvas.

After the water leak, the linoleum flooring had to be removed. What was left was a plethora of problem areas. Cracks, crumbled concrete and an uneven surface resembling the moon.

Before putting down any new flooring, we had to have a smooth and level surface. Adding a self leveler was the best answer to the problem. We purchased most of the supplies from Lowe’s and borrowed a large drill. And here’s how we did it:

Materials:

• Mapei Ultraplan (Self Leveler)
• Mapei Primer T
• Flat Trowel
• 5 Gallon bucket
• 4′ x 8′ Foam insulation sheet
• Utility knife
• Painter’s Tape
• Paint roller
• Paint tray
• Quart measuring cup
• Warm water
• Drill with a large chuck and attachable second handle
• Concrete mixing paddle
• Concrete patch (if you have a crack)
• Knee pads

The picture above shows two drills. The smaller one won’t accept the mixing paddle. You need a drill with a larger opening. And, adding a handle to the side will help mix the heavy self leveler without it taking you for a “spin”.

Preparing the concrete floor:
Before pouring the self leveler there is some prep work required.

First remove any loose and chipping concrete. I used a scraper and lightly hammered any spots that sounded hollow underneath to loosen any weak pieces.

It is recommended that you rough up the concrete. I skipped this step because our subfloor was far from smooth.

Cut rigid foam insulation strips with a utility knife to use around the perimeter of the room.

The insulation serves two purposes. 1. To create an expansion joint as the leveler expands and contracts with heat and cold.  2. And to prevent the self leveler from running into any cracks or through doorways. Plus, it created a nice channel to run some wires inside (more about that later in the week.)

Use painter’s tape to secure the insulation around the perimeter of the room.

Speaking of cracks, be sure to seal any large cracks with concrete filler and sealer. I neglected to fill this crack in the floor and literally poured 2.5 gallons of leveler into it before creating a little dam to stop all the leveler from pouring into the hole. Learn from my mistake, be sure to seal any large cracks in the concrete, or you’ll be doing the job twice.

Let the concrete filler dry before continuing.

Apply a primer to help the leveling material adhere to the concrete subfloor. Pour a small amount of primer into a paint tray.

Using a paint roller, roll the primer onto the floor and wait for the primer to dry per the instructions on the bottle.

The dried primer is tacky to the touch. If you wait more than 24 hours it will be necessary to reapply the primer.

Pouring and spreading the self leveling liquid:

Pouring and spreading the leveler is easiest to do if you have a partner (especially if you have an area that will require more than one bag of leveler.) One person can mix the next batch while the other is pouring and spreading. It is important to work into the wet edge or you will create ridges and bumps.

Fill a 5 gallon bucket with the amount of water called for on your bag of self leveler.

Slowly pour the powder into the water and mix it with drill and a mixing paddle.

The mix will be soupy like tomato soup when it is properly mixed. But, it will be much heavier!

When the bag is empty and the mix is completely mixed. Let it sit for 2-3 minutes. Then mix it again and begin your pour.

Immediately pour the liquid in 4′ sections and trowel it out, pushing more leveler toward any low spots.

Self leveler will do as it says, it will self level. But, only to a certain extent. Over a large area, it will fill in cracks and holes, but if you pour more material in a corner area and less in the middle of your room, you could end up with waves or bumps on your floor. Try to pour a consistent amount in each area.

Work into the wet pour with your next batch until you have finished leveling your area. Let the leveling liquid dry overnight before walking on it. The self leveling liquid will dry lighter and to a matte finish.

Clean out your bucket and trowel with LOTS of water. Hopefully you won’t have much leveler to dispose of. If you do, let it harden in a container you don’t mind throwing away.

Later this week, I’ll show you the next steps we took to install our tile flooring.