How do I level a sloped concrete floor?

Answered by Jeffrey ~ January 28, 2012 ~ Comments

We have converted our home's exterior patio into an enclosed porch with walls. There is a slope to the concrete floor, which I would like to level prior to framing the interior walls and installing the trim and floor covering. What is the best way to level a sloping concrete floor?

Robbie ~ North Carolina

Jeffrey Anderson

Hi Robbie. The best method for leveling a sloped patio or porch floor is to pour a layer of self-leveling concrete on the surface of the existing concrete. However, the prep work you do first often determines whether or not the project is a long term success. The existing patio floor should be thoroughly cleaned and then the surface needs to be roughed up with a wire brush or concrete grinder. This helps to facilitate the action of the bonding agent you apply prior to pouring the new concrete.

In my experience, the new layer of concrete has a better chance of adhering and lasting a long time without cracking or peeling if it is at least 1 inch deep over the entire porch. This normally isn't a problem at the low end of the slope, but it could be an issue at the high end where the floor meets the home and entrance door from your living space. If there is a step up into your house, allow for an inch of new concrete at that point and then pour out level to the new exterior walls. If you have already framed the exterior door for the porch, you may have to raise the header to accommodate the new floor height.

If your patio currently has an even transition into your home and the only thing that prevents water from entering is your front door's threshold, there may be a little concrete demolition in your future. A grinder or electric jackhammer should be used to remove some of that concrete where the patio meets the house. You may not be able to get it down a whole inch, but every little bit helps. If the new concrete is less than 1/2 inch thick, there is a good chance it may crack and start coming up over time.

Grinding concrete is a labor intensive dirty job so you may want to get a contractor involved if this task is needed. Any concrete contractor should be able to do it and I'm sure there are many around your part of North Carolina.

Once the existing floor is ready, use a string line and line level to mark the depth the new concrete will be where it meets the exterior walls. Any openings should be blocked off to that same depth to prevent the concrete from leaving the enclosed porch. Most self leveling concrete can be mixed on the job and have enough water added that the mixture will seek its own level, but a little bit of finishing may still be required so that you have a smooth surface for the new flooring. I assume your new framing is untreated lumber with the exception of the bottom plate. If this is the case, use a strip of 30# roofing felt at your exterior walls to protect the framing where the depth of the new concrete will be higher than the treated plate.

A concrete bonding agent should be applied to existing concrete floors prior to the new pour being done.

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