How To Level A Concrete Floor That Slopes

A concrete floor that slopes downward toward one end or corner usually results from concrete poured during the initial construction. Sometimes, the grade of the lot on which the home is built causes this problem. If you choose to tackle this project yourself, be aware of these points before you begin:

Important Rules:

● The four-inch rule: A pan that drains into the sewer requires at least 4 inches (10 cm) of freeboard – that’s how much higher than its rim it needs to be – for every foot (305 mm) between its lowest point and its base. That means if the floor slopes enough to leave just 1 inch (25 mm) of freeboard between the pan’s drain and its base, there should be at least four inches (10 cm) of freeboard between it and the wall. Otherwise, water backs up in the drainpipe and overflows into your home.

● The code requires at least one-half inch (13 mm) per foot (305 mm) for every foot between the lowest point of a foundation wall or foundation element that meets or is supported by soil or rock and the finished grade immediately adjacent to that wall or element.

Quick Ways:

So, you have a concrete floor that slopes. You want to level it out before applying your tile or stone surface. Here are some options:

It’s also the most expensive solution ($400-$500 for 9 feet of linear coverage), meaning this option is most likely out for most people – unless you can do it yourself (it can’t hurt to try).

If you go this route, make sure the jack has enough hydraulic fluid (suggest buying two jacks and splitting half with a friend). The most common complaint I hear about these jacks is they run dry in 2 minutes because they only hold 1 cup of liquid. This shouldn’t be an issue if you’re splitting the jack with a friend.

The cheapest solution ($50-$100 for 9 feet of coverage). A 3-5 horsepower unit should work fine, but I like using a 7-10 horsepower model because it doesn’t bog down when cutting wet concrete (I recommend buying two units and splitting half with a friend).

It’s also nice to have two units to make multiple passes while the other waits its turn (this makes your job go much smoother). The downside is these saws aren’t “machine grade” like they used to be. Mine died after four months of heavy use. If you buy this option, please drain the saw’s oil first. The engine tends to suck up whatever liquid is left inside if you don’t.

If you have access to one, it might be worth the investment (cost varies). Keep in mind, though, that lasers are inherently inaccurate. It will require at least two passes – one pass for positioning and another for cutting/grinding.

I’ve only used this option once, but it worked pretty well. Expect this option to bog down even on low RPMs due to wet concrete’s weight and torque…unless you’re using a cordless, of course (the Milwaukee M18 Fuel 7″ Cordless Sawzall isn’t too bad).

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• An oscillating multi-tool with an additional 4″ diamond blade

It will require two passes like the laser – one pass for positioning and another for cutting/grinding. One advantage this method has over the laser, and reciprocating saw is it will take less time. Remember that multi-tools can be very loud (the Milwaukee M18 Fuel 4″ Cordless Multi-tool isn’t too bad, though).

• A router with a guide and diamond blade

This option is as quick as using an oscillating multi-tool, but it’s much more versatile – if you’re willing to pay for the additional cost. A plunge router should work well for this, but I don’t recommend using one because they lack versatility compared to standard routers. However, before committing to buying one, consider measuring your floor first, so you aren’t wasting money.

• Rubber mallets/hammers/dead-blow hammers

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These are useful for tapping down concrete that’s starting to set too high (or when other methods aren’t working). Be warned, though, that tapping concrete while it’s wet can be like hitting a bowl full of jelly, though – not all areas will respond to your input! This method also takes more time than using other tools.

The first thing you’ll want to do is determine how much your floor slopes. I usually eyeball this because it’s not too difficult to measure if you have a tape measure or other tool that can help you transfer measurements point to point (for example, take a picture of the floor with a camera).

The easiest way, though, is probably just putting two buckets of water on opposite ends of the room…the difference in height between the two will be the maximum slope. The next step would be to buy an oscillating multi-tool or router since they are quick and won’t bog down as quickly as other options. If you decide on an oscillating multi-tool, make sure you get a 1/4″ carbide bit to go with it.

If using a router, be aware that some routers – significantly cheaper ones – will NOT work for this due to the types of bases used on them (for example, older models from Ryobi and Fein).

If, after leveling your floor out, you still notice uneven areas that seem high, then use a wet vacuum or shop vac to clean off those areas first. Don’t forget to charge your battery since some tools can use one up faster than others! Once those pockets are free from excess concrete, you’ll have an easier time grinding them down with a 7″ floor grinder or reciprocating saw, respectively. Now let’s begin leveling!
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• Start by focusing on the low points of your floor, not just because this is where you’re most likely to find pockets of excess concrete but also because these areas are usually surrounded by hardwood that’s difficult if not impossible to replace. So you must bring them down first before they set too much (or before someone bumps their head).
• After finishing the lower sections, let the floor dry for at least 24 hours (if it’s still warm or humid outside). The drying time will vary based on how thick the concrete was poured and air temperature/humidity levels. For damp weather, increase this time frame to 36 hours (and keep kids and pets off until!). Once dried, use an oscillating multi-tool to shave off the high points of your floor. If using a saw, use a 7″ blade with 8 TPI.
• Next, you’ll want to vacuum or sweep areas that have excess concrete powder/dust residue before going on to the next step. That way, it won’t start sticking to wet concrete. The less dust, the better!
• Now you’ve got two options:

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Using an oscillating multi-tool or router for quickness OR 2) Grinding it down yourself with a 5″ angle grinder or reciprocating saw not set at full power. I usually prefer option

#1 since it doesn’t bog down as quickly and yields cleaner results, in my opinion.

If you decide on option #2, make sure not to set the grinder/saw too high otherwise, it will start chipping away at your concrete! Also, note that after leveling with an angle grinder, see if any low spots remain. If so, wet them down and let them dry for 36 hours before re-grinding (to avoid having dust mix into your wet concrete!).
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• Sweep or vacuum again. Then use a heat gun to heat any areas you ground down earlier but had trouble getting smooth. That process is called “healing” in the curing world. Remember how I mentioned adding water to fresh concrete? Well, this is where it can come in handy since heat can remove excess moisture (especially if your concrete is still fresh enough).
• After heating, sweep/vacuum again. Then you’re ready to seal your floor with a concrete sealer !!! The floor must be dried for at least 24 – 48 hours before applying the waterproofing agent. As always, follow manufacturer instructions!

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