A guide to levelling concrete flooring and floor screed using a floor levelling compound

This project is sponsored by ZLevel

Summary: How to level floors using floor levelling compound to fix your uneven concrete floor. A guide to getting your concrete floor level to lay carpets, laminate flooring, floor tiles and other flooring. Including floor levelling for tiles and vinyl and also for laminate and hardwood floors.

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Do you have uneven floors? Don’t worry many concrete floors and floor screeds are not 100% level, and there is a solution.

Laying a concrete floor slab or floor screed over a fairly large area lends itself to a little inaccuracy simply because of the difficulty in moving and laying an extremely wet and heavy material like concrete.

When to Use Self Leveling Compound

Using Self levelling compound to get a concrete floor slab level depends on how much it is out of level in the first place. It can only be used if the floor is out of level by 5mm or less. This can be checked in the following way.

  • Strip off all existing carpets, tiles or other flooring
  • Brush the floor thoroughly removing any carpet tape, carpet gripper, tile adhesive or nails
  • Drop a marble or golf ball in many places on the floor and see which way it rolls to get a picture of where the floor is at its lowest
  • Use a long spirit level to measure exactly how much out of level it is. This should be a 6 foot (1800mm) level to get a proper level because it is such a big area. Hold the up the low end of the level until the bubble is in the middle, then measure the gap between the floor and the raised end of the level
Using a spirit level to check the level of a floor

Using a spirit level to check the level of a floor

If the floor slab or screed is less than 5mm out of level you can use a self levelling flooring compound, or self levelling screed. You can buy these from builder’s merchants or DIY shops such as Wickes or trade outlet stores such as Screwfix and there are many brands available on the market.

Essentially there are two types of self levelling compound. The first is a powder which comes with a latex liquid in a separate container. To prepare it for use the two are mixed together to form the compound.

The second type of self levelling compound is a bag of powder, with the latex compound already included. This just needs to be mixed with water to use.

If the depth of screed you require is greater than 5mm you will not be able to use Self levelling screed, and another method will need to be used. Should this be the case with your floor, please scroll down to the second half of this guide.

What is Floor Screed?

A self levelling floor screeding compound usually contains latex because the compound is laid in a very thin layer and the latex gives it the flexibility it needs to move without cracking. Once it is prepared, mixed and poured it will flatten out across the uneven floor and ‘self-level’ due to gravity (with a little help – see below).

There are a number of types of compound but they all usually require mixing in a bucket using a mixing paddle. This involves attaching a special paddle to an electric drill and mixing it thoroughly to make sure the components are evenly distributed through the mixture.

Can I use screed if I have Under-floor heating?

Latex compounds are now very advanced and most can be used with under-floor heating but please check on the instructions. Concrete floors, slabs or screeds often need priming before laying a self levelling screed or compound in order to take some of the porosity away from the surface.

No Nonsense Self leveling flooring compound to level floors from 5mm to 50mm deep

No Nonsense Self leveling flooring compound to level floors from 5mm to 50mm deep

Using Self Leveling Compound to Level a Floor

To lay a self leveling floor screed or compound you should:

  • Ensure surface is dust free and primed according to the manufacturer’s instructions
  • Mix the compound with a mixer paddle until the required consistency is obtained. Mix only enough quantity to make the required number of screed lines as shown below.
  • Pour the mixture onto the floor, ideally into the areas you have identified to be the low spots
  • Using a steel float, trowel the mixture over the area to be leveled watching to see where it runs down any slopes to form its own level in the hollows. Despite its name the compound will not self-level automatically as there is surface tension to be overcome. The mixture should be pushed around the floor with the trowel to break this tension and gradually the compound will find a level.

Using a Zlevel to Level a Concrete Floor

If the floor is more than 5mm out of level, you must use a different method to level the floor. This method involves thickening up the same flooring compound with some sharp sand and laying it like a floor screed (See the video below). Tip: to make this easier DIY Doctor is using a handy little product called a Zlevel.

Zlevel, as you can see from the image, is a Z shaped piece of metal which can be used to transfer a level across a room easily.

Packet of Z Levels

Zlevel for leveling floor screeds and compound between 20mm and 5mm thick

Fix Zlevel to floor and bend to correct level to suit concrete floor

Fix Zlevel to floor and bend to correct level to suit concrete floor

  • Sweep floor removing all dust and debris.
  • Find the high and low spots in the floor as above in Method 1
  • Paint floor with solution of 3 water to 1 PVA to seal
  • With your spirit level on the highest point of the floor, hold the spirit level, level and place a Zlevel under the end so it supports the spirit level. Adjust the Zlevel so the spirit level shows the top of it to be level with the high spot.
Transferring floor levels around the room using ZLevels

Transferring floor levels around the room using zlevels

  • Repeat this procedure, transferring the highest floor level around the room in single lines of Zlevel.
  • Mix self leveling flooring compound to the Manufacturers specifications which you will find in the instructions for the product you have chosen. It is better to mix the flooring compound after you have fixed all the Z levels
  • Add sharp sand until the mixture is only just self supporting as shown by the image below
Mixing flooring compound with sharp sand to get a thicker, stronger mix for screeds over 5mm

Mixing flooring compound with sharp sand to get a thicker, stronger mix for screeds over 5mm

  • Once the Zlevels are in place, and the screed is prepared, spread the flooring compound out in a strip over the Zlevels. Use a straight edge to ensure that the top of the screed lines are level with the top of the Zlevels in all places.
  • Trim off the screed lines as you can see in the image below.
  • Leave the screed lines to dry for about an hour until they are firm enough to push down on lightly without causing a depression
  • Mix enough floor leveling compound to fill the spaces in between the lines of screed
  • Using a straight edge, fill between the lines of screed making sure there are no voids by tamping down gently on the surface with the straight edge as shown in the video below.
Floor area with Z Levels fixed and screed applied to the correct level of each Z Level

Floor area with Z Levels fixed and screed applied to the correct level of each Z Level

Zlevels can be bought directly from www.zlevel.co.uk. We hope you enjoy using them as much as we do. They certainly make leveling a concrete floor a great deal easier than it used to be!

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