How To Screed A Floor

Installing a screed layer on a floor in your home can often be a difficult task without any experience of doing the job previously. It can also be tough to know exactly what tools you will need if you have indeed decided to do it yourself. If the floor has been screeded to a poor degree, you can run into plenty of issues including damage to the floor itself. This will then lead to more expenses in the future, as you’ll need to pay for the floor to be fixed.

What Is Screed?

Screed is a thin layer of material that is similar in nature to concrete, that can be applied to a concrete subfloor or over floor insulation.

The makeup of screed is a mix of sharp sand, water and cement, the ratio of which is often 1:3 or 1:4 cement: sharp sand. Screed can also be ‘improved’ in certain ways by adding ingredients to it for benefits such as better thermal conductivity for underfloor heating or faster drying time.

Screed is ideal for covering underfloor heating pipes and can help to even out a floor surface to ensure that it is safe and level. Screed varies from concrete in that it focuses on using finer aggregates for a smooth finish, whereas concrete focuses on providing strength. Screed is often more expensive too.

If you’re looking for tips on how to insulate a floor well, check out our floor insulation guide.

What Are the Different Types Of Screed?

Screed comes in several different forms, so deciding which type you’re going to go through with is crucial.

Bonded Screed

Bonded Screed does what the name suggests, and bonds directly with the base of the floor.

Unbonded Screed

Unbonded Screed is separated from the base via a damp proof membrane that lies in between the two.

Floating Screed

Floating Screed is laid onto insulation with a slip membrane over it and is seen as a form of Unbonded Screed.  It can also be laid over an underfloor heating system.

How To Screed The Floor

How you will go about screeding a floor will depend on the type of screed that you have decided to go with.

How To Prepare for Laying Bonded Screed

As you’ll be setting the screed to the concrete subfloor, the following steps should be taken:

1. You’ll need to use a pick or a chipping hammer to roughen up the surface of the concrete, so that it’ll be easier for the screed to bond with the subfloor.
2. Make sure to remove any dust and dirt, with the easiest way being with a vacuum cleaner.
3. Apply the bonding agent to the concrete.
4. Then add the screed straight away, as if it is left for any amount of time then the bonding agent and screed will not mix.
5. After these steps have been taken, you can lay the screed.
6. Bonded Screed should be around 35-40mm thick.

How To Prepare for Paying Unbonded Screed

1. Clean the concrete floor to make sure there is no dirt present, which would negatively affect the screed from settling.
2. Then, lay down the membrane to separate the concrete to the screed, overlapping the sheets by 20-30cm and taping them together.
3. Protect the walls from any damage for when the screed shrinks once it dries.
4. You can also reinforce the screed with fibres to stop the screed from cracking in the drying process.
5. The Unbonded Screed should be around 50mm thick, aiming for 70-75mm when pouring the screed, to allow for a differing height on the concrete subfloor.

How To Lay The Screed

1. The easiest way to lay screed down is to divide it up into sections of floor, rather than trying to do the whole thing in one go. We would recommend using straight pieces of timber that are cut to the same height as the layer. You can also wet the timber so that it’s easier to remove at the end.
2. Now it’s time to apply the first layer of screed, beginning in the furthest place from the room’s entrance, so that you can exit easily. Use a trowel to move the mixture and use a screed board to compact and flatten it out.
3. The next step is to use a straight piece of timber or a straightedge to level the screed layer. If the screed is self-levelling, then it should smooth by itself.
4. Keep repeating the process until the entire floor is filled with screed. After this is complete, you can remove the timber and fill in the remaining gaps.
5. Any imperfections can then be removed from the screed layer, after the concrete has properly bled.
6. On average, it can take seven days for the screed to cure, if it is left untouched under a sealed sheet of polyethylene.
7. The last step is to leave the floor to dry. The general advice is to leave it for around three weeks before installing any flooring. A screed floor can tend to dry at a rate of 1mm per day.

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