What is the Difference Between Bonded and Unbonded Liquid Screed?

When it comes time to find the liquid screed that is best suited to your project, there are a number of options to choose from, all of which offer a number of different advantages, and produce slightly different results. The trouble is, since the various types of liquid screeds are all made up out of similar components, it can be difficult to work out exactly what the differences are.

One of the main benefits of using liquid screed over pourable concrete is the ease with which floor screeding contractors can achieve a smooth, even finish can be achieved — but what is the difference between bonded and unbonded screeding, and what will allow you to achieve the best possible results with your project?

While both options offer many of the same benefits that liquid screed is favoured for — from an excellent finish to faster drying times — there are a few differences that can influence your choice between bonded or unbonded screeding.

Bonded Liquid Screed

This is a screed that has been ‘bonded’ directly onto the subfloor beneath, using an adhesive to ensure that the bond between the screed and the subfloor is strong. A bonded screed is very strong, which makes it ideal for spaces that experience heavy footfall or machinery.

A bonded liquid screed also offers the thinnest option for pouring, and can be laid at a minimum of 25mm, although your floor screeding contractors will be able to advise on the exact depth needed for your particular project. Typically, this will mean that your screeding will dry faster, at a rate of approximately 1mm per day.

Unbonded Liquid Screed

If you choose for your screeding to be ‘unbonded’, then this means that the screeding will be separated from the subfloor by a polyurethane membrane. The use of this membrane prevents the screeding from forming any sort of bond with the substrate below.

When unbonded, the liquid screed will typically need to be poured a little thicker than a bonded screed around 30mm at its thinnest but it will also mean that your screed is protected by a damp-proof layer and that, should the subfloor break, the liquid screed on top will remain intact.

What About a Partially Bonded Liquid Screed?

You may have heard of partially bonded liquid screed. This is a more cost-effective option, as it is poured directly onto the subfloor without the use of a polyurethane membrane or an adhesive. As a result, the liquid screed forms a weaker bond with the subfloor beneath, and needs to be poured more thickly to maintain structural integrity. It works best when the subfloor is rough enough to create a good grip with the screeding.

Plan Ahead

Meeting with your floor screeding contractors and discussing the exact requirements of your site — and its intended use — will enable you to make the right decision about your liquid screed, and ensure that your project is completed to the highest standard.