In the UK, applying a layer of liquid screed over a concrete base is a common practice in constructing floors. Liquid screen reinforces and smoothens the resulting surface. To some extent, a person with some experience in the process can perform a DIY screed application.
But, DIY screed application is not recommended if the area is large. It is also not recommended if the flooring material over the screed is thin or requires special installation skills, or if the purpose of screeding involves underfloor heating. In any of these cases, you should hire a liquid screed contractor to get the job done professionally. This article will discuss the two methods of applying liquid screed which you can do yourself.
Unbonded screed application
Unlike other types of application, unbonded liquid screed is applied above a layer of plastic. The purpose of putting plastic sheets is to ensure that your floor is not exposed to moisture. These sheets also protect the screed from issues such as settling. But, one problem you may encounter is curling. To avoid this problem, you need to reinforce the screed layer by making sure that the coating is even and at least two inches thick. The following are the steps in prepping your floor for application:
- The concrete base should be clean and free from all debris.
- Put the plastic sheets on the floor. Tape overlaps to keep them in place.
- Use edging foam to line pillars and walls. Lining these surfaces prevents damage in case of shrinkage.
Since unbonded screed is more prone to cracking, you need to reinforce the mixture. One method you can use is adding polypropylene fibre. Another alternative is using a steel mesh to control cracking.
Bonded screed application
Bonded screed means you are directly applying the mixture over the concrete base. This application method prevents cracking and curling. However, this method is only best used when you are applying a thin layer of liquid screed. The thickness should be even and at most 1.6 inches. Anything thicker than this will require modifications to the screed mixture to prevent it from de-bonding from the concrete base. Preparing the floor for screed application begins with the following steps:
- Roughen the concrete base so that it bonds better with the liquid screed. You can use a shot blaster or floor scrabbler, or manually expose the aggregate using a pick or a chipping hammer.
- After roughing up the surface, remove all dust and debris using a vacuum.
- The next step is to apply a bonding agent. You can either use SBR, or make a mixture by combining PVA glue, cement, and water. In making your bonding mixture, make sure to follow the exact instructions; otherwise, you may encounter problems with bonding.
Once you have prepped the floor, the next step is to apply the liquid screed. You can buy a prepared screed mixture for a hassle-free application. The advantage of a ready-mix screed is that it contains additives that slow down the setting. This way, you can take your time carefully applying the mixture.