Why floor screed

First, clean the concrete floor to get rid of any dust or grease. Any particles of dirt or grease can prevent the mixture from settling evenly. Once the flooring area is clean and free from dirt or dust, lay down polythene sheets , or another form of membrane, to keep the concrete flooring separate from the screed.

The sheets should also go up the walls by around 10cm. Use insulation, edging foam or polystyrene to run around the walls. This will prevent any damage occurring to the walls when the screed shrinks in the drying process.

If necessary, reinforce the screed with fibres — these will prevent the screed from cracking when it dries, and help to increase its overall strength. Alternatively, take screed reinforcement mesh and lay it over the subfloor. This should then sit in the top half of the screed when it has been laid.

How to prepare to lay bonded screed Bonded screed involves the adhesion of the screed to the concrete subfloor. The first step is to roughen the surface of the concrete, to maximise adhesive potential. This can be done by using a chipping hammer, or a pick, but you can also choose to use a shot blaster or floor scabbler. The aim is to expose the aggregate in the concrete, as this is what will bond with the screed.

Next, remove any dust, debris or dirt, and sprinkle with water — this will reduce the number of airborne particles. The best way to do this is to use a vacuum cleaner. Now apply your bonding agent to the concrete. The most popular options tend to be a mixture of PVA glue, water and cement, or styrene-butadiene rubber SBR , which is ideal to use in rooms that will be in contact with water. How to lay screed In regards to thicknesses, unbonded screed should always be around 50mm thick — so when pouring the screed, aim for at least mm.

First, divide the floor up. It is much easier to work on sections of the floor than try to achieve an even finish across the whole floor in one go. Try to aim for around 10ft between each guide, and ensure all battens are level using a spirit level. Now the screed can start being laid. Take enough screed to fill around 2ft of the first section. Spread the screed out with a trowel, then get a screed board or a straight-edged tool to compact and flatten it out — use a chopping motion for best results.

Alternatively, vibrating screed boards are available amongst other compacting tools. Put the straight edge over the battens, resting on each side, and move down the length of the section in a sawing motion.

Try to keep the straight edge tilted slightly to have a sharper edge in contact with the screed. Once two sections have been filled, take the batten out and fill the gap between them, ensuring it remains level and even. Repeat until the whole floor has been screeded. Now it is time to finish the concrete using a bull float. Repeat this again once all the excess water has evaporated or stopped coming out of the concrete.

If desired, you can create a textured surface on the concrete, by using a wooden float and moving it across the surface in arched motions. Alternatively, create a smooth finish with a steel trowel flat against the surface. After the screed has been laid, it needs to be cured.

This is most commonly done by placing sheeting across it, sealing it around the edges. Leave this untouched for around 7 days. Once the 7 days have passed, leave the floor to dry for a further three weeks before installing any flooring.

What is floor screed made of? What types of floor screed are there? The three most commonly used types of floor screed are: Traditional screeds: This is most commonly used to create a level surface in the final finish of a floor made up of sand cement Self-levelling compounds: When a greater degree of tolerance is required for the application of sensitive floor finishes, this is applied to the top layer of a screed, with varying thicknesses from 1mm to 40mm, this is also commonly known as latex Reinforced screeds: Through the use of fibres or metal mesh, this is used to support stress upon the screed that can occur during the drying process.

In addition, curling, cracking and shrinkage can also be prevented. Liquid screeds: Also know as free-flowing or Anhydrite screeds, these can be installed quickly and easily in a range of commercial and domestic environments. Where is floor screed used? However, the anhydrite screeds are not suitable for areas that are prone to getting wet. They cannot be used as a final wearing surface and are not compatible with cementitious products.

Floor levelling compounds: These compounds vary from the general screedsin that they are used for levelling or as the final layer of screed to increase the tolerance while laying the floor finishes such as tiles, vinyl etc. They are generally expensive and are used for screeding in warehouses and areas which require a very high level of surface regularity or flatness.

Structural Screeds: This type of screed suitable for installing on precast floor surfaces. It is important to seek accurate specifications and calculations from a structural engineer before the installation of structural screeds as the information is vital to decide on the load requirements, flexural strength, bending moment, point loadings, etc. The Right Screeding Mix The right screed mix is one that is homogenously blended in the right proportion, following the agreed mix design.

The three methods that are generally followed by screeders for site mixing of screeds are: Hand Mixing: This is suitable only for very small areas and is not recommended for bigger projects, as the work is strenuous and the estimated quantities and manual errors while mixing can seriously affect the quality of the screed.

Free Fall Mixers: Free fall mixers are sometimes used by screeders for mixing larger quantities of screed at the work site. When these are sufficient for mixing general concrete mixes and mortar which are of a fluid consistency, screeds mixed using free fall mixers are often found to be of poor quality, weak and crush easily under impact. Forced Action Mixers: Forced action mixing is the most efficient and economic method for producing high quality screed mixes on site.

Forced action mixing blends the cement and mix homogeneously and is ideal when additives or admixtures are to be added.

Forced action mixers are usually of two types: i Screed Pumps: These are generally used for forced action mixing of large quantities of screed at the work site. The Right Process for Installing the Screed It is important to carry out the process of screed installation in a systematic manner to achieve the best results. There are several steps to be followed while preparing to install the screed: Check the specification is fit for purpose Make sure the substrate is ready to receive the screed.

Check the access and egress is suitable for screed installation, plant and materials. Check the building is watertight.

Check the datum levels, record the measurement down to finished screed level to ensure minimum and maximum depths are achievable and compliant with tendered nominal allowance. Check that running potable water is available at an adjacent point of the material location. Check that a waste facility is adjacent to the working areas. Check the mixing plant is safe and suitable to use.

Mix the screed in the correct proportion.