How to Guide – Laying Liquid Screed
Liquid or pumpable screed has many advantages over traditional cement screed including reduced labour time, self-compacting and self-levelling qualities, reduced depth, and quicker drying times.
Screed is used to provide a smooth, flat surface to flooring in advance of finishing materials such as ceramic tiles or wood. It is the ideal option for underfloor heating systems because of its excellent thermal capabilities.
Types of Floor Screed
There are 3 main types of screeds:
- Traditional cement screed
- Pumpable calcium sulphate screed
- Pumpable cement-based screed
Traditional screed can be self-mixed cheaply and easily but is labour intensive and does not achieve the same results as liquid screed. Calcium sulphate screed is quick to lay and pour, very level and less prone to shrinking. Pumpable cement screed has quicker drying times than even calcium sulphate screed and does not require any preparation before applying the final finished surface.
The most common type of liquid screed is a calcium sulphate which is the active ingredient making up around a third of the volume. This becomes gypsum when water is added, and as a result can be referred to as a “calcium sulphate screed”, “gypsum screed” or even “anhydrite screed” which refers to the form of the mineral – anhydrous calcium sulphate – which is used.
Cement Based Pumped Screed
More recently cement based pumped screeds have become available. These can be pumped like a gypsum screed but does not have the downsides. The active ingredient is cement rather than calcium sulphate.
Preparation for Laying Liquid Screed
There are six basic steps required to successfully lay liquid screed:
Measure the Amount of Screed Required
When liquid screed is supplied via volumetric truck it is not critical to get exact measurements correct. However, waste bags are always a good idea on site to collect any small excesses.
Clean the Floor Area of any Debris
Ensure to prepare the area by clearing any dust and debris, leaving a clean, flat surface.
Lay a Watertight Membrane
Use polyethylene sheeting to create a waterproof membrane of 1000 gauge or thicker to ensure the area is watertight.
Form work will be required around pipework is required and expansion foam across doorways.
UFH pipes should be protected by the polythene. It is important nothing can float to the surface during pouring. It is also advisable to fill the UFH pipes in order to weight them.
Screed levelling tripods are required in various points across the site and set so that the flat plate at the centre of the tripod is at the height that the screed will be. This is done using a datum which is transferred to each tripod using a laser level.
Pouring Liquid Screed
Screed cannot be poured if the temperature is over 30°C or under 5°C and falling.
The Driver/Pump Operative will arrive and assess the site for pouring.
Screed Mixing and Pumping Preparation
The volumetric screed mixer will be set to mix the correct components and the pump will be set up so that it can be piped directly to site.
Liquid Screed Pouring
The screed is poured into the designated area and spread out by someone wading through it. It will run to all corners of the polyethylene continue until it touches the plate on the screed tripod. At this point you have enough screed to the pump will be stopped and the tripods are removed.
The screed is tamped using a Screed Dapple Bar firstly to get any air bubbles out of the screed and then to leave a smooth surface finish.
Screed Drying Process
The drying process begins for up to 72 hours. Doors should be closed to reduce ventilation and to keep humidity high.
Liquid Screed & Drying Times
Liquid screed is pumped in and poured across the floor surface. This liquid finds its own level and drying times vary dependent on the chosen mix, but some designs are dry within hours and allow the finishing surface to be laid within days of application.
Liquid screeds time vary, and it is important to discuss your requirements with us in advance but broadly it is 1 day for every mm up to 40mm, and 2 days for depths over 40mm. After about 24 hours you should be able to walk on the surface and it will be at least week before the finished flooring can be applied.
The screed must be totally dry before finishing with your desired floor covering.
Laying a Floor Covering over a Liquid Screed Floor
In the case of calcium sulphate screed, as the screed dries a thin crust forms across the top which is called laitance. This needs to be removed by sanding before the floor is tiled, however if using floor covering without the need for an adhesive, then a brush or vacuum of the residue will suffice.
Axtell Floor Screed Specialists
Axtell are the leading providers of traditional and liquid screed services across Surrey, Hampshire and East Sussex. We have over 20 years of knowledge and experience in the floor screed business, and have developed a customer-first approach allowing us to provide you with the highest quality of screed products and services at the best prices.
Reach out to a member of the Axtell team today using the form below to get a quote to find out how we can help with your floor screed project requirements.