How to Pour or Lay Liquid Screed
Posted on: 10th June 2020
Last updated: June 2026
As with everything in the building game, preparation is key!
There are several steps that you’ll need to take to prepare a floor for screeding. The actual screeding is most likely to be carried out by an experienced team of professional screeders, as this is a typical requirement from many material suppliers that generally train their material installers – these include Tarmac, Breedon, Cemex and many more.
Step 1: Measuring the Amount of Screed Required
It is critical to get the right amount of screed; a contractor will probably not leave this to the end-user, but will visit the site and accurately measure the amount of screed needed.
Step 2: Remove debris and lay insulation
The most important thing is to ensure that the area to be screeded is made watertight to protect the subfloor. But before you do that, it’s best practice to remove all the dust and debris from the floor. Then, if you’re adding insulation, you should do it now, before laying down the waterproofing membrane.
Step 3: Lay the watertight membrane
Polythene sheeting (1000 gauge or thicker) needs to be laid down to create a waterproof membrane to ensure that there is no leakage of the screed when it’s pumped in. This is important to get right, because if the slip membrane hasn’t been put in place properly it can have a serious effect on the screed and the final result.
To save your screed contractor headaches, make sure that:
- All perimeter insulation is tucked away behind the membrane
- Any corners in the polythene sheet are cut or folded in and taped out of the way
- All perimeters are also lined neatly with polythene and allow 90 degree angle of screed
- The screed is protected from direct sunlight once it’s been poured
When finished there will be a shallow, water-tight polyethene “pool” where the screed will collect.
Step 4: Waterproof Shuttering
Formwork will be needed around obstacles and troublesome pipework etc to ensure that water and screed doesn’t get to them.
If you have shuttering across doorways or steps for example, this needs to be sealed with mastic or expanding foam so that it’s watertight. Expansion foam will generally be needed across doorways.
Step 5: Secure Under-floor Heating Pipes
If using under-floor heating, then the pipes or trays should be secured now. The clips are generally self-sealing, but it is important that nothing is able to float up when the liquid screed is poured. So using Metex PipeTak or a similar pipe clipping tool to secure the clips in place is a good idea. Make sure the UFH pipe is clipped in at close and regular intervals to avoid issues later on.
Now that everything is sealed and watertight, the site is ready for the screed to be poured. At this stage, it is a good idea to fill the under-floor heating pipes as this will stop them floating up in the liquid screed and stop them from being squeezed by the weight of the screed.
How to Pour Liquid Screed
The same “rules” apply for screed as they do for concrete; do not layover 30°C or under 5°C and falling. You’re good to go if the temperature is over 3°C and rising.
As mentioned, it is unlikely that a material supplier will allow a client to pour the screed themselves, so the contractors will arrive a few hours early to get ready before the mixer arrives with the screed. They will check that the area to be screeded is watertight and then will work out the level that the screed will go to across the room using screed levelling tools.
They will use screed levelling tripods positioned in various points across the room. The liquid screed tripods (sometimes called screedpods) are then adjusted so that the flat plate at the centre of the tripod is at the height that the screed will be. This is calculated using a datum level which is transferred to each screed tripod using a laser level.
They will also get the pump ready so that when the mixer arrives with the screed it can be poured straight into the pump and piped to where needed.
The screed is poured into the area where it is needed and spread out by someone wading through it. It is the consistency of cream so runs to all corners of the polyethene pool. It is filled up until the level of the plate on the screed tripod. At this point, there is enough screed and the pump will be stopped and the floor screed tripods removed.
The screed is then tamped using Screed Dapple Bars twice; once fairly vigorously to get any air bubbles out of the screed and the second time more gently without leaving the surface to get a smooth finish.
They will work back to the doorway leaving the whole surface smooth, ready to start drying. This whole pouring and dappling process will not take long; 15 minutes for around 25m2. Now close the doors for up to 72 hours so that the initial drying does not happen too quickly as cracking might occur; humidity needs to be kept high to slow the drying.
Drying Time for Liquid Screed
Liquid calcium sulphate screeds dry at a broadly similar rate as traditional screeds; 1 day for every mm up to 40mm, and 2 days for depths over 40mm.
As above for the first 72 hours, keep doors closed to reduce ventilation so that drying does not happen too quickly and lead to weaknesses or cracking.
After about 24 hours it should be possible to walk on the surface, but it will be a week before building non-load-bearing structures like partition walls can start.
It is possible to speed the drying process by using a dehumidifier after 72 hours, and if there is under-floor heating this can be turned on gradually from the lowest setting after 7 days. Removing the top surface laitance will also help the screed to dry out more quickly.
The screed should be totally dry before finishing with your desired floor covering!
Preparation for Laying Floor Covering on a Liquid Screed
One of the issues with using a calcium sulphate liquid screed is that there is a little work to be done before the floor finish can be laid.
As the screed dries a thin crust forms on the top which is called laitance. This needs to be removed by sanding before the floor is tiled, however if other floor coverings that do not need an adhesive are to be used you only need to brush and vacuum the residue.
Removing the laitance is one of the disadvantages of a (gypsum) anhydrite liquid screed. It will need to be sanded off, ideally after about a week as it gets harder to remove if it is left too long.
Once the laitance has been removed the floor needs to be sealed before your adhesive is applied as it is a porous surface and will absorb the moisture from the adhesive causing it to dry too quickly.
Frequently Asked Questions
Who can lay liquid screed?
Liquid screed installation is almost always carried out by a specialist screeding contractor rather than a general builder or DIYer. Most material suppliers require this as a condition of supply, as the preparation, levelling, and pour process needs to be managed correctly to achieve a good result. Getting it wrong is expensive to fix once the screed has set, so using an approved contractor is the right approach for any project where the quality of the finished floor matters.
How do you prepare a floor for liquid screed?
Preparation involves several steps in the correct order: clearing the floor of all dust and debris, laying any insulation, fitting a watertight polyethene membrane of at least 1000 gauge across the entire area, sealing around obstacles and doorways with mastic or expanding foam, and securing any underfloor heating pipes so they cannot float up when the screed is poured. Skipping or rushing any of these steps creates problems that show up either during the pour or in the finished floor.
How are screed levelling tripods used when pouring liquid screed?
Screed levelling tripods are set up across the floor before the pour to give the screeding team a fixed reference point for the finished floor level. Each tripod has a central threaded shaft with a disc that can be raised or lowered to a precise height. The first tripod is set to the datum level, usually derived from a fixed point such as a door sill, and the remaining tripods are adjusted to match using a laser level. The screed is then poured up to the height of the discs, and the tripods are removed before the material begins to set.
How long should you keep doors closed after pouring liquid screed?
The area should be kept closed for at least 72 hours after the pour. During this period the screed needs to dry slowly and evenly, and draughts or ventilation will accelerate surface drying and increase the risk of cracking. After 72 hours careful ventilation can be introduced, but the screed should continue to be protected from direct sunlight and extreme temperature changes until it has reached sufficient strength to be walked on safely.
What temperature conditions are needed for laying liquid screed?
The same rules that apply to concrete apply to screed: do not lay in temperatures below 3 degrees C and rising, and avoid laying above 30 degrees C. The ideal range is between 10 and 20 degrees C. In cold conditions the screed will cure too slowly and may freeze before it gains sufficient strength; in hot conditions it can dry too quickly at the surface, leading to cracking and a weakened finish. If site conditions fall outside these parameters it is better to delay the pour.
What is laitance and how do you remove it from liquid screed?
Laitance is a thin, weak layer that forms on the surface of calcium sulphate screed as it dries. It looks like a pale, dusty crust and needs to be removed before any floor finish or adhesive is applied, as it is not strong enough to bond to. It is typically sanded off using a floor sander or buffer after around a week, when it is still relatively easy to remove. Left too long it becomes harder to sand. Once laitance is removed the surface should be sealed before adhesive is applied, as the screed beneath is porous and will otherwise absorb moisture from the adhesive and cause it to fail prematurely.