Frequently Asked Questions
What is a flowing screed?
Screedflo flowing anhydrite liquid screed is selected sharp sand mixed with anhydrite binder and water.
How does Screedflo compare to traditional sand and cement floor screeds?
Anhydrite screed is calcium sulphate based. As it is a liquid, the finish is much smoother, flatter and the screed is faster to install. It is a stronger product than traditional sand and cement screed, and so can be laid thinner. It conducts the heat from UFH pipes up to 5 times more effectively.
What can liquid screed be used for?
Flowing screed can be used for almost any internal application to provide a level, flat, smooth surface to an SR2 finish, for all types of floor coverings, either domestic or commercial. Please see the Our Products page on our website.
Can flowing screeds be used with under floor heating?
Anhydrite screeds are ideal for application over both electric and water under floor heating systems because of the flowable consistency that fully encompasses the heating pipes. Flowing screeds have excellent thermal conductivity and minimal thermal expansion.
Projects with underfloor heating will benefit from significant savings in energy costs by using anhydrite screed.
Standard sand and cement screeds conduct underfloor heating at a rate of 0.41W/mk.
Liquid screed is up to 2.3W/mk, and Screedflo Thermal screed is up to 2.5W/mk. (This is very beneficial when relying on ground or air source heat pumps with a lower flow temperature).
What about cracking? Do flowing screeds need reinforcement to prevent cracking?
Flowing screeds are much stronger than traditional screeds and do not require reinforcement as they do not curl and shrinkage is extremely low, minimising the risk of cracking. Joints are required less frequently than with traditional screeds, but recommended through doorways and between areas of heated and non heated screeds. Check out our preparation advice.
How much do I need?
You can get an approximate guide by using our calculator.
When can I walk on the screed?
Leave to dry for 48 hours, and then open the windows or building to allow ventilation.
Light foot traffic after 48 hours.
Protect from rain or the ingress of water. Protect from direct sunlight.
Then after 7 days you can work on the screed as normal, and put up any non-load bearing partitions etc.
How do I contact Screedflo?
You can use any of the methods shown on our contact page, or by phone on 01621 874781 or email to info@screedflo.co.uk, or social media.
We will be happy to discuss your project requirements with you.
Is my job too large/small?
Depending on location, our minimum delivery is 0.6m3 and there is no upper limit.
Does Screedflo deliver to my area?
We operate in East Anglia, the South East, London and the Home Counties. For larger jobs outside these areas please telephone us as we may still be able to deliver to you.
Will the Screedflo vehicle be able to access my site?
Our vehicles can access most sites that a concrete lorry can access, but must always be on a hard standing area. We can pump the material 100-150 metres from wherever the Screeedflo vehicle is parked. We will make a site visit before the installation date to check access, water supply and that the preparation of the floor is suitable for liquid screed.
What do I need to do before the delivery arrives?
We need a safe hard standing area for the Screedflo vehicle.
A mains pressure water supply (we will bring a hose pipe with the vehicle).
An area to wash out or a lined skip for the final residue and water which we flush through the hoses.
We will check these points with you at the site visit a few days before installation.
What happens once the delivery arrives?
Once the delivery vehicle arrives, the team will greet you and look at your datum point and critical points on the floor. We set up the tripods using a laser, connect the water and delivery hoses to the Screedflo vehicle and start to mix your chosen Screedflo product. After 10 minutes we will be ready to start pumping. It takes approximately 8 minutes to pump each m³. Once we have finished mixing and installing, we will then wash out any residue and ask you to sign our delivery note.
Is it ok to use a stiff brush instead of using an STR sander to remove laitance and put a key in the screed?
Sanding, or mechanically abrading the screed is not just to remove laitance and the sanding process is something that should be followed for all screeds. A mechanical sander (such as an STR701) should be used to provide a key for primer and any adhesive. A stiff brush can remove loose laitance but will not give the floor a key and may not remove stubborn construction debris such as plaster and mortar dropped during the construction phase.
Will commissioning the underfloor heating after 7 days cause the screed to crack?
Anhydrite liquid screed is much stronger and flexible than sand and cement screed. If the UFH is commissioned from a low temperature through the recommended cycle there will be little need to worry about cracking or 'shocking' of the screed.
Will the underfloor heating clips tear the membrane or cause leaks?
Anhydrite liquid screed is a thick liquid, that will not seep through the holes made by the UFH clips. If there are any splits in the membrane, seal these with waterproof gaffa tape before the screed is laid.
Can I have a 75mm screed depth so that I know it will be strong enough and won't crack?
Anhydrite liquid screed is designed to be laid at 40mm on insulation and 50mm with UFH. 75mm is not required but can be laid if requested. It will take longer to dry at this depth. It is often better to increase the insulation and reduce the screed which not only saves money but also gives a much better performing floor. We can assist with this specification change when requested.
Why do I need the edge strip on the perimeters if I am not having underfloor heating in the screed?
Screed expands as it dries, so a 6mm, 8mm or 10mm expansion foam will allow the screed to expand onto something soft and prevent any cracking as it dries.
Can I put re-enforcement mesh into the screed?
Standard Screedflo liquid screed is much stronger than sand and cement and requires no mesh or reinforcement. Mesh just makes it harder to lay a smooth liquid screed and is of no benefit to the floor.
Is it true that sand and cement screeds don't need a special treatment. They don't need sanding. They don't need a special primer. Why does yours?
All screeds require sanding to clean up the floor and provide a key for the primer. The primer stops the moisture being sucked out of the adhesives or smoothing compounds into the screed. With anhydrite screeds, there can be a chemical reaction between anhydrite and cement based products, so a suitable primer is always required.
Is it true sand and cement screeds don't have to have the UFH commissioned?
No, in all cases where UFH is installed, this must be commissioned (18-21-day heating cycle) to thermally heat and move the floor in a controlled way, and force any moisture trapped in the screed out.
Does Anhydrite screed have 'fat' on the surface that is hard to get off.
Anhydrite screed can sometime produce laitance, which is a loose powder than comes to the surface as it dries. This should be removed after around 4 days and can be done with a stiff broom. But the mechanical sanding of the screed also needs to be done, ldeally before the UFH is commissioned, but always before floor coverings are laid.
My tiler says Anhydrite screeds are too much work.
Anhydrite screeds can produce laitance, which needs to be removed, and then also require the same preparation as cement based screeds, but the difference is that an anhydrite compatible primer should be used when sealing the floor. All screeds need sanding and all need to have the moisture levels tested and UFH commissioned prior to laying floor coverings. Just pay attention to which product has been laid, and to the instructions relating to the products to be applied to the screed.
Do Anhydrite screeds take too long to dry?
Screedflo Rapide screed can be dry in 14 days at 50mm. Screedflo standard screed is around 28 days at 50mm. Sand and cement-based screeds need to cure and take longer to dry and be ready for floor coverings. They are generally laid at 65mm -75mm depths.
Anhydrite screeds can be force tried with UFH after 7 days, so a 50mm screed can be dry in 28 days from the install date.
All screeds require ventilation of the room they have been laid in the reduce humidity an encourage drying.
Can Anhydrite screed be laid on garage floors?
Yes, we recommend Screedflo Extra. Once dry this can be painted with an industrial resin paint to protect the surface and is much stronger than standard sand and cement screeds.
If I have more questions, who do I contact?
Contact Screedflo any time by emailing us at info@screedflo.co.uk (please ensure you include your contact details) or call us on 01621 874781.
