Frequently Asked Questions

What is a flowing screed?

Screedflo flowing liquid screed is selected sharp sand aggregate 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 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 more effectively.

What can flowing screed be used for?

Flowing screed can be used for almost any internal application to provide a flat, smooth surface for all types of floor coverings, either domestic or commercial.

As an unbonded screed it can be laid to a minimum of 30mm thickness. This is where the screed is separated from the solid base with a polythene membrane.

As a floating screed it can be laid to a minimum thickness of 35-40mm. This is where the screed is separated from the solid base with an insulation layer and a polythene membrane.

Where the floor zone incorporates underfloor heating a minimum cover of 20mm cover over the pipes can be achieved. Generally, a 45-50mm screed is installed.

Can flowing screeds be used with under floor heating?

Flowing 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.

Do flowing screeds need reinforcement to prevent cracking?

Flowing screeds do not require reinforcement as they do not curl and shrinkage is extremely low, minimising the risk of cracking.

How much do I need?

You can get an approximate guide by using our calculator.

How do I contact Screedflo?

You can use any of the methods shown on our contact page. 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. When supplying Screedflo as part of the Screedflo dB acoustic floor system, coverage is national.

Will the Screedflo vehicle be able to access my site?

Our vehicles can access most sites but must always be on a hard standing area. We can pump the material 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?

Make sure that there is a safe hard standing area for the Screedflo vehicle.

Make sure that we have a dedicated mains pressure water supply (we will bring a hose pipe with the vehicle).

Provide us with an area to wash out or a lined skip for the final residue once the delivery is complete.

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 we connect the water and delivery hoses to the Screedflo vehicle and start to mix your Screedflo. After 10 minutes we will be ready to start pumping. It takes 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.

Can I use a liquid DPM instead of a polythene membrane? Do I need to install a membrane for the screed as I already have a DPM underneath the insulation.

Liquid DPM does not always prevent a reaction between liquid screed and insulation. The 500 gauge polythene membrane tanks the floor, isolates the screed and prevents any leaks onto the insulation. This should be lapped up the walls to prevent any leaks and lapped up in front of the expansion strip.

My plumber/underfloor heating engineer has told me that Screedflo need to advise on where the vertical control joints need to be placed as it to do with the screed and not the underfloor heating.

The UFH causes the screed to expand as it heats up. The UFH designer should advise on where the expansion joints should be placed. These should, as a minimum, be between unheated and heated areas, and in doorways. The maximum bay size should be limited to 300m2 and 20m length with a maximum aspect ratio of 6:1. The shape of the bays should also be considered.

Why do I need to commission my underfloor heating? Can I lay my final floor covering and then commission the underfloor heating afterwards?

The UFH should be commissioned first in line with industry guidelines. The UFH causes the screed to expand, so the commissioning cycle should be followed before any floor treatments or coverings are applied. The underfloor heating can also be very effectively used to force dry the screed beginning after just 7 days.

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 same process should be followed for all screeds. A mechanical sander should be used to provide a key for primer and any adhesive. A stiff brush 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 tears 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 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.

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.