What Is Liquid Floor Screed?

My name is Andy Parkin, Managing Director of the Multi-Award Winning Speed Screed. I’m here today to talk about “what is liquid floor screed”.

What Is Liquid Floor Screed?

What is liquid floor screed, is a question that we are often asked and the ready-mixed version is a relatively new product on the market.

Having said that, it took a few years to get to the position that it currently stands at, and the factory produced version was introduced into the UK around  16 years ago, but it is relatively new in terms of the market,  Liquid floor screed market share has been slowly increasing, and I would say it accounts for around about 15 to 20% of the current screed market.

If we look at the calcium sulphate liquid floor screed (with a calcium sulphate binder), there is a liquid floor screed that is cementitious on the market, however we will look at the calcium sulphate version because that is by far the biggest-selling liquid floor screed on the market.

Pumped Liquid Floor Screed

The product is pump applied only (small bagged volumes can be mixed on site),  it is the only way for large volumes of the product for it to be supplied.  It is supplied via a truck mixer, discharged into a screed pump and then pumped directly to the area where it is needed.

Where Can Liquid Floor Screed Be Used?

Floor levelling screeds are normally used where there is a structural substrate, the screed itself isn’t normally structural.  It can be used in the following applications:

Low Shrinkage

Calcium sulphate liquid floor screed has very low shrinkage, when compared with traditional sand and cement.  This means there is a minimal risk of cracking and no curling that you can sometimes see with cementitious products.

With low shrinkage comes less joints.  Assuming the aspect ratio is 2:1 or less with no restraints in the screed, re-entrant corners, columns, then the maximum area without joints would be 1000m2.  For liquid floor screed with underfloor heating assuming the same things would be 300m2.  With a greater aspect ratio and/or restraints the maximum m2 would be reduced.

You may want to consider movement joints if you have a heated screed, and would want to separate different zonal areas.  Placing a joint between zones will minimise egress of heat into the neighbouring zone.  With thermal movement, having two areas heated at different temperatures, with no joints could cause thermal movement cracking.

The weakest area within a screed would be the shortest span, this is likely to be across doorways, and would be an obvious place to form a joint.

Foot Traffic

Liquid floor screed can generally be trafficked after 24 -48 hours.

Productivity

The screed is pumped into place and this enables high productivity, laying up to 2,000 a day.  Productivity is dependent on the following:

  •  How open is the building, is it one large room or all small?
  • How far is the plant from the site?
  • Does the ready-mix producer have enough trucks to service a large project?

With everything favourable then 2,000m2 would be achievable.

 Drying Times

When compared to traditional sand and cement, the thickness of liquid floor screed can be reduced.  A thinner screed will generally give you a fast drying screed.

It can be force dried after seven days,  by turning the underfloor heating on, and/or using dehumidifiers  (cementitious screeds, would not be forced dried).  After seven days, the crystallisation of the binder has taken place, and the moisture is not needed and can just be extracted.

Any commissioning of the heating needs to be controlled under the British Standard guidelines.

At 20 degrees and 60% relative humidity a calcium sulphate flowing screed would dry as follows:

  • 1-40mm  1 day per mm
  • Over 40mm 2 days per mm

The screed must be dry before the floor coverings can be applied, and a moisture test is essential.  For permeable floor coverings such as carpet, 1%  or less is suitable, and .5% moisture or less for non permeable.

If it is laid on a damp substrate, then it is likely to delamination.  It is never advisable just to rely on the product drying times on the datasheet, as there are lots of factors that can enhance or prevent the drying process.

Thermal Conductivity

Because of the density of the product, the efficiency and thermal conductivity is greater than a sand and cement screed.  Calcium sulphate liquid floor screed is quicker to respond, quicker to heat, quicker to also cool down.

Compaction

Calcium sulphate liquid floor screed is not a self-levelling product, however it is self-compacting. With a tradition sand and cement, you need to compact the product to make sure that you get full strength, with this product, it is self-compacting.

Wearing Surface?

In terms of durability of the product, it is not a wearing surface. There are a few screeds out there that are wearing surfaces, but the majority are non-wearing surfaces and require a suitable floor covering to be laid on top.  You can cover it with tiles, wood, carpet, and is very flexible.

Wet Areas

It is not suitable for permanently wet areas such as changing rooms, where a cementitious product would be more suitable.

Deliveries

A 6m3 delivery would take approximately 30 minutes to discharge, from truck mixer to project.

Dapple

Once the screed is in position, it would then be finished with what is called a “dapple bar”, a rounded aluminium bar, to first of all remove the air bubbles, on the first pass.  Then at 90 degrees to the first pass, you would then pass again, and this time the bar would just bounce on the surface of the screed, and this would produce a smooth levelled surface that is then suitable for your floor coverings.

Bonding

When applying floor coverings, calcium sulphate liquid screed and cementitous adhesive directly are not compatible.  A primer would be required when using any cementitious products.  You can also purchase adhesives that are calcium sulphate, and would be compatible.

Minimum Depths

  • TS15 15mm Bonded
  • “Standard” Calcium Sulphate Liquid Screed Bonded 25mm
  • Unbonded 30mm
  • Floating 35mm domestic – 40mm commercial
  • Underfloor Heating HTC 20mm above the pipes
  • “Standard” 30mm above the pipes

I hope that helps. If you’ve got any further questions regarding what is liquid floor screed, please contact me.

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