How to use UltraFloor Smoothing Underlayments on Calcium Sulphate Screeds

Flowable calcium sulphate screeds, also known as anhydrite, hemi hydrite and gypsum screeds have many advantages over traditional sand / cement screeds.

Calcium sulphate screeds can be laid more thinly than sand / cement resulting in lighter weight loadings, are often formulated using industrial by-products, helping you reach environmental goals and because they can be pumped, calcium sulphate screeds are much quicker to install.

Before a flooring installation takes place it is important that calcium sulphate screeds be identified as they have different application requirements to other screeds. Visually, calcium sulphate screeds do not differ from traditional screeds, therefore it is always a good idea to enquire about the subfloor, particularly if it contains underfloor heating.

Unlike sand / cement and cementitious products, which can still have extremely impressive tensile and compressive strengths whilst retaining a high level of moisture, calcium sulphate screeds need to reach a specific level of dryness in order for them to perform correctly underneath floor coverings. It is essential to know the moisture reading of a calcium sulphate floor before applying any smoothing underlayment.

Moisture testing before the application of smoothing underlayments

The approved method for testing moisture is to use a surface hygrometer. This insulated box is fixed to an unheated floor, typically for 4 days, after which time any moisture in the air will have been trapped in the box and reached equilibrium. The air in the box can then be tested using either an analogue or digital hygrometer and if the reading is less than 75%RH (relative humidity), the screed is dry enough to proceed with the installation.

Other indicative tests can be used to help identity if moisture is present or if the screed is close to dry. One such test is to tape a piece of plastic to the floor for 48 hours. Moisture condensing on the underside of the plastic, or a darkening of the screed, indicates moisture levels are still significant. The recommended drying times for calcium sulphate screeds, as quoted by most manufacturers, are usually based on drying conditions at 20°C, low air humidity and an open surface with no materials overlaid. However, these conditions do not always represent a typical site scenario so they should not be relied upon.

Underfloor heating within the screed

It is also important to remember that underfloor heating must be fully commissioned before continuing with a flooring installation. A simple air pressure test is not sufficient enough to achieve this and a full cycle through the heating range should be completed instead. This is necessary for a number of reasons including:

  1. To ensure there aren’t any leaks in the system
  2. To see if there are weaknesses in the screed by identifying any likely points of cracking and spalling (typically due to poor installation of the screed with heating)
  3. To assist drying of the screed

If underfloor heating is present, expansion strips should be used between the different heating zones to enable the screed to move independently, around any perimeters and at upstands and door thresholds. In all cases, the expansion strips must not be covered over and should be carried through to the upper floor finish using a silicone sealant, or similar, to achieve a continuous floor.

When underfloor heating has been installed we advise that a polymer modified smoothing underlayment is used. It is also beneficial to use a fast setting product to help minimise the migration of moisture between the screed and smoothing underlayment during curing.

Preparation

Once the above criteria has been completed and fully met, it is advisable to mechanically abrade all screeds using a rotary disc to remove any laitance and weak upper surface, usually caused as a result of fibres floating to the surface during wet installation. Some screeds have specific requirements to complete this process so advice should always be sought from the manufacturer.

It is imperative that all laitance is completely removed and any dust and debris has been vacuumed to leave a stable, open textured, dust free surface. Failure to do so will result in costly failure when the smoothing underlayment is applied.

Choosing a smoothing underlayment

UltraFloor have developed a number of smoothing underlayments that are perfectly suited for use on calcium sulphate screeds. These include:

Detailed product information and the technical capabilities for each of these products can be found by visiting ultrafloor.co.uk.

Priming

It is essential to prime when using UltraFloor’s smoothing underlayments as the risk of an adverse chemical reaction (Ettringite attack) with calcium sulphate screeds will be reduced when levelling is carried out.

It is always good practice to prime your substrate as it ensures finer dust particles are bonded and sealed. Priming also creates an effective barrier and assists in consolidating the prepared surface, making it more stable as well as ensuring your chosen smoothing underlayment is fully bonded to the screed. For optimum results, we recommend using UltraFloor Prime IT Multi-surface Primer.

For more information on how best to approach calcium sulphate screeds or for further technical information on any of the products mentioned, please contact UltraFloor’s team of experts by emailing ultrafloor@instarmac.co.uk, calling 01827 254402 or visiting ultrafloor.co.uk.

Why should you prime?

Priming of subfloors/substrates is key to ensuring the selected smoothing underlayment can perform to its optimum. It improves the flow and workability of the smoothing underlayment. There are three basic reasons why priming is important. Firstly, priming reduces the absorbency of the floor; secondly it increases adhesion and finally, correct priming acts as an interface between materials preventing failure by reaction. The simple process of using the appropriate primer will minimise issues and result in:

  1. A smoother underlayment
  2. A stronger underlayment
  3. A reduction in labour time
  4. A surface fit to lay the thinnest of decorative floor coverings to

Underfloor Heating

Various underfloor heating manufacturers exist including Warmup who offer a range of systems across the different types, including Sticky Mat and Total-16. We recommend that you always refer to the manufacturer’s instructions when installing underfloor heating.

It is becoming increasingly common to come across floors with underfloor heating systems incorporated. It is important to note the following points and check the underfloor heating before you begin work.

Where warm water underfloor heating systems are incorporated, they must have been fully commissioned and brought up to their maximum temperature, and ideally switched off 48 hours before the application of UltraFloor products. It is important to establish that the commissioning of the system has been carried out, consult the underfloor heating manufacturer for confirmation. In the absence of other heat sources, the underfloor heating may be set to ‘cutback’ position to achieve an air temperature of 15°C. Any expansion or movement joints must be carried through to the finished floor surface.

The cables of radiant electrical underfloor heating systems must be secured to a sound, strong mechanically fixed cement faced backer board. UltraFloor products may also be used where electrical underfloor heating is used over cementitious or calcium sulphate subfloors. In all cases our smoothing underlayments must be applied at a minimum thickness of 5mm above the cables for resilient, textile and timber applications and a minimum of 3mm for applications of stone, ceramic or porcelain products.

Warm water systems fixed within pre-formed insulation panels must be mechanically fixed to the existing subfloor/substrate these must be sound and solid with no movement. The panels should be primed depending on the porosity and type. In all cases our smoothing underlayments must be applied at a minimum thickness of 5mm above the cables for resilient, textile and timber applications and a minimum of 3mm for applications of stone, ceramic or porcelain products.

There is no requirement to commission warm water systems fixed within pre-formed insulation panels or radiant electrical underfloor heating systems before the application of UltraFloor products. These systems should be commissioned 7 days after the UltraFloor products have been applied. To commission these systems the heating should be increased 5°C per day from ambient until the maximum operating temperature has been reached, and then decreased back down again by 5°C per day.

The Instarmac CPD – Specifying Tiling to Underfloor Heating Systems – will provide you with an understanding of the benefits of heated tiles and the types of system available.  It will also cover key design and specification considerations and product choices for tiling to underfloor heating and selecting appropriate materials.  It will teach you how to confidently specify typical tiling system build-ups for underfloor heating, and you should also understand the importance of warranties and confidence in complete performance systems. Please visit ultratilefix.co.uk or call 01827 254402 for more information.

Pre-smoothing of Subfloors/Substrates

Where there is an absence of a damp proof course and provided there is no risk of hydrostatic pressure, pre-smoothing can be carried out. UltraFloor Level IT Two, UltraFloor Level IT Bond, UltraFloor Level IT Top and UltraFloor Level IT Base are all suitable for pre-smoothing use, please refer to their respective datasheets for further guidance.

Wear Surface/Surface Finish

When installing a wear surface ensure that the subfloor/substrates has been tested for moisture, any contamination or laitance has been removed, prime if required and check for underfloor heating. Both UltraFloor Level IT Top and UltraFloor Level IT Super Flex 30 may be used as a finished wear surface. Please refer to their respective datasheets for further guidance.

 

The drying characteristics of cementitious smoothing underlayments

The drying characteristics of cementitious smoothing underlayments are directly influenced by ambient air and floor temperatures. Cement within the smoothing underlayment cures through a process of hydration using moisture. Extreme site conditions can affect this process i.e. below 5°C and above 30°C.

Ideal ambient air and floor temperatures for application are between 10°C and 22°C. These temperatures should be maintained throughout application and curing periods. Outside of these temperatures consideration should be given to the following guidelines for good practice. Floor temperatures will be slower to respond to ambient air temperature so should be considered in advance.

High humidity and low temperature prolongs evaporation of moisture from the freshly applied smoothing underlayment and therefore extends drying times. This may ultimately delay installation of floor coverings. In such conditions planned heating (not gas heating) may be required before, during and after application of the product in order to promote ideal site conditions. Heat should be directed into the air not direct to the floor creating hot spots. Good ventilation without direct drafts will also assist removal of moisture in the air from the building. Failure to adopt such practices in such adverse site conditions may result in damp patches, slow drying and potential surface bleed within the curing smoothing underlayment.

Low humidity and high temperature conditions will speed up drying by fast removal of moisture from freshly applied smoothing underlayment. Such conditions may cause rapid loss of moisture, required for the curing process, leading to irregular structure and strength build up. Such tensions within the drying smoothing underlayment could leave hairline surface defects. Under such conditions, smoothing underlayments should be protected from direct sunlight and drafts across its surface. Good air flow within the build without causing drafts is essential to reduce high temperature build up.

 

An A-Z of floor coverings

There is a vast array of final floor coverings available, the following describe each of the most popular kinds:

Carpet

A textile floor covering typically consisting of an upper layer of pile attached to a backing.

Cork

The bark of a cork oak tree which is ground into sheets that are used as tiles to create a floor covering.

Engineered Wood

Engineered wood is man-made/manufactured.

Laminate

A multi-layer synthetic flooring which is fused together using a lamination process.

Linoleum (Lino)

A floor covering made from materials including solidified linseed, pine rosin, ground cork dust, wood flour and mineral fillers such as calcium carbonate. A burlap or canvas backing is most commonly used.

LVT (Luxury Vinyl Tile)  

LVT is made of a series of layers including a photographic and the flooring’s primary component, PVC. The product offers a look of real wood or stone flooring.

Paint

Either a water or resin based decorative surface coating that others a wear proof finish.

Parquet

This floor covering is made of small blocks of timber that are usually adhered to the subfloor/substrate using a bitumen adhesive. Parquet is often laid in a herringbone pattern.

Raised Access Flooring

A raised surface providing an elevated structural floor above a solid substrate, creating a hidden void for the passage of mechanical and electrical services.

Resin

A hard wearing plastic surface, created by mixing together a selection of ingredients. The chemical reaction creates a highly durable finish. Resin is ideal for the heaviest of use areas.

Rubber

Can be made from either natural tree rubber or from synthetic materials, including recycled vehicle tyres.

Solid Wood

Solid wood flooring planks milled from a single piece of timber.

Tile

A hard wearing material such as ceramic, stone or glass available in various sizes and shapes.

Vinyl

PVC chips are formed into solid sheets of different thicknesses by heat and pressure.

UltraFloor European Standards explained

All UltraFloor smoothing underlayments, repair and finishing compounds and our damp proof membrane are fully CE classified, their ‘Declaration of Performance’ certificates can be downloaded at the click of a button from ultra-floor.co.uk or via our Product Planner App.

The European Standards explained:

BS EN 13318:2000 states the definition of a screed as:

Layer or layers of screed material laid in situ, directly onto a base, bonded or unbonded, or onto an

intermediate layer or insulating layer, to obtain one or more of the following purposes:

– to obtain a defined level;

– to carry the final flooring;

– to provide a wearing surface.

BS 8204-1:2011 gives recommendations for the design and laying of concrete bases and cementitious levelling screeds to receive in situ floorings. It also gives recommendations for constituent materials, design, work on site, inspection and testing of concrete bases that are to receive in situ wearing screeds.

BS EN 13813:2002 is entitled ‘Screed material and floor screeds – Screed material – Properties and requirements’.

It defines for fresh screed material the performance related to setting time, consistency, pH value and for the hardened screed material, compressive strength, flexural strength, wear resistance, surface hardness, resistance to indentation, resistance to rolling wheel, shrinkage and swelling, modulus of elasticity, bond strength, impact resistance, reaction to fire, acoustic performance, thermal resistance and chemical resistance.

Cementitious smoothing underlayments (CT) are classified on both compressive (C) and flexural (F) strength and abrasion resistance (AR*) where relevant e.g. CT C35 F6 AR0.5.

*abrasion resistance, in the UK for wear resistance use British Cement Association test.

BS EN 8203:2017 titled: Installation of resilient floor coverings – code of practice, provides recommendations for installation of cork, linoleum, plastics and rubber floor coverings, as well as including recommendations for bases.

BS EN 5325:2001

This British Standard provides recommendations for the installation of textile floor coverings in new or existing buildings. It covers all products composed of textile material with a pile or non-pile use surface, and includes the laying of carpet tiles, either with the use of a permanent adhesive or a tackifier. It details suitable methods of design and installation and advises on the selection of the materials required for their implementation.

BS EN 8201:2011

Code of practice for installation of flooring of wood and wood-based panels. It gives recommendations and guidance on the material, environment and installation variables that combined have a fundamental effect on the performance and serviceability of finished wood flooring. It outlines the most up-to-date specifications involved in laying flooring and illustrates typical constructions on which it might be laid.

 

Underfloor Heating Preparation Guidance

Various underfloor heating manufacturers exist including Warmup who offer a range of systems across the different types, including Sticky Mat and Total-16. We recommend that you always refer to the manufacturer’s instructions when installing underfloor heating.

 

It is becoming increasingly common to come across floors with underfloor heating systems incorporated. It is important to note the following points and check the underfloor heating before you begin work.

 

Where warm water underfloor heating systems are incorporated, they must have been fully commissioned and brought up to their maximum temperature, and ideally switched off 48 hours before the application of UltraFloor products. It is important to establish that the commissioning of the system has been carried out, consult the underfloor heating manufacturer for confirmation. In the absence of other heat sources, the underfloor heating may be set to ‘cutback’ position to achieve an air temperature of 15°C. Any expansion or movement joints must be carried through to the finished floor surface.

 

The cables of radiant electrical underfloor heating systems must be secured to a sound, strong mechanically fixed cement faced backer board. UltraFloor products may also be used where electrical underfloor heating is used over cementitious or calcium sulphate subfloors. In all cases our smoothing underlayments must be applied at a minimum thickness of 5mm above the cables for resilient, textile and timber applications and a minimum of 3mm for applications of stone, ceramic or porcelain products.

 

Warm water systems fixed within pre-formed insulation panels must be mechanically fixed to the existing subfloor/substrate these must be sound and solid with no movement. The panels should be primed depending on the porosity and type. In all cases our smoothing underlayments must be applied at a minimum thickness of 5mm above the cables for resilient, textile and timber applications and a minimum of 3mm for applications of stone, ceramic or porcelain products.

 

There is no requirement to commission warm water systems fixed within pre-formed insulation panels or radiant electrical underfloor heating systems before the application of UltraFloor products. These systems should be commissioned 7 days after the UltraFloor products have been applied. To commission these systems the heating should be increased 5°C per day from ambient until the maximum operating temperature has been reached, and then decreased back down again by 5°C per day.

 

The Instarmac CPD – Specifying Tiling to Underfloor Heating Systems – will provide you with an understanding of the benefits of heated tiles and the types of system available.  It will also cover key design and specification considerations and product choices for tiling to underfloor heating and selecting appropriate materials.  It will teach you how to confidently specify typical tiling system build-ups for underfloor heating, and you should also understand the importance of warranties and confidence in complete performance systems. Please visit ultratilefix.co.uk or call 01827 254402 for more information.

 

Pre-smoothing of Subfloors/Substrates

Where there is an absence of a damp proof course and provided there is no risk of hydrostatic pressure, pre-smoothing can be carried out. UltraFloor Level IT Two, UltraFloor Level IT Bond, UltraFloor Level IT Top and UltraFloor Level IT Base are all suitable for pre-smoothing use, please refer to their respective datasheets for further guidance.

 

Wear Surface/Surface Finish

When installing a wear surface ensure that the subfloor/substrates has been tested for moisture, any contamination or laitance has been removed, prime if required and check for underfloor heating. Both UltraFloor Level IT Top and UltraFloor Level IT Super Flex 30 may be used as a finished wear surface. Please refer to their respective datasheets for further guidance.

How can you remove contamination and laitance?

Following British Standard 8204 all subfloors/substrates must be free from contaminants that may prevent adhesion such as dust, oils, grease, surface laitance, water soluble adhesive residues and weak smoothing underlayments etc.

Various methods and machines exist which are designed for the preparation, removal and finishing of subfloors/substrates prior to the application of any UltraFloor product. They include STGs, Shotblasters, Planers, Grinders, Multi-strippers and Dust Extractors.

We recommend that you contact The Preparation Group for advice on the appropriate method for your job and hire details www.ppcgroup.co.uk.

Smooth dense surfaces can be roughened by mechanical scabbling to enhance the key.

Please click here for more information on products.

 

How do you test for moisture?

85% of complaints are as a result of moisture, Source: FITA

If a subfloor/substrate has not reached the required level of dryness before a floor covering is laid then residual moisture held between the aggregate and cement (or other binder) will slowly be released, reaching the subfloor/substrate preparation and the floor covering causing damage from beneath.

Testing the moisture of a subfloor/substrate can be relatively straightforward, providing you know what you are assessing and have the appropriate equipment. British Standards are in place and subfloors/substrates should be tested in accordance with the British Codes of Practice BS 8203, BS 5325 and BS 8201. A BS hygrometer box should be used. This will provide a Relative Humidity (RH) reading. A reading above 75%RH is higher than is recommended to lay floors without a surface DPM.

If a moisture reading taken is greater than 75%RH then the subfloor/substrate is considered wet (when laying textile/resilient floor coverings, 65%RH for wood). Provided the subfloor/substrate is suitable to receive moisture protection products either a DPM or a MVS can be used. If using either UltraFloor DPM IT or UltraFloor Suppress IT, follow the product’s respective usage instructions as detailed on the datasheet.

Only as a two coat application, UltraFloor DPM IT may be used on subfloors/substrates where there is an absence of a constructional base DPM provided there is no hydrostatic pressure. UltraFloor DPM IT should not be used in projects where hydrostatic pressure is a concern. In such cases the use of pressure relief drainage and/or external tanking systems must be the primary method of protection against moisture.

Please click here for more information on products.

Is your subfloor/substrate suitable?

The suitability of a subfloor/substrate should always be fully assessed before carrying out any preparation or installing a floor covering. British Standard 8204 should be referred to for full guidance and clarification.

The main criteria to be assessed is:

  1. Sound/solid – is the subfloor/substrate strong and stable?
  2. Dry – has the subfloor/substrate dried/cured completely?
  3. Free from contamination – is the subfloor/substrate clean?
  4. Laitance free – is the subfloor/substrate surface free of fines?

If the answer to any of these is ‘no’, then the subfloor/substrate is not suitable to be laid onto and further preparation is required.

Please click here for more information on products.

Subfloor/Substrate Types

The UltraFloor range of products are suitable for use on all subfloor/substrate types. These fall into two categories, porous and non-porous, the most common include:

POROUS

  • Concrete
  • Sand:Cement
  • Flooring Grade Plywood
  • Anhydrite

NON-POROUS

  • Epoxy Resin Damp Proof Membrane
  • Power Floated Concrete
  • Flooring Grade Asphalt
  • Porcelain, Ceramic, Quarry or Terrazzo Tiled Floors
  • Steel Mezzanine Decks
  • Access Panels

It is important to establish the type of floor you are laying onto so it can be prepared in the correct way.

Please click here for more information on products.