The following sample M10 Specification has been produced so it can be copied and pasted into your specification and amended accordingly

FlexiDry - Fast drying semi-dry cementitious screed with choice of 3, 7, 14 or 21 day dry times.

A unique additive enabling accelerated drying and hardening of floor screeding systems. Suitable for bonded, unbonded, floating and heated screeds to receive finished floor coverings such as tiles, wood flooring, laminate, PVC, natural stone, carpet and a variety of other floor finishes.

Product reference:

FlexiDry F0 - 3 day dry screed

FlexiDry F1 - 7 day dry screed

FlexiDry F2 - 14 day dry screed

FlexiDry F3 - 21 day dry screed

Manufacturer:

FlexiDry Global Limited

Chancery Court

Lincolns Inn

Lincoln Road

High Wycombe

Bucks HP12 3RE

Tel. 0845 555 5656

e. .(JavaScript must be enabled to view this email address)

Screed construction:

Fully bonded as clause

Unbonded as clause

Floating as clause

Recommended thickness (minimum):

Bonded screed: 25 mm

Unbonded screed: 40 mm

Floating and heated screeds: 60 mm

Over pipe work: 30 mm

Flatness/ Surface regularity: SR1, SR2 and SR3 as determined in BS8204

Finish: Trowelled as clause

Movement joints: an edging strip of minimum 5mm thickness should be placed around the perimeter of all areas to be screeded. Proprietary movement joints are to be as per drawing.

Daywork joints: as clauses and pointed with a hard setting sealant.

Mix design:

1:3 - For minimum strength of 30N/mm2 after 28 days

1:4 - For minimum strength of 25N/mm2 after 28 days

The surface preparation is similar to traditional floor screeds, requiring a structurally sound surface, free from dust, laitance, dirt and contaminants such as oil and grease.

EXECUTION

Suitability of substrates

General:

- Suitable for specified levels and flatness/ regularity of finished surfaces. Consider permissible minimum and maximum thicknesses of screeds.

- Sound and free from significant cracks and gaps.

Concrete strength: To BS 8204-1, Table 2.

Cleanliness: Remove plaster, debris and dirt.

Moisture content: To suit screed type. New concrete slabs to receive fully or partially bonded construction must be dried out by exposure to the air for minimum six weeks.

Proprietary levelling/ wearing screeds

General: Materials, mix proportions, mixing methods, minimum/ maximum thicknesses and workmanship must be in accordance with recommendations of screed manufacturer.

Standard: To BS 8204-3.

Conduits

Under floating screeds: Before laying insulation for floating screeds, haunch up in 1:4 cement:sand on both sides of conduits.

Cast into or under screeds: Overlay with reinforcement placed mid depth between top of conduit and screed surface.

Screed cover over conduit: 40 mm (minimum).

Fully bonded construction

Preparation: Generally in accordance with BS 8204-1.

Removing mortar matrix: Shortly before laying screed, expose coarse aggregate over entire area of hardened substrate.

Texture of surface: Suitable to accept screed and achieve a full bond over complete area.

Cement slurry bonding

Application: Shortly before laying screed, thoroughly wash clean the surface and keep well wetted for several hours. Remove free water then brush in cement slurry bonding coat of creamy consistency.

Screeding: While slurry is still wet.

Unbonded construction

Separation: Lay screed over sheet dpm or a separating layer.

Separating layer: Lay on clean substrate. Turn up for full depth of screed at abutments with walls, columns, etc. Lap 100 mm at joints.

Floating construction

Insulation: Lay with tight butt joints. Continue up at perimeter abutments for full depth of screed.

Separating layer: Lay over insulation and turn up at perimeter abutments. Lap 100 mm at joints.

Mixing

Water content: Minimum necessary to achieve full compaction, low enough to prevent excessive water being brought to surface during compaction.

Mixing: Mix materials thoroughly to uniform consistency. Mixes other than no-fines must be mixed in a suitable forced action mechanical mixer. Do not use a free fall drum type mixer.

Consistency: Use while sufficiently plastic for full compaction.

Do not retemper.

In situ crushing resistance (ISCR)

Standards and category: To BS 8204-1 table 4.

• Testing of bonded and unbonded screeds: To Annex D.

• Testing of floating levelling screeds: To Annex E.

• Make arrangements for test to be witnessed/ certified.

Adverse weather

Screeds surface temperature: Maintain above 5° C for a minimum of four days after laying.

Hot weather: Prevent premature setting or drying out.

Flatness/ Surface regularity of floor screeds

Standard: To BS 8204-1, Table 5.

Test: To BS 8204-1, Annex C.

Sudden irregularities: Not permitted.

Deviation of surface: Measure from underside of a 2m straightedge (between points of contact), placed anywhere on surface using a slip gauge to BS 8204.

Surface regularity standards:

- SR1: 3mm high standard

- SR2: 5mm normal standard

- SR3: 10mm utility standard

Screeding to falls

Minimum screed cover: Maintain at lowest point.

Falls: Gradual and consistent.

Compaction of screeds

General: Compact thoroughly over entire area.

Screeds over 80 mm thick: Lay in two layers of approximately equal thickness. Roughen surface of compacted lower layer then immediately lay upper layer.

General/Fibre Reinforcement

Steel fabric: To BS 4483, table 1.

Type: 12mm PP Fibres

Installation: To be mixed with the screed in accordance with the mixing method and dosage recommended by the manufacturer.

Joints in levelling screeds

Laying screeds: Lay continuously using 'wet screeds' between strips or bays. Minimize defined joints.

Daywork joints: Form with vertical edge.

Crack inducing grooves in levelling screeds

Groove depth: At least half the depth of screed.

Cutting grooves: Straight, vertical and accurately positioned. Select from the following:

- Trowel cut as screed is laid. To be placed in all doorways.

- Saw cut sufficiently early after laying to prevent random cracking.

Strip movement joints

Installation: Set securely into screed to exact finished level of floor. Extend joints through to substrate.

Finishing

Timing: Carry out finishing operations at optimum times in relation to setting and hardening of screed material.

Trowelled finish to levelling screeds:

• Floating: To an even texture with no ridges or steps.

• Trowelling: To a uniform, smooth but not polished surface, free from trowel marks and other blemishes, and suitable to receive specified flooring material.

Curing

General: Curing not required under general conditions but prevent premature drying from wind, draughts and strong sunlight.

Do not subject screeds to artificial drying conditions that will cause cracking or other shrinkage related problems.

FlexiDry recommends that protection to levelling floor screeds should be carried out as soon as possible after installation.

• The expected traffic type and volume should be considered to determine the type of protection required.

• Instructions on heavy loadings on to the levelling floor screed should always be sort from a qualified structural engineer.

Consideration will provide the floor in perfect condition for the floor finisher to achieve best results.

Download the FlexiDry Floor Screed Maintenance Sheet pdf document for further advice on how to best protect your floor screed after it has been installed.

Floor protection products can be purchased online at www.flexidryshop.com.

For further information on the types of protection available visit www.screedprotection.com.

The product information below is from the NBS Plus library of product clauses offered in NBS specification products for FlexiDry fast drying floor screed. It has been created by NBS for FlexiDry Global Ltd. Each product clause is authored in NBS format and is intended for inclusion in project specifications.

Detailed description: A unique additive enabling accelerated drying and hardening of floor screeding systems. Suitable for bonded, unbonded,floating and heated screeds.

Application: Typically used as an additive to levelling screeds to receive finished floor coverings such as tiles, wood flooring, laminate, PVC, natural stone, carpet and a variety of other floor finishes.

Click on the above link to be taken to the RIBA Product Selector Page for FlexiDry Fast Drying Floor Screed.

Download a Sample M10 Cement Based Levelling Screed Specification

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The images were produced by a recognised University and show that a cementitious screed is 20 to 30% more efficient as a thermal conductor than an anhydrite screed.

Cementitious screeds are more efficient due to their greater compaction and due to cement being an active conductor. 

Anhydrite

FlexiDry Fibre Screed

FlexiDry Fibre Screed vs anhydrite

The comparison thermal image shows the heat generated by the UFH pipes.  The heat transferred through the cementitious screed can be seem on the left.  Whereas with the anhydrite screed, on the right, the heat from the UFH pipes is visible but the screed acts as an insulator rather than a conductor so the heat transfer through the screed is less.

3 D Thermal Images: FlexiDry Fibre Screed (left), Anhydrite Screed (right)

Screed Strength Testing – BRE Drop Hammer Test

The strength testing method for FlexiDry fast drying floor screed is a BRE drop hammer test in compliance with the current standard of BS8204:1 2003.

The device consists of a 1m long cylindrical guide rod along which an annular weight of 4kg (for Categories A and B), or 2kg (for Category C), travels when released. At the bottom of the guide rod the weight strikes the collar of a case hardened steel anvil which transmits the impact to the selected area of screed. Four successive impact blows on the same spot are sufficient to create an indent in the screed. The depth of the indent determines the strength of the screed.

Frequently Asked Questions about FlexiDry and Floor Screeding

What is FlexiDry?
FlexiDry is an accelerated screed additive which can be used on a wide range of floor applications. The dry time of a FlexiDry screed is not dependant on a controlled temperature of 20 Deg C & 50% RH.

What is the difference between FlexiDry F1, F2 and F3?
It is the same liquid additive but by altering the dosage the dry time of the screed can chosen at 7, 14 or 21 days.

FlexiDry F0 is a different liquid additive which dries the screed in just 3 days ready for final floor finished to be laid.

What is the difference between FlexiDry and standard screeds?
Depending on the FlexiDry fast drying screed used, final floor finishes can be installed after 3, 7, 14 or 21.

Standard screeds laid at 75mm will take approximately 110 days to dry before final floor finishes can be installed.

Is FlexiDry easy to use?
Being a low concentrated non hazardous liquid it is just added to the screed mixture on site.

How much can be laid in one day?
Depending on the size of the screed team between 100 – 250sm per day.

How quickly can I walk on it?
12 hours to receive light foot traffic.

How quickly can it take general traffic?
General traffic can go on top of the screed after 48 hours.

Is it necessary to cure the screed under polythene for days after it has been laid?
No, unlike standard sand & cement screed and some fast drying screed additives it does not need curing for 7 days after it has been installed. This removes the associated H&S trip hazard with the polythene, means no revisit to the site to remove it and also saves the issues of its disposal and the environmental impact.

Is there any waste issue with FlexiDry?
No, FlexiDry Screeds are mixed on site so there is minimal wastage.

Does the screed have to be laid flat?
No, unlike flowing floor screeds it can be laid to falls.

Can it be used for taking up intolerances?
Yes it is perfect due to its high compaction it can be laid at thinner depths.

Is FlexiDry Screed water repellent?
Yes it is water repellent unlike anhydrite and traditional sand & cement screeds.

Is the product recyclable?
FlexiDry fast drying screeds are completely recyclable and provide a whole life solution which can be recycled and blended with concrete for further use.

Do I need to protect the floor from direct traffic?
We recommend that protection is used to provide optimum performance as it is a levelling screed and not a wearing surface.
If the screed will only have a light traffic then protection could be ignored. FlexiDry provide a screed maintenance sheet

Does the building have to be watertight?
Care should be taken to keep the screed dry as re-watering could result in extended dry times.

Can I use FlexiDry outside?
Yes, FlexiDry is suitable for internal & external use.

Is FlexiDry suitable for UFH?
FlexiDry is a perfect screed solution for Underfloor Heating. It provides a good conductor of the heat dissipated from the pipes and due to its high density and easy compaction optimum performance is achieved.

What’s the difference between Anhydrite and cementitious Screeds?
Please see our comparison sheet.

How can I order FlexiDry?
You can go to our secure online shopping site, email your enquiry to .(JavaScript must be enabled to view this email address) or call the team at the office on +44 (0)845 555 5656.

How do I know how much to order?
We have a calculator to assist you with the quantities required. There is a mobile option to calculate on your Blackberry or iphone.

How do I know it works?
It has been used on thousands of installations in the UK and throughout Europe and in the UK it has been adopted by many Tier 1 main contractors and specialist Underfloor Heating installers.

Design Considerations of how to achieve a successful interface between Hydronic (wet) Underfloor Heating and Screed.

Please find the following information that is essential for the successful implementation of floor screeding systems on hydronic (wet) underfloor heating. The terminology of the screed type is important that it remains consistent (wearing screed or leveling screed) with the underfloor heating contractor & M&E designers.

Design Inputs

The designer would need to describe all types of final flooring, whether it is flexible or rigid, tiles, natural stone, conglomerate, carpet tiles, linoleum, wood flooring, etc.

The locations of columns, protrusions, insets should all be identified and described fully to assist in the definition of joints. This is highly important to mark up onto drawings used by all parties.

The screeding specialist would require information from the designers as to detailed knowledge of the pipe work fixings and whether it will sit on the insulation or to the concrete substrate. The information and detail should be provided for all service access points such as pipe work manifolds.

Design Outputs

In addition to the M&E / Underfloor heating Contractor outputs, the following should be provided by the architects / specifier to all parties.

Floor construction, all thicknesses relating to total void / depth of final floor finish / insulation depth / screed depth, joint location and any inherent shrinkage allowance.

Full details of proposed screed system(s) such as cementitious, calcium sulphate, fast drying, water reducing, or any other system should be known.

The proposed final flooring finish and the surface finish of the floor screeding system in relation to the final flooring.
All relevant codes of practice and standards.

Screed Materials

A screed can be described as a layer of material that provides a flat surface to receive final floor finishes at a defined level on a structural base.
There are a number of different terminologies for screed in the industry and it is important that all parties are agreed as to what is expected and what is offered and fit for purpose. Therefore it is important that the proposed floor screeding system(s) falls under BS8204 – Part 1 – 2003 (current  standard).

Levelling screed is a suitable finish to provide a level surface to receive final finishes and a wearing screed that is substantial enough to be the final flooring.

The following refers to leveling screeds to avoid confusion and are more popular on underfloor heating systems where insulation is used and the screed construction is floating. This floating system is isolated from other construction components such as walls, pipe penetrations, raised manholes, etc. There are other definitions such as fine concrete screeds which incorporate a greater single sized aggregate and generally used for heavy use and greater depths. There are all types of additives and cement replacements which reduce the risk of cracking, inherent in cementitious products.

Cement / Sand Screeds

Cement / Sand Screeds are mixed to an earthy, semi-dry consistency in order to achieve the desired workability and reduce the water / cement ratio. The screed should be well compacted and thicknesses greater than 75mm should be compacted in layers of 50mm. The surface finish depends on the type and quality of the sand and can vary dramatically from area to area. The sand would need to conform to BS EN 13139 – 0-4mm grade. Levelling compounds are required to install thin sheet floorings as aggregate can be picked up during installation. The standard thickness of screeds should be a minimum of 75mm for commercial use and 65mm for residential / light use and a minimum coverage of 35mm over the top of the underfloor heating pipe.  Cementitious screeds enable improved thermal conductivity due to their compaction. There are numerous modified cementitious screed systems that can be laid at thinner section, such as FlexiDry.

Free Flowing Anhydrite Pumpable Screeds

Free flowing Anhydrite / Hemi Hydrite floor screeding systems are a by-product of the chemical industry and when processed, it forms a gypsum binder and is blended with aggregates and additives. These systems are laid very wet and achieve a dense construction with a low shrinkage value. Free flowing screeds require a degree of preparation to ensure that all joints are taped and perimeter strips are sealed and a tanked system provided to ensure the screed does not weep under the insulation or into cavities, etc. The requirement for minimum depths are 30mm in residential properties and 40mm for commercial but the minimum coverage over the top of the pipes has to be 30mm. It is always best to allow a bit for intolerance in the substrate but always recommend a level survey is carried out prior to commencement.

Fast Drying Screeds

Program should always be considered and quite often the drying time of floor screeds will not suit the project. The standard drying time is 1mm per day for the first 40 days and 0.5mm per day thereafter. This means a standard 75mm screed could take 110 days to dry, based on 20C. There are many types of  additives and cement replacements that can dry from as little as three hours and all the way back to natural but the faster the dry time the more expensive the product. Certain products can also allow a thinner screed to be applied and data sheets should be read in conjunction with BS 8204 – 1 – 2003 (current standard).

Drying the Screed

1. Cementitious Screeds
   Standard cementitious screeds need to be cured for seven days after installation in order to keep moisture in the screed and stop the top drying faster than the bottom. The curing method is a thin polythene layer over the screed and applied the morning after installation; this helps to reduce curling and cracking. This method is often overlooked and generally not required due to cost implications and understanding. The screed needs to be well ventilated and protected from direct sunlight. Forced drying should not be applied as this could lead to a reduction in strength and increased random cracking which could affect final floor installation and lead to failure. Curling can sometimes be reversed by re-watering but this could affect dry times for final finishes. Underfloor heating should not be commissioned until the screed is dry. Follow underfloor heating procedures to commission the system and increase temperature incrementally.
2. Free Flowing Anhydrite Pumpable Screeds
   These types of screeds do not require a polythene cure and it is recommended that after three days the screed is exposed to ventilation. Commissioning of underfloor heating can take place after seven days but again on incremental basis and manufacturer’s instructions should be followed.

All screeds should be tested prior to installation of sensitive floor coverings and the recognized methods are hair hygrometer or carbide bomb test. 3% moisture content for ceramics and 2% for sensitive coverings.

Floor Construction

Generally the design should be from the top down rather bottom up in order to consider all finishes will work. The condition of the concrete substrate needs to be checked as preparatory work might be required prior to insulation being installed. Severe undulations and steps could cause voids which will lead to future failure.

The bay sizes may differ in relation to different applied finishes and these should be considered and marked up on drawings to avoid confusion. Movement joints need to be agreed as underfloor heating can aggravate residual moisture in the screed and cause random cracking, so aspect ratios generally 3:1 should be considered and irregular shaped rooms.

It is imperative that all joints are considered and absolute detail confirmed as to the construction and location.

We hope this publication helps to understand the design issues around screeding on underfloor heating. All information deemed correct at time of publication 16th November 2009.

It can be clearly demonstrated that if the site mix screed is forced action mixed, generally in a screed pump which has the same capability of a ready mix plant, there should be no reason for failure if the correct proportions are followed. The cement, preferably CEM 1 class 42.5N, is gauged into a 260 litre mixing vessel and filled with sand complying with BS EN13139 0-4mm grade plus the addition of any proprietary products to the pre-agreed mix design.

This gives complete control of quality, quantity, mix and water content to the screed specialist in order to achieve optimum performance. Due to the general mix parameter of 1:3-4.5 this method is completely satisfactory and testing can always be carried out to ensure that the screed is fit for purpose. The recognised testing method is a BRE drop hammer test in compliance with the current standard of BS8204:1 2003 and perhaps this should form part of the screed package. Ready mixed screeds would not necessarily pass the test as compaction and workability play a huge part.

The major quality benefits of mix screed over ready mix screed are:

• better efficiencies
• increased quality control
• more cost effective
• better waste management
• lower carbon footprint

Site mix advantages

• complete control over start times as sand and cement can be delivered in advance
• minimal waste as the screeder has total control of the mixed quantities resulting in improved carbon footprint
• screed is permanently fresh and installed in optimum time
• easy to manage change requests and varying depths
• added control of starting and finishing points
• reduced risk of re-agitated mix and dry jointing which leads to poor compaction
• allows site mixture of additives and cement replacements which is not possible with ready-mix
• more competitive pricing structure
• very easy to postpone/cancel due to unforeseen circumstances

Ready mix disadvantages

• no control over plant breakdown
• many logistical hurdles to overcome in order to guarantee delivery on time to site
• High volume of waste if screed -
  • is thinner than anticipated and no other areas are available to use the screed
  • if next joint location cannot be achieved
• seasonal changes to the consistency  of the screed – in summer too dry; in winter too wet
• poor compaction if screed is too dry
• poor finish if screed is too wet plus increased shrinkage due to high water/cement ratio
• day joints would be random with no control to comply with pre-agreed locations
• not guaranteed to contain correct retarders and mix design due to risk of human error caused by varied mix design requirements by different clients
• additional loads might not be an option if there is a variation of screed depth or will attract a premium cost for small loads
• high cost to purchase plus high cost to discard

This section is designed to contain more detailed technical information on the performance of FlexiDry fast drying floor screed in a variety of applications, as well as supporting documentation on the chemical processes behind the material's performance.

Please contact us should you be unable to find the answers you require in the white papers listed on the right.

Moisture testing – CM MoistureTest Method

FlexiDry floor screed must be moisture tested using the CM Moisture Test Method. This can be completed with either a Tramex CRH Meter (non-destructive) or using a Calcium Carbide Moisture Tester (destructive) before laying sensitive floor coverings.

The residual moisture in the screed should be less than 3% before laying permeable floor surfaces such as stone and ceramic tiles and less than 2% before laying sensitive floor coverings such as vinyl, linoleum, parquet etc.

You can purchase the full moisture testing kit via the Accessories section in the FlexiDry Shop on our website or we can arrange for the tests to be carried out on your behalf. Please see the Services section of our website for further information on the testing services we offer.

Moisture testing video (Calcium Carbide Test)

The way to achieve best results is to consider the final performance requirement based on the floorzone. Most flooring is designed from the concrete upwards and final floor finishes are generally left as a later decision. Quite often this leads to failure as potentially the requirement in the British Standards of each floor finish are different, leaving joints in the wrong place, no intermediate movement joints, change of usage category, drying time suitability and compatibility, etc, etc. It is therefore best practice to consider designing from the top down, being the final floor finish, back to the concrete substrate.

Our recommendation would be to collate all the requirements from the floorzone and consider all options with their particular design requirements and associated standards. Once this information is complete the design and markup of drawings can be produced. It’s always a good idea to have this information shared with all relevant parties in order to achieve best results.

Once all the above has been completed, the screeding installation process can begin as follows:-

• Check the area is free of debris, materials and trades.
• Check the area is watertight.
• Check the correct depth of screed can be achieved by measuring down from the datum level.
• Ensure the correct depths, movement joints, expansion perimeter strips, acoustic / thermal layers, membranes are in place.
• Check the specification of the screed mix design.
• Ensure the mixer is a forced action type such as a pan mixer or screed pump.
• Dilute the required amount of FlexiDry and disperse the Fibres into the water bucket used for each mix and agitate for two minutes.
• The mix should be of a plastic consistency.
• Continue to complete the screeded area.
• The following day, protection can be installed if high volumes of traffic are expected.
• Protection to remain in place until final floor finishes are installed.

The technicians at FlexiDry fast drying floor screeds are always available for advice, both by telephone, email or live internet chat.

An advanced and highly adaptive fast-drying screed additive

FlexiDry is an advanced and highly adaptive screed system which can be used on a wide range of floor applications. This new innovation in screed science has been specifically designed to deliver optimal performance and quality on a number of fronts.

Unique Advantages of the FlexiDry Fast Drying Floor Screed System

• A choice of dry times - 3, 7, 14 or 21 days - which are NOT dependant on controlled temperatures of 20 Deg C & 50% RH
• Does not require curing under polythene for 7 days after installation removing H&S risks on site
• Removes the need for liquid DPM's
• Light foot traffic after 12 hours
• Greatly reduced shrinkage due to the highly controlled drying process enabling much larger bay sizes
• Better compressive and bending strength properties
• Major cost savings due to the ability to dry the screed in-line with the actual project timescales required to best meet completion dates. This can potentially lead to significant cost savings
• Increased compressive strengths of 25N/mm² or 30N/mm²
• Better compaction enables improved thermal conductivity (perfect with UFH systems)
• Allows reduced thicknesses on top of insulation and UFH systems and therefore uses less screed, so less cement and better for the environment
• No need for mesh reinforcement

Download the FlexiDry Benefits document.

The FlexiDry Expert Centre is designed to help you make the most of using FlexiDry fast drying floor screeds in your project, containing:

• Sample M10 Specification to be downloaded
• Articles
• White papers
• Guides
• Datasheets
• Safety documents
• Videos

We would like to help you make your FlexiDry experience a successful one. Please take a look through the sections within the expert centre, for guidance, technical and safety information, and all the supporting information you may need for specifying and using FlexiDry fast drying floor screeds.

Should you not find the answers you are looking for within the expert centre, please call us for further support on 0845 555 5656.