Sample Specification for M10 Proprietary Quick Drying Levelling Screeds

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.