Screed Flooring in London Victorian Terraces: Sand-Cement Screed, Anhydrite, and Hanson Cemfloor

SAND-CEMENT SCREED (ALSO CALLED TRADITIONAL SCREED OR CONVENTIONAL SCREED) IS THE LONG-ESTABLISHED AND MOST WIDELY USED FLOOR SCREED TYPE IN UK RESIDENTIAL RENOVATION — A MIXTURE OF ORDINARY PORTLAND CEMENT (OPC) AND WASHED SHARP SAND IN A SEMI-DRY CONSISTENCY (THE MIX IS DAMP ENOUGH TO COHERE AND BE LAID AND TAMPED INTO PLACE BY A SCREED LAYER — BUT NOT WET ENOUGH TO BE POURED OR TO FLOW — IT IS MIXED ON SITE OR DELIVERED AS A PRE-MIXED SCREED MORTAR BY A SPECIALIST SCREED SUPPLIER).

STANDARD SAND-CEMENT SCREED MIX RATIO: 1 PART OPC : 4 PARTS WASHED SHARP SAND (BY WEIGHT — THE MOST WIDELY USED DOMESTIC SCREED MIX — PRODUCES A SCREED WITH A COMPRESSIVE STRENGTH APPROXIMATELY 20-25 N/MM² AFTER CURING — SUFFICIENT FOR MOST DOMESTIC FLOOR APPLICATIONS IN A LONDON VICTORIAN TERRACE). SCREED DESIGNATION (FROM BS 8204:2003 PART 1 — SCREEDS, BASES, AND IN-SITU FLOORINGS — PART 1: CONCRETE BASES AND CEMENT-SAND LEVELLING SCREEDS — THE CURRENT UK STANDARD FOR FLOOR SCREED SPECIFICATION): THE STANDARD SCREED DESIGNATION FORMAT IS CT-C25-F5 WHERE: CT = CALCIUM SULPHATE (ANHYDRITE) OR CT = CEMENT SCREED (DEPENDING ON THE BINDER); C = COMPRESSIVE STRENGTH CLASS (C25 = MINIMUM 25 N/MM² COMPRESSIVE STRENGTH); F = FLEXURAL STRENGTH CLASS (F5 = MINIMUM 5 N/MM² FLEXURAL STRENGTH). FOR A DOMESTIC SAND-CEMENT SCREED IN A LONDON VICTORIAN TERRACE EXTENSION: THE MINIMUM SPECIFICATION IS CT-C20-F4 OR CT-C25-F5 (THE LATTER BEING PREFERABLE AND ENSURING A MORE CONSISTENT AND DURABLE SCREED). SCREED THICKNESS FOR SAND-CEMENT SCREED: BONDED SCREED (THE SCREED IS BONDED DIRECTLY TO THE CONCRETE SLAB BELOW — USING A BONDING AGENT SUCH AS SBR LATEX BONDING AGENT — THISTLE BONDING GRIT OR SIKA BOND T54 — APPLIED TO THE CONCRETE SLAB BEFORE THE SCREED IS LAID): MINIMUM THICKNESS 25MM — TYPICALLY 40-50MM FOR DOMESTIC USE. UNBONDED SCREED (THE SCREED IS SEPARATED FROM THE CONCRETE SLAB BY A DPM — VISQUEEN SUPER FLEXIBLE PLUS 300 MICRON OR EQUIVALENT — OR BY THE INSULATION LAYER IN A FLOOR BUILDUP — SO THERE IS NO ADHESIVE BOND BETWEEN THE SCREED AND THE SLAB BELOW): MINIMUM THICKNESS 50MM. FLOATING SCREED (THE SCREED IS LAID OVER COMPRESSIBLE INSULATION BOARDS — CELOTEX GA4000 PIR OR KINGSPAN KOOLTHERM K3 — THE INSULATION IS COMPRESSED SLIGHTLY BY THE SCREED WEIGHT AND THE SCREED FLOATS ON THE INSULATION — THE STANDARD BUILD-UP FOR A HEATED FLOOR SLAB IN A LONDON VICTORIAN TERRACE EXTENSION): MINIMUM THICKNESS 65MM FOR SAND-CEMENT SCREED — 75MM IS STANDARD FOR A HEATED SCREED (ENCLOSING UFH PIPES WITH MINIMUM 30MM OF SCREED ABOVE THE PIPE — THE 30MM MINIMUM ABOVE-PIPE COVER IS REQUIRED TO DISTRIBUTE THE HEAT EVENLY ACROSS THE SURFACE AND PREVENT HOT SPOTS).

LIQUID SCREED (ALSO CALLED FLOWING SCREED, PUMPABLE SCREED, OR CALCIUM SULPHATE SCREED — THE MOST COMMON PROPRIETARY BRAND IS HANSON CEMFLOOR — THOUGH OTHER BRANDS INCLUDING GYVLON — SAINT-GOBAIN — FLOWCRETE FLOWSCREED, AND LAFARGE AGILIA ARE ALSO USED) IS THE MOST SIGNIFICANT DEVELOPMENT IN UK DOMESTIC SCREED TECHNOLOGY IN THE PAST TWO DECADES — AND IS NOW THE PREFERRED SCREED SPECIFICATION FOR UNDERFLOOR HEATING SYSTEMS IN NEW LONDON VICTORIAN TERRACE EXTENSIONS AND BASEMENT CONVERSIONS.

HANSON CEMFLOOR (HANSON BUILDING MATERIALS — A HEIDELBERGCEMENT GROUP COMPANY — THE LARGEST PRODUCER OF READY-MIX CONCRETE AND LIQUID SCREED IN THE UK): CEMFLOOR IS AN ANHYDRITE CALCIUM SULPHATE LIQUID SCREED — ANHYDRITE IS A CALCIUM SULPHATE MINERAL (CASO4 — THE ANHYDROUS FORM OF GYPSUM — CALCIUM SULPHATE DIHYDRATE CASO4·2H2O — ANHYDRITE IS PRODUCED BY DEHYDRATING GYPSUM AT ELEVATED TEMPERATURE) — THE ANHYDRITE BINDER PRODUCES A SELF-LEVELLING, PUMPABLE SCREED THAT IS DELIVERED TO SITE BY TRUCK AND PUMPED INTO PLACE AT VERY LOW VISCOSITY — IT FLOWS AROUND AND UNDER UNDERFLOOR HEATING PIPES WITHOUT THE NEED FOR MANUAL TAMPING OR COMPACTION AND SELF-LEVELS TO A FLAT, SMOOTH SURFACE. KEY PROPERTIES OF HANSON CEMFLOOR: COMPRESSIVE STRENGTH: C25 (25 N/MM²) OR C30 (30 N/MM²) — MEETING THE BS 8204 MINIMUM REQUIREMENTS FOR DOMESTIC FLOOR APPLICATIONS. FLEXURAL STRENGTH: F5 (5 N/MM²) OR F7. FLOW CHARACTERISTICS: SELF-LEVELLING — THE LIQUID SCREED FLOWS UNDER GRAVITY TO FILL ALL VOIDS AROUND PIPES AND PIPE FIXINGS — ENSURING 100% CONTACT BETWEEN THE SCREED AND THE UFH PIPES (CRITICAL FOR EFFICIENT HEAT TRANSFER — A SAND-CEMENT SCREED TAMPED BY HAND IS MORE LIKELY TO LEAVE VOIDS AROUND CURVED UFH PIPES). INSTALLATION THICKNESS FOR HANSON CEMFLOOR OVER UFH: MINIMUM 30MM ABOVE PIPE + PIPE DIAMETER = TYPICALLY 45MM TOTAL FOR 15MM DIAMETER UFH PIPE AT 45MM TOTAL DEPTH (30MM ABOVE 15MM PIPE) — OR 50MM TOTAL FOR 16MM MLCP UFH PIPE AT 50MM TOTAL DEPTH — SIGNIFICANTLY THINNER THAN THE 65-75MM MINIMUM FOR SAND-CEMENT SCREED OVER UFH. THIS REDUCED THICKNESS IS A SIGNIFICANT ADVANTAGE IN LOW-HEADROOM SITUATIONS SUCH AS BASEMENT CONVERSIONS AND GROUND FLOOR EXTENSIONS WHERE FLOOR LEVEL IS CONSTRAINED. DRYING TIME: HANSON CEMFLOOR REQUIRES MINIMUM 28 DAYS BEFORE FOOT TRAFFIC AND MINIMUM 6 WEEKS (42 DAYS) BEFORE LAYING TILE OR STONE FLOOR FINISHES — LONGER DRYING TIME THAN SAND-CEMENT SCREED (WHICH IS TYPICALLY WALKABLE AFTER 24-48 HOURS AND READY FOR TILING AFTER 21-28 DAYS) — THE DRYING TIME FOR CEMFLOOR IS DETERMINED BY THE MOISTURE CONTENT (TARGET <0.5% BY WEIGHT FOR STONE/TILE AND <0.3% FOR TIMBER/LVT FINISHES — MEASURED BY CARBIDE BOMB TEST OR OVEN DRY METHOD). ANHYDRITE SCREED MUST BE SANDED BEFORE TILING: THE CALCIUM SULPHATE BINDER IN CEMFLOOR PRODUCES A SURFACE LAITANCE (A WEAK CALCIUM SULPHATE PASTE LAYER ON THE SURFACE) — THIS LAITANCE MUST BE REMOVED BY LIGHT SANDING OR GRINDING (TYROLIT SFG OR SIMILAR DIAMOND GRINDING DISC) BEFORE APPLYING TILE ADHESIVE — FAILURE TO DO SO WILL RESULT IN TILE ADHESIVE BONDING TO THE LAITANCE (WHICH IS WEAKLY BONDED TO THE SCREED BELOW) AND SUBSEQUENT TILE DE-BONDING.

UNDERFLOOR HEATING (UFH) SCREEDS — HEATED SCREEDS — ARE THE MOST TECHNICALLY DEMANDING SCREED APPLICATION IN A LONDON VICTORIAN TERRACE RENOVATION BECAUSE THE SCREED MUST PERFORM AS BOTH THE STRUCTURAL FLOOR WEARING COURSE AND THE THERMAL DISTRIBUTION MEDIUM FOR THE UFH SYSTEM — IT MUST CONDUCT HEAT EFFICIENTLY FROM THE PIPES TO THE FLOOR SURFACE WHILE MAINTAINING STRUCTURAL INTEGRITY AND FLATNESS.

NU-HEAT LOOPSTRATE (NU-HEAT UK LTD — THE MARKET-LEADING UFH SYSTEM MANUFACTURER AND INSTALLER IN THE UK — BASED IN HONITON, DEVON): THE NU-HEAT LOOPSTRATE SYSTEM IS THE MOST WIDELY SPECIFIED UFH PIPE SYSTEM IN UK DOMESTIC NEW BUILD AND RENOVATION — THE LOOPSTRATE PANEL IS A PRE-FORMED EXTRUDED POLYSTYRENE (EPS) PANEL WITH RAISED PEGS (STUDS) THAT HOLD THE UFH PIPE IN POSITION AT THE SPECIFIED SPACING (TYPICALLY 100-200MM PIPE CENTRES) WITHOUT THE NEED FOR MECHANICAL STAPLES — THE LOOPSTRATE PANEL IS LAID ON THE INSULATION LAYER (OR DIRECTLY ON THE CONCRETE SLAB FOR A BONDED HEATED SCREED) AND THE PIPE IS PRESSED INTO THE PEG MATRIX. UFH PIPE SPECIFICATION FOR A LONDON VICTORIAN TERRACE EXTENSION UNDER CEMFLOOR LIQUID SCREED: 16MM MLCP PIPE (UPONOR OR POLYPIPE MULTILAYER COMPOSITE PIPE — AN ALUMINIUM SANDWICHED BETWEEN TWO POLYETHYLENE LAYERS — DIMENSIONALLY STABLE — RESISTANT TO CREEP AND MOVEMENT AFTER INSTALLATION — THE RECOMMENDED PIPE FOR HEATING SCREEDS): MINIMUM 30MM SCREED COVER ABOVE THE PIPE CENTRELINE (THE BS 8203 AND MANUFACTURER RECOMMENDATION). WARMUP STICKY MAT (WARMUP PLC — A GLOBAL UFH MANUFACTURER WITH UK HEADQUARTERS IN LONDON): THE WARMUP STICKY MAT IS THE MOST WIDELY USED ELECTRIC UFH SYSTEM FOR INDIVIDUAL ROOM APPLICATIONS IN UK RESIDENTIAL RENOVATION (TYPICALLY BATHROOMS AND EN-SUITES) WHERE A FULL WATER-BASED UFH CIRCUIT WOULD BE IMPRACTICAL DUE TO SCALE OR PIPE ROUTING — NOT A SCREEDED SYSTEM — THE STICKY MAT HEATING CABLE IS LAID DIRECTLY ON THE SUBSTRATE AND TILE ADHESIVE IS APPLIED OVER IT — THICKNESS ABOVE THE MAT IS GOVERNED BY THE TILE ADHESIVE THICKNESS (MINIMUM 6-10MM ABOVE THE HEATING CABLE). FOR A FULL-PROPERTY WATER-BASED UFH SYSTEM UNDER LIQUID SCREED IN A LONDON VICTORIAN TERRACE GROUND FLOOR EXTENSION: NU-HEAT LOOPSTRATE + 16MM MLCP PIPE + HANSON CEMFLOOR ANHYDRITE LIQUID SCREED IS THE RECOMMENDED SPECIFICATION — THIS COMBINATION PROVIDES THE BEST THERMAL EFFICIENCY (LOWEST FLOW TEMPERATURE — MOST COMPATIBLE WITH AIR-SOURCE HEAT PUMPS) AND THE MOST RELIABLE BOND BETWEEN SCREED AND UFH PIPES DUE TO THE SELF-LEVELLING CEMFLOOR FLOWING AROUND AND UNDER THE PIPES.

SCREED FLATNESS IS GOVERNED BY BS 8204-7:2003 (SCREEDS, BASES, AND IN-SITU FLOORINGS — PART 7: PUMPABLE SELF-SMOOTHING SCREEDS — SPECIFICATION AND WORKMANSHIP). THE STANDARD FLATNESS TOLERANCES FOR FLOOR SCREED UNDER DIFFERENT FINISH TYPES: SR3 (DEFINED FLATNESS CLASS — THE LEAST DEMANDING — SUITABLE FOR CARPET AND SIMILAR SOFT FLOOR COVERINGS): MAXIMUM DEVIATION FROM A 2M STRAIGHTEDGE: 10MM. SR2 (MEDIUM FLATNESS CLASS — SUITABLE FOR GENERAL TILING AND MOST ENGINEERED TIMBER FLOORS): MAXIMUM DEVIATION: 5MM. SR1 (THE HIGHEST FLATNESS CLASS — REQUIRED FOR LARGE-FORMAT PORCELAIN TILES — 600X600MM AND ABOVE — AND WIDE-PLANK ENGINEERED TIMBER FLOORS): MAXIMUM DEVIATION: 3MM. HANSON CEMFLOOR TYPICALLY ACHIEVES SR1 FLATNESS WHEN CORRECTLY INSTALLED AND APPROPRIATE PRIMER HAS BEEN APPLIED — SAND-CEMENT SCREED CAN ACHIEVE SR2 OR SR1 WHEN HAND-SCREEDED BY AN EXPERIENCED SCREED LAYER BUT IS MORE VARIABLE.

PRIMER (REQUIRED OVER HANSON CEMFLOOR ANHYDRITE SCREED BEFORE APPLYING TILE ADHESIVE — AND OVER SAND-CEMENT SCREED IN DRY OR POROUS CONDITIONS): MAPEI PRIMER G (THE MOST WIDELY USED PRIMER FOR ANHYDRITE SCREEDS IN UK RESIDENTIAL RENOVATION — A WATER-BASED ACRYLIC PRIMER APPLIED OVER THE SANDED CEMFLOOR SURFACE — REDUCES THE POROSITY OF THE SCREED SURFACE AND IMPROVES THE ADHESION OF THE TILE ADHESIVE — APPLY BY ROLLER IN TWO COATS — ALLOW FIRST COAT TO DRY BEFORE SECOND COAT). MAPEI PRIMER L (AN ALTERNATIVE PRIMER FOR SAND-CEMENT AND ANHYDRITE SCREEDS — ALSO ACTS AS A BONDING BRIDGE BETWEEN OLD CONCRETE SUBSTRATES AND SELF-LEVELLING COMPOUNDS). SELF-LEVELLING COMPOUND (WHERE THE FINISHED SCREED IS NOT FLAT ENOUGH FOR THE SPECIFIED FLOOR FINISH — A SELF-LEVELLING COMPOUND CAN BE APPLIED OVER THE CURED SCREED): MAPEI ULTRAPLAN ECO (THE MOST WIDELY USED SELF-LEVELLING COMPOUND IN UK RESIDENTIAL RENOVATION — A FAST-SETTING GYPSUM-CEMENT COMPOUND — APPLIED BY POUR AND SPREAD OVER A PRIMED SURFACE — SELF-LEVELS TO ±1MM FLATNESS — RE-COATABLE AFTER 3-4 HOURS — SUITABLE FOR TILE, LVT, CARPET, AND TIMBER OVER BOTH SAND-CEMENT AND ANHYDRITE SCREED SUBSTRATES — MUST NOT BE APPLIED OVER PERMANENTLY DAMP SUBSTRATES — ALWAYS CONFIRM SCREED MOISTURE CONTENT IS BELOW MAXIMUM BEFORE APPLYING).

FLOOR SCREED COSTS IN LONDON (2025 — SPECIALIST SCREED CONTRACTOR — SUPPLY AND FIT — LABOUR AND MATERIALS — PER M²). NOTE: LIQUID SCREED (ANHYDRITE) REQUIRES A SPECIALIST PUMP TRUCK — TYPICALLY A MINIMUM AREA OF 80-150M² IS REQUIRED TO MAKE THE LIQUID SCREED CONTRACTOR'S MOBILISATION COST-EFFECTIVE (BELOW THIS AREA THRESHOLD, SAND-CEMENT SCREED IS MORE ECONOMICAL PER M²).

SAND-CEMENT SCREED (SUPPLY AND FIT — 65MM FLOATING SCREED — LABOUR AND MATERIALS — LONDON): APPROXIMATELY £20-35/M² (FOR AREAS ABOVE 30M²). FOR SMALLER AREAS (UNDER 30M²) THE UNIT COST RISES SIGNIFICANTLY: £30-55/M². SAND-CEMENT HEATED SCREED (65-75MM — OVER UFH PIPES — INCLUDES CARE IN AVOIDING PIPE DAMAGE DURING LAYING): APPROXIMATELY £25-40/M².

HANSON CEMFLOOR ANHYDRITE LIQUID SCREED (SUPPLY AND PUMP — 50MM DEPTH — MINIMUM AREA 80-150M²): APPROXIMATELY £18-30/M² (FOR AREAS ABOVE 80M²). FOR SMALLER AREAS WHERE A PREMIUM IS CHARGED FOR MINIMUM TRUCK MOBILISATION: APPROXIMATELY £25-40/M². CEMFLOOR HEATED SCREED (50MM DEPTH — OVER UFH — INCLUDING COMMISSIONING HEAT TEST): APPROXIMATELY £22-35/M².

ADDITIONAL COSTS: SURFACE PREPARATION OF CONCRETE SLAB BEFORE SCREED (VACUUM CLEANING, CRACK FILLING, LEVELLING HIGH SPOTS): £3-8/M² ADDITIONAL. PRIMER BEFORE TILING OVER ANHYDRITE SCREED (MAPEI PRIMER G — SUPPLY AND APPLY): £2-4/M² ADDITIONAL. SELF-LEVELLING COMPOUND OVER SCREED TO IMPROVE FLATNESS FOR LARGE-FORMAT TILES (MAPEI ULTRAPLAN ECO — 3-6MM DEPTH): £8-15/M² ADDITIONAL.

TYPICAL GROUND FLOOR EXTENSION IN A LONDON VICTORIAN TERRACE (20M² — HEATED LIQUID SCREED OVER UFH — CEMFLOOR 50MM — MINIMUM AREA PREMIUM APPLIES): MATERIAL AND PUMP: APPROXIMATELY £22-35/M² X 20M² = £440-700 (PLUS MINIMUM AREA MOBILISATION PREMIUM — TOTAL TYPICALLY £700-1,200 FOR 20M² WITH CEMFLOOR). COMPARABLY, SAND-CEMENT SCREED FOR THE SAME 20M²: APPROXIMATELY £30-45/M² X 20M² = £600-900 (LOWER MOBILISATION COST — MORE ECONOMICAL FOR SMALL AREAS). FOR FULL-PROPERTY GROUND FLOOR SCREED IN A LONDON VICTORIAN TERRACE (60-80M² INCLUDING KITCHEN EXTENSION, LIVING ROOM, HALLWAY): CEMFLOOR AT 60-80M² IS ECONOMICAL — APPROXIMATELY £18-28/M² X 70M² = £1,260-1,960.