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215 SURFACE HARDNESS OF SUBSTRATES TO RECEIVE POLYMER MODIFIED WEARING

SCREEDS

• General: Substrates must restrain stresses that occur during setting and hardening

of wearing screeds.

• Test for surface hardness: To BS EN 12504-2 using a rebound hammer with

compliance values selected from the following:

Screed thickness Rebound hammer value

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15 mm or less Greater than 25

Greater than 15 mm Greater than 30

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• Report: Submit details of areas where substrates surface hardness does not comply

with these values.

220 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.

250 CONDUITS UNDER FLOATING SCREEDS
• Haunching: Before laying insulation for floating screeds, haunch up in 1:4
cement:sand on both sides of conduits.

251 CONDUITS CAST INTO OR UNDER SCREEDS
• Reinforcement: Overlay with reinforcement selected from:
- 500 mm wide strip of steel fabric to BS 4483, reference D49, or
- Welded mesh manufactured in rolls from mild steel wire minimum 1.5 mm
diameter to BS 1052, mesh size 50 x 50 mm.
• Placing reinforcement: Mid depth between top of conduit and the screed surface.
- Width of reinforcement (minimum): 300 mm.
• Screed cover over conduit (minimum): 25 mm.

260 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.
• Bonding coat: Manufacturer's standard.

270 PARTIALLY BONDED CONSTRUCTION
• Preparation: Generally in accordance with BS 8204-1.
• Substrate surface: Brushed finish with no surface laitance.
- Texture of surface: Suitable to accept screed and achieve a bond over
complete area.
• Bonding coat: Manufacturer's standard.

RotF generic (intermediate) NBS 2014 6118-AEW-XX-XX-NBS-A-01