Page 250 - McD_6118-AEW-XX-XX-NBS-A-001_Neat

130 COLD DECK ROOF COATINGgenerally
• Substrate: Existing covering.
- Preparation: site specific.
• Separating layer (loose laid): Reinforced bitumen sheathing felt.
- Laps (minimum): 50 mm.
• Coating: Mastic asphalt to BS 6925.
- Type: R988/ T25.
- Application: 20 mm nominal thickness in two coats.
• Surface protection: siet specific but generally chippings.
• Accessories: site specific but may include:
- Movement joints;
- Perimeter trims; and
- Ventilators.

180 SKIRTINGS/ VERTICAL WORKgenerally

• Substrate: site specific; generally birckwork of timber.

- Preparation: site specific.

• Separating layer: Reinforced bitumen sheathing felt with 50 mm minimum laps.

• Keying: Generally not required, but where required: Expanded metal lathing to BS

8204-5, clause 5.4.

• Coating: Mastic asphalt to BS 6925.

- Type: R988/ T25.

- Application: 20 mm nominal thickness in three coats.

- Height above finished roof level: site specific but 150 mm (minimum).

- Fillet profile: 45° angle, 40 mm minimum width on face.

• Surface protection: site specific.

• Accessories: site specific.

PRODUCTS

320 PRIMERgenerally
• Type: As recommended by mastic asphalt manufacturer.
• Manufacturer: Contractor's choice.
- Product reference: Contractor's choice.

325 BONDING COMPOUND
• Type: As recommended by mastic asphalt manufacturer for conditions and
surface.
• Manufacturer: Contractor's choice.
Product reference: Contractor's choice.

330 TIMBER TRIMS, ETC
• Quality: Planed. Free from wane, pitch pockets, decay and insect attack (except
ambrosia beetle damage).
• Moisture content at time of covering (maximum): 22%.
• Preservative treatment: As recommended for purpose by mastic asphalt
manufacturer.

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