Technical Specifications - UNDP

7 Bitumen Roofing
Where roof finishings are required to be of a bitumen and sand mix this shall be composed of a mix to the
following proportion ( by weight ) :
Bitumen 60 /70 penetration 13 %
Filler (passing 200 sieve) 11 %
Sand 76 %
Mixing shall be carried out in an approved machine until all materials are thoroughly mixed. The mixing
temperature shall be between 163OC and 191OC and it shall be applied at a temperature sufficient to
maintain the workability of the mix. The covering shall be laid in one coat to give a consolidated thickness
of 20mm after rolling with a light hand roller. 150x150mm angle fillets shall be laid at edges of roofs
against parapets etc., properly bonded to the roof covering and with top edges turned into joints of walls.
The covering shall also be pressed into rainwater outlets and under flashings.
8 Asphalt
Asphalt roofing and tanking shall be executed by an approved specialist using mastic asphalt to BS 988 .
The asphalt shall be applied in the thickness and number of coats described in the Particular Conditions,
with each successive coat breaking joints at least 300mm (12") and with properly formed angles, double
angle fillets and fair edges .
Joints of blockwork shall be raked out and all vertical surfaces hacked for key.
Horizontal work shall be laid on a layer of stout sheathing felt.
9 Completion
On completion all roofs etc are to be left sound, water- tight and in clean condition before handing over.
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