Technical Booklet D Structure·Page 69·4C.15
Mortar designation and strength requirements
Mortar used in masonry construction must meet one of three specifications: BS 5628 Part 1 designation (iii), BS EN 998-2 strength class M4, or a specific mix of CEM1 cement, lime and fine aggregate.
Mortar should be –
(a) of mortar designation (iii) as given in BS 5628: Part 1;
(b) strength class M4 as given in BS EN 998 -2; or
(c) CEM1, lime and fine aggregate mixed in the ratio of 1:1:5 measured by volume of dry materials.
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