mortar bedn. a layer of mortar between courses of brickwork or masonry.
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1842 J. GwiltEncycl. Archit.ii. iii. 517 The propriety of the mortar beds being as thin as possible.
1993 Collins Compl. DIY Man. (new ed.) iii. 235/1 The roof covering is usually turned up the wall to form a ‘skirting’ which is tucked into the mortar bed of the brickwork.