Building a cavity wall — from setting out to capping

Start by clarifying the unit type, the mortar's M class and the control class (reduced / normal / tightened) in accordance with DK NA:2019. These are load-bearing design choices — they are determined by the designer, not on site. Note that DS/EN 1996-3 (simplified methods) is NOT approved in Denmark and must not be used.

Set out the plumb line and wall line from the reference points and put up a course line. The course height is the brick height plus one bed joint — for Danish standard bricks (DF) with a 12 mm bed joint this is 66 mm per course (54 + 12). Build the corners first and stretch the line between them.

The wall must start from the top of the foundation with the damp-proof course/moisture barrier correctly fitted, so rising damp is stopped from the first course. See the separate guide «Damp-proof course and moisture barrier» for the layer build-up.

Choose the mortar according to the project's M class (DS/EN 998-2). KC mix mortar is mixed according to Aalborg Portland's mixing tables; factory-made designed mortar is CE-marked with a DoP. See the guide «Mixing mortar on site» for the mixing itself.

Lay the bond consistently (stretcher, English or English cross bond as the design specifies), so that the perpends are offset from course to course. Keep the joints at the normal joint's nominal 12 mm — in normal inspection class the bed joint must be within 8–16 mm and the perpend joint within 8–20 mm (Mur & Tag based on DS/INF 167). Even joints give regular coursing and a calm brickwork appearance.

In cavity walls, fit a minimum of 4 corrosion-resistant wire ties per m², evenly distributed, with max. 400 mm spacing and extra ties along edges, openings and movement joints. The top row of ties is placed max. 200 mm from the top edge and is counted at 50 % reduced capacity.

The minimum number is a lower limit — number and capacity MUST always be verified by calculation for the actual wind load.

Open perpends (weep holes) are placed directly on the damp-proof course in the outer leaf so any condensation or rainwater in the cavity can drain out. Take care that the weep holes are not blocked by mortar droppings during bricklaying.

Continuously check plumb, alignment, fall and joint width with a spirit level and gauge rod. Masonry is unforgiving — a facade out of plumb or joints of varying width are visible forever. Deviations are recorded and clarified with the designer.

Cover the top of the fresh masonry at the end of work and in rain, so that the mortar is not washed out and does not run down the facade. Washout causes permanent discolouration and weakens the joints.

Complete the process control form (x.400) and process photo documentation (x.490) as you go, and record tolerances and deviations in the QA log (x.700). The documentation is the proof that the work has been carried out as agreed and to the standard.