Once the concrete has hardened enough for construction to begin (typically overnight), the masonry can be erected on top of it. To begin the process, the bricklayer will set up their string lines off of stakes driven into the ground, using tape measures and folding squares to set out the position of the two masonry skins. Due to the vertical nature of masonry, each course follows the plumb line of the masonry below, all of which is determined by the position of the first course. Therefore, it's imperative that this first course is straight and square, meeting the required dimensions specified on the drawings, as well as centred upon the footing. Typically, spots of mortar will be slapped onto the concrete footing at various points along and in the corners of the trench. Using a trowel guided by the string lines, visible marks are scored into the wet mortar that guide the location of the first courses. For standard cavity masonry buildings, two skins of masonry are erected on top of the footing with a void or cavity in between them. These two skins begin in the ground on top of the footing and reach all the way to the top of the structure. The specific materials that are used in the ground are concrete blocks or bricks. These blocks are laid on both skins within the trench under the common ground level.

To start the laying process the corners are built up first, with the joints of the blocks or bricks being staggered in a brick bond pattern for strength. Once the corners are established, and the overall dimensions are correct, each course can be “run out”, following string lines to maintain the correct tolerances. As the blocks are laid, cavity wall ties are installed in the mortar beds in order to tie the two skins together. These ties are installed frequently - every other course with approximately 3 blocks between them. As is the case all the way to the top of the masonry structure, each course of the outer skin is slightly lower in level than the courses of the inside skin. This prevents any water from tracking along the cavity ties towards the inside skin.  

At this point the cavity is left open as the courses are laid, in preparation for a lean concrete cavity fill to be installed. The inside course is brought up to the relevant height in relation to the oversight for the concrete to be laid. As the masonry begins to rise above the common ground level, some considerations are made. If the outside skin of the building is to be erected using face brickwork, then this must begin as the masonry leaves the ground. Additionally, the DPC (Damp Proof Course) layer must be installed at a height of around 150mm from the common ground level, though the exact height depends on the heights of the courses. If the outside of the building is being rendered or cladded, then concrete blocks can still be used. It's typical for the outside skin to be left lower than the inside skin at this point for the installation of the cavity fill concrete.

 This cavity fill lean mix is a relatively dry mix of concrete that is poured into the cavity all the wall down to the concrete footing, filling the void between the two skins. The concrete can be packed down tight into the cavity using a thin batten or timber. The top of the cavity fill should remain at least one block course down from the inside concrete height, in order to prevent rising damp transference. With the cavity fill installed and the inside skin up to the correct height, we’re ready to move onto backfilling and establishing the oversight.