. PRE-CAST CONCRETE COPINGS AND CAPS

Pre-cast concrete units (see Fig 207) are a cheaper alternative to a brick-on-edge finish, being much quicker to construct. They have other advantages in that they are designed to be wider than the wall or pier so have the weathering or overhang in-built. They are commonly cast with a sloping surface to shed water and a groove or throating is often cast into the underside edge. This acts as a drip to ensure that rainwater that tracks under the coping falls clear of the wall face below. As they are large in size (typically 600mm long), the number of cross-joints in the overall length of the wall is greatly reduced. This is advantageous as the cross-joints are potentially vulnerable points where rainwater can penetrate, particularly if they are inadequately filled. The disadvantages are that pre-cast copings do look rather utilitarian or industrial, and pre-cast units for piers are generally only available for square piers, so the choice is somewhat limiting.

The two most common pre-cast concrete copings for walls are ‘feather-edge’ and ‘saddleback’. Saddleback pier caps are also available.

. PRE-CAST CONCRETE COPINGS AND CAPS

Fig. 238 Pre-cast concrete feather-edge coping.

. PRE-CAST CONCRETE COPINGS AND CAPS

Fig. 239 Pre-cast concrete saddleback coping.

. PRE-CAST CONCRETE COPINGS AND CAPS

Fig. 240 Pre-cast concrete saddleback pier cap.

When laying pre-cast copings, the same principles apply as when laying brick-on-edge copings. Lay one coping at each end, level with one another and on 10mm beds of mortar, then run in to a string-line. Before running in, ensure that the overhang front and back is equal and consistent along the length of the coping – check it with a measuring tape to ensure accuracy. One key consideration is how to set the end copings level on top of the wall both widthwise and lengthwise. In terms of levelling along the length, a spirit level can be placed on the underside of the overhanging edge. However, this is not completely reliable, as the underside surface of the concrete cannot be guaranteed to be flat or even. Instead, level the coping along the top, making sure that the spirit level is placed exactly parallel with the edge of the coping. Failure to do this will provide a false reading due to the spirit level being on a slope. Levelling the width is a little trickier and the only completely accurate method is to manufacture a timber template that will accommodate the profile shape of the coping and provide a flat surface on which to place the spirit level (see Fig 241). The cutting line for the profile is marked simply by using the top of one of the copings as a template.

I’-I;! I*?! I Kill!*“■! Kill

. PRE-CAST CONCRETE COPINGS AND CAPS

Concrete saddleback Concrete feather-edge

Fig. 241 Timber profiles to assist widthwise levelling of concrete copings.

. PRE-CAST CONCRETE COPINGS AND CAPS

Fig. 242 Concrete coping extended to provide a weathering at a stopped-end.

As with a brick-on-edge coping, concrete copings can be run-in using two string-lines – one at the front and one at the back – or by using one string-line and levelling each coping across the width. As is the case with brick oversailing courses, if the concrete coping is positioned above head height, the string-line should be positioned so as to run-in the copings to the lower edge, as this is the edge to which the eye-line will be drawn.

Cross-joints between copings should not exceed 10mm but it is common for joints to be made tighter (6mm) to increase weather resistance. Bed joints under concrete copings should be jointed-up as should cross-joints, which should be jointed all the way round, including under the overhang. The groove or throating under the edge of the coping must be continuous along the length of the wall, so the mortar at cross-joints should be jointed flat into the throating with a flat-bladed jointing iron.

Подпись: Setting-Out and Cutting Copings More often than not, copings will need to be cut in order to fit the length of the wall. Any cuts should be placed in the middle of the wall where the coping has at least one free end. Where the coping is laid in between two attached piers, cuts of equal size are usually placed at both ends, adjacent to the piers and not in the middle. Small cuts should always be avoided as they are very noticeable. It is better to have two or even three cuts of larger size that blend in better than one small, highly visible cut. Where the wall on which the copings will be

Good practice with concrete copings, as with an oversailing course or a tile creasing, is to extend it at a stopped-end in order to provide a weathering and protection to the stopped-end brickwork.