Building Research Establishment, UK

Collar-jointed walls – also termed double-leaf walls – are walls built from two separate leaves of masonry held together with stout wall ties, with the gap between the leaves – the collar-joint – being filled with mortar. Experience suggests that bricklayers find it difficult to fill this collar-joint fully with mortar. The aims of this work were to determine, for both brickwork and blockwork:
1. whether it is possible to build a collar-jointed wall with the
collar-joint fully filled
2. the effect an empty collar- joint has on the performance of a
collar-jointed wall
3. the relative performance of equivalent solid and collar-jointed
A full programme of testing was carried out to determine the relative performance of the different wall types. The conclusions of the tests were:
1. Buildability
That a collar-jointed wall can be built with a full collar-joint.
2. Full collar-joints versus empty collar-joints
The results showed that there is a difference in performance
between a filled and an unfilled collar-joint.
3. Solid walls v. collar-jointed walls The results of the comparison between solid and collar-jointed walls are different for the two materials: for the brickwork walls, the bonded solid walls had the lowest failure load of the three sets of tests; for blockwork walls, the solid 215mm thick blocks have the highest failure load. The results suggest that there may be reason to differentiate between the two unit materials.