Uneven troweling and application of chippings can cause patchy appearance on walls.
Waterproofing agent is recommended to help prevent differences in suction rates, resulting in difficulties in embedding and chippings evenly to the mortar. This results in the chippings being more pronounced in some areas than others leaving an irregular finish. The aggregate should be applied in a damp but not soaked state, as this helps with adhesion to the render. Care should be taken to ensure that the moisture content of both the aggregate and the render is consistent as differences caused by atmospheric conditions can create problems. Care should be taken to obtain a wide and even spread in order to distribute the aggregate.
Particular attention should be taken around scaffolding to avoid shadowing the lift line. Irwin’s do not recommend the re-use of aggregate that has been collected up following the first application. This is likely to have mortar stains on it, which if applied can result in a patchy finish. Bags of aggregate should be decanted onto a clean surface before application. Fines usually fall to the bottom during the bagging process. If they are then mixed on the ground it will help eliminate patchiness which can be caused by an uneven distribution of the fines.