![]() ![]() ![]() The cause of the failures is most likely due to the strength of the render being too high for the background and can result in cracking through the block. These have often worked well but on several occasions single coat proprietary renders have failed and caused horizontal and vertical cracking through the blocks. Proprietary single coat renders may also be used on aggregate block backgrounds. We recommend the use of traditional renders wherever possible due to their proven history and success.įor proprietary two coat renders the manufacturer’s literature should be consulted for base coat and final coat recommended thicknesses, but these are generally similar to those for traditional renders. ![]() Design detailing should ensure that there are good overhangs at eaves, sills and other projections in order to throw rain away from walls.The minimum amount of water required to provide a workable mix should be used. Mixes should be accurately gauged the ingredients being thoroughly mixed before adding the water.Sands that are too fine tend to have high water demand. Sands in accordance with BS EN 13139 should be used.Cement, lime, sand mixes without air entrainment are preferred.Corner beads and stop beads suitable for external work should be used.Provision should be made for external fixings, brackets and supports prior to commencing rendering work.Movement joints in the background blockwork should be carried through the render and be formed using stainless steel stop beads.Mortar joints should be left rough and not struck off or tooled.Rake back mortar joints to provide an additional mechanical key, particularly if using closer textured blocks.There is generally no need to wet the blocks prior to applying the render.Clean all dirt and debris from the block surfaces. ![]()
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