Retro Flex Remedial Wall Tie
During the 1970's research was conducted into the need for replacement wall ties. The actual durability of the protective zinc or galvanised coatings of the original built in wall ties was studied and this now affects the design and use of walls ties for both new build and replacement. The results of the research was found to be quite beyond any previous expectations:
Early attempts at producing a method for replacing existing wall ties highlighted many of the pitfalls that were to be encountered. The expansion type of tie has been found to induce additional stresses into the masonry - similar to the expansion caused by the existing, rusting walls ties - and were costly to make and fit. The use of heavy section re-bars was soon outlawed because of the need for flexibility to allow the necessary differential horizontal and vertical movement between each leaf using a bar of 8mm diameter or above was found to act like mini crowbars and would eventually work themselves loose. The introduction of BSI DD140, BRE Digest 329 and the more recent BRE Digest 401 at last gave guidance for manufacturers and specifiers of remedial wall ties.