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Hi My questions/advice needed relate to an extension that I am finishing off. I have 2 RSJ's spanning about 3m and the edge of them is exposed to the external elements. The whole extension will be rendered with a monocouche render to match the rest of the house. You may question why there is a mixture of brick and block ... well unfortunately the first bricklayer let me down significantly, so I had to ask another guy I knew from a while before (but was not available when I originally started the project) to complete the work (hence the change from facebrick to render). My question/concern is that although the RSJ's are painted in a red primer, I am concerned that they will rust over time causing the external render and brickwork to crack. There are no fitted cavity trays, but there is a damp membrane a little further up the cavity that directs water from the internal brickwork skin to the external brickwork. There even appears to be some early discolouration that may be some surface rust. So before I cover everything ... am I being overly paranoid and if not then what should I use to protect? Also, even if I paint/cover the edges exposed, will the weather/rain penetrate the first skin of bricks/blocks and cause rust to continue? I was thinking of putting cement board up across the whole frontage and then rendering? But I am not even sure if the render itself will prevent the water ingressing to the RSJ's? (I will be having some bifold doors under these RSJ's) Thanking you all in advance!