To prevent moisture leaking through your walls and also to allow for slight movement and contraction of render to occur, it is very important to ensure that windows and control joints are properly sealed with a paintable, flexible sealant.
It is essential to separate render from all abutting substrates, which allows for differential expansion and contraction movement to occur. These areas need to be properly sealed with a paintable flexible sealant to prevent the ingress of moisture at these points.
Over the past Rockcote has seen many examples where adequate separation and sealing has not occurred resulting in ugly cracks, render delamination and water ingress at these points.
We have to remember that each element used in construction has a differing coefficient of movement. Simply put, some elements will expand and contract more than others. When these different elements are butted up tight together, pressure is exerted at these points and in the case of render, it will cause cracking and delamination.
To avoid this occurring it is recommended to cut the render out and form a neat vee joint right back to the substrate and once cured, caulk with a flexible paintable sealant such as Sika-Flex or similar. This will not only allow for expansion/contraction in these areas, but will also prevent the infiltration of moisture into the structure.
