Exterior rendering

Hello, What type of render is it? Is it a lime based render or concrete render? Are the new windows made of timber? Generally, provided the render is adhering to the substrate and does not sound hollow when tapped- it is possible to rake out the cracks and fill them with a breathable, flexible filler that does not contain plastic. A lime mortar/ lime plaster mix would work well as it will allow for condensation to vapour through the cracks instead of getting trapped around the window frames. If the cracks are minor, a restoration grade filler such as Toupret exterior filler would work as well. It sand down easily (to avoid sharp edging marks) and should be painted with a more breathable paint such as silicate mineral based paint- not acrylic based emulsion. It is not necessary to render the whole area, a spot repair should solve the problem. In case you want to apply a full thickness "new render" : It may not bond properly over the old render, the old render may have to be removed back to back, then a lime mortar base render applied. Please do not render the cottage with a cement based render as it will cause condensation problems affecting timbers and brick structure.

In my experience, for a 120-year-old property I would not recommend simply rendering over the existing painted render.For a more reliable and long-lasting result, I would remove the existing render and inspect the substrate underneath. This allows any cracks, weak areas or movement around the new windows to be properly dealt with before applying the new render system.It may involve more work initially, but it gives a much better opportunity to achieve a sound and durable finish rather than covering potential problems underneath.