It is absolutely vital that sash windows be repaired using the best materials and processes to achieve a good long term repair. I use both.
I believe I can effectively repair almost anything and that repair often provides a large saving over replacement.
Sash windows have weak points at the joints that commonly and repeatedly suffer. Water enters the joint, follows the wood grain and eventually rots. Common areas include the joints of the sashes and the joints or ends of the sills. The use of traditional filler and softwood to fix these areas does not last and relies on paint to keep the water out.
Rot is removed and a wood stabiliser painted onto the wood surface. Two part resin is then applied and shaped to replicate the removed area. Large areas of timber are replaced with a section of sapele hardwood that is glued into position using the same system. Once cured, areas are sanded and coated with primer for protection until decoration can occur.
I have successfully used this approach for over ten years and I offer this service throughout Norwich, Norfolk, Bury St Edmunds, Suffolk and Cambridge.