Filling gaps

[Bayardmm]

We have a bay window in a bedroom with a wooden internal windowsill, which is made of three boards mitred together at the angles. Despite my best efforts, when decorating, cracks appear along the joins after I have filled and painted over. Can anyone suggest a really good filler which may counteract the cracking?

 

[Wayners]

Repair care dryflex resin

 

[^woody^]

Rebate the surface 5mm or so deep by 30mm or so wide spanning the joint, glue in a strip of timber then finish the surface flush before painting

 

[opps]

As per @Wayners post, I too would use an epoxy resin. You may however need to enlarge the crack first.