I have a pair of mahogany French doors ... south facing, full sun (when we
>get it), fitted about 5 years ago...
>They have developed fine cracks along the grain in many places...
>a year ago I tried filling them with plastic wood (opening the bigger crack
>with a Stanley
>knife to get more filler in)... then finished with wickes quick drying wood
>stain (microporous)...
>However, the crack have opened again and the woodstain has cracked with it
>(it seem rather
>brittle stuff)...
>I don't think I'll ever successfully fill the cracks
>What's the best "coloured varnish" (prep) that would help fill hairline
>cracks (sort of glue them together ??)
>and cope with future movement ... and resist further cracking?
You could try a coloured crayon. Wouldn't crack but might soften unduly in full sun.