I don't know if this is an easy or a difficult question, but I can't find an answer surfing around.
Our glass porch is many years old and the sill between the glass and the foundations is in fair condition, except on an exterior corner where water has got in around the upper edges, and developed quite deep holes where the wood is rotting. I can't just dig it out, treat and fill as the hole seems to be "bottomless", ie it must go down into the foundation gap, and I can't get at the inside of it.
Can anyone tell me a good way to treat and "cover in" the hole so that I can fill and paint it? I notice that spray Polyfiller foam is recommended for some kinds of filling, but it's harder when there isn't a complete base to the hole. And I don't know if that would help to protect it from water.
The wood is about 25 years old, probably eastern hard wood of some kind, and finished in that reddish-brown 1980s stain/varnish as installed.
Also, should I drill out the underneath of the sill to assist air circulation/drainage? Or leave it be and just try and treat and fill?
Also - I see Americans have "borate treatments" which I can't find any example of here, either fillers or treatments. What are we missing?
Thanks for any advice.