I don't know what the answer is but I have two observations:-
First, varnish doesn't seem to seal knots. I have varnished several things and found that the sap comes through. Knotting compound is shellac, I believe.
Second, sap always seems to come through on woodwork that catches direct sun, i.e. gets hot. Someone may know better, but I imagine you'd not need knotting if the woodwork is permanently out of strong sunshine,
Andy.
The title says it all really. The skirting is currently varnished pine and we want to paint it. I've given it a rub down enough to act as a key, but will I then need to treat the knots in the wood or will the varnish already have sealed the knots? Will I be OK painting over the (keyed) varnish, or must it really be rubbed down to bare wood. NB. The paint we've got is Dulux Realife Tough Satin, [in Barley White :-) ]
I would imagine that if the knots haven't made themselves known before they are unlikely to do so now
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