I have been restoring an old staircase. I started sanding it with fine sandpaper and then tried rougher paper. It seems that the varnish layer on the wood is melting when sanding over it and sticking to the sandpaper, rendering it useless in a matter of seconds. It is hard to peel the varnish off the paper.
The staircase has a lot of perpendicular surfaces and corners; these are hard to reach and the edges of the sandpaper gets cluttered immediately.
The current result is a staircase where the varnish is sanded in the middle of the surfaces and around the edges there is still a lot of varnish left.
I have used cellulose thinner twice, but that was not effective at all. What did I do wrong here?
My question is: how can I remove the varnish from the wood easily, especially in the corners?