Done_Fishin

Hi There Doubletap .. got a woodworking problem for you .. if you have time ..
I've made these frames for pet cage sliding doors out of what I suspect is pine .. I've sanded down , filled in some gaps and re-sanded and I am now stuck wondering whether I should varnish or wax OR whether I should apply some protective later or treatment before continuing.
The cage is for my daughter's iguana .. so it's going to be fairly hot and moist inside. It'll have plastic windows and she wants it to be as free as possible of any chemical substances that might affect the iguana's health .. so most of any stuff that goes into it should be organic in a healthy sense ..

My question is .. what should I do to treat the wood to avoid rot either through the fact that the wood is effectively dead or that the environment is hot & humid ?
Any ideas ? Suggestions?
btw the cage is going to 90cm * 90 cm at the base and 180cm tall. The doors are 47cm * 169cm but only using thin pine of 44mm * 18mm with a strip in the centre for strengthening and support.