Pine Tongue & Groove Ceilings

[mayennaise]

Our small bathroom ceiling is covered in this and varnished. Likewise our flat roofed sun-room. Is there a reason why these surfaces can't be painted white?

[Buenchico]

To do the job properly you'd need to get rid of the layer of varnish that tongue-&-groove pine comes with. However it's not impossible:
http://www.home-dzine.co.za/decorating/decorating-pinepanel.htm

[melv16]

No need to strip the T and G. A rub down with wet and dry, tack off and a coat of shellac based primer, as shown in the link. https://www.screwfix.com/c/decorating/paint/cat850142?brand=zinsser&cm_sp=landingpage-_-azbrands-_-zinsser&ds_kid=43700026096882629&utm_source=bing&utm_medium=cpc&;utm_campaign=Brands%20InvM%20%7C%20Zinsser&utm_term=zinsser%20products&utm_content=Zinsser%20-%20Pure&ds_rl=1249478&ds_rl=1245250&gclid=COTQr4rc-9kCFQ0LGwodM1YPJQ&gclsrc=ds&dclid=CPztzorc-9kCFcKM7QodzswKRA

[melv16]

I should have mention that it needs finishing off with 2 coats of oil based eggshell.

[Khandro]

As long as you clean the surface, and sugar soap is the best for this https://www.screwfix.com/p/no-nonsense-concentrated-liquid-sugar-soap-500ml/61880, there should be no need for the laborious process of stripping off the varnish, BUT do not use emulsion paint, use only oil based paints, undercoat and finish.