Two questions

Hi all, Just 2 quick questions. What are thinners used for ? Do they do anything that turps or white spirit doesn't do ? Saying that, what's the dif between turps and white spirit anyway ?
Secondly, am gonna paint a room that's been emulsioned in the past but twelve months later brown damp stains are coming through. Do I undercoat with watered down undercoat first and then emulsion ? Should this cure the problem ? Many thanks.

Turps is more or less a Biproduct of petrol

White spirit comes from Parafin

Both are similar..your confusing them with thinners somehow...they are thinners..both of them..but although its common practice to use Turps white spirit is the best thing to thin paint with.

Turps can destabilise paint, especially gloss.

Turps is so called becasue its a cheap replacement for Turpentine (which cost a fortune these days and only available in art shops etc..as its the ideal solvent for thinning artist colours.)

Its derived form the resin in trees.

As for the stains..dont 'WATER' down the paint...use oil based undercoat and thin it with either white spirit or turps..add about 10% and give the stains a couple of coats.

Cheers Zampa. Meant thinned u/coat actually not 'watered down' My mistake