Just wondering what sheen to use on the interior trim?

Can you re-paint oil base semi gloss paint with another color oil base without sanding or priming? My bathroom walls and ceiling are painted with alkyd base white semi-gloss paint. I want to repaint it in a Yellow with alkyd base paint in a velvet or satin sheen. The walls

Can you texturize walls that have wallpaper on them and then paint or do you need to remove the wallpaper first?

I got paint on the ceiling when I was painting the walls. How could I fix it without doing the whole ceiling? Any tips?

On a new build I am working on the skirts and door arcs are MDF and come ready primed. But after a further undercoat and two gloss coats the finish is poor compared to wood skirts and arcs I have done in the past. I also used fine grade paper

I want to know how many coats of primer do I need to cover my wall murals? I’ve painted Dinosaurs in my son’s room (and sports themed in my others) and the colors that I need to cover up are black, burgundy, hunter green, etc. (dark colors for the sports

Will my paint job still look OK if I paint a semi-gloss coat over the flat coats in a dark color?