Know your coats: primers, seal­ers, and un­der­coats

The Shed - - House Painting -

What’s the dif­fer­ence? Rob tells us that ‘un­der­coat’ is an older term for heavysolid­s paints that blank out dif­fer­ent colours on the sub­strate. It was needed when pig­ments in top­coats weren’t as good at cov­er­ing as they are now.

Rob’s rule of thumb is one coat of primer and two top­coats. A sec­ond top­coat evens out any thin patches you might have missed when paint­ing the first coat and gives suf­fi­cient paint depth for the coat­ing to work.

“It’s hard to get that depth in one coat with­out drips, or runs, or sag­ging,” he says. “I’ve never seen some­one do one coat and do it per­fectly.”

The primer just en­sures that the top­coats will stick. And it is de­signed to work as a thin layer, so a heavy ap­pli­ca­tion is def­i­nitely not bet­ter. Rob even ad­vises prim­ing holes, dents, and gouges be­fore ap­ply­ing a filler.

Note that new weath­er­boards are of­ten de­liv­ered painted, but this is usu­ally just a primer for ba­sic pro­tec­tion dur­ing trans­porta­tion. Make sure that you check the la­belling on each plank for paint­ing in­struc­tions spe­cific to that prod­uct, says Rob. Most will need a proper primer for ex­ter­nal use and you should think about ap­ply­ing the first top­coat to the boards be­fore fix­ing them in place.

Rob doesn’t ad­vise ap­ply­ing gap filler to seal be­tween weath­er­boards. They need to be free to move past each other, as they ex­pand and con­tract

Re­paint­ing wooden win­dows is a good test of your met­tle

Decks and fences will re­quire thor­ough clean­ing to get them ready for paint or oil­ing

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