This is commonly caused by moisture beneath the paint film and by paint applied over grey denatured wood, dirt, oil, grease, polish and other surface contamination. Resin and resin gases from knots can also cause blistering, particularly where dark colours are used on external south facing surfaces. Wood movement, such as in joints in window frames, can lead to splits in the paint, allowing moisture to penetrate the wood and cause flaking. To prepare, scrape back areas of flaking or blistering paint to a firm edge and rub down to feather edges using an abrasive paper. If the problem is extensive, strip completely using a hot air gun or chemical paint remover. Clean out open joints with a stripping knife and dusting brush. Make good all open joints and surface imperfections.Treat knots and resinous streaks with one or two coats of a suitable Knotting Solution before priming. When finishing with water-based gloss or eggshell, use bleached white knotting, as brown shellac knotting may bleed through and cause discolouration.
Category: Using Exterior Paints