Water-based versus Oil-based enamels
Oil based enamels have a tendency to yellow over a very short period of time and is particularly noticeable with white..our favourite trim colour! The featured picture is a cavity sliding door which has yellowed from being in shade within the wall cavity.
Occurs in two situations...
1. Lack of light, inside cupboards, cavity slider doors, behind doors in shaded areas (reversible..expose surfaces to light)
2. Ammonia is present in the air. Reacts with solvent based enamels. It is found in many acrylic water-based paints. This includes water-based undercoat...commonly used under solvent enamel. (not reversible)
1. Use water based paints first. Do not use oil-based enamel paints on the same day as acrylic paints.
2. Use oil-based undercoats under oil-based enamels.
3. Use a good quality water-based enamel. These will not yellow.
Oil-based enamels...PROS...very hard wearing, very high gloss in gloss finishes, extremely smooth finish, can use on external areas. CONS...Yellows over time, solvents, fumes, long time drying, difficult clean-up, re-coat next day
Water-based enamels...PROS...doesn't yellow, Clean consistent colours, highgloss finish, same day re-coat, low odor, easy clean-up, relatively tough. CONS...requires 2 coats for full gloss and protection, only interior, not quite as hard wearing, finish appears slightly ropy (brush marks may be visible)
Paint Adhesion... Up close and personal
Enamel paints dry to hard wearing smooth finishes especially good for doors, trims and windows. When painting previously enameled surfaces...a solid, sound surface and a 'good key' is essential. Any previous enameled surfaces being re-coated need to be sanded (to provide the key) and undercoated prior to subsequent top coats. Enamel paint, over time cures to a 'glassy' tough finish and general top coats will not adhere to them unless an undercoat is applied first. The only exception is 'second coating' new enamel. This however must be done AFTER the first coat cures (usually 16-24hrs). A good rule of the thumb is never re-coat new enamel in the same day. I also recommend re-coating new enamel within 7 days for best adhesion as the film becomes very 'glassy'. "Always undercoat your OLD enamel surfaces before you paint" "There are no second chances here!!"
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