Aluminum capping is the WORST thing anyone can do to a window sill. Most home owners with wood windows think they are solving a problem by having aluminum capping installed....but they are just hiding the real problem.
Exterior paints are expected to last 9 to 14 years according to paint manufactures but wood window painters think that is a joke. Let's make some observations first by looking at the vertical and horizontal brickmolding (the wood on the sides and top of the window frame). Paint on those parts seems to last way longer than the bottom sill. But why? Most home owners and painters say it is the effect of weathering, but why only the bottom sill and not the top of the horizontal brickmold as well.
Paint peels off the bottom sill even if the wood had a good primer applied. Why? The only reason that paint peels is because it no longer sticks to the wood so why does the paint only lift off the sill and not the sides or top? TOO MUCH MOISTURE IN THE WOOD.
Very few painters or home owners use a moisture meter to determine if the wood is actually dry enough to prime and paint so the paint keeps peeling off....and this is the problem that aluminum capping HIDES. Dry and wet rot starts to occur under the capping and no one sees it until the window sinks into the dry rot or the dry rot starts to appear beyond the edge of the capping.
The reason capping does damage to the covered wood sill is because the moisture that gets into the wood comes from INSIDE the house. Heat and water vapour are trying to escape from the house interior all winter... due to the second law of thermodynamics...heat always goes to cold, so the heat dissipates and the water vapour condenses where the water gets trapped behind the capping.
Keeping water out of the wood by painting only when the wood is dry is better and cheaper than capping.
Last edited by thermoklear; 06-03-2012 at 02:17 PM.
Reason: bad advice