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The Cause: Trapped Moisture
So...there's water, water everywhere, but where is it coming from?
To understand why you or your customer's homes experience paint failure, see how the following elements contribute to the problem:
What is your temperature? [back to top]
Due to the temperature differential between a home's interior and exterior, a sweating process occurs and causes condensation to develop in between the partitions. The best example of the process is to look at a window without a storm window on a cold day. Moisture condenses on the inside of the windowpane and you can write your name on the foggy glass. It is the contrast between low exterior and cozy 68-70°F interior temperatures that causes the vapor to condense on the inside of the cold glass.
How is your home heated? [back to top]
Most homes that experience paint failure and/or cedar bleed due to trapped moisture release are heated by forced hot water systems. Homes with hot air and electric heat systems also encounter the problem, but it is usually not as severe. In general, the forced hot-water heating pipes are commonly positioned at the base of the interior surface walls on each floor of a dwelling. The water in those pipes is normally heated to 180°F. The temperature differential between the inner wall and the exterior substrate on a cold night can be as much as 160-180°F - a condition lasting throughout a six-month heating season. During that time, heated air condenses into water vapor inside wall cavities. You can readily see what happens to the interior window surfaces with a 68-70°F temperature differential, so you can imagine what happens between wall partitions with a 160-180°F differential!
Spring cleaning anyone? [back to top]
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Cedar Bleed |
After a long cold winter, spring arrives and you open the house to air it out. Right? WRONG! All of the moisture trapped behind the substrate wants to escape. The sun hits the side of the building and acts like a clothes dryer (without the tumble dry option), drawing the moisture out through the siding. The surface temperature of siding exposed to the sun for an hour or more in the summer can reach 140°F. If the moisture cannot get through the pores of the paint, it will build up such pressure that a blister will form on a painted surface, and/or cedar bleed will occur on a stained surface (see photo).