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The Problem: Paint Failure
A major problem facing painting contractors and homeowners, alike, is paint failure and/or cedar bleed (tanning) caused by unwanted moisture buildup. The problem is common to houses of all types and ages, but it is most prevalent on houses with red cedar shingles or clapboard siding.
New cedar shakes are also prone to tannic acid and moisture bleeding. Add insult to injury and prime and paint over a moisture bound surfaces and you have a major problem on your hands.
There are 3 major symptoms of paint failure due to trapped moisture buildup:
blisters
cedar bleed (or tanning)
rusty nailheads
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Water Blisters | Blisters can range in size from inches to feet and may actually have water held in them. (see photo). Notice the almost half inch of tannic rust colored water in the glass jar from breaking the blister?
Cedar bleed, a rust colored surface discoloration, appears in and near soft and split wood grain since moisture will always follow the path of least resistance.
Rusty nailheads occur when moisture, following the easiest route out, flows past the steel nail causing rust to form around the head.
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The Cause: Trapped Moisture
So there's water, water everywhere, but where is it coming from? In most cases through unprimed clapboards on the interior backside of siding. To understand why your home experienced paint failure, see how the following elements contribute to the problem:
What is your temperature?
How is your home heated
Spring cleaning anyone?
Shade vs. Sun?
What is your temperature?
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 window pane 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?
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 cavaties. 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!
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Spring cleaning anyone?
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.)
| Tannic Cedar Bleed |
Shade vs. Sun
Moisture problems are most common on the surface areas that are interior-heated and receive a large amount of sunshine. Areas shaded by shutters, blinds, eaves or overhangs will usually show little if any paint failure or cedar bleed, since the absence of extreme heat differentials minimizes the moisture accumulation and drawing effect. As a result, the side of the house that rarely receives direct sunlight will commonly show less paint/stain failure due to unwanted moisture release.
The Solution?
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