Moisture Related Problems When Painting
We have covered a variety of finish problems that can be caused by moisture. However, because moisture is a major concern in the trade, further discussion is warranted. You will see that many moisture-related problems are caused by construction methods or other factors outside the control of the painting trade. You will also see that there are corrective measures that can be taken to reduce the impact of these factors on the finish.
The increased use of insulation and vapor barriers for energy conservation has caused a significant increase in problems related to condensation. Heat travels from a warmer area to a colder area. In cold weather, some of the warm, moisture-laden indoor air escapes through the walls. When this air contacts the cold exterior walls, tiny droplets of water form in the space between the inner and outer walls. This is called condensation; it is the same as that seen in hot weather when warm air contacting a cold drink causes water droplets to form on the outside of a glass.
The condensation problem is magnified if the building is tightly sealed because the moisture trapped between the walls cannot escape in winter months when the house is closed up. Trapped moisture can have several possible effects:
- It can soak into wood siding, causing it to swell and put stress on the exterior finish, which could result in cracking.
- It can penetrate the siding and cause blisters on the painted exterior surface. It can cause siding to stain by leaching extractives from certain woods.
- It can cause mildew on the surface.
Remedies For Condensation Problems
There are several methods that can be employed in the construction phase to reduce condensation problems. For example:
- Except for coastal areas, vapor barriers are required in the northern section of the country Vapor barriers are usually made of polyethylene or similar material. The vapor barrier must be tight around windows, doors, electrical outlets, and other locations where air could escape.
- If blanket insulation with a vapor barrier backing is used in place of a wrap barrier, the flanges must overlap to prevent moisture migration.
- Foil-backed drywall may also be used to provide the vapor barrier. Again, the seal around doors, windows, outlets, etc. must be tight.
The methods just described can be effective if used in the initial construction. If a moisture- related exterior finish problem is discovered, it’s already too late to apply such methods. In those cases, other methods can be effective.
Interior humidity should be kept at 30% to 40% during cold weather. This is a balancing act because, in very cold conditions, the air will be too dry, causing static electricity, furniture problems, and respiratory problems. If the relative humidity rises above 40%, on the other hand, condensation problems will likely occur. Persistent condensation on the inside glass of double-glazed windows is a good sign that the humidity is too high.
Homeowners experiencing problems with moisture need to manage the humidity levels in the house. The addition of a hygrometer, which measures relative humidity, is a good start. Using exhaust vents in kitchens and bathrooms is one way of holding down humidity. These vents can be operated by the occupants or can be placed under the control of a humidistat, which senses humidity and operates the ventilation system whenever the humidity exceeds a set level.
Another way to reduce humidity is to have the forced-air heating system modified to duct outdoor air into the return side using an automatic damper. Dehumidifiers help but are generally unable to pull the humidity below 50%. Other ways to cut humidity area:
- Reduce the number of house plants.
- Make sure the clothes dryer is vented to the outdoors.
- Do not store firewood indoors.
- If the house is built over a crawlspace, make sure the crawlspace has a vapor barrier. Otherwise, moisture will leach from the soil into the building.
- Make sure that there is good drainage around the outside of the house.
- If the basement is damp, add a dehumidifier.
If the humidity swings too low during very cold weather, a humidifier can be added. In homes with forced-air heat, the humidifier can be added to the furnace.
Humidifier Added To A Furnace
Condensation can be a major problem with new construction, especially if the building is enclosed just before winter. The moisture leaching from the cement slab or foundation as it cures will not be able to escape from the house. As a result, the humidity in the house will be high and there will be a greater chance of moisture damage to the exterior finish.
Damage caused by melting snow and ice
Water damage from melting snow and ice is a common problem in northern climates. The problem occurs when heat rising through the house causes snow on the roof to melt. When the water hits the roof overhang where there is no heat, it will freeze again, causing an ice dam. At some point, the ice dam will back up to the edge of the heated portion and the melt-off will be forced under the shingles. From that point, the water will trickle down between the walls, causing water damage to both interior and exterior walls. It will also follow rafters and floor joists and deposit water in ceilings. A significant amount of such runoff over time can cause a ceiling to collapse, resulting in damage to the interior and its contents. Worse yet, an occupant who is at the wrong place at the wrong time could be seriously injured by falling, moisture-soaked drywall. The best that can be expected is water-stained interior walls and ceilings and the usual moisture-related damage to the exterior finish.
The solution to ice-related moisture problems is to first eliminate the source of the problem. Adequate attic insulation is essential to minimize the amount of heat escaping through the roof. Adding attic insulation will not only help reduce the water backup problem but should increase energy efficiency at the same time. Proper venting of the roof and the eaves are also needed to help equalize the temperatures on the inner and outer surfaces of the roof.
If homeowners are experiencing runoff problems, they should contact a roofing contractor for advice on how to permanently correct the problem. The painting contractor can repair the damage to the finish, but if the cause isn’t fixed, the problem will occur again.