7 Steps to Minimize Premature Paint Failures

In a recent poll conducted this spring, 60% of contractors identified weather as their biggest concern when painting exteriors. Now summer is here and, in addition to weather, there remains other prudent guidelines to ensure a quality paint job. This month we focus on steps to best minimize premature failure on exterior painting. With advances in technology, most manufacturers offer premium exterior products suited for exterior applications. However these products are not fool proof. Selecting the right paint for the right surface to be painted to ensure the best durability. And during application, a good rule of thumb is to follow the manufacturers recommendations. Speaking of exterior painting, remember too, that the technology that offers the best UV protection, with the ability to tune key durability properties such as adhesion, gloss and color retention, dirt resistance, is 100% acrylic technology -- look for this on the can!

So what causes exterior paint to fail?

Failure to smooth rough edges

Why:
- Poor adhesion due to poor wetting and
  non-uniform coverage
- Poor Appearance and Poor Dirt Resistance
  (as dirt and moisture collects on surface)
- Inconsistent film thickness as paint pools in
  valleys and thins on edges

How Fix:
- Taper edges of old paint by "feather sanding". Use
medium grit (#120) followed by fine grit (#220) -- especially for semi gloss or gloss paint.

* Caution:
- don’t be too aggressive with your feather sanding. Painters report, for example, that power sanding may generate enough heat to degrade the adhesion of the old paint, resulting in failures. And, of course, do not sand if lead may be in the old paint

Failure to prepare weathered wood

Why:
- Controlled exposure tests conducted by the Rohm and Haas Paint Quality Institute and others have clearly shown that, all else being equal, primer and paint will not adhere to wood that has been weathered as well as it will to the same wood that has not been weathered.

How Fix:
- Prior to priming or staining, refresh the surface of weathered wood by thorough sanding. Remove any wood that is gray from weathering. Medium grit (#120) garnet paper works well. If you’re going to ultimately apply a gloss or semigloss paint, re-sand with fine grit (#220) sand paper.

- Careful Power washing can also be effective. It is best not to use power washing on softer siding woods such as cedar and redwood, particularly if well weathered. If power washing, use plain water without a cleaning agent or bleach.

Failure to use a primer

Why:
- The benefits of using an appropriate primer
  are consistent with those gained from good
  surface preparation. They include maximizing
  all of the following:

• Adhesion of the finish coat
• Uniformity of sheen or gloss
• Hiding and hiding uniformity
• Gloss development of the finish coat
• Mildew resistance
• Lack of discoloration from the substrate

In general, prime any surface that has not been previously painted. Also prime any surface areas exposed by loss of paint, such as those that have peeled after years of exposure or have been exposed as part of surface preparation. It’s important to note that almost any paint job, even over existing surfaces that are sound and continuous, will benefit from the application of an appropriate primer.

Failure to correct a source of water behind the substrate

Why:

• Reduce opportunity for blistering and peeling.
• Masonry - reduce efflorescence

How Fix:

• Masonry - fix cracks (spot prime then use conventional topcoat for small cracks or EWC for larger cracks)
• A rain cap placed over the flue opening on brick and stucco chimneys can often avert this paint failure

If you can’t eliminate the source of water intrusion yourself, be sure to make your customer aware of the situation so that he or she can take the necessary corrective action.

Failure to apply paint at the correct spread rate

Why:

• Thicker coats can lead to premature cracks which lead to water intrusion, loss of adhesion and generally poor durability
• Thin coats can lead to poor mildew resistance and poor durability
• In the case of primers, one can get poor stain blocking and corrosion resistance.

So be sure to follow the manufacturer’s recommended spread rate.

How Fix:

• Avoid thinning paint prior to application can also compromise these properties. Thinned paint applied at the recommended spread rate will dry to a thinner than intended film, because of the reduced solids concentration, and this can hurt performance.
• Follow the manufacturer's recommended spread rate

Failure to apply latex paint at the proper temperature

Why:

• Low Temperature
  - compromises film integrity. Latex particles harden at low temperatures and do not fuse to form an optimum film
  - Drying times are longer as water leaves more slowly at low temperatures
  - avoid applying latex paint unless the temperature is predicted to stay above the minimum recommended application temperature for the next 36 hours.
• Substrate Temperature
  - must be at or above the minimum application temperature at the time of painting
• High Temperature
  - compromise film formation. If the paint dries too quickly, the binder particles loose mobility and don’t have enough time to form an optimum, durable film.

How Fix:

• Avoid painting in temperatures over 90oF; painting in bright, direct sunshine; painting in very dry and/or windy weather; and painting a dry, porous surface that will quickly absorb water from the wet paint.

Failure to use correct type and quality of paint

A paint designed for the job is essential. For example, gloss paint designed for use on metal will probably crack if applied to wood. Similarly, paint designed for indoor use will likely perform unsatisfactorily if used outdoors. The quality of the paint is just as important.

The Rohm and Haas Paint Quality Institute recommends using a top-of the- line product for most exterior applications. Choosing an exterior paint based mainly on low initial price can compromise both protective and decorative properties.

Generally speaking, top-of-the-line 100% acrylic latex paints provide the best overall performance. Compared with oil-based paints, and assuming good surface preparation, these paints will provide considerably better longterm performance with respect to color and gloss retention, mildew resistance and crack resistance.

As you can see, many factors impact the performance of an exterior paint job, including the seven described here. Keep these in mind and they will help you achieve a quality, longer-lasting paint job.

And when painting, don't forget to think about safety for you and those around you. Here are some helpful hints on ladder safety.