MPI Manuals Archive
Specify Paint Access to what you need to know about paint system
choices, paint system surface preparation, approved paint products,
painting specifications for both new construction (architectural
painting) and maintenance painting.What Went Wrong?
A Bad Choice of Paint System
A Bad Choice of Paint System
This is a good example of where the choice of a coating system for a specific
use would save a lot of time and unnecessary cost and labour.New dimensional exterior wood stairs leading up to a wood deck. The coatings were applied to the ends, edges and backs, as well as the top treads. The peeling appeared shortly after application and exposure to a week of rain. There is inter-coat adhesion failure and substrate adhesion failure -- indicating that the primer's bond to the surface is marginal as is the top-coat's adhesion to the primer.
The primer is a water-based material originally designed for application to previously painted siding (vertical). The finish coating is an alkyd porch and deck coating applied in two coats. Moisture readings averaged 13% at the time of the inspection and there was no visible evidence of blistering due to moisture trapping under the film.
What is most noticable is the lack of penetration into the wood by the latex primer that likely could be attributed to the type of use for which it was intended. On new dimensional stair treads, a reduced coat of the alkyd porch enamel to improve penetration then two full coats applied would have served the purpose much better.