Following directions, specifications, and recommendations is not a guarantee that you won’t have a problem on the job. The quality of a paint job depends on certain variables such as weather conditions, cleanliness of the surface, exposure to the sun, and amount of foot traffic.
Below I will describe two personal scenarios that illustrate exactly what I am talking about.
SCENARIO 1: The subject is a never-before painted panelized exterior wall surface made from a ceramic type substrate. The two-foot square tiles have a glazing which is highly polished.
Process for Scenario 1
1.Problem: Remove smooth glaze.
Solution: Sand surface by using orbital sander with #80 grit abrasive disc.
Result: Surface gloss is removed; good anchor pattern is produced.
2. Use recommended primer. Apply two-part epoxy type primer; thin accordingly with Methyl Ethyl Ketone; then spray finish using airless system.
3. Let material cure overnight.
4. On-site inspection revealed broad paint failure. Paint released from the surface; peeling on more than 80% of the total surface.
5. Manufacturer investigated claim. Checked for proper surface preparation and moisture content. Inspection determined that the cause of paint failure was due to primer being incompatible to substrate type. The use of an epoxy primer was refuted by the manufacturer. They said its recommended use was for bare metal surfaces only.
NOTE: The directions called for either that, or a chemically or abrasive etched surface.
6. Recommendation: Recondition surface; and apply an exterior alcohol based shellac type product. Finish with desired topcoat.
7. The surface withstood the new application; job well done.
SCENARIO 2: The surface is a linear bare roof flashing made from aluminum.
Process for Scenario 2
1. Problem: Paint bare metal flashing.
Solution: Sand surface according to instruction, using #120 grit sandpaper.
Result: Created anchor pattern for paint to adhere to.
2.Use recommended oil based primer using brush and roller methods. Let cure overnight.
3. Following day inspection revealed total paint failure. One hundred percent of surface peeled and surface had an unexplained oily feel to it.
4. Manufacturer inspection ensued. The surface preparation and chosen product were approved. A moisture test was completed, with negative results. The metal was determined to be polished bare aluminum, not compatible with an oil based primer.
5. Recommendation: Recondition surface. Sand appropriately with #120 grit sandpaper. Treat with Muriatic acid wash; and rinse with water. When dry, apply thin coat of galvanizing metal primer by brush and roller. Finish with desired topcoat.
6. Finished product acceptable; it withstood the scratch test.
Adhesion problems to look out for: oily residue on surface, humidity over 72%, dust, alkaline or cracked surface, substrate incompatible with primer or finish material.
Methods for correcting adhesion problems: Sand surface with abrasive that corresponds to the surface’s smoothness. Wipe surface with de-glossing agent or high evaporating solvent. Use tack cloths to all but rough surfaces. Paint exterior surfaces on a dry day.
It is easy to overlook a step in preparing a surface. If you do that too often, you will be reminded of it when you are least likely to want it.
Give preparation the time it deserves. It will pay off in the final product. So will the customer.
Rule of thumb: When painting, keep a rag in one pocket and a piece of sandpaper in the other. Believe me, you will need them.
Thank you for visiting “Painting with Bob.”
Copyright 2016. Robert D. Hajtovik. All rights reserved.