Primer and Sealing

Primer Has Its Own Two Clocks, and Both of Them Matter

Most people think of primer as a cheaper coat of paint that goes on first. It is not. It is a different product doing a different job, and unlike a topcoat it has a window at both ends. Go over it too early and you trap solvent under a film that is trying to leave. Go over it too late and, with some primers, you have lost the surface chemistry that made it worth using.

That second half surprises people. A bonding primer works partly because its own film is still receptive when the topcoat arrives. Leave a bonding primer on a glossy door for three weeks in dry Pasadena air and it has hardened into just another slick surface, and the paint you put over it is now bonded to a primer that is bonded to nothing in particular.

Choosing the Primer, Which Is Not a Formality

There is no general purpose primer that does every job adequately. There are several specific primers that each do one job well.

Bonding primer goes over surfaces the topcoat cannot grip on its own. Old oil based enamel on trim and doors, previously glossy walls, tile, laminate, cabinet boxes with a factory finish. It is chosen for adhesion, not for hiding.

Stain blocking primer goes over anything that will bleed through. Water marks from a past roof or plumbing leak, tannin from the old fir and redwood trim in the pre-war houses here, smoke, marker, crayon. Two extra coats of finish paint will not stop a tannin bleed. It will come through both of them over the following month, usually as a yellow shadow that appears after everyone has agreed the job looks great.

Masonry primer goes on stucco, block and any bare cementitious surface. New stucco is alkaline and stays that way for a long time, and an ordinary primer put over it can be saponified by the alkali, which turns the film soft and sticky from underneath.

Drywall or plaster sealer evens out absorbency. A patched wall where new compound sits beside old plaster will drink at two different rates, and without a sealer the topcoat dries to two different sheens over the same color.

Picking the wrong one of these is not a small error. It is the difference between a coating that lasts a decade and one that peels off in sheets in the second winter.

The Pasadena Complication

Primers flash off very quickly in this climate, which produces two specific problems.

The first is that the surface lies to you. A stain blocking primer on a hot stucco wall in July can be touch dry in fifteen minutes and still be actively working the stain into itself underneath. Topcoat that and the stain has somewhere new to travel. We wait for the actual interval, in the shade, and if the sun has already moved onto that elevation we come back the next morning rather than push it.

The second is flash setting. When a primer skins over before it has flowed out, it never properly wets the surface it was meant to grip. You get an even looking coat that is mechanically doing very little. This is the most common reason we find peeling on exteriors that were painted recently and expensively. It looked fine on the day.

Our answer to both is unglamorous. Follow the shade around the house. Start on the east elevations in the morning and the west ones late or not at all. Check surface temperature rather than air temperature, because a stucco wall in direct sun runs a long way above whatever the forecast says. Stop when the wall is too hot rather than finishing the elevation.

Old Paint and Pre-1978 Housing

Much of the housing stock around here was built well before 1978, and the layers under the current color can contain lead. Sealing is often the better answer than removal.

Where the old film is sound and adhered, a primer over an intact layer leaves it undisturbed and encapsulated, which is safer and cheaper than opening it up. Where it is failing and has to come off, we test first and then use wet methods, containment and proper waste handling rather than a dry sander that puts the problem into the air of the whole house.

We will tell you which situation you are in after looking at it rather than before.

Sealing Before a Color Change

If you are going from a deep color to a pale one, a tinted primer does more work than a third coat of finish would. It is cheaper per gallon, it hides better than most people expect, and it means the two finish coats can be applied for appearance rather than for coverage.

If you are going the other direction, into a deep saturated color, primer tinted toward the final shade is what stops the base showing through in the corners and around the cut lines. Deep bases carry less hiding pigment by design. Painting a strong red over white without a tinted undercoat is a three coat job that people usually stop at two, and then look at the patchy result for years.

Call (626) 987-3694 and we will tell you which primer the surface needs and what the interval looks like before the finish can go over it.