A primer is an intermediary material applied to the roof beneath the intended coating, otherwise called the topcoat. Primers aren’t meant to replace the topcoat but work with them, adhering to the roof exceptionally well while providing a surface with better adhesion. This serves to increase adhesion on surfaces that are difficult to stick to, improving the topcoats own lifespan, and enhance other properties.
Why are primers beneficial?
A good primer can help a less adhesive but strong and protective roof coating adhere better to it’s surface. Some surfaces such as aluminum are naturally difficult to adhere to, in which case it’s easier to design two coatings, a primer able to focus on adhering to aluminum but suffers as a topcoat and a stronger paint that adheres to the primer while acting as the surface layer. A primer may also improve coatings such as filling in cracks to make a flatter surface for the topcoat or prevent a water based coating rusting a steel roof.
Oily surfaces such as tar and asphalt are known to cause bleed through in certain paints, yellow oils seeping through a topcoat they’re not compatible with. Also called stain blocking, primers can be designed to guard the topcoat from these substances.
Can a primer improve water resistance?
In some ways, yes. Moisture often penetrates into the topcoat and weakens it’s bond to the roof. A primer can greatly improve the topcoat’s bond and be more resistant to water, resulting in a tighter bond between the topcoat and roof material.
Why is my primer gray? My roof needs to be white.
Some primers are discolored to act as an indicator for how much of the roof has been covered, such as the gray 295-G. While it’s true topcoats are often white or tan in color, primers should not be left out for many days before the final coat is applied.
When would I not need a primer?
Primers do cost extra relative to just the topcoat itself and will require work to apply coats of both primer and paint. It’s also important to note not all primers work with all topcoats and will need to be considered together. While a good primer generally improves the application of it’s topcoat, if it can adhere to the surface on it’s own and doesn’t need the extra strength it may be more cost effective to ignore the primer. And while a primer does provide a better surface for a coat to stick to, it’s no replacement for preparing the cleaning the surface properly