The question often arises: What’s the Difference between choices of Primers?
Here in this blog I will attempt to explain the difference between latex primer, oil-based primer and shellac-based primers and how you can choose the right one for the job,
in other words, this is a primmer on primers ! (sorry, couldn’t resist)
For every interior and exterior paint job, you have to choose between Latex, or Oil-based paint. -Latex paint is most often preferred, because it emits fewer odors than oil-based paint, and it cleans up much more easily.
In one area, however, oil-based products still hold their own over latex, and that is: primers.
There also is another option when choosing a primer: shellac-based primers. Any of these three primers can be used under latex topcoats.
You will need to choose a primer based on the state and condition of the substrate to be primed as well as its location. Before you open the can, or even make your purchase, you want to be sure to completely prep the surface that will be primed. There is no primer that can perform well if the surface is just not ready for painting.
Here now are the three choices available to consumers when choosing a primer:
First off, we have Latex Primers.
Latex primers are good for wood that is in good condition. These products will remain flexible after drying, which is important during expansion and contraction of the structure, especially exteriors. However, they will not perform their best if they are applied when the temperature is not between 50° – 90°F. And, Latex primers also just do not perform well on weathered or damaged wood. Neither will they block knots or stop the bleed-through of tannins found in cedar and redwood, and they will raise the wood grain more than oil-based or shellac-based primers.
Cleanup is easily accomplished with plain water.
Next we have, Oil-Based.
Oil-based primers are much better than latex at sealing over nails, covering over the knots in bare wood, and also blocking stains or tannin from bleeding through. They are preferred for sealing window muntins that will be in contact with oil-based window glazing. These primers penetrate wood more readily than latex primers, which makes them a much better choice when preparing weathered wood. The best penetration is achieved because it is a slow-drying primer, but there is a trade-off due to the longer wait before topcoating.
Oil-based primers will continue to harden as they age, which can be a problem with exterior applications. This is because as the wood underneath expands and contracts, the primer remains rigid, and the older it is the dryer and more brittle it becomes, which weakens the bond the wood has with the paint.
Cleanup is also more intensive and costly, since it is most often done with mineral spirits.
Last but not least, we have Shellac-Based
Because there is a solvent in shellac-based primers that is based on denatured alcohol, such primers are often used to kill bacteria that causes certain odors.
They are also great at covering knots, heavy stains and tannin bleed. If you have a problem stain from a knot bleeding through or from a water stain that other primers will not stop, then you should switch to shellac-based primer.
Because shellac will become soft in high temperatures, its use on exterior surfaces is best limited to spot-priming. On the other hand, shellac-based primer is the only primer that can be applied in freezing temperatures.
They do not penetrate wood as deeply as latex or oil primers, since they are the fastest-drying primers available.
Cleanup uses denatured alcohol or an ammoniated detergent.