Latex is better than oil on raw wood
High-quality latex acrylics definitely have the advantage over oil based lettering enamels on raw wood (and masonry). Paint films that dry to a hard shell will usually crack and fail when there is movement of the substrate, as is the case with wood. Latex, by contrast, is stretchy and will move with the wood. Latex is also semi-permeable, giving it a great advantage over oil paints when moisture is present in wood or masonry. House painters have long known that moisture contained in wood house siding can escape through a latex film but is trapped by an oil enamel, resulting in blisters.
Color-fastness is another issue to consider. Experience gained at the Walldogs festivals has revealed a clear advantage of acrylic latex over lettering enamels in color holdout over time. One Shot, at least in its current formulation, fades quicker. Further, an acrylic latex mural paint like Nova Color has an advantage over acrylic house paints because of the practice of adding significant amounts of white to house paints to achieve opacity. Nova Color mural paints, by contrast, are heavily pigmented and the pigments are purer, not being heavily fortified by titanium dioxide or other whites. This allows for cleaner blending and tinting, and colors that are, generally, more vibrant than can be achieved with house paint mixes. Also as many of you may know who have done pictorial work, lightening One Shot greens or browns with white often resulted in muddiness. For this reason, many billboard painters used yellows as a workaround to this problem, instead of using white when lightening and blending.
The disadvantages of paint like Nova are obvious to any old school sign painter the moment you start working with it. If you are used to pulling long opaque lines with a loaded quill, you will be disappointed. You must learn a new skill set in brush manipulation and accept double coating as the norm. Also, quills made of animal hairs do not work well in water-based paint. The hairs swell and lose resilience. Lettering brushes for latex need to be synthetic or a synthetic mix. Switching is an easy transition for wall work if you're experienced using fitches on bricks. Simply switch from bristle fitches (and cutters) to synthetics. The moves are much the same. Using synthetic quills is a longer learning curve. A newbie might have the advantage here due to not needing to "relearn."
Both quills and fitches are being made now with a synthetic content that holds up well in water based paint.
Admittedly, working with latex paint and using synthetic quills is a slower process (though not so much with fitch work). You must modify lettering time estimates and allow for double coating. But it is a mistake to cling to a paint product that is inferior (at least on raw wood and masonry) just because you're used to it.
Of course, on metal, or on an overlaid product like MDO, or on PVC or HDU, where the paint film does not actually touch wood grain, acrylic polyurethane beats all others for longevity, as kccollins in Illinois mentioned. But on redwood or cedar where the film is in contact with the wood? I am skeptical, but I admit I don't have much experience using polyurethanes on sandblasted wood except on very small areas. kcollins probably has more experience than I do in this regard.
If you are required to use sandblasted wood, I can understand not using high-density urethane. But HDU will easily outlast any wood product when it is put out in the elements. It accepts all paints and will not rot, even when completely exposed. Of course, it will eventually go away, as will all petroleum-based products. But there is tremendous pressure, and progress, in the paint and coatings industry to produce coatings, pigments and solvents made from renewables. A good thing, even if we old dogs must learn lots of new tricks.
Brad in Kansas City
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