| Nestor_Kelebay |
| (Specializing in Non-Fiction) |
| 10/15/07 09:51 PM |
Re: painting southern yellow pine furniture
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You should understand the following:
1. The purpose of a primer is to stick to the substrate and provide an easy-to-stick-to surface for the top coat to stick to. Normally, you only prime BARE materials, like bare wood, bare metal, bare drywall or bare plaster. The purpose of sanding down a paint or varnish prior to repainting or revarnishing is to provide "tooth" so that the next coat of paint or varnish sticks well. So, unless you sand right THROUGH the paint or varnish on your furniture to reveal the bare wood, you normally would not need to prime. The sanded paint or varnish is rough enough to ensure that the new coat of paint will stick well to it. Priming would normally be a waste of time in your situation.
2. However... with paints, the higher the gloss level of the paint you choose (and everything else being equal), the less well it will hide an underlying color. That's because the higher the gloss of the paint, the smaller the volume percent of the paint is occupied by pigments, and the larger the volume percentage occupied by clear or transluscent plastic binder. So, if your project is dark brown now, and you wanted to paint it with a high gloss white paint, it might take 3, 4 or even 5 coats to completely hide the underlying brown. However, white primers necessarily contain a lot more pigment (and coarser pigment) so they can to dry to a matte gloss, they'll hide an underlying colour much better than a high gloss paint will. So by putting on a coat of primer first, you get a better head start and might only need one or maybe two coats of high gloss white paint over the primer. The same thing is also true if you wanted to paint your project with a coloured paint. If you want to paint with a high gloss red paint, then tint your primer with red pigment to get a head start on the colour change as well.
So, combining 1 and 2, you generally only prime bare surfaces and sand painted or varnished surfaces, but it makes sense to prime over sanded paint or varnish if you want to change the colour.
3. If you use a primer, use an interior OIL BASED primer. If it were me, I would use an interior oil based paint over that primer as well. Oil based paints dry to much harder films which stand up better on working surfaces like table tops and shelving than latex paints. Latex paints simply aren't hard enough for a working surface, and dirt gets embedded in them making them look very dirty very quickly. It's never a good idea to use an oil based paint over a latex primer on a working surface because the latex primer is too soft to support the oil based paint well. As a result, you're likely to find the oil based paint cracks and chips easily because the primer under it is too soft.
4. To reduce brush strokes, thin your paint (and primer). Water based primers and paints can be thinned with water or a product from the Flood Company called "Floetrol". Oil based paints can be thinned with mineral spirits (also called "paint thinner") or a product from the Flood Company called "Penetrol". In both cases, if you're painting a horizontal surface like a window sill or table top, then water or mineral spirits is all you need since thinning will both reduce the viscosity of the paint and lengthen the drying time, thereby allowing brush strokes to self-level flat before the paint dries. However, if you intend to paint any vertical surfaces, then you have to be a lot more careful when thinning with water or mineral spirits because the combination of lower viscosity and longer drying times on a vertical surface results in the paint "sagging" as it dries resulting in a horrid looking paint job. In those cases you need to use Floetrol or Penetrol. Both are considerably more viscous than water or mineral spirits, so they don't reduce the viscosity of the paint nearly as much, thereby preventing the paint from sagging on vertical surfaces. Both of these will extend the drying time of the paint to allow brush strokes to self level out, tho.
MOST do-it-yourselfers are under the delusion that to eliminate brush strokes, you need to buy a better brush. The truth is that thinning your paint is far more effective at allowing brush strokes to self level than even buying the world's best brush. Also, put your paint on, spread it quickly and then LEAVE IT ALONE. Gravity and the laws of physics will make your paint film level out to a far smoother film than you can with a brush. Too many people keep brushing over drying paint, and the result is that by the time they finish playing with it, so much water and mineral spirits have evaporated from the paint that it is too viscous to self level on it's own anymore. So, the people that strive for perfection by working the paint with their brush are working harder to produce a poorer paint job.