Thread: I am totally confused about primer

Some primers are specially comprised to adhere more firmly to the wood than the 'main' paint, sometimes by simply having different ratios of the same contents.

But, putting that aside, a neutral base coat is always a good idea if you're painting. It gives you a solid base, so that the applied colour doesn't go "blotchy" if sections soak into the underlying wood - as the primer has already 'soaked in' instead.

(Mind you, some primers are rip-offs when all is said and done! )

Skew has summed it up nicely, the only thing I'd expand on is that primers can also contain a filler for the grain to enable a smoother top coat to be achieved.

If you are using acrylics, primers are not usually absolutely necessary. The use of primers dates back to the oil based paint days where the primer was rich in Linseed oil and was to penetrate the timber surfaces and feed it with oil. I think paint manufacturers just like to sell you more of their products by advocating the use of primers. Of course there are some things that have to be primed with the appropriate undercoating primer, rusty metal and the like but if you have stripped it back to raw timber, I feel acrylics will serve the purpose quite well. Good luck with your project;

The final quality of a painted finish is the result of the builtup and smoothing of the layers underneath. I've never been fully clear on the difference between primers and undercoats, but it has something to do with sealing the underlying structure and depends somewhat on whether the final use is for interior or exterior.

As to the undercoat, I have found the undercoat layer to be most important as it fills the grain and usually dries to a sandable surface quicker than a usual topcoat formulation. Getting the undercoat applied and sanded to a good finish is the most important part of getting a good finish.

I've found knotty pine to be a particular problem. The knots bleed through the undercoat and top coat layers. Even priming with pink primer before undercoat has not stopped this. I believe shellac my be a primer that could stop the knot bleed through and if I ever paint something like that again I might give it a try.

Originally Posted by Fuzzie

I've found knotty pine to be a particular problem. The knots bleed through the undercoat and top coat layers. Even priming with pink primer before undercoat has not stopped this. I believe shellac my be a primer that could stop the knot bleed through and if I ever paint something like that again I might give it a try.

Aluminium paint will seal it just fine and stop the bleeding. Make sure you use an oil based aluminium paint though and not a bitumen based product. If you want a clear finish though, of course it would be no use using a paint to seal the pine. Best shot is probably shellac.