I tore out and replaced our stair railings, splindles, newel posts and all. Should've painted them first, but I didn't.
My plan is to prime and then paint at least two coats (sanding in between each).
What should I use to apply the paint on my last coat to keep it smooth?
Spraying is not an option. Will the sponge brushes do better than a regular brush for a final coat?

The best quality paint you can get, go to a pro paint store for it like Sherwin Williams, Benjamin Moore or another. Great paint will tend to self level with whatever one applies it with. If it were me, I would use a great quality brush for this type of application. My paint brushes are expensive, but taking good care of them, makes them cheaper in the long run.
A very light/fine sanding (that you are planning) between coats, and wiping down any dust prior to recoating will help create that smoothness also. Just because hand rails get so much use, I might opt to go ahead with a third coat?

it's not what brush but what type of paint are you using? latex or oil, that will determen the type of brushes. if this would be my job the primer is 2 coats of oil primer with light sanding in between and 2 coats of oil enamel light sanding in between.brushes would be chinese bristle sash type (brisles are cut on a slant)about $6 each.take 1 brush and shorten the handle so you can get between tight places.
you also need a good supply of blue tape and newspaper to keep the paint off the stairs.

The Luckster8:

Certainly, the most important thing is to use a durable paint because bannisters take a lot of wear and tear. If I were you, I would definitely want to use an oil based paint simply because they're much more durable than latex paints. However, there are a lot of "hybrid" paints coming out on the market that consist of oil based paint resins suspended in water. So, they're water clean-up, but the resulting film that remains on the surface is exactly the same as if you'd painted with an oil based paint.

The second thing is to THIN your paint so that it can self level quickly and easily on it's own. With a water clean-up paint, you'd think you should thin it with water, but that would make the paint run on vertical surfaces. You need to use something that slows down the drying time of the paint so that it can self level on it's own, but doesn't lower the viscosity of the paint so that it doesn't lose viscosity and start to run on vertical surfaces as it dries either.

I would contact the Flood Company (which Google should be able to find for you) and see if their product called Floetrol would be suitable for thinning those hybrid water clean-up oil based paints. If not, then use a conventional oil based paint if you can still get them where you live, and thin it with another Flood Company product called "Penetrol" which you should be able to buy (along with Floetrol) at any paint store.

Thinning the paint so that it self levels well on it's own pretty much eliminates the need to get an expensive brush that will supposedly put the paint on smoother for you. You're further ahead spending more on the right thinner for your paint than spending more on an expensive brush.

Another thing you should do is if you're going to be using a water based paint, dunk the brush in water and shake out the excess water before using it. If you're using a conventional oil based paint, dunk the brush in mineral spirits and squeeze out the excess mineral spirits before using the brush. The reason for this is that some paint will always get high up into the "heel" of the brush, where the bristles of the brush are held tightly together by the brass of stainless ferrule that holds them together.

If paint gets into the heel, it'll dry in that heel while you're using the brush. Then when you wash the brush out, the dried paint won't wash out of that heel. Instead the dried paint up there will simply put all the bristles out of place, and you'll end up with the bristles of your brush flaring out. By putting the brush in thinner first, that thinner prevents any paint that gets up there from drying, and that ensures the paint up there washes out when you wash out the brush. It;s a good idea to use an eye dropper to add a few drops of thinner to the bristles at the heel periodically to ensure the thinner up there doesn't evaporate either, thereby allowing the paint up there to dry too. That'll protect your investment if you do buy a more expensive brush. You just don't need an expensive brush.

This message has been edited. Last edited by: Nestor,

I use enamel paint for hand railing.
Yes it can come in latex for easy clean up.
Yes you can get it in differant sheens.
Enamel is a very tough paint, it's hard to even try to sand it.
A reguler quality 2-1/2 sash brush will hold more paint and give you more control then a foam brush.