Sanding sealer vs undercoat

[AllFramed]

Hello All. I am looking further at producing more hand finishes using bare wood mouldings. Sanding sealer literature suggests it is best for preparing wood for waxing, but I have used it as a sealer undercoat for paint too.

Would you use it in this way? Or would you use an undercoat of sorts if using paint rather than a stain?

Thanks, Tim.

[strokebloke]

Sanding sealer is effectively talcum powder (pig bone) and shellac with a dab of varnish added.
It's purpose is to fill the grain of timbers (usually hardwoods), prior to applying wax.
It depends in what way you intend to hand-finish your frames.
For a painted finish, I'd suggest that an appropriate undercoat would possibly be more economical.
Quite what effect the shellac & varnish would have upon subsequent coats of paint, in terms of keying, I don't know.

Jack

[Not your average framer]

My understanding is that the usual solid matter in sanding sealers is zinc stearate. Talcum powder (talc) is magnesium silicate.

http://www.wisegeek.com/what-is-zinc-stearate.htm

Zinc stearate is cheap to buy, if you want to make your own sandable finishes.

[CalicoFraming]

My understanding is that any wood finish (wax, varnish, lacquer, paint, etc.) will seal the wood - it doesn't have to be 'Sanding Sealer'. I believe that if it does have a use it's to make sanding easier when you sand the first rough coat of finish, but it doesn't sound like that's your objective here. As for filling pores, that can also be achieved either just with layers of whatever finish you're going to apply or with wood poor filler, but again doesn't sound like your objective and in any event isn't strictly necessary, just gives a different sort of finish. If you're planning just to wax the raw wood I don't see why you'd need a separate sealer beforehand. if you're going to paint it, then you need to prime it - the primer has less pigment, more binder, ensuring the first coat is well bonded to the wood. Happy to stand corrected on this stuff of course!

[Not your average framer]

any wood finish (wax, varnish, lacquer, paint, etc.) will seal the wood

That depends upon both the wood and the finish employed. Wax tends to be a mobile material, which can easily be displaced, or even absorbed into the wood in a way that negates any sealing effect intended. Also some woods such as pine contain substances which can disolve or penetrate any wax finish applied to the wood.

it doesn't have to be 'Sanding Sealer'

That depends upon what you are trying to do! If you just need to seal the surface, then the sanding qualities may not matter so much. However, don't forget that the solid matter is sanding sealers will generally assist in building thicker coatings per application and thicker coatings will help to hide imperfections, with less time and effort.

If you're planning just to wax the raw wood I don't see why you'd need a separate sealer beforehand

Using a sealer before waxing tends to prevent any loss of shine with time, which may be caused as the wax finish is slowly absorbed into the wood. In such cases a simlpe coating of shellac will solve the problem.

[AllFramed]

Interesting responses, thanks. My objectives are to produce a good quality finish that has longevity, but also to take as little time and create as little mess as possible. The question is regarding suitability as a base coat for different finish materials. I find sanding sealer, being more fluid, easier to work with and less messy when sanding than paint primers though i guess there is no reason why I couldn't dilute them.

Part of the objective is also to fill some imperfections such as the open grain in obeche. At the end of the day with that one there is probably no escape from layering and sanding and the mess that generates.

[Graysalchemy]

I use osmo Polyx oil directly onto bare wood. 1 coat is fine but two is better depending on the finish. It can be brushed on or wiped on and gives quite a durable finish.

However if I am paintong wood I use 2 coates of ripple paint and sometimes seal it with acrylic gel medium. then paint at least 2 coates of paint over the top.