Sealing grains before painting so that they dont rise up

[Wahka_est]

Hi,

 

I would need little help.

Food grains on some details will raise up when painting. I use acrylic paints. Even if i sand it so that last is 1000 sandpaper.

Is there any products to use to seal the grains before painting?

 

Problem is at the moment with walnut.

 

Vahur

[Canute]

Yes, there are sanding sealers available. Paint shops or possibly craft stores usually carry these.

[Jaager]

Wood fibers swelling upon the first exposure to water is a factor when using penetrating aqueous (water based) aniline dye also.

The fix is to treat the wood to a prior exposure to water alone, let the surface dry, then sand or scrape the swollen fibers smooth.

It works even better when the water treatment is a ~10% solution of PVA (1 part glue, 9 parts water).  This locks the wood fibers.

1000 grit may be over kill - depending on your scale - and era.  If 1:96 or larger and pre - 1860 - 220 grit - 320 grit may be fine enough.

Grit finer than 320 is aimed at use on metals and plastic - and perhaps to buff a final clear coat.

 

Since your wood is a species of Walnut and there is a problem with open pores, a sanding sealer may be appropriate.  The problem with

Sand & Seal type products here in North America is that they are aimed at use on full size furniture made with open pore species like

Oak, Ash, Hickory, Walnut.  It is thick and it fills the often large pores.  This produces a smooth surface for clear finishes that follow it. 

It adds a noticeable layer to the surface.  This is not a desired factor at model scales.  The solution is to use closed pore, tight grained species of wood.

These do not need to be sealed.  Primers such as 50% cut shellac do an excellent job without adding a significant thickness on the surface

 

[Wahka_est]

3 minutes ago, Jaager said:

Wood fibers swelling upon the first exposure to water is a factor when using penetrating aqueous (water based) aniline dye also.

The fix is to treat the wood to a prior exposure to water alone, let the surface dry, then sand or scrape the swollen fibers smooth.

It works even better when the water treatment is a ~10% solution of PVA (1 part glue, 9 parts water).  This locks the wood fibers.

1000 grit may be over kill - depending on your scale - and era.  If 1:96 or larger and pre - 1860 - 220 grit - 320 grit may be fine enough.

Grit finer than 320 is aimed at use on metals and plastic - and perhaps to buff a final clear coat.

 

Since your wood is a species of Walnut and there is a problem with open pores, a sanding sealer may be appropriate.  The problem with

Sand & Seal type products here in North America is that they are aimed at use on full size furniture made with open pore species like

Oak, Ash, Hickory, Walnut.  It is thick and it fills the often large pores.  This produces a smooth surface for clear finishes that follow it. 

It adds a noticeable layer to the surface.  This is not a desired factor at model scales.  The solution is to use closed pore, tight grained species of wood.

These do not need to be sealed.  Primers such as 50% cut shellac do an excellent job without adding a significant thickness on the surface

 

So if i understand correctly to use sanding sealer or sellac before painting should do the work?

[Jaager]

Yes.   For the reasons stated in my editorial, I think shellac the better choice - but half strength for the first coat.   But, since I bend towards a belt and suspenders when it is important.  I would first paint the surface with water and sand again after it dries and then use the shellac.  Use a plastic pot scrubber pad on the dried shellac and tack rag before the paint.

[wefalck]

Try to find some nitrocellulose-based sanding sealer. Sand the wood, wet it, sand again (as previously mentioned by Jaager), let dry thoroughly and then apply the sanding sealer. Rather than using sandpaper, rub down the wood first with 000 steel wool and then with 0000. This gives you a nice surface without appreciably adding thickness, as you basically rub down to the wood and just leave the sealer in the open pore space. Such wood surface can be buffed to get a nice satin sheen, or indeed it can be spray-painted with any paint, preferably one that does not contain organic solvents, such as acrylics.

[Bob Cleek]

Shellac is one of the best water barriers available. It's sold pre-mixed in cans, usually at "two pound cut." The "cut" is how the dilution of the shellac flakes is indicated. "Two pound cut" means  "two pounds of shellac flakes to every gallon of alcohol." This is usually fine for sealing wood. It is the consistency of water and won't build up if a single heavy coat is applied. If you want to thin it, simply add more alcohol. The alcohol evaporates quickly. The shellac soaks into bare wood, permeating the surface and hardening it. Sand your wood smooth, shellac it, and when the shellac is dry, you can sand it again with fine sandpaper or buff it with steel wool, and it can easily be smoothed perfectly. Just don't sand so much that you remove the layer of wood on the surface which has been impregnated with the shellac. What raises the grain is the water soaking into the bare wood. Acrylic paints are water-based, generally, so they raise the grain when applied to unsealed wood. (Another reason why oil-based paints are generally preferred by those who know the difference between oil and water based paints.) Shellac is the only sealer you need. It's cheap. There are lots of products on the market sold as "sealers." There's no need to pay more for them. Anything can be applied over shellac. It's compatible with everything. It cleans up easily with alcohol.

[Wahka_est]

Thank you all for help. I will order shellac and try with that. 
Found one product called shellac here in Estoni also-lucky me.

[wefalck]

In Germany and France at least there are nitrocellulose- or shellac-based sanding sealers that are 'filled' with pumice dust. The idea is simplify and speed up the traditional process of 'french polishing', whereby the wood was 'sanded' with a pumice stone and then shellac was applied, which consolidated the pumice dust in the wood pores, thereby evening out the surface.

 

When you rub the wood down with steel-wool, it just takes away the excess sealer, but does not actually cut into the wood itself, as when you are using sandpaper. You immediately get a shiny and smooth surface without scratches. I have been using this process for at leat forty years now in furniture- and model-making.

 

BTW, shellac is not really water-proof, as anyone knows, who put a wet glass onto a french-polished piece of furniture. Alcoholic beverages obviously are even worse. However, when you spray-paint with acrylics, the water (and the alcohol, if your paint also uses alcohol as thinner) evaporates so quickly, that no harm is done.

[Wahka_est]

Shellac Sanding sealer primer 500ml transparent by Broma wachs

So i ordered this one. Hope it works.