MESSIS

Prepare wood for acrilyc paint

First time I need to paint my wooden model with paints. Am going to use the vallejo label, its water based... and I wonder if before painting and after fine sandpaper a varnish will help? Gloss or matt... thats maybe irrelevant because the paint will  cover the varnish  anyway. But is it really essential to use  before paint a varnish or even another acrylic clear paint? Or can I go ahead with painting after sanding and tha will do?

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Acrylic paints are water-based and will raise the wood-grain. So one would need to sand it again afterwards. Assuming that you are talking about a fully covering, opaque layer of paint, I would prepare the wood with a good solvent-based sanding filler, sand/scrape it smooth, and then apply the paint.

 

Solvent-based fillers are to be prefered over water-based (acrylic) fillers, because they penetrate the wood better.

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Thank you my friend... so varnish is not needed. The problem tough in my case is that I cant use easily solvent based filler because of my asthma.... ok if I must then I ll look for some safety mask etc. But I just thoght that a varnish will do...

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What kind of varnish are you talking about, acrylic-based ?

 

Even water-based acrylics may give off fumes, as they often contain some alcoohol. I believe there are also water-based acrylic sanding fillers. You may have to experiment with the wood you are working with. Something I haven't tried on wood myself, but that may give reasonably good penetration are pure acrylic emulsions, without pigment and and fillers. You can buy these in art-materials shops as primers. It may be also possible to dilute them with alcohol to further enhance the wood penetration, but this requires some experimentation.

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I was told by a modeller of AL that a nitrocellulose varnish can do the job... I dont know....I never tryed it and dont know about the fume

 

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I use only acrylics and specifically Badger Airbrush Co's Marine Paints - they have virtually no odor.  I doubt that you have access to this brand.  I often just airbrush a light coating of water onto the wood and when dry sand the raised wood.  If it was raised a lot - softer woods raise more than hard woods - I sometimes spray another coat and sand that when dry and then apply the acrylic paints.  Sometimes the model will not work well with sanding due to tight corners, etc and then I use a coat of shellac under the paint.  The shellac doesn't raise the grain and once it seals the wood there isn't any way that the acrylic will affect the wood.

Kurt

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Kurt very kind of you to help me. Very reasonable arguments/tips... tell me please what is shellac?

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Shellac is a very common finish for furniture and wood projects - it was used extensively here in the US until sturdier finishes became available and fine furniture makers still use it.  It is still easy to get here and to use.  The woodworking stores sell cans of ready to use shellac and they also sell the flakes so one can mix up a fresh batch and it can be made to different consistencies by adding more flake to the liquid.   If you buy any, get the smallest amount you can get as it doesn't have a real long shelf life once it's mixed but if the can is kept tightly closed I have used stuff that was 2 years old.

Here is a link to the Wikipedia definition https://en.wikipedia.org/wiki/Shellac

Hope this helped.

Kurt

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    I know the original topic was "Prepare wood for acrylic paint", not "Acrylic Paint", but I wanted to chime in regarding the use of artists acrylics (out of a tube).  While BADGER brand may not be available to you, I am sure artist acrylics are. 

 

    I used to use BADGER almost exclusively, then I read some of Chuck P.'s posts on painting in his CONFEDERACY or WINCHELSEA logs.  He uses many coats of highly diluted artist acrylics and comes up with a GREAT finish.  Since I am a fan of the more earthy colors that one might find in the1 700s, rather than the artificially bright colors of today, I find these paints give me a lot more flexibility.  I have at least 8 different hues of red.  YOWZA.  Anywho, just a thought.

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In North America we have nitrocellulose lacquer, which is solvent based.  Lacquers are fast drying, so the solvents are very strong (very volatile), so you will want to avoid it since you have asthma. 

Varnishes are technically resin and oil based, so there is no nitrocellulose in the mixture.  

Shellac flakes are dissolved in ethyl  alcohol and heated to make it liquid.  As Kurt mentioned, it can be purchased pre-mixed.  Shellac is the basis for French polishing, so you may be able to find it following that path.  It is also the traditional method for finishing musical instruments.

 

As a simple alternative, try diluting white glue with water.  Brush it on, let the mixture soak in for a few minutes and then wipe the excess off.  The water will raise the grain, so sand after it dries.

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I have used both acrylic-based and water-based sanding sealer, and I don't think there is much to choose between them in terms of performance.  However, it is much easier to clean brushes after the water-based sealer, so I tend to use that all the time now.

However, I do not sand the result when dry.  I use only medium grade wire wool, which leaves a much finer finish and does not blur sharp edges.  It also has the advantage that you use it in small throw-away bunches, so it never clogs.  A word of caution - it can burn spectacularly, so keep it away from flames.

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Caution - if you are using acrylics do not use common steel wool - a piece will inevitably be left behind someplace despite blowing off the dust and it will rust through your nice paint job.  Use a synthetic sanding pad like the 3M pads or similar.

Kurt

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Good point about water-based paints/sealers and steel wool. Some people use magnets to pick up the wire residues. There is also aluminium wool apparently, but I don't have come across a source for it yet.

Apart from the steel wool, I also use razor-blades as scrapers after applying sanding sealers, which gives a nice smooth finish too. It only works on flat surfaces though.

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On 3/14/2017 at 10:13 AM, MESSIS said:

Am going to use the vallejo label, its water based

Just keep in mind that some acrylics contain Cadmium, so wear a mask.

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Which ones ? To the best of my knowledge the respective red and yellow pigments have been phased out a long time ago, at least in the EU. The paints may have retained 'Cadmium' in their name though. Nothing really to worry about - a day out in a city gives you more exposure to nasty things ...

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49 minutes ago, wefalck said:

Which ones ? To the best of my knowledge the respective red and yellow pigments have been phased out a long time ago, at least in the EU. The paints may have retained 'Cadmium' in their name though. Nothing really to worry about - a day out in a city gives you more exposure to nasty things ...

Vallejo specifically, I know their latest range is cadmium free, but there might still be older stock around with cadmium in it. 

Anyway, it is only good practise to wear a respirator when airbrushing.

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Another good way is to do a mix of 50/50 white glue and water, give it a good stir and then brush a light coat over the part. Once dry use one of those washing up pads, the green ones are ok to gently rub down the part, then paint. No odurs, no mess. Just for info.... Most if not all paints now sold in the UK come under European safety rules, so there should be no nasties in any paint unless it is licensed for specialist use and then the operator would be trained as such.

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Messis, to answer your question about shellac,

 

"Shellac is a resin secreted by the female lac bug, on trees in the forests of India and Thailand. It is processed and sold as dry flakes and dissolved in ethanol to make liquid shellac, which is used as a brush-on colorant, food glaze and wood finish."

 

You probably know it by another name in your own language.

 

Steven

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