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BobG, a rule of thumb would be: sanding sealer on wood, primer on other materials (if needed). Sanding sealer is almost always (except for some very dense and hard woods) required. For primers it depends on the material and what you are doing with the part afterwards. Parts that are to be handled afterwards (as in working model) probably need priming, but for a small-scale show-case model I would rather not do it, because priming may flood details. To some metals (e.g. brass and copper) aqueous paints in particular do not stick very well, because they form a slightly hydrophobic oxide layer very quickly. Here priming may be really needed. The same may apply to plastics, particular, when one brush-paints. I normally air-brush plastics without priming and have no problems with that. I also air-brush brass and copper without priming and it works very well. However, I found it quite a challenge to brush-paint with acrylics on these materials.

 

For me the base coat of paint kind of acts like a primer before applying washes, wheathering and dry-brushing techniques. Acrylics stick well on acrylics. So once the first layer(s) are on, it is easy to put in the details with a brush.

 

As an example, this resin hull with brass and steel parts was first spray painted with acrylics and then finished off with washes in acrylics:

 

https://www.maritima-et-mechanika.org/maritime/models/botter/BotterModel/BotterModel-080.jpg

https://www.maritima-et-mechanika.org/maritime/models/botter/BotterModel/BotterModel-088.jpg

 

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11 hours ago, vaddoc said:

Between various coats it was wiped with isopropyl alcohol.

After "rough dusting," generally with compressed air, I use a tack cloth to remove all residual dust immediately before applying finish coats. 

 

  • Tack_cloth.jpg
     
    (Wow! I didn't expect a picture this big! :D 
     
    Tack cloths are cheesecloth impregnated with a long-lasting "tacky" coating. Dust sticks to them, rather than simply being "moved around" by other dusting methods. They are designed to remove all residual dust before painting finely finished surfaces. They are sold at paint and hardware stores and are inexpensive "consumables." If one folds the cloth to expose a clean square of the surface when a previously exposed square surface becomes full of dust and no longer tacky, a considerable area can be cleaned with them. They will dry out if left exposed to the air for long periods of time. Storing them in a zip-lock plastic bag will keep them tacky for a long while. There is nothing as effective for dusting surfaces prior to finish coating. 
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On 1/14/2020 at 11:39 PM, vaddoc said:

In the past I ve used a lot of humbrol or automotive primer (not good) but for wooden models is really not needed most of the time. There is no problem with adhesion and to smooth imperfections, a filler is needed. It might be useful if the colour of the underlying surface needs to change dramatically, for a large red surface applying a red or grey primer will reduce the number of coats needed. But since you can add 4 coats in an hour with acrylics, maybe not worth the cost and trouble. I usually sand away the primer leaving a thin smooth film. Never tried the Valejo primers, I ve been using the Humbrol white and grey spry can primers which I think are good but will not fill in imperfections. 

 

I like using sanding sealer as it seals the wood leaving a very smooth surface so the paint later does not soak into the wood and does not raise the grain. Painting on sealed wood is a better experience than painting raw sanded wood. I very much like the decoart/Americana water based sealer, the large bottle should last a very long time and has a very long self life. Dries in 15 min, sands very nicely. This sealer sits on top of the wood, filling the valleys and essentially levelling the surface. I usually sand the wood to 400 grit, apply a coat, sand smooth with 400 grit and repeat with a second coat. The surface should reflect light afterwards and be smooth  and slippery. No worries, the paint will adhere very nicely.

 

Never tried weathering, on my to do list!

 

Do not dismiss enamels completely, they are wonderful. Low odour mineral spirit will allow you to paint in the house but cleaning the brushes is a pain, it takes a long time to dry so attracts dust and if you leave everything on the table waiting to add another coat in 6 hours, you will inevitably spill the mineral spirit on the table/floor and the admiral will not be impressed and will ban indoor modelling activities. Much easier to use acrylics...

I searched online for the Decoart Americana Sealer and found several. Are you using the Decoart Multipurpose Sealer that you brush on? If you have a photo of what you are using that would be great. Thanks!

 

Bob

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  • 3 weeks later...
4 minutes ago, Moab said:

I’m not an expert painter. I use thinned acrylics and brushes. The info from Vaddoc has been VERY HELPFUL. I think I may over thin the paint but I’m finally getting very good results. It takes several extra coats (5-6) but the results are great...Moab

The information on this thread helped me a lot with my painting on my current Medway Longboat build. I tested 4 different shades of Vallejo red and decided I liked the color of the Vallejo Model Air RLM23 paint which is formulated for airbrushes but I brushed it on and still got good results. It comes out of the bottle a lot thinner than the regular Vallejo Model Color paint but, even so, I thinned it a bit more. I must have put 20 coats on the cap rail and cockpit seats. I just kept adding coats until I was pleased with it. The challenge for me was being able to keep a wet edge so I didn't end up with noticeable lap marks since the acrylics dry so fast. The advantage of the fast drying time though was that I could add another coat after about 15-20 minutes. 

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Just now, BobG said:

The challenge for me was being able to keep a wet edge so I didn't end up with noticeable lap marks since the acrylics dry so fast. The advantage of the fast drying time though was that I could add another coat after about 15-20 minutes. 

I often use retarder when brushing on acrylic paints to slow down the drying time and avoid lap marks. This is particularly true of Tamiya acrylic paints which have a tendency to dry very quickly and are difficult to brush on because of that.

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21 minutes ago, CDW said:

I often use retarder when brushing on acrylic paints to slow down the drying time and avoid lap marks. This is particularly true of Tamiya acrylic paints which have a tendency to dry very quickly and are difficult to brush on because of that.

I picked up some Vallejo Retarder recently but haven't tried it yet. I'll have to test it out soon.

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While we are on the subject of acrylics I have some questions about obtaining a high gloss finish with acrylics. I prefer using only water-based paints because I hate the fumes that oil based paints give off and like the satin or flat finish that I get with acrylics but how do you go about getting a high gloss finish using acrylics? Also, since high gloss finishes expose the tiniest defects in the surface, what are the steps you take in preparing the surface to be painted for a high gloss finish?

 

The Pen Duick by Artesania Latina and the Venetian Gondola by Amati are two models I have in my stash that will require a high gloss finish. My wife gave me a complete Grex airbrush set for Christmas but I haven't begun learning to use it. I would assume that airbrushing would be the best application method for obtaining a high gloss finish but I also think that the surface preparation will need to be free of the smallest defects and 100% smooth to be successful. I used a rattle can on my Indian Canoe model to spray gloss green but I hate the spitting globs that you can often get from rattle cans. When that happens I have to prime and sand again and then hope the rattle can doesn't spit any globs again.

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Well, a good paint surface begins with the preparation of the surface you are painting. You are right, gloss paints are much less forgiving than flat paints. So sanding, filling, sanding, ... and finally fine steel-wool until you have an almost polished surface that is also geometrically correct.

 

Most acrylics dry up quite flat, which is due to the pigment-content and sometimes also fillers and matting agents. There are acrylic gloss varnishes that you can spray all over. Some manufacturers also have pure acrylic emulsions, without any pigment or filler, which dry up to a gloss.

 

Gloss surfaces, such as those on the gondola, are normally produced in a somewhat lengthy procedure of applying lacquer to the surface, rubbing it down and repeating this several times. This is something that is difficult to do with acrylic paints or varnishes, because they do not harden sufficiently to allow this rubbing down e.g. with steel-wool. It is, however, possible to apply say nitrocellulose-based varnishes to surfaces painted with acrylics. The varnish then can be rubbed down, more varnish applied, rubbed down with steel-wool and then polished with a polishing compound and a mop or polishing wool (automotive suppliers).

 

You may also want to have a look on the Internet at the processes used by those doing decorative painting on cars or motorbikes.

 

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Acrylic paint is not tough at all and needs some protective finish. Humbrol gloss varnish is great and can be brushed (on cured acrylics also) with great results but is enamel based. 

A few years ago I tried Valejo water based acrylic varnishes but could not make them work. At the time I also tried the Valejo polyurethane varnish which I did not like. However, I tried the newer Valejo polyurethane varnish which are different and improved and this time I had very good results with a brush. I could not find any info though whether it should be diluted and what with. I think in the end my conclusion was to use water but not too much otherwise it breaks down. Application is the same as the paint but the self levelling properties are even better than the acrylic paint! I think 2 coats 4 hours apart or something similar. I also think they claim it will not yellow over time. The matt varnish needs very thorough stirring and quick application afterwards with minimal brushing and even then the matt particles might spread unevenly leaving brush-like marks. 

Still, enamel varnishes are much tougher

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9 hours ago, BobG said:

Vaddoc, do you apply a protective finish to everything you paint with acrylics

I do Bob, but my models are large and do not live in a case but are temporarily-permanently stored wherever there is space and are moved. I know, not good, in good time this will change. Also, the hull is the first to make and paint and then on it will take years to finish the rest so the hull will have a hard life tilting, scratching and bumping all over the place. I have an old model that had the hardest of lives, spent his life in shelves under direct sunlight constantly falling of its flimsy base, hull is 0.8 mm plywood with automotive primer, humbrol acrylic spray and humbrol enamel varnish on top. Still looks good!

 

1 hour ago, Moab said:

If I’m using acrylic paint are there any recipes for thinning (eg. paint, water, retarder) or is it basically trying various options...Moab

I d say Moab, just use the thinner the company offers. Cheap and much better than homemade ones or pure water. 

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  • 8 months later...

One problem I find with acrylics is that because they dry fast they stay on top of the wood and the paint tend to ship out.

I have solved the problem by mixing the acrylic paint with water-based wood stain conditioner.

The mixture penetrates the wood in the first coat and never ship, the paint becomes fluid and much easier to apply with a brush, the time to dry is extended by 2 or 3 fold depending on the amount of wood conditioner.  A on part acrylic, three part conditioner will require 5 coats to paint (recommended by Chuck) and will leave a finish that will last.  

The only inconvenient is that the wood conditioner adds a little shine to the finish but I correct this with a translucent matte finish over the paint.

hope this help,

G

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