Painting and Weathering Plaster Stonework

This painting tutorial is designed with the beginner in mind, but is intended for all.

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A quality paint-job is not that hard to do if you have the visual resources.

Observing the real world

The biggest help to accurately paint a plaster stone, or brick wall is by arming yourself with photographs of the wall you are trying to depict.  

As modelers we have a tendency to assume too much.  In real life stonewalls are not simply one color, but are a conglomeration of different earth tones that result in a mottled look.  This mottling is just natural color variations in the stone and can be fairly subtle and be of one dominant color, but with variations in shade.  This is what we like to refer to as the base coloring.  Base coloring is not a complete paint; gray, iron oxide brown, or burnt sienna.   The neutral gray is used in all of our wall painting, but the locale of the wall will determine what browns to use.  Varying between the gray and the browns two will cover most stone coloring requirements.  Specific stone colors will be dealt with in subsequent clinic pages.

Check out the reference picture page on our site for ideas.  Look at the stone coloring closely and you will see variations of grays and browns and even hints of green (from fungus).   Notice the weathering and staining and how wet areas look in real life.  We’ll expand on these areas and treatments farther down, but for right now we’ll concentrate on some more of the basics.

Let’s take a look at some examples to get a better idea of what some real walls look like.

Here’s a good example of a prototype New England wall that holds back the fill of a bridge approach.  The base of this retaining wall is sitting in a stream and is therefore wet most of the time.   Although the stones look to be gray at first glance they’re actually brown.  The gray is the result of lichen and the green tint is from moss and other fungus which thrives in moist conditions. 

The wall in thepicture above shows gray granite stone that is a mixture of a base of light gray and slight hints of brown with dark gray streaking.  The wall on the right (actually the backside of a wall) has a very light gray coloring on some stones, but has darker brown stones interspersed between.  The one big thing to notice of all three examples is that not one stone is simply one color.  Each one has varying shades within themselves and that’s the key to creating realistic looking stonework.

 Application

The following is the basis for all of our stone wall painting, although sealing and colors may be changed depending on what the modeler is trying to duplicate.  Steps to create a particular type of stone will be handled in separate clinics.

Our technique is a five step process

1. Sealing (sealing is dependent)
2. Base (sponge application)
3. Fill (independent stones)
4. Joint darkening or Ink wash
5. Specific treatment (weathering and natural staining)

Step 1.   To Seal or Not to Seal

This is not so much a step, but a technique that should be used for certain types of stone.  When we refer to sealing we mean only to dust the casting lightly with a clear polyurethane sealant.  You don’t want to coat the casting as if you were trying to paint it.   Sealing does two things.  1. It prevents the paint from being absorbed into all of the plaster at once, which helps create the mottled effect and it allows more time to work.  2. It seems to make the colors a bit more vibrant, depending on the base color. 

 This does not mean that we seal every time.  Sealing is dependent on what type of stone you are trying to replicate.  There is natural stone, sandstone for instance, that is best represented by not sealing thus giving the plaster a flat look.  Granite is actually varying degrees of black and white or pink and is best reproduced using the sealing technique.  The only problem is that walls are usually a mix of various stones, some that are best represented by sealing and others not.  The trick is to seal individual stones, which may or may not be worth the hassle.  The smaller the stones in the wall the less need for getting specific.  Save it for the O-scale diorama.

For example, we use it to create the look of light colored granite.

These are pictures of the back (smooth side) of a casting that was sealed (dusted) with clear polyurethane spray with a gray wash applied. Notice how nicely it creates the look of polished granite. The casting on the left is very close to real gray granite and by adding a small amount of iron oxide or russet to the wash the plaster begins to look like tan or pink granite (right).

Step 2.   The Base

Unless you are a glutton for punishment you don’t want to paint each stone individually.  This can produce great looking stone work, but it is way too time intensive for the average modeler. Also, in an attempt to be random the modeler has a tendency to make the wall look like a checkerboard.  Better and more natural results can be had using our techniques.

The Sponge

The sponge creates an effect similar the leopard spot method except that instead of painting individual stones with a brush we use a sponge and don't worry about individual stones at this point.  Sponges have the distinct advantage over a brush because they can carry a load of paint and apply it to a large area very quickly and the openings in the sponge leave blank areas on the castings that don’t get painted, this helps create varying shades of the color being applied by overlapping during subsequent applications.  These blank areas will eventually be filled in by applying the sponge over the casting a multitude of times, thus creating a mottled effect.  You want to use the sponge in a rolling motion to prevent “tiling” or repetitive patterns.  By varying the colors slightly during this step will help randomize the overall coloring of the wall.  See following photos.

The Rolling Technique used with a sponge for application.    We use a rolling movement to prevent tiling of the pattern, which is what would happen if you simply use the sponge like a stamp.  If you have to use the sponge like a stamp, apply light pressure and rotate the sponge after each application.  It doesn’t have to be much.  We just don’t want to create any repetitive patterns.  Also, not shown in these photos is that I usually cut a disk out of the rectangular kitchen sponge.  I then pick at the cut edge to remove any smooth scissor cut.  This is more of a precaution to help prevent obvious repetitive tiling.  BTW, don't throw the rest of the sponge that was cut away.  Those pieces can be used for getting into corners and tight spots.

Remember to rotate the casting to prevent “Tiling”.

The Sponge Roller

The modified sponge roller

This is pretty much the same as the previous technique except that instead of using a sponge a modified foam roller is used. 

Application

You will need a piece of sponge, or sponge roller, a small paint tray or similar and some earth tone paints.    Apply a pea size blob of base color  and add a tablespoon of water to thin it out.  Mix up the paint and water into a wash.  Watch out for blobs of pigment.  You don’t want heavy concentrations of paint on the casting.  It’s best to blot the sponge on a piece of paper, or on the backside of the casting first to make sure that this won’t happen.

Note: You will still need to individually fine tune the stones, but the majority of the casting’s coloring will be done by these quick application techniques.  See the next section.

Don’t be afraid to use a thinned sierra or red oxide at this stage, even if you are creating a gray granite wall.  The browns add a tad bit of contrast that breaks the wall up from looking like one color.    It is a detail in itself.  We’ve found that a light brown wash on random individual stones helps give the impression of quartzite rocks and/or dirt staining. 

Step 3.  Fill

The base step is used to establish the overall color of the wall.  This step helps create the look of individual stones.  The trick here is not to get too crazy.  You want to give the hint of separate stones, not create a checkerboard.  Be subtle.  You can always add on top if you start out with light colors. 

Granite schist and other metamorphic rock like gneiss along with veining can be created by using a wash with more pigment and some simple brush strokes.  Individual sedimentary (sandstone/brownstone) stones can be created by using a light to dark chocolate colored wash

The colors are not as apparent in these photos as they are in real life.  The stonework on the right hand side of the arch is gray base coloring with no fill work and was left this way to show the difference between the two.  Notice that the gray is not uniform, but is made-up of varying shades, or in this case, overlapping roller applications.  The stonework on the left has been touched up with light brown washes and some darker gray to individual stones.

Don’t forget to wrap the color around the stone when painting corner stones.  You don’t want to end up with two-tone stones.

Step 4. Joint darkening or Ink wash

Although it’s not necessary for you to use an ink wash on NE Brownstone’s walls due to their deep grout lines, it is recommended because of how well it helps bring out the colors and make the stonework stand out.  There is no special formula.  We simply place a dot of ink into our mixing tray; add some water (you can use alcohol) and mix it up a bit.  We use black drawing ink, but India ink works fine.  Beware that some inks will give a bluish tint when thinned.

Use a round (flame tip) brush to do the painting.  This type of brush is great because sucks up and holds a lot of paint eliminating the amount of times you need to reload. What you do here is to stick the tip of the brush down into the grout lines.  The wash will be drawn into the grooves by capillary action.  What little bit that slops over and onto the adjacent stones can be blended in and will add contrast within the individual stones.

Here’s a comparison of an inked and not inked casting.  The area to the left of center has not received any wash and is flat in color.  It is actually better looking in real life than what is shown here, but it still has a flat look to it.  The area to the right of center has received the wash and typifies the dramatic change that an ink wash can have on any stone wall.

Step 5.  Specific Treatment

 This section deals with the final details like weathering and staining.  The environment that the stones are in has a lot to do with this, so if you model arid regions (western USA) your stonework will be light in color.  If you model an area like New England, soot from years of steam locomotives and exhaust from automobiles mixed with rain will give stone a dark gray, streaky appearance.

Thinned washes of graphite paint will recreate the streaking rather nicely. 

Notice the color of the stone and the concentration of dark gray towards the bottom of the abutment pictured above.  The staining works its way higher up the abutment the closer it gets to the bridge girders.  Another detail you might like to add are the weeds at the bottom between the road and the bottom course of stones.   

There’s Fungus among us. 

Just like moss grows on the north side of a tree, so it does on a rock.  Stone walls near water or moisture will soon begin to grow moss and lichens, which as shown before will alter the final colors of any rock.  Green is often overlooked as a weathering color for stone, but it is quite evident once you know it’s there.   We’re not talking about painting the rocks with full strength green, only about light washes to give a hint of mold.  Paints like pale or celery green work great.  They dry light and give the impression of dry mold  Also notice the wet spots and how they are darker.  See how to create dark wet spots below.

Both of these walls have a slight hint of green due to mold growth.  Do not over do it. 

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  A darker black/green is perfect for depicting wet or moist mold and is especially useful in and around waterfalls and river scenes  Once it has dried you can paint on some clear polyurethane or a gloss medium to make it look wet.  Hint:  When creating  a waterfall or rapids scene it is a good idea to have contrasting wet and dry areas.  This will help convey the wet/dry look and feeling to the scene.  Please check out our reference picture page for more examples.

Chalks and weathering powders

If your wall looks a bit too dark, a light dusting of yellow or burnt sienna will lighten it up and give the wall a dry dusty look.   The key here is light dusting.  Be Subtle.

 Efflorescence

  Efflorescence is a white chalky  crystalline growth left over after water has leached out salts in the mortar and deposited them on the face of the wall.   Although we are talking about stone walls here it is a common affliction of brickwork, too.   This is an often overlooked detail that can improve a model stonewall quite nicely.    Here are a few pictures of some real walls.

Useful information

•Use light washes

•Use a modified paint roller for fast fill.

•Plaster stonework base coloring should look bone dry.  Flat.  Add “wet spots” later.

•Light brown wash on random individual stones helps give the impression of quartzite rocks. 

•If the stonework is “Dry Stacked” then use Alcohol/Ink (AI) stain after the main colors are employed.

•Wet is dark and dry is lighter in color.  

•Mosses and Fungi will grow in and on wet areas and on the north side.

•Wet slimy moss is a dark Green/Black (good for streams and waterfalls)

•Dry moss is a lighter brown or pale green

•Some stones can have a totally different color due to lichens and other moldy stuff growing on them. 

•Don’t be afraid to add gray.  Use stippling with light grays to create lichen growing on rocks

Tools

A medium sized round (flame tip) brush works great for applying washes to individual stones and for ink washes. You can get these in a variety pack from most craft stores.

Foam roller   You can get these at any home improvement center and will last you lifetime if you take care of them.

A lid from a margarine bowl can be used as a mixing palette for the washes.

Latex gloves to keep paint from staining your hands and fingers.

A can of flat clear polyurethane spray for sealing.  You can get this at any home improvement center.  It should also be used on top of your stonework once it is painted to help prevent unintentional paint removal.

A roll of Paper towels helps.  You can’t have enough of these.

Distilled water is recommended.  You don’t have to use it, but we do.

Appendix

Sublight- the opposite of highlight.  The use of another color, usually earth tone, that is applied during the base color application, which adds a subtle and natural contrast to the base color.  It is not used to bring out the casting’s detail.  It is a detail in itself.

Highlight- The use of lighter colors added after and on top of the base and fill coats to help build contrast and to emphasize detail.

Course- A continuous row of stones or bricks in a wall or abutment and is not a term used for random stacked walls.

Abutments

Standard  Walls

Dry Stacked Walls

Cut stone Strips

Viaducts and Culverts

Adapters

Brick