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Water-based Paints and Finishes

Craftsman Tool Chest: 7
Applying Water-based Finishes to Your Models

By George Riley/photos by the author

The finish on any model will make or break that project. The type of paint and how it is applied is crucial to building an attractive and credible model. This choice is further complicated since most of our projects use more than one type of material in their construction therefore our choice of paint needs to be versatile and work on many media.

Historically solvent based paints, be they enamel, oil or lacquer types, have been used to good effect. However, these paints raised their own inherent safety issues due to their composition. The introduction of latex emulsion house paints in the late 1960s led to several ventures into water-based model and craft paints. While acceptable to the craft market, these products did not work well for the fine finishes required by modelers and tended to obscure the fine details on miniature models. In view of this, several formulas of water based paints for the model builder have been developed in the intervening years. While some worked well when brushed on, they had a propensity to clog air brushes. Others were easily airbrushed but proved to be unstable once opened having limited shelf lives.

Water-based Paints and Finishes

The recent discontinuation of one widely distributed and popular brand of water based model railroad paint has opened the door to a new line of color matched acrylic resin model paint distributed by MicroMark, a leading model builder’s supply outlet. Available in two ounce bottles under the MicroLux brand name or in one half ounce bottles under the Vallejo brand name, both come premixed for use in airbrushes directly from their containers. The line is color matched to the Floquil Polly Scale line of model paints.

Additionally, these paints can be brush applied directly from their bottles or thinned with water for use as washes with equally good results. The colors remain stable even when thinned and when applied directly from their containers have excellent opacity. Brush or airbrush touch ups yield excellent results with the touch up layer leveling to blend seamlessly with the base coat.

To put production samples of the paint to the test on a number of different materials they were used to finish a church and grave yard modeling project for an O scale traction layout. A laser cut BTS Rural Church consisting of basswood, thin plywood, strip-wood and card stock is the focal piece of the project. In addition to the wood and card parts the kit also features several die-cast metal and resin parts. The vault and grave stones are from a BCH injection molded plastic O scale Grave Yard Kit. Monster Model’s laser etched laser board concrete pavement sheets provide the walkways and sidewalks. The basic landscaping consists of dirt and static grass held in place with dilute white glue.

Preparation began with applying sanding sealer to the wooden parts of the church kit. This is my normal procedure for laser kit construction whether using solvent or water based paints. While these parts dried all of the resin, metal and plastic parts were washed in detergent to remove any mold release or oils that would prevent paint from adhering properly.

Once the wood pieces were dried and burnished with 0000 steel wool, they were painted either white or the dark green trim color prior to being assembled. To test the paint no primer was used on any of the parts and the paint applied with an airbrush directly onto each individual piece. My most finicky double action internal mix airbrush was chosen for this test. The air pressure was set to ten psi and the paint was applied smoothly without any incident. Due to the covering ability of finely ground pigments a surprisingly small amount of paint was needed. Even the white paint covered completely and was opaque in one light coat on the unprimed wood and set ‘dry to the touch’ in less than an hour. In addition none of the parts warped as is sometime the case when using water based paint on even sealed wood. The parts were allowed to cure overnight to complete a hard finish. Unlike solvent based paints, most water based model paints do not technically ‘dry’ but are cured upon exposure to air. With the wood parts painted, the plastic, resin and metal parts were painted in appropriate colors and set aside to completely cure overnight before assembly began.

Water-based Paints and Finishes

Since the paint sets very quickly once applied it is best to clean your airbrush at once. One tip shared on the MicroLux website is to have a tub of water handy to clean out the airbrush immediately once either painting is complete or when colors are changed. I found that a deli-tub with lid holding water with a drop or two of dishwashing liquid works well for a quick clean up and as well as for thinning the paint.

The church model was assembled per instructions and the roof lightly shaded with a mixture of roof brown and water thinned half paint, half water. This shadow color was airbrushed at five psi along the joints in the ‘tar paper’ roofing as well as adding weathering streaks to the roof. The resin ‘brick’ foundation piers were given a wash of concrete and water with a paint brush to high light the mortar joints.

Next the vault and grave stones were airbrushed with several blended colors of gray before being shaded with dark grays and roof brown washes. These washes were applied with an airbrush set at five psi. The last step before placing the models on their plywood base was to finish the walkways. These are a laser engraved resin impregnated paper product available from Monster Model Works. Once cut to shape a wash of engine black thinned with water was brushed over the walkways and allowed to dry overnight. The black will settle into the cracks and textures to highlight these features. The process was completed by drybrushing aged concrete over the surfaces of the walkways. Several of the grave stones were dry-brushed with this same color as well.

As one can see in the photo of the finished Church yard vignette, the paint work met the standards for a quality finish yielding an attractive finished model. The MicroLux and Vallejo acrylic resin paints proved easy to use and apply while offering a superior finish when applied with either an airbrush, by paint brush, dry brushed or as a wash. The colors match those long used by model railroaders while providing an opaque and colorfast finish to most any paintable modeling material.

MicroLux and Vallejo water-based paints and finishes and other useful model building tools are available from Micro-Mark.

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