A Slick Coat is a “grease” coat applied to a surface in preparation for a glaze application. The purpose of greasing the surface is to allow the next layer to be moved and manipulate easier and stay open longer. It is a clear solution and usually applied with a roller, sponge, mist spray, or rag. A water-based slick coat would only be used if the following layer is an acrylic glaze.
(If using oil glaze on the following layer, a slick coat of 50% linseed oil, 50% turpentine, and a touch of Japan drier is applied)
When the previous coat is absorbent, the water-based glaze in the next layer will be sucked up at a faster rate than a non-absorbent surface. Some absorbent surfaces are: flat or satin paint, applied textures, plaster, canvas, or raw wood (when staining over a light wood, use a stain conditioner as a slick coat).
How to test if your surface is absorbent? First, know the surface material. Then, wet a sponge and wipe an area. If the color of the substrate turns lighter or darker or changes colors once the water has evaporated, you know there is a transfer of moisture.
So imagine what happens when you cover a chalky surface with a glaze — it dries at an increased speed and therefore you have a shorter window of open time for a decorative finish. Lap marks and difficulty of maniputations are signs of an absorbent base surface.
A slick coat for water applications could consist of 100% water (perhaps misted or sponged onto the surface). More often, 2 parts water to 1 part glazing medium creates a slick coat that will not only fight the absorption rate but nourish the surface.
The downside of using slick coat is that it’s an extra step. Also, the curing time could be extended and prevent a quick finish of the final steps.
Most commonly, a slick coat is used on large or sensitive surfaces. However, as seen in previous post (Red Griotte part 1), a slick coat was used in the activation step of a faux marble.
Adding a greasy slick coat before a veining step (with crystallization) can allow for better blending into the previous step.