First, step is to know the surface material.  Test the absorbency of your surface area using a wet sponge and wipe off 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.  A chalky surface is difficult to work with and will need a slick coat applied prior to your glaze.  Mix and apply your slick coat in the manner below.

FOR WATER-BASED MEDIUMS:  A slick coat for water applications could consist of 100% water (perhaps misted or sponged onto the surface).   More often though it’s 2 parts water to 1 part Glazing Medium that will create a slick coat that will not only fight the absorption rate but nourish the surface.

Mix and apply your slick coat using a roller, sponge, mist spray, or rag.  It is important to note that a water-based slick coat should only be used if the next layer is an acrylic Glazing Medium.  

After applying the slick coat above, the water-based glazing medium in the next layer will be absorbed by the surface below at a slower rate.

FOR OIL-BASED MEDIUMS:  If using oil glazing medium on the next layer, a slick coat of 50% linseed oil, 50% turpentine, and a touch of Japan drier is applied.