Here's what I used. I used the matte clear over the base color (primer) before spackling the mortar, then bombed matte clear over the spackle. This keeps too much of the color bleeding into the mortar and then preserves a bit more of the mortar color when doing the acrylic washes and final weathering. Hope that makes sense - it goes color, clear, spackle, clear, final wash, highlights, drybrushing, etc.
