Pond Shield primer is a bright what acrylic polyurethane base that can be used on a variety of surface types such as wood, concrete, brick, block, steel and other metals, and many more. Its primary function is to aid in filling small pit holes and such in rough surfaces like concrete. In doing so, this can eliminate many types of problems that occur with certain substrates such as outgassing (where unwanted bubbles for in the finished coating). Pond Shield Primer will displace the air in these tiny holes making it easier for you to apply Pond Shield nontoxic epoxy. Being bright white in color, Pond Shield Primer also allows you to even out the color of the substrate you plan to coat with Pond Shield nontoxic epoxy. If the surface area being worked on has varying shades of color due to things like prior patches or other attempted repair work, Pond Shield Primer can be sued to even up that color so the finished epoxy then cures out in one single shade.