When using ProGlas 1000, most of the time, a seal coat will be needed. A seal coat will seal in the air pockets that exist in the substrate. The reason this is necessary is that when you apply a flood coat, the heat generated by the epoxy resin will cause the air in the pores of the wood (or substrate) to expand. Simple chemistry. By applying a thin seal coat, the epoxy does not generate the heat that causes the air to expand. Once the seal coat has hardened, the flood coat can be applied without the worry of air bubble forming on the substrates surface.