On a copper gasket , you seal them with the copper gasket spray, Permatex Hitack spray or I even know folks that use silver paint. On the composite gaskets they can go on dry, but the racer in me won't let me do that, because when the composite gaskets are put on dry they stick to head and block so hard, if and when you change it you would have to scrape the gasket off with a putty knife, so I use Hi Tack on them as well, its really not needed, unless you need o take the gasket back off easliy (which racers do). Bottom line the copper or metal gaskets (like Cometic) need a sealer, the composite gaskets do not, but if you choose to use one, it will seal fine. Hey, if it works for me on 15 to 1 race engine it should work on a street motor. We started coating composite head gaskets years ago on the 1275 race cars when we were using the Metro Turbo head gaskets, they were like almost $200 a piece, and could be reused atleast 3 times, if you could keep the composite material from sticking to the head when you disassembled. It was a pretty common practice among the SCCA FP and GT5 guys because the cost and availabilty issues with the Metro turbo head gasket