Which gaskets are you talking about specifically? If you're talking about the gaskets that are part of the carburetor itself, they should be paper-thin. However, the base gasket (which goes between the carburetor base and the intake or EGR spacer plate) should be about a quarter-inch thick. The gasket that goes in between the EGR spacer plate (if equipped) and intake should be a thick steel-woven gasket, which should be replaced at this time too. The first gasket sometimes comes in the kit, sometimes not - the second gasket never comes in the kit. However, some kits include paper-thin base gaskets; these should never be used.

No sealant of any kind should be used on carburetor gaskets.