The gaps are caulked; this caulking normally needs to be renewed annually. These low molecular weight polyisobutylene polymers are used for caulking and as sealants. Polyurethane is the basis for some construction adhesives in a caulking tube format. Alternatively, ziram is used as an additive ingredient in industrial adhesives, caulking, and paint. The Chumash used the tar and oil from these seeps for caulking and adhesives. Originally done by hand much like wooden vessel caulking, pneumatic tools were later employed. However, Knox-Johnston had managed a good repair by diving and caulking the seams underwater. The Caulker maintained and repaired the caulking of the ship's hull. On average lasts longer than the more common acrylic latex caulking. Modern caulking materials are not ideal mediums of repair. Modern caulking materials are used for caulking in replacement glass. With the advent of electric-arc welding for ship construction, steel ship caulking was rendered obsolete. The use of window screening and caulking to prevent entry is a good structural tactic. Rosin has been used for centuries for caulking ships. A two-hour-rated pipe-penetration firestop may consist of a layer of caulking over packed rockwool.