Harbor Freight sold these welding units for years. Most important is the removal of the slick finish from plastics extrusion or mold release glazes,roughen the surfaces and clean with a non residual cleaner like alcohol for best results. Old keene wax impregnated rough surfaced yellow pontoons don't hold good at all. Wax impregnation ruins the adhesion but many others good to go. Black pitch like sealent sold on rolls for underground sealent for pipes,cables and such works great and nuttn' to buy but it. Same same as above to prepare,cut a patch 2" bigger than hole/crack lay down with no air bubbles. Take a can,push hard and roll a few times to conform to hole. Leave in the sun for a few hours to soften the patch or at home use the wifes/shackup hairdryer to soften,roll again and good to go for many MANY years. Underwater or out don't matter and sticks great to old school wax marlex pontoons. The only boonie fix there is with no electricity-John