Everbuild acoustic sealant amp adhesive ac50 everbuild ac50c4 ac50 acoustic sealant amp adhesive is a high strength permanently flexible sealant and adhesive specifically formulated for sealing and bonding plasterboard and other kraft lined insulation boards typically used for walls ceilings and dry lining applications independently tested to bs en iso 1403 everbuild ac50c4 acoustic sealant amp adhesive c4 ac50