What is the best sealant for a metal roof?
Short answer. The best metal roof sealants are butyl tape for hidden panel laps and closures, and polyurethane or hybrid polymer sealants rated for metal for exposed joints and flashing. Avoid asphalt roof cement, which cracks as metal moves, and avoid vinegar smelling acid cure silicone, which can harm metal finishes.
Match the sealant to the job
- Panel side laps and end laps: butyl tape or butyl sealant placed in the lap before fastening. It stays tacky and flexible inside the joint for years.
- Exposed flashing joints and penetrations: polyurethane or hybrid polymer sealants labeled for metal roofing. They bond well, flex with movement and can often be painted.
- Silicone: use only neutral cure types rated for metal. Most other products will not stick to cured silicone later, which complicates future repairs.
- Pipe penetrations: a flexible pipe flashing boot made for metal roofs, sealed and fastened per its instructions, rather than a blob of sealant.
What to avoid
- Asphalt roof cement: stiff, cracks with thermal movement, and makes later repairs messy.
- Acid cure silicone: releases acetic acid while curing, which can attack some metal coatings.
- Sealant over dirt or chalky paint: clean and prime per the product's instructions, or it will peel.
Sealant is not a fastener fix
Most leaks on exposed fastener roofs come from screws that backed out or washers that dried and cracked. Smearing sealant over them is temporary. The lasting fix is replacing the fastener with a new one, often a size larger, with a fresh sealing washer, driven snug but not crushed.
Expect maintenance
Even good sealants weather in Georgia sun. Inspect exposed sealant joints every couple of years and after storms. See metal roofing in Georgia and roof flashing explained.