What to know
Acrylic and water-based mastic
Thick, paste-like, applied with a brush or a gloved hand. They cure into a flexible seal that moves with the ductwork and bond well to the galvanised metal and duct board most systems are built from.
They clean up with water before curing, which matters more than it sounds when work is happening inside somebody's house.
Silicone
Cures to a rubbery, waterproof finish and copes well with movement and temperature swings. It is excellent at what it is designed for.
The trade-offs are that it bonds poorly to some surfaces unless they are properly prepared, it is difficult to apply neatly over a wide seam, and very little will stick to it afterwards, which limits repairs and coatings later.
Why most duct sealing uses the acrylic family
- It bonds reliably to the materials duct systems are actually made of.
- It can be worked into irregular shapes and wide seams, which tape and cartridge sealants cannot.
- It stays flexible as the ductwork expands and contracts.
- It can be inspected easily, because you can see where it was applied.
What matters more than the chemistry
Preparation and coverage. A good sealant applied to a dusty joint, or applied only where somebody could easily reach, will fail before a lesser product applied properly.
It is worth asking how joints are prepared and how the work is checked, rather than which brand is in the bucket.
One thing to be clear on
Sealant closes gaps at joints. It does not hold a duct together. A run that has come apart needs mechanically reconnecting first, and any company treating sealant as the fix for that is storing up a return visit.
Where to start
Which of these applies to your house is not something a page can tell you. It depends on how the ducts were built, what has been done since, and how much of the system is reachable.
Our inspection is free. We will show you what we find, and if the ductwork is sound and simply needs cleaning, that is what we will say.