If it smells of vinegar as it cures, it is acetoxy. That smell is acetic acid, and it is a by-product of the cure — the sealant releases it while it goes off.
On a bathroom tile that does not matter. On a building facade it does.
Quick answers
Can acetoxy silicone be used on aluminium?
No. Acetoxy silicone releases acetic acid as it cures, which attacks anodised and coated aluminium, galvanised steel and masonry, and it bonds poorly to them. Use neutral cure.
How do I tell acetoxy from neutral cure silicone?
Smell it. A sharp vinegar smell means acetoxy. Neutral cure releases alcohol or oxime instead of acid.
Why is neutral cure slower to skin over?
That is the chemistry of the cure. Our weatherproofing grade is tack-free in about 2.5 hours, against well under an hour for a typical acetoxy.
What the acid does
Acetic acid attacks the materials a storefront is made of:
- Anodised and coated aluminium. The acid works at the coating and at the oxide layer under it. What you get is dulling, staining, and in time pitting at the bond line — usually after the job is signed off.
- Galvanised steel. The zinc reacts. The protection you paid for goes first, exactly where the sealant sits.
- Concrete, masonry and mortar. Alkaline surfaces and an acid cure make a poor bond, and the acid etches the substrate.
- Some mirror backings. A classic way to ruin a mirror wall.
Acetoxy also tends to give a weaker bond on those same surfaces, so you lose adhesion as well as finish.
What neutral cure does instead
Neutral cure silicone releases alcohol or oxime as it cures, not acid. It is non-corrosive to coated metal, it bonds better to masonry and to painted and anodised finishes, and it does not attack the substrate it is sitting on.
It is slower to skin over — our weatherproofing grade is tack-free in about 2.5 hours against well under an hour for a typical acetoxy — and it costs more to make. Both of those are the reason acetoxy still exists at the consumer end.
Which is why every sealant on this site is neutral cure
Not as a selling point. Because on the work our customers do, acetoxy is the wrong product:
- Seimeda neutral cure — general weatherproofing, case of 20
- Silande MF898 — architectural weatherproofing, five colours
- Silande MF899 — structural grade
- DOWSIL 795 — where the spec names it
How to check what is in the van
Open a tube and smell it. Sharp vinegar means acetoxy — keep it for glass-to-glass work where there is no metal and no masonry in the joint. Anything going against a frame, a panel or a wall should be neutral.
If you are not sure what a tube is, send us a photograph of the label and we will tell you.