Short answer
Acetoxy silicone releases acetic acid as it cures, so it smells of vinegar and can attack some metals, natural stone and uPVC. Neutral-cure silicone releases no acid, so it's the safer choice on mixed or sensitive surfaces. In our range, MP and 802 are acetoxy; AF and N are neutral cure.
Both types cure by reacting with moisture in the air. The difference is what they give off while they do it, and that decides which surfaces they can go on.
Acetoxy: fast, strong on glass, limited elsewhere
Acetoxy silicone bonds very well to glass, glazed ceramic, aluminium and other non-porous surfaces, and it cures quickly. The acid it releases is the catch.
Pereseal 802 is our acetoxy glazing silicone. It is certified to ASTM C920 Class 25, with ±25% movement, for glass and metal glazing, curtain wall, skylights and sheet metal. It is not for marble, quartzite or natural stone, not for structural glazing, and the acid may corrode susceptible metals.
Pereseal MP is our general-purpose acetoxy silicone. It skins in about 7 minutes. It isn't for uPVC, and copper and lead may be attacked.
Neutral cure: the safer choice on mixed surfaces
Neutral-cure silicone releases no acid. It's non-corrosive to metals and alkaline surfaces such as concrete, and it has only a mild smell, which matters in an occupied room.
Pereseal N is our weatherproof neutral silicone for windows, masonry, concrete, stone, aluminium, most plastics and roofing joints. It takes ±30% movement. Pereseal AF is the neutral-cure silicone for bathrooms and kitchens, with a fungicide added.
Neutral isn't universal either. The AF and N data sheets exclude paint coatings, copper, and polycarbonate or acrylic sheet under tension.
The smell
The vinegar smell of acetoxy silicone is strongest while it cures and fades once it has cured. In a small bathroom or a closed room, ventilate while you work, or use a neutral-cure product. Smell tells you the cure type, not the quality: a sharp smell doesn't mean a stronger seal.
Choosing between them
Start with the two surfaces. If either one is natural stone, uPVC, copper, lead or a sensitive metal, use neutral cure. If both are glass, glazed tile or aluminium, acetoxy works well and cures fast. Then pick for the job: weather, wet area, glazing or general sealing. For the wider choice between sealant families, see acrylic vs silicone.
Which Pereseal silicone
Glass and aluminium glazing, skylights, sheet metal
Pereseal 802, acetoxy, ASTM C920 Class 25.
General sealing on glass, tile and other non-porous surfaces
Pereseal MP, acetoxy. Not for uPVC.
Windows, uPVC, concrete, stone, exterior joints
Pereseal N, neutral cure, ±30% movement.
Baths, showers, basins and sinks
Pereseal AF, neutral cure with fungicide.
Not sure which silicone?
Tell us the two surfaces and whether the joint is inside, outside or in a wet area. We'll tell you which Pereseal to use.
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