Every sealant job starts the same way — with the surface it's going onto. Get that right, and everything else follows. Miss it, and even the best product in the range won't perform the way it should.
The good news is that proper preparation isn't complicated. But it does need to be deliberate. A quick wipe and a visual check aren't enough. Different substrates have different traps, and knowing what to look for on each one makes the difference between a seal that lasts and one that lets go long before it should.
Hidden contamination
A surface can look perfectly clean and still be working against you. Dust, soap residue, grease, cutting oils, polishes and traces of old sealant can all sit invisibly on a substrate and prevent a new bead from getting a proper grip. Even a small amount of contamination creates weak spots, and those weak spots are almost always where cracking or peeling starts.
The fix is straightforward: clean the surface properly with an appropriate solvent or degreaser, and make sure it's fully dry before the bead goes in. A wipe with a damp cloth isn't degreasing. It moves contamination around more than it removes it.
Old sealant and leftover films
Old silicone is one of the most common causes of poor adhesion, and it's one of the most underestimated. A thin, almost invisible film of old silicone left on a frame or substrate is enough to prevent a new bead from bonding to the actual material. The new bead bonds to the old film instead, and when that lifts, everything goes with it.
Removal needs to be thorough. That means a proper silicone remover or a careful mechanical clean, not just cutting away the bulk and assuming the rest will be fine. Run your finger along the surface afterwards. If it feels waxy or slick, there's still residue present.
The same applies to paint and coatings. Freshly painted timber where the paint isn't fully cured, or a surface with a failing topcoat, will cause the same problem. The bead bonds to the coating, not the substrate beneath it.
Getting it right on different surfaces
Different substrates have their own quirks, and knowing them saves time on site.
Timber is one of the more demanding surfaces to seal against. It's porous, it moves with moisture and temperature changes, and it can hold hidden damp even when it feels dry to the touch. Always check that timber is fully dry before sealing. Damp timber that's sealed in will continue to move as it dries, breaking the bond from the inside. Any loose or flaking paint should be removed before the bead goes in.
PVC and uPVC frames are smooth and non-porous, which sounds straightforward, but they're often coated with a release agent or polish from manufacture or cleaning, and that will prevent adhesion. Wipe down with an appropriate cleaner before sealing and avoid silicone-based cleaning sprays near any joint you're about to seal.
Metal surfaces, like aluminium, steel or galvanised sections, can carry surface oxidation, machining oils or coatings that interfere with the bond. A clean with a suitable solvent is usually enough, but it's worth checking the condition of the surface carefully. Powdery or flaking oxidation needs to be removed mechanically before any sealant goes on.
Masonry and concrete are porous and can hold moisture below a dry-looking surface, particularly in cooler or damp conditions. The surface also needs to be sound. Loose render, friable concrete or a dusty surface will all cause adhesion loss. Brush off any loose material and make sure the substrate is genuinely dry before you start.
A quick prep checklist
- Remove all traces of old silicone — bulk and film
- Degrease properly, not just a surface wipe
- Check paint and coatings are sound and fully cured
- Confirm the surface is genuinely dry, not just dry-looking
- Remove any loose, flaking or powdery material from masonry
Every sealant in the EVO-STIK range works best on a substrate that's clean, sound, dry and free of anything that might interfere with adhesion. The prep takes a few extra minutes, but it's the part of the job that determines whether the bead is still performing in years to come.
That said, if conditions aren't ideal, products like EVO-STIK Sticks Like Sh*t Waterproof Sealant are formulated to handle the unexpected — curing reliably even when the weather doesn't cooperate.