Two main families of sealants dominate residential and commercial jobs today: silicone and polyurethane. To the eye, a fresh bead looks similar — but the chemistry, the way to apply and the lifespan differ substantially. Picking the wrong product on a given joint means a redo in 2 or 3 years. Here's the clear comparison, alongside our step-by-step application guide.
Silicone in short
Silicone is a mineral-based sealant. It stays flexible throughout its lifespan, resists UV, water and temperature swings very well. It's the go-to for anything glazed, wet, or sun-exposed.
Strengths
- Excellent UV resistance — doesn't yellow or degrade under sun.
- Long-lasting flexibility — stays elastic 15 to 20 years in good conditions.
- Adheres well to glass, ceramic and non-porous metals.
- Mold-resistant in bathroom-grade formulations.
Limitations
- Cannot be painted. A silicone bead stays visible as-is — no color matching to the frame.
- Limited adhesion on porous surfaces (bare wood, untreated brick) without a specific primer.
- Acetic acid smell during curing (so-called "acid" versions).
Polyurethane in short
Polyurethane is an organic-based sealant. It bonds to nearly anything, paints without issue, and absorbs structural movement very well. It's the default choice for exterior joints between different materials (brick-to-frame, frame-to-cladding, etc.).
Strengths
- Excellent multi-material adhesion — wood, concrete, brick, aluminum, PVC.
- Paintable — visually blends into the envelope.
- High movement capability — absorbs the building's expansion-contraction cycles.
- Mechanical resistance higher than silicone (abrasion, impact).
Limitations
- Sensitive to prolonged direct UV — on unpainted south-facing exposure, lifespan can be reduced.
- Poor adhesion on bare glass. It's the wrong product for a glass joint.
- Longer curing time before being fully functional.
Which product for which joint?
Windows and doors (interior and exterior)
For the joint between frame and glass: silicone, no question. For the joint between frame and exterior envelope (brick, cladding, stucco): polyurethane, often painted afterwards to match the frame for a clean finish.
Expansion joints (masonry, slabs, façade)
Polyurethane — its ability to absorb movement without tearing is decisive on these joints, which constantly move with Quebec's freeze-thaw cycles.
Bathroom, kitchen, plumbing
Bathroom-grade silicone, which includes a fungicide and prevents mold growth in wet areas.
Joints to be painted
Always polyurethane (or a quality acrylic for low-movement interior joints). Silicone doesn't paint well — paint doesn't 'grip' and eventually flakes off.
What matters more than the product itself
The lifespan of a caulking joint varies with the product used, surface preparation, exposure and installation conditions. Full old-sealant removal, cleaning, drying and compliance with application conditions are therefore essential. See our article on real caulking lifespan.
Our crews pick the product based on substrate and exposure, never "by default." On a full exterior job in Montreal or Greater Montreal, it's not unusual to use three different products on a single site. Why this matters — 8 reasons to replace old exterior caulking.
Bottom line
- Silicone: glass, wet rooms, direct UV exposure, no paint needed.
- Polyurethane: multi-material exterior joints, expansion joints, joints to be painted.
- In every case: full old-sealant removal, respect for weather conditions, application at the right thickness.
Not sure which product fits your case? All practical terms (products used, warranty, pricing) live in our FAQ, or on our caulking service page.