Properly installed, a DOWSIL CWS joint lasts a very long time, far longer than a latex or acrylic sealant. The manufacturer does not publish a lifespan in years, and nobody can honestly promise you one. What makes the difference is mostly the installation. Here's what matters.
What is DOWSIL CWS?
DOWSIL CWS (Contractors Weatherproofing Sealant) is a one-component, neutral-cure silicone sealant made by Dow. It is designed for exterior building joints: around windows and doors, between two sidings, on brick. It's the sealant we use at Protek.
According to the manufacturer's technical data sheet, it accepts ±40% movement and adheres without primer to most common non-porous surfaces. Once cured, it stays flexible.
Why we won't give you a precise number
The DOWSIL CWS technical data sheet gives no lifespan in years. That makes sense: the same product won't age the same way on a wall in full sun as under a covered porch, or in a well-designed joint versus one that's too thin.
Be wary of a quote that promises a precise number of years for the sealant itself. Ask instead how the old joint will be removed, which product will be applied, and what the written warranty covers.
What makes a silicone joint last
- Complete removal of the old sealant. New silicone applied over an old joint sticks to the old joint, not to the frame. When the old one lets go, the new one goes with it.
- A clean, dry surface. Dust, residue, moisture or frost all hurt adhesion.
- The right joint shape. A joint must bond on its two sides, not at the bottom. In deep joints, a foam backer rod is added to control the thickness.
- Sufficient thickness. A bead that's too thin cracks faster under movement.
- Proper tooling. It presses the sealant against both sides and creates a surface that doesn't hold water.
What wears it down over time
Even a good silicone works hard in Quebec. Materials expand in the sun and contract at night. Winter adds freezing and thawing.
- Sun: south- and west-facing walls get the most UV rays and the widest temperature swings.
- Movement: joints between two different materials, like aluminum and brick, move more.
- Standing water: a joint where water collects wears out faster. The manufacturer does not recommend this product for permanently submerged joints.
- Impacts: ice scrapers, pressure washers, animals.
Our article how long caulking lasts compares the different types of sealants, and silicone or polyurethane explains when to choose one over the other.
How long before it's fully cured?
DOWSIL CWS is no longer tacky to the touch after a few hours. Full curing takes longer: the technical data sheet states 7 to 14 days for a 9 mm joint, at 25 °C and 50% humidity. In cold weather, it's slower.
That doesn't stop the joint from doing its job, but it's best not to touch it during that period. It's also an advantage of silicone: it can be applied in cold weather, on a dry surface, with no frost or ice. See our winter caulking page.
How to tell if it needs redoing
Walk around your joints once a year, in spring or fall. Look especially for:
- a joint pulling away on one side or the other;
- cracks in the sealant;
- missing sections;
- water or a draft around a window or door.
A silicone that has slightly changed colour or picked up dust can still be watertight. What matters is that it stays flexible and well bonded on both sides. See our 5 signs it's time to recaulk.
In short
- Properly installed, DOWSIL CWS lasts a very long time. The manufacturer publishes no lifespan in years.
- It's a flexible silicone, designed for the outdoors, that accepts a lot of movement.
- Its real lifespan depends mostly on the installation: complete removal, dry surface, proper joint shape, tooling.
- Sun, movement and standing water are what wear it down the most.
- One inspection a year is enough to see it coming.
Are your joints due for a redo? At Protek, we remove all the old sealant before applying DOWSIL CWS. The inspection and quote are free, and we answer within 24 h. Call us at 438-405-4195, or check our caulking price guide.