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The Short Answer
| The job | The type of caulk | An example |
|---|---|---|
| Cracks in a stucco wall | Textured elastomeric sealant | Sashco Mor-Flexx |
| Small, still gaps at stucco trim, windows and doors | Paintable acrylic latex caulk with silicone | DAP Alex Plus |
| Wider joints that move, such as around windows and doors | Polyurethane sealant | Sikaflex-1a |
| Tubs, sinks and glass, where paint won't go | Silicone or kitchen-and-bath caulk | Not for stucco |
Caulk for Cracks in Stucco
A crack across a stucco wall needs a caulk that stays flexible and looks like stucco. A smooth caulk seals, but it leaves a shiny stripe across a textured wall. A textured elastomeric sealant stretches as the wall moves and blends into the texture.
Sashco Mor-Flexx is made for exactly this: its maker says its texture "mimics that of real mortar and stucco," and it comes in gray, white, beige, charcoal and ironstone, so unpainted stucco can often stay unpainted. It takes exterior latex paint after 4 hours.
For crack sizes, patches and more products, see our guide to stucco crack repair products.
Caulk Around Windows and Doors in Stucco
Where stucco meets a window frame, a door frame or trim, two different materials move at different rates. The caulk joint between them takes that movement, which is why it wears out faster than the stucco.
- Small gaps that don't move much: a paintable acrylic latex caulk with silicone. DAP Alex Plus is rated for joints up to 1/2 inch wide and 1/2 inch deep, takes paint in 30 minutes, and lists window and door frames and trim among its uses.
- Wider joints, or joints that move: a polyurethane sealant. Sikaflex-1a is a one-part polyurethane that meets ASTM C920, Type S, Grade NS, Class 35, the standard for elastomeric joint sealants. Sika's specification calls for foam backer rod in moving joints, with the sealant no deeper than 1/2 inch at the center of the joint. It's tack-free in about 4 hours and fully cured in 4 to 7 days.
Polyurethane is the tougher choice, but it's stickier to work with and cleans up with a solvent, not water. Check the label before painting over any sealant.
What not to caulk
Leave the drainage paths open. On a frame wall, the weep screed at the bottom of the stucco is where water behind the wall drains out, so it should never be caulked shut. The same goes for the small weep holes at the bottom of many window frames.
Can You Use Silicone Caulk on Stucco?
It sticks, but 100% silicone has two drawbacks on a stucco wall: paint won't cover it, and other caulks won't stick over it later. DAP notes that Alex Plus "will not adhere over 100% Silicone." On a wall that's painted, or will be, use a paintable sealant. If old silicone is already there, it has to come out completely before a new caulk goes in.
Caulk for Other Surfaces
The same rule applies everywhere: match the caulk to the materials and to how much the joint moves.
| Where | The usual choice |
|---|---|
| Kitchen and bath (tub, tile, sink) | Silicone or a kitchen-and-bath caulk with mildew resistance |
| Glass | Silicone made for glass |
| Concrete slabs and driveway joints | Polyurethane, often self-leveling for flat joints |
| Interior trim and baseboards | Paintable acrylic latex caulk |
| Gutters and roof flashing | A gutter or roof sealant made for metal and roofing |
How to Caulk Stucco Joints
- Pick a dry day above 40°F, with no rain due before the caulk cures. In Florida, that usually means a dry morning, ahead of the afternoon storms.
- Cut out the old caulk. A utility knife and a stiff brush get the joint down to clean, sound edges. Old silicone has to come out completely.
- Clean and dry the joint. Dust and loose stucco keep new caulk from bonding.
- Set the depth. In joints deeper than about 1/2 inch, press in foam backer rod so the caulk is the right thickness and only sticks to the two sides.
- Run a steady bead and tool it. Push the caulk into the joint, then smooth it with a wet finger or a tooling stick so it bonds to both sides.
- Let it cure, then paint. Follow the label: 30 minutes for Alex Plus, 4 hours for Mor-Flexx, and several days for a polyurethane to fully cure.
This video from a plastering contractor shows a stucco crack being caulked with a textured sealant:
Video: "Caulking cracks in stucco use Mor-Flexx or Quikrete with sand" by Kirk Giordano Plastering on YouTube. Follow the label of the product you use for drying and painting times.
When a Caulk Joint Isn't the Problem
If caulk keeps failing at the same window, or the stucco around it is soft, stained or cracked, the trouble may be behind the joint, in the flashing or the barrier. That's a repair someone should see in person. Your local Stucco HQ contractor, from Jacksonville to South Florida, looks at the wall and gives you a free written estimate. See how a stucco repair works.
Frequently asked questions
What kind of caulk do you use on stucco?
For cracks in the wall, a textured elastomeric sealant such as Sashco Mor-Flexx. For joints where stucco meets windows, doors and trim, a paintable acrylic latex caulk with silicone for small gaps, or a polyurethane sealant for wider joints that move.
Can you use silicone caulk on stucco?
It sticks, but paint won't cover 100% silicone and other caulks won't stick over it later. On a painted wall, use a paintable sealant instead.
Is polyurethane caulk good for stucco?
Yes, for joints that move, such as around windows and doors. Polyurethane sealants that meet ASTM C920 stretch and recover with the joint. They're harder to work with than acrylic caulk and clean up with a solvent.
What is the best caulk for stucco around windows?
For small gaps that don't move much, a paintable acrylic latex caulk with silicone. For wider joints, or where the frame moves, a polyurethane sealant over foam backer rod. Leave any weep holes at the bottom of the frame open.
Should you caulk the bottom of a stucco wall?
No. On a frame wall, the weep screed along the bottom edge lets water behind the stucco drain out. Caulking it shut traps that water.
Can you paint over caulk on stucco?
Paintable caulks, yes, once they're dry: 30 minutes for DAP Alex Plus and 4 hours for Sashco Mor-Flexx under exterior latex paint. 100% silicone can't be painted.
Sources and data used on this page
The figures and facts on this page come from public records and official sources. Links open in a new tab.
Product makers
- Mor-Flexx Sashco Mor-Flexx texture and colors.
- Mor-Flexx: Sealant for Textured Surfaces Sashco Mor-Flexx paint time.
- Alex Plus All Purpose Acrylic Latex Caulk Plus Silicone DAP Alex Plus joint size, paint time, uses, and that it won't stick over silicone.
- Sikaflex-1a Sika USA Sikaflex-1a: polyurethane, ASTM C920 Class 35, backer rod, depth and cure times.
Industry guidance
- TechTimes: Weep Screed for Stucco Stucco Manufacturers Association The weep screed drains water from behind stucco on a frame wall.
Last reviewed:
Stucco HQ is not affiliated with, and is not paid by, Sashco, DAP, Sika or the Stucco Manufacturers Association, and earns nothing from these products. Product details were checked against each maker's own pages on November 12, 2026. Always follow the label of the product you use.