Small cracks matter more than they look in a storm. The Florida Division of Emergency Management's Hurricane Retrofit Guide says a hairline crack in stucco only 6 inches long and 1/64 inch wide has the same area to let water in as "a square hole over 1/4\" on a side," and a gap of the same width between a window frame and the wall lets in as much as a hole 1/2 inch on a side. Its advice: "sealing cracks on your house is critical." This guide follows that retrofit guide step by step, with a few tips from UF/IFAS, and marks our own advice as ours.
Stop and call a pro before you start if:
- A crack is wider than about 1/2 inch. The state guide's caulking advice stops at about 1/2 inch.
- The stucco bulges, is falling off, or sounds hollow when you tap it. The National Park Service says stucco that has lost its bond "will echo with a hollow sound when tapped gently." Our advice: that needs a proper repair, not caulk.
- There's a stair-step crack in a block wall, or a crack that keeps growing. Our advice: have it looked at; it can mean movement, not just weathering.
- Water is already getting inside, or the wall behind is soft or stained. Our advice: find the source first; see our post on stucco cracks and water behind stucco.
- The home was built before 1978 and you'd be scraping or sanding paint. The EPA says those homes are more likely to have lead-based paint.
- The wall has textured paint or patching compound you'd disturb. The EPA lists both among materials that may contain asbestos and says "Taking samples yourself is not recommended."
- The gap is around the electric meter or panel and you'd have to open anything. Our advice: seal only the outside joint where a box meets the wall, never inside it; leave anything else to a licensed electrician.
- The water came from a flood or sewage. The EPA says to call in a professional experienced in cleaning buildings damaged by contaminated water; see our floodwater cleanup guide.
- There's structural damage: a leaning or bowing wall, a sagging window or door header, or framing you can see is damaged. Our advice: stop and have a licensed contractor look at it.
- You'd need a ladder above the first floor. Our advice: call a pro.
- Mold covers more than about 10 square feet. That's the EPA's do-it-yourself limit.
What you'll need
| Item | Why | Where to buy |
|---|---|---|
| Exterior-grade caulk or sealant | The state guide says to use only caulks suitable for outdoor use | Home Depot · Lowe's |
| Caulking gun | Applying the caulk | Home Depot · Lowe's |
| Tape measure or crack gauge | Checking crack widths against the 1/4- and 1/2-inch limits | Home Depot · Lowe's |
| Stiff brush | Our advice: brushing dust and loose bits out of cracks first | Home Depot · Lowe's |
| Urethane caulk (only if you use spray foam) | The state guide says foam left in sunlight must be coated with urethane caulk | Home Depot · Lowe's |
| Downspout extension | Moving roof water at least 3 feet from the wall | Home Depot · Lowe's |
Step by step
Step 1: Walk the wall with the state's checklist
The state guide says to "look very carefully for even the smallest hole or crack and look at the undersides of things even if means you have to get down on your knees." Its checklist covers gaps around:
- Water faucets and gas pipes where they enter the house
- A/C lines
- Electrical outlet boxes, junction boxes, breaker boxes, disconnect switches and electric meters
- Light fixtures
- Dryer, water heater and range hood vents
- Cracks or voids in mortar under window sills
- Any penetration within 6 inches of the ground
Our advice: mark each spot with painter's tape and take a photo so you can find it again.
Step 2: Measure each crack
The state guide says you can use a single application of caulk for small cracks up to about 1/4 inch wide, and multiple applications for cracks up to about 1/2 inch. Anything wider goes on your call-a-pro list (see the box above). Our advice: measure the widest point, not the average.
Step 3: Get the right caulk
The guide says to use only caulks suitable for outdoor use: "Caulks used for interior paint work are not suitable for outside use because they will degrade, shrink, and become hard and brittle. They will be ineffective within a year." For larger holes, it says spray foam can work, but foam breaks down within a year in sunlight, so it has to be coated with urethane caulk.
Step 4: Clean and seal
Our advice: brush dust and loose stucco out of the crack and let the wall dry before you caulk. For stucco patching material, the state guide says, "For best functional results push it into cracks and for cosmetic results spread it over as narrow an area as practical." Seal every gap from Step 1, working the caulk into the joint rather than smearing it over the surface.
Step 5: Clear the base of the wall
The state guide says soil can build up against a house "sometimes by several inches" as mulch and plants accumulate, and that you can have leaks at the base of the wall if the floor isn't well above the ground. Its fix is "pulling away dirt and mulch that has accumulated in flower beds around the house," and its checklist asks whether the floor is at least 6 inches above soil and mulch. UF/IFAS recommends a thin layer of mulch (less than 2 inches) within 12 inches of the foundation, not watering next to foundation walls, and about a 6-inch inspection space.
Step 6: Move downspout water away
The state guide says water from downspouts "should discharge on the ground at least 3' away from walls," and that downspout extensions "have to be secured so wind does not pick them up."
Step 7: Check again after a hard rain
Our advice: after the next heavy rain, look inside behind each spot you sealed for stains or damp drywall, and recheck the caulk once a year. The state guide notes that walls painted with only one thin coat can soak through in long, wind-driven rain, and that a paint company's technical representative can recommend a coating. It says elastomeric paints "are generally not recommended" because, unless installed perfectly, "they can bubble and trap water."
How long it takes
None of our sources gives a time for this job. It depends on how many cracks and gaps your walk-around turns up and how much mulch needs pulling back. Caulk drying and curing times are on the product label.
Stop and call a pro if you find:
- Cracks wider than about 1/2 inch, or stair-step cracks in block
- Stucco that's bulging, loose, or sounds hollow when tapped
- Rust or brown stains running from a crack
- Soft, stained or wet drywall on the inside of the wall
- Gaps you can only reach from a ladder
Frequently asked questions
What kind of caulk should I use on stucco?
The Florida Division of Emergency Management's guide says to use only caulks suitable for outdoor use; interior caulks degrade, shrink and become brittle within a year outside. It also says spray foam used outside must be coated with urethane caulk.
How wide a crack can I caulk myself?
The state guide says a single application of caulk works for cracks up to about 1/4 inch wide, and multiple applications for cracks up to about 1/2 inch.
Should I paint stucco with elastomeric paint?
The state guide says elastomeric paints are generally not recommended because, unless installed perfectly, they can bubble and trap water. It suggests asking a paint company's technical representative for a recommendation.
Why does mulch against the wall matter?
The state guide says soil and mulch can build up by several inches and cause leaks at the base of the wall. UF/IFAS recommends keeping mulch under 2 inches thick near the foundation and leaving about a 6-inch inspection space.
Sources
- Florida Division of Emergency Management: Hurricane Retrofit Guide, "Water Leaks Through Walls" (PDF)
- UF/IFAS: The Facts About Termites and Mulch
- National Park Service: Preservation Brief 22, Historic Stucco (PDF)
- EPA: Protect your family from sources of lead
- EPA: Learn about asbestos
- EPA: Protect your family from exposures to asbestos
- EPA: A Brief Guide to Mold, Moisture and Your Home