The best polyurethane sealant for sealing pipe penetrations and hose bibbs is Sikaflex-1a, an ASTM C920 Class 35 sealant rated for ±35% joint movement that bonds most building materials without primer. Sikaflex Construction Sealant is the same class in a simpler line. For vinyl or wood siding, Loctite PL Window, Door & Siding is a good fit. For concrete, use Loctite PL Concrete Non-Sag on walls and foundation cracks, and PL Concrete Self-Leveling on slab and driveway joints.
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Sealant closes the gap around a pipe. It does not fix a leaking pipe or a dripping faucet. If water is coming from the hose bibb itself, start with our outdoor faucet leak guide, or replace it with a unit from our frost-free spigot guide, then seal around it.
Polyurethane sealants compared
The ASTM C920 rating on the data sheet tells you most of what you need. Type S is single component. Grade NS is non-sag for walls; Grade P is pourable for floors. The Class number is the movement rating in percent.
| Sealant | ASTM C920 | Movement | Best job | Service temperature |
|---|---|---|---|---|
| Sikaflex-1a | Type S, Grade NS, Class 35 | ±35% | Pipe and hose bibb penetrations, mixed materials | -40°F to 170°F |
| Sikaflex Construction Sealant | Type S, Grade NS, Class 35 | ±35% | Masonry, wood and metal frame joints up to 1 in. wide | -40°F to 170°F |
| Loctite PL Window, Door & Siding | Type S, Grade NS, Class 25 | ±25% | Siding, trim and sill penetrations | -40°F to 180°F |
| Loctite PL Concrete Non-Sag (1618522) | Type S, Grade NS, Class 25 | ±25% | Foundation walls, block, vertical concrete joints | -40°F to 180°F |
| Loctite PL Concrete Self-Leveling (1618150) | Type S, Grade P, Class 25 | ±25% | Horizontal slab, driveway and garage joints | -40°F to 180°F |
BEST OVERALL · CLASS 35 · NSF/ANSI/CAN 61
Sikaflex-1a: best polyurethane sealant for pipe penetrations
Sika’s data sheet lists Sikaflex-1a as a one-part, moisture-cured, non-sag polyurethane meeting ASTM C920 Type S, Grade NS, Class 35, with ±35% movement. Sika says it bonds most construction materials without a primer and lists 0% adhesion loss in peel tests on concrete, aluminum and glass. It is tack-free in 3 to 6 hours, paintable with water-, oil- and rubber-based paints after testing, and certified to NSF/ANSI/CAN 61. Apply between 40°F and 100°F. It comes in 10.1 fl oz cartridges and 20 fl oz sausages.
Choose it when a copper or brass hose bibb, a PVC drain or a gas line passes through brick, stucco or siding. Mixed materials and a pipe that moves with temperature are exactly what a Class 35 sealant is for. Sika also says it can go on green or damp concrete.
Skip it where the sealant would be more than 1/2 inch deep without backer rod behind it, in pools, or next to silicone that is still curing; Sika lists all three as limits. Allow a week of cure before painting or water immersion. White may yellow in sun, so pick a color that matches the wall.
BEST ALTERNATIVE · CLASS 35
Sikaflex Construction Sealant: same movement class, joints up to 1 inch
Sika lists Construction Sealant as a premium-grade, one-component, non-sag polyurethane meeting ASTM C920 Type S, Grade NS, Class 35, with ±35% movement. It is for vertical and horizontal joints in brick, masonry, wood, concrete and metal frames. Sealant depth runs 1/4 to 1/2 inch at a 2:1 width-to-depth ratio, and Sika caps width at 1 inch. Tack-free time is 3 to 6 hours and final cure is 5 to 7 days.
Choose it when you want a Class 35 sealant for the gap where a water service or sewer line leaves a block or brick wall, and you do not need the NSF listing of Sikaflex-1a.
Skip it for joints wider than 1 inch, on asphalt or bitumen, or above 100°F air or surface temperature.
BEST FOR SIDING · CLASS 25 · PAINTABLE
Loctite PL Window, Door & Siding: best for siding and trim penetrations
Henkel lists this polyurethane as ASTM C920 Type S, Grade NS, Class 25, with ±25% movement. It bonds wood, vinyl, aluminum, concrete, brick, fiberglass, metal and stucco, and is paintable after about 7 days of cure. Service range is -40°F to 180°F. It skins in about 24 hours and Henkel lists a maximum 72-hour tack-free time, so it stays soft longer than Sika.
Choose it when a PVC vent, condensate line or water line passes through vinyl or wood siding and you want a bead that can be painted to match the trim.
Skip it on bare copper, stainless or galvanized pipe unless you prime; Henkel says those metals typically need primer. Also skip it over old silicone or butyl, which Henkel lists as not compatible.
BEST FOR CONCRETE WALLS · NON-SAG
Loctite PL Concrete Non-Sag 1618522: best for foundation walls
Henkel lists PL Concrete Non-Sag as ASTM C920 Type S, Grade NS, Class 25, for exterior and interior joints in concrete and masonry, including foundations and block walls. It handles joints up to 1.5 inches wide, with sealant depth at half the joint width and closed-cell backer rod in deep joints. Concrete and masonry need no primer, but Henkel says copper, galvanized steel and plastics typically do. Item 1618522 is the 10 fl oz cartridge in limestone.
Choose it when you seal the gap around a sleeve where a pipe passes through a poured foundation, or a crack beside a basement floor drain.
Skip it for a crack that is actively leaking water or getting wider. That is a structural or drainage problem, not a sealant job. Hydraulic cement or a foundation contractor is the next step.
Buy PL Concrete Non-Sag 1618522 from a Loctite dealer; we found no in-stock new single-cartridge Amazon listing on October 14, 2026.
BEST FOR SLAB JOINTS · SELF-LEVELING
Loctite PL Concrete Self-Leveling 1618150: best for slab and driveway joints
This is the pourable version: ASTM C920 Type S, Grade P, Class 25. Henkel lists it for driveways, garage floors, sidewalks and concrete floors and decks, on horizontal surfaces only. Maximum joint width is 1.5 inches, and joints deeper than 3/8 inch need backer rod. It is functional in about 3 days and cures in about 7. Item 1618150 is the 10 fl oz cartridge in concrete gray. On October 14, 2026 we found it on Amazon only as a 12-cartridge pack.
Choose it when you patch a saw-cut joint after trenching a slab for a drain line, or seal the joint where a garage floor meets a cleanout cover.
Skip it on any wall or sloped surface; it will run. Henkel also advises against exterior use if rain is expected before the first cure.
Check PL Concrete Self-Leveling 1618150 (12-pack) on Amazon →
How to choose polyurethane sealant
Measure the gap
Measure the widest point of the gap around the pipe. Sikaflex Construction Sealant tops out at 1 inch wide; the Loctite concrete sealants go to 1.5 inches. Keep sealant depth within the maker’s limit: Sika caps Sikaflex-1a at 1/2 inch deep, and Henkel sets depth at about half the joint width. If the gap is deeper, push in closed-cell backer rod first. A gap much bigger than that needs a wider fix, such as a flange, a sleeve or mortar, before any sealant.
Match the movement class
Class 35 handles more movement than Class 25. Pick Class 35 for a pipe that grows and shrinks with water temperature, or where two different materials meet. Class 25 is fine for siding trim and concrete control joints.
Check the pipe material
Copper, brass and galvanized pipe are where adhesion fails first. Sika says Sikaflex-1a bonds most materials without primer. Henkel says its PL sealants typically need primer on copper, stainless and galvanized steel. Clean the pipe to bright, dry metal either way.
Check the weather
Sikaflex-1a and PL Concrete Self-Leveling both list 40°F as the low end for application; check the data sheet for the tube you buy. Polyurethane cures with moisture, so cure is slower in cold, dry air. Plan the job for a mild day.
Polyurethane vs silicone sealant
Use polyurethane outside the house and silicone inside. Polyurethane is paintable and holds up on masonry, wood and concrete, which is why it is the trade’s choice for siding and foundation penetrations. Silicone stays flexible around tubs, sinks and fixtures and is the usual pick for wet areas indoors; our silicone sealant guide covers that side.
Do not mix them in the same joint. Sika says not to cure Sikaflex-1a around curing silicone, and Henkel lists silicone as not compatible with its PL sealants. Cut out old silicone completely before you apply polyurethane over it.
Gas pipe penetrations are sealed the same way, but if the gas line itself has moved, is bent, or smells of gas, stop. Leave the area and call your gas utility and a licensed plumber.
Polyurethane sealant FAQ
What is the best polyurethane sealant?
For pipe penetrations and mixed materials, Sikaflex-1a is the strongest all-around pick. It meets ASTM C920 Class 35 for ±35% movement, bonds most construction materials without primer, and is paintable once cured.
Is polyurethane sealant better than silicone?
It depends on where it goes. Polyurethane is paintable and suits exterior masonry, siding and concrete. Silicone is the usual pick for tubs, sinks and fixtures indoors. Do not put one over the other in the same joint.
How long does polyurethane sealant take to cure?
Sikaflex-1a is tack-free in 3 to 6 hours and fully cures in 4 to 7 days. Loctite PL polyurethanes skin in about 24 hours and cure in about 7 days. Cold and dry air slow cure.
Can you paint polyurethane sealant?
Yes, once it cures. Sika says Sikaflex-1a takes water-, oil- and rubber-based paints after testing, and Henkel says its PL sealants are paintable after about 7 days. Rigid paint over a flexible bead can crack.
What sealant should I use around an outdoor faucet?
Use a Class 35 polyurethane such as Sikaflex-1a around the hose bibb where it passes through brick, stucco or siding. Clean the pipe first, and fix any leak in the faucet itself before sealing.
How we chose
This is a document-based comparison from a licensed plumber’s point of view. We read the maker’s product data sheet for every sealant and kept only polyurethanes with a published ASTM C920 rating, movement class, temperature range and limitations. We sorted them by the places a plumber actually seals: hose bibbs and pipe penetrations, siding, foundation walls and slab joints. Sources and linked listings were read October 14, 2026; sellers and availability change. We do not publish prices or claim hands-on testing. More about our selection method and Plumbing Picks.
Primary sources
- Sikaflex-1a product data sheet (PDF) (usa.sika.com): ASTM C920 Class 35, ±35%, NSF/ANSI/CAN 61, primer, tack-free and cure, temperatures, limits, sizes.
- Sikaflex Construction Sealant product data sheet (PDF) (usa.sika.com): ASTM C920 Class 35, joint width and depth, cure, limits.
- Loctite PL Window, Door & Siding data sheet (PDF) (datasheets.tdx.henkel.com): ASTM C920 Class 25, substrates, primer on copper and galvanized, paint, cure, compatibility.
- Loctite PL Concrete Non-Sag data sheet (PDF) (datasheets.tdx.henkel.com): ASTM C920 Class 25, joint width, backer rod, primer, item number.
- Loctite PL Concrete Self-Leveling data sheet (PDF) (datasheets.tdx.henkel.com): ASTM C920 Grade P Class 25, horizontal only, joint size, cure, item number.