Home / Where a Coating Should Stop at the Door Opening
Where a Coating Should Stop at the Door Opening
Every coated floor has to end somewhere. At a wall the answer is easy, because the wall stops it. At a garage door opening the choice is open, and it affects how water behaves, how the door seal fits, how the edge looks, and how long the finish lasts. There are three common endpoints, and each has a different set of trade-offs.
Option one: stop inside the door line
The coating ends a few inches inside the closed door, leaving bare concrete beneath the seal and outside. This is simple and keeps the finish out of the weather. It also puts the coating edge in a spot where the seal presses against bare concrete, which seals well because the surface is rough and porous.
The weakness is the edge itself. A coating that stops in the middle of a slab leaves a visible line, and water running in can soak the bare strip and creep under the film. To prevent lifting, the termination should be cut into the concrete rather than feathered out. A saw cut, about the depth of a coin, makes a groove where the coating tucks in and locks. Without it, a thin feathered edge peels with the first scrub of a tire.
Option two: run under the door to the slab edge
The coating continues beneath the door, ending at the outer edge of the slab or just short of the apron joint. This gives a continuous look from inside to the threshold and protects the strip that takes the most abuse. It also lets the door seal rest on a smooth coated surface, which is cleaner and more effective at blocking drafts than bare concrete.
The cost of this approach is exposure. That strip faces sun, rain and temperature swings, so a UV-stable topcoat is a requirement. Aliphatic polyurethane and polyaspartic finishes hold up better than basic epoxy, which chalks and yellows outdoors. The outer edge of the slab is also prone to chipping, so any damaged corner should be repaired before coating, with a patching compound sanded to a clean line.
Option three: continue onto the apron
Some projects carry the coating a short way onto the outside slab. This makes a seamless appearance, but it is the most demanding choice. The surface faces weather, tires and sometimes de-icing chemicals, and it must withstand water drainage from the driveway. Materials designed for exterior use are essential, along with a nonslip texture, because a smooth coating becomes slick when wet.
Many professionals advise against it for this reason. The apron is a different slab, possibly a different age, with its own joints and cracks. A coating that spans the joint between slabs will crack along it as the two move independently.
Handling the joint at the opening
Most garages have a control joint or an expansion joint near the opening, where the garage slab meets the apron. Wherever the coating ends, that joint needs to be treated. A rigid coating bridging it will split. The practical solution is to stop the coating at the joint, fill the joint with a flexible sealant, and keep the sealant slightly recessed so tires do not tear it.
- Clean the joint thoroughly and remove old filler.
- Install a foam backer rod if the joint is deep.
- Apply a flexible polyurethane or polysulfide sealant.
- Tool the surface smooth and allow it to cure before coating adjacent areas.
Forming a clean edge
A crisp line looks better and lasts longer. Painter's tape lays down a straight boundary, but tape can leave a raised ridge of coating. Remove it while the material is still soft, pulling at an angle away from the coated area. For a more durable edge, cut a shallow groove along the termination with a diamond blade or a grinder and set the coating into it. The groove acts like a keyway, locking the film into the concrete so that it resists peeling.
At the edge, avoid building too thick a layer. A thick lip catches wheels and chips. A gentle taper of the body coat, finished by a thin topcoat, provides a smooth transition. Grinding the concrete a little beyond the planned edge provides a profile for the bond.
How the seal interacts
The door's bottom seal presses on whatever lies beneath. On a smooth coating it forms a tight line, while on bare concrete it may leave small gaps in the texture. If the coating stops at the seal line, a split between the two surfaces can collect water. If the door is replaced later, a new seal with a slightly different profile may fall on the line between coating and concrete, and gaps will appear. Plan for that by extending the coating a little past the seal.
Light-colored coatings can stain from a dark rubber seal sitting on them for months. A clear topcoat protects, and a vinyl seal reduces the risk.
Choosing among them
- Inspect the slab edge and apron for cracks or chips.
- Decide how much weather exposure the finish can handle.
- Choose a UV-stable topcoat if the coating reaches the opening.
- Cut a keyed edge where the coating stops.
- Seal the joint with a flexible product and keep it recessed.
For most garages, running the coating to the slab edge with a well-sealed joint gives the best appearance and protection. Where the budget of effort is limited, stopping inside the door line with a keyed groove is acceptable. Whatever the choice, the edge deserves as much attention as the center of the floor, because that is where failures begin.
Drainage across the finished edge
The way water leaves the floor is affected by where the coating stops. If the coating ends before the slab edge, the bare concrete strip drains differently, absorbing a little and holding moisture at the film edge. A coating that reaches the edge sheds water cleanly but can be slick. A fine broadcast of grit in the last foot gives traction without trapping water. Check by pouring a bucket of water and watching how it leaves the floor.
Repairing a failed edge
When an edge has peeled, do not simply glue it down. Cut back to sound, well-bonded material with a blade, grind the exposed concrete, cut a shallow keyway, and recoat with primer and body coat feathered into the existing film. Then seal the line with a flexible product. This takes an afternoon and avoids repeated patching.