Paint blistering on south-facing entry doors is not random. It follows a predictable pattern tied directly to surface temperature: the paint looks fine through spring, shows bubbles by midsummer, and by fall the blistered areas have ruptured and left raw spots on the door face. Standard exterior paint applied to a door in direct afternoon sun blisters because solvent vapors trapped beneath a skinned-over film have nowhere to go except outward. Surface temperatures on a dark door in full summer sun routinely exceed 150 degrees Fahrenheit, which is far above the application and cure temperature that any standard paint formula tolerates. This is not a priming failure or a preparation failure. It is a paint selection failure that results from treating a south-facing door the same way you would treat a shaded north-facing garage door on the same house. The two surfaces operate in fundamentally different thermal environments and require correspondingly different paint products.

Why Sun-Facing Doors Fail Faster Than Other Exterior Surfaces

Exterior doors facing south or southwest receive the highest cumulative UV dose of any painted surface on the house. They also collect more direct solar thermal energy because a door is a vertical surface with no overhang protection in most entry configurations. The paint film on a south-facing door undergoes rapid temperature cycling: heating to 130 to 150 degrees Fahrenheit or higher during afternoon sun exposure and cooling to ambient temperature overnight. Over a season, that daily cycling stresses the paint film hundreds of times.

The thermal cycling creates two failure modes. First, the paint film must expand and contract with each heating and cooling cycle. A paint that has lost flexibility through UV binder degradation cracks under this movement, and the cracks admit moisture that undermines adhesion from below. Second, the high peak temperatures accelerate the UV degradation of both the binder and the pigment. South-facing doors repainted with standard exterior paint in dark colors frequently show visible fading within one to two years and film failure within three.

Oil-based paints are particularly unsuitable for sun-facing doors. As alkyd resin cures and continues to oxidize over time, it loses flexibility and becomes brittle. A rigid paint film on a door surface that cycles 60 to 80 degrees Fahrenheit in temperature daily will crack at the panel edges, around hardware, and along grain lines in the door face. That cracking is not repairable by repainting without addressing the underlying brittleness problem. Stripping to bare wood and repainting with a flexible acrylic is the correct repair.

Dark colors compound all of these effects. A charcoal or dark navy door absorbs substantially more solar energy than a light gray or off-white door at the same orientation, resulting in surface temperatures 20 to 40 degrees Fahrenheit higher than a lighter color in the same sun conditions. The practical implication is that dark-colored south-facing doors require not just high-quality paint but specifically formulated paint that maintains film integrity at those temperatures.

Choosing Heat-Tolerant and UV-Resistant Paint for Entry Doors

Two paint products consistently lead the category for high-UV exterior door applications:

Benjamin Moore Aura Exterior uses Color Lock technology with infrared-stable pigments that resist UV-induced fading. Color Lock slows the degradation of pigment molecular bonds under UV radiation, which is the mechanism behind premature fading on south-facing surfaces. Field-reported color retention on heavily exposed doors and trim with Aura Exterior is significantly better than standard exterior paints in the same color range. The product is priced at approximately $99 to $112 per gallon. For a single door with modest coverage, a quart is typically sufficient for two coats over a primed surface.

Sherwin-Williams Emerald Exterior includes a self-cleaning property where rain washes surface dirt from the film, reducing the chalking cycle that accelerates fading. Field reports document 12-plus-year performance on south-facing applications. The Emerald line is frequently available at 30 to 40 percent off during promotional periods at Sherwin-Williams stores, which brings the effective cost significantly below the list price of approximately $109 per gallon.

Both Aura and Emerald contain high levels of titanium dioxide for UV reflectance and use permeable film designs that allow moisture vapor to pass through rather than being trapped beneath the film. This permeability is what prevents blistering from moisture migrating through the door substrate: the vapor finds a path through the film rather than building pressure beneath it.

For surface temperatures that exceed what standard exterior formulas handle well, Sherwin-Williams Emerald Urethane Trim Enamel provides the urethane modification that maintains film flexibility at elevated temperatures better than standard acrylic. The urethane-alkyd chemistry resists the softening and flow issues that can affect acrylic-only formulas on very hot dark surfaces, while still remaining flexible enough to handle thermal cycling without cracking.

Semi-gloss is the correct sheen for exterior doors. The higher sheen in the 45-to-65 gloss unit range resists moisture adhesion better than satin, is easier to wipe clean, and holds up better under the UV and heat exposure that a south-facing door receives. Satin finishes on high-exposure doors tend to chalk faster than semi-gloss, and the reduced sheen of a chalked satin looks poor under any sun angle.

Prepping and Painting an Exterior Door in Direct Sun Conditions

The single most important rule for painting a sun-facing door is to do it in the shade or on a cool-temperature day. A surface that is at 120 degrees Fahrenheit when you begin applying paint will dry the first few mils of coating almost instantly on contact, trapping subsequent paint layers over a skin that cannot bond properly. The result is a paint film that adheres to itself but not to the substrate, and blistering follows within days to weeks as the trapped layers expand and contract.

Time the painting to late afternoon when the sun has moved past direct exposure on the door face, or to an overcast day when surface temperatures are close to ambient air temperature. Check the surface temperature with an infrared thermometer. Surface temperature should be below 90 degrees Fahrenheit before applying either primer or topcoat. If the surface feels warm to the back of your hand, it is likely above that threshold and should cool before painting begins.

The prep sequence for a door that has been previously painted and is in sound condition is:

Sand the entire door face and edges with 120-grit to break the gloss and create a mechanical key for the new coat. Step up to 220-grit for a final smooth pass. Wipe all sanding dust with a tack cloth. Clean with a degreasing cleaner to remove any hand oils, glazing compound residue, or silicone contamination from hardware installation. Silicone in any quantity on the surface causes fish-eye failures in the new coat. Rinse and allow to dry fully.

Apply primer, even over previously painted surfaces, before the topcoat on a sun-facing door. Primer improves adhesion and reduces the blister risk. A high-quality acrylic bonding primer such as INSL-X Stix or Benjamin Moore Fresh Start applied in one coat, allowed to dry fully per label directions, creates the bonding layer that makes the topcoat more resistant to thermal cycling and UV stress. Two thin topcoats over primer, each applied at the correct surface temperature, produce a more durable film than one heavy coat.

How to Avoid Blistering and Bubbling on South-Facing Doors

Blistering on exterior doors is the most common failure on south-facing surfaces and has two distinct causes that require different solutions. Identifying which type of blister you are dealing with determines whether the fix is paint selection, timing, or moisture management.

Heat blisters appear when only the newest coat of paint has blistered. The surface beneath is intact painted wood, not bare substrate. Heat blisters form when the paint is applied to a hot surface, when the surface heats rapidly after application before the coat is fully cured, or when volatile solvents that were trapped during fast skin-over expand under heat. The fix for heat blisters is to scrape the blistered area, feather the edges with 120-grit sandpaper, prime the repaired spot, and repaint under correct temperature conditions, specifically when the surface is below 90 degrees Fahrenheit and shade covers the door face.

Moisture blisters go through multiple paint layers down to bare substrate. They originate from water moving through the door from the interior side or from exterior water infiltrating through failed caulk at the door frame or through degraded glazing compound on a window panel. Repainting over active moisture blisters without eliminating the moisture source produces the same failure within months. The moisture source must be identified and corrected before repainting.

Proper caulking at all frame and panel junctions is part of the blistering prevention protocol. Apply a high-quality acrylic caulk to all gaps where the door frame meets the adjacent siding, where the sill plate meets the door bottom, and around any glass inserts. Sashco Big Stretch caulk stretches over 500 percent without cracking, handles service temperatures from minus 30 to 250 degrees Fahrenheit, and is paintable with latex within four hours. It is specifically rated for vinyl windows and siding, making it appropriate for door frame assemblies as well. Sealing these joints before priming eliminates the most common exterior water infiltration path for entry doors.

On south-facing doors with a full-sun exposure and no protective overhang, recoating every four to five years with high-quality acrylic is a realistic maintenance interval regardless of paint selection. The UV and thermal load on that surface is simply higher than on any other painted surface on the home, and planning for a shorter maintenance cycle prevents the deeper prep and repair work required if the paint is allowed to fail completely.