Clay Soil Settlement Cracks
The most common call a St. Louis drywall contractor gets is about cracks that keep coming back. Patch them in spring, they're back by fall. Patch them again, they return. The cause is almost never the drywall work — it's the soil underneath the house.
St. Louis sits on expansive clay soils that swell when wet and shrink when dry. A dry summer followed by a wet fall can cause minor foundation movement of a fraction of an inch. That fraction of an inch shows up as diagonal cracks radiating from window and door corners, horizontal cracks along top plates, or stair-step cracks in masonry that translate through to interior walls.
The pattern to look for: diagonal cracks specifically at the upper corners of window and door openings, often 30-45 degrees, sometimes multiple inches long. If you have these cracks in multiple locations on the same wall or floor, or if they've grown over time, that's soil movement until proven otherwise.
For minor ongoing movement, flexible caulk rather than rigid compound is the appropriate repair. It won't stop the movement, but it can accommodate it without re-cracking every season. For significant movement, a structural engineer or foundation specialist is the right call before doing any cosmetic work.
Moisture Damage on Exterior Walls
St. Louis brick construction is generally solid, but brick isn't waterproof. Brick veneer absorbs and releases moisture, and in older homes, the flashing and waterproofing behind the brick may be failing or missing entirely. When moisture migrates through the brick wall assembly, it reaches the interior wall system, which in older homes means plaster and in renovated homes often means drywall installed over the original plaster or directly on furring strips.
Signs of moisture infiltration in St. Louis brick homes: paint peeling at the base of exterior walls, soft or spongy drywall on exterior walls, visible water staining, or a persistent musty smell in rooms on exterior walls even after cleaning. In severe cases, the drywall paper will be visibly damaged or delaminating without any obvious interior water source.
The fix always starts on the exterior — addressing the flashing, repointing deteriorated mortar joints, and ensuring water is directed away from the foundation. Interior repairs done before the exterior problem is fixed will fail again, usually within one or two seasons.
Plaster-to-Drywall Interface Problems
In many St. Louis homes built before 1950 — which covers a significant portion of Soulard, Tower Grove, Benton Park, The Hill, and similar neighborhoods — the original walls are plaster over wood lath. Somewhere along the way, the previous owners patched sections with drywall. The transitions between plaster and drywall are some of the most problem-prone areas in these homes.
The thickness difference alone creates issues. Three-coat plaster on wood lath is typically 3/4 to 7/8 inch thick. Standard drywall is 1/2 inch. The 1/4 to 3/8 inch step between the two materials requires careful shimming and feathering, and even when done correctly, the different flexibilities of the two materials cause cracks at the seam over time.
If you're working on a plaster-drywall transition in a St. Louis home, the approach that holds best is: bevel the plaster edge carefully, use a setting-type compound (not pre-mixed) for the first coat to get a hard, stable base, then paper tape embedded with all-purpose compound for the seam. Pre-mixed compound alone at these transitions tends to crack.
Summer Humidity and Drying Problems
St. Louis summers are genuinely humid in a way that affects drywall work. From roughly mid-June through September, outdoor humidity regularly exceeds 70%. On overnight and early-morning readings, 85-90% is common.
Joint compound dries by evaporation. High humidity slows evaporation. What should dry overnight might still be tacky after 36 hours in August. Applying a second coat over an incompletely dried first coat traps moisture, which eventually causes the compound to crack or pop as it continues to cure.
The practical adjustments: run air conditioning or dehumidifiers in the work area to keep interior humidity below 60% if possible. Wait for the compound to turn uniformly white and feel hard — not just surface-dry — before sanding or recoating. Schedule finishing work for spring or fall when you can. If you're working in summer, budget extra time between coats.
The USG application guidelines note that temperatures below 55°F or humidity above 95% can prevent proper drying entirely. St. Louis rarely hits those extremes indoors, but consistently operating at 75-80% humidity still significantly extends drying times.
Freeze-Thaw Seam Cracking
St. Louis winters aren't as severe as Chicago or Minneapolis, but the city does go through repeated freeze-thaw cycles from roughly November through March. Temperatures drop below freezing, warm back up, drop again. Each cycle causes minor movement in wood framing, concrete foundations, and the connections between them.
The result is seam cracking along butt joints and along the edges of ceiling-wall connections, particularly on exterior walls where temperature differentials are highest. These cracks typically open slightly in winter and close back in summer — they're responding to seasonal movement rather than progressive settlement.
Caulk handles these better than compound for the same reason it works at window frames: it accommodates movement. For ceiling-wall joints on exterior walls, painting the joint with a flexible caulk then painting over it holds better than trying to build up a compound repair that the movement will crack again.