Many St. Louis homes have a bookcase pushed against an exterior wall, often in a basement, a spare bedroom, or the lower floor of an older brick house. Books and paper are sensitive to damp air, and the wall behind a shelf can run cooler and wetter than the rest of the room, especially in summer when warm, humid air meets masonry that has not warmed up yet. This guide explains how to spot trouble early and what to change.
Why the wall matters
An exterior wall is colder than the air in the middle of a room for much of the year. When humid air touches that cooler surface, moisture can condense on it. A closed shelf with little airflow holds that moisture against the wall and the books. Brick, block, and poured concrete all absorb water, and moisture can wick into the back of a shelf and sit there for days.
Signs to look for
- A musty smell that is strongest near the bottom shelves or the back of the case
- Pages that feel limp, wavy, or cool to the touch
- Covers that stick together, or boards that cup away from the spine
- Fuzzy gray, green, or white growth on spines, endpapers, or back panels
- Dark specks on page edges that look like pepper
- Rust on metal staples, binder clips, or shelf hardware
Check the room before you move anything
Start with a simple reading. Place a hygrometer, a small device that shows relative humidity, on the shelf at book height. Do not put it on the floor or against the wall itself. Read it over several days, including a humid stretch of St. Louis summer and a dry stretch in winter. Then feel the wall behind the case with the back of your hand. A wall that feels noticeably cold or damp compared with an interior wall points to condensation or moisture moving through the masonry.
Next, look at the room as a whole. Does the room stay closed up most of the time? Is there a dehumidifier running? Does the basement get damp after a heavy rain? Water entering through the foundation or a gutter problem must be fixed first, because no shelf setup can keep up with water coming in from outside.
Practical changes
- Pull the case away from the wall so air can move behind it. Use small spacers or blocks, and leave the back open rather than covering it with a panel.
- Move the most valuable or fragile books and paper to an interior wall, a higher shelf, or a closed cabinet that does not sit against masonry.
- Raise the case on a base so it is not sitting directly on a damp floor, which is common in basements.
- Run a dehumidifier in the room and empty or drain it on a regular schedule. Keep the room door open a little so air circulates.
- Use a fan on a low setting to move air across the shelves. Do not aim it directly at the books.
- Do not pack books tightly. Leave some space so air can reach the spines.
If you find mildew
Take affected books out and move them to a dry, ventilated spot away from the rest of the collection. Brush off loose surface growth outdoors or in a space you can clean, wearing gloves and a dust mask. Do not wet the paper, since water can set stains and swell the pages. Let items dry slowly in open air, out of direct sun. For rare or important items, a paper conservator can advise on treatment. A local library or historical society in the St. Louis area may be able to point you toward one.
Keep the pattern from coming back
Once the shelf is clean, check it again after the next rainy stretch. Wipe the wall lightly if it shows dust or staining, and keep a short note of what you see each time. If the wall stays damp even after you move the case, the cause is likely outside the room. Common culprits include grading that slopes toward the house, a downspout that discharges near the foundation, or a gutter that overflows in heavy storms. These are worth checking in older St. Louis neighborhoods before you invest more in storage.