Mold on Books and Paper: How to Clean and Save Them

Paper is made from plant fiber. The National Park Service's conservation guidance says cellulose-based materials, such as cotton, linen, paper and wood are particularly susceptible to mold. It also notes mold can cause scattered brown spots on paper known as foxing, and can make paper absorb water more easily, which sets it up for the next round.

The conditions that help mold are familiar to anyone in Texas. The National Archives lists high temperature, high relative humidity, stagnant air, and darkness. The NPS says relative humidity should ALWAYS be kept below 65%.

Timing matters with wet paper. The NPS says mold may begin to grow when objects are left damp for approximately 72 hours, and its photo guidance warns mold can begin to grow within 48 hours. Plan on a window of about two days.

• A musty smell. The NPS says the first sign is often a characteristic musty odor.
• Velvety or powdery growth. Mold can appear as a velvety growth of almost any color, or a powdery deposit.
• Stains and spots on page edges, the gutter and the cover.
• Pages stuck together or wavy pages in a book that got wet.

Check the whole shelf, not just the one book. The NPS isolates moldy objects specifically to prevent the spread of spores to other objects.

Mold on paper is the same mold that affects people elsewhere. The National Archives notes that many people are sensitive to mold, and NARA's family archives page advises you limit handling of the moldy items.

For a small number of books, the EPA lists a minimum of an N-95 respirator, gloves and goggles (EPA Table 2). People with asthma, allergies or weakened immune systems should leave the work to someone else.

Be honest about value before you spend hours on a book. EPA guidance gives three paths for water-damaged books and papers (EPA Table 1):

What to do with water-damaged books and papers

The NPS puts it plainly: drying books takes effort, and not everything can be saved. Items that have little value or can be easily replaced should be a lower priority or considered for disposal.

For family Bibles, letters, diaries and rare books, NARA advises: consult a conservator to have valuable or sentimental items treated.

These steps come from the National Archives, the National Park Service and the Library of Congress.

1. Isolate the item

The NPS says to seal a moldy object in a polyethylene bag or enclose it in polyethylene sheeting so spores don't spread to other books. It also warns: do not touch the mold, as this will spread the spores. Don't leave wet items sealed for long, though; they need to dry or be frozen.

2. Dry it first

The National Archives says the first priority is to dry moldy items. The NPS suggests a room with circulating air and, if possible, run a dehumidifier. NARA cautions against fans that aim air flow directly at drying materials.

3. Tell active mold from dormant mold

This is the step most people skip. NARA explains that active mold looks fuzzy or slimy. Dormant mold is dry and powdery. Don't try to remove active mold, because it may only spread or smear. Dry the item until the mold is powdery.

NARA says active mold may be treated with brief (1-2 hours) exposure to ultraviolet radiation from the sun, but too much sun will speed deterioration and may cause fading. Keep it short.

4. Brush or vacuum off the dry mold, outdoors

Once it's dry and powdery, take it outside. NARA recommends a soft, clean, light-colored brush and a gentle pushing motion, changing brushes often.

A HEPA vacuum is the other option. The EPA lists HEPA vacuuming as the cleanup method for moldy books and papers of any size (EPA Table 2). The NPS says to vacuum with the lowest effective suction and protective screening, and to use a soft brush to dislodge stubborn mold toward the nozzle.

5. Throw out the dirty materials

The NPS says to seal the vacuum bag, gloves and other contaminated materials in a plastic bag and put them in the trash outside, and to dispose of all contaminated storage materials that held the object. That includes the cardboard box the books were in.

6. Watch for regrowth

For items with mold stains, the Library of Congress says to keep relative humidity between 35-55% to prevent regrowth and check them regularly. Stains often remain after cleaning; NPS notes mold can produce irregular stains that may permanently damage an object.

What not to do: don't spray books with bleach or household disinfectants. The NPS says chemical treatment should only be done with a conservator's advice, partly because a biocide could itself become a potential nutrient for certain types of fungus as it breaks down.

No. Freezing stops it, buys you time and keeps wet books from getting worse, but it doesn't kill mold. NARA says placing damaged items in a personal or commercial freezer will not kill mold, and the NPS says extreme cold, freezing and heat deactivate spores or spore growth but do not kill them. When thawed items warm up, mold can grow again, so dry them as soon as they come out.

After Hurricane Harvey, rainfall exceeded 30 inches in many locations in southeast Texas. If your papers and books got wet in a flood or leak, here's how to triage.

If you can't dry them within two days, freeze them. NARA says wet items that can't be air dried within two days should be frozen to inhibit mold growth. The NPS suggests wrapping wet books in wax paper, freezer paper, paper towels, or unprinted newspaper, gently shaping them first, then freezing them and taking out small batches to dry.

Air drying books (NPS method):

1. Interleave paper towels or unprinted newspaper every 20-30 pages.
2. Stand damp books on end on absorbent towels and fan the pages slightly. Don't force the book wide open.
3. Replace interleaving as it gets soaked, and flip the book head to tail each time.
4. Run a dehumidifier and keep air moving in the room.
5. When dry, press the books gently under boards or between other books to reduce swelling.

Glossy and coated paper (magazines, art books, yearbooks) sticks to itself. NARA says bound glossy items must be interleaved between every page, and recommends wax paper.

Loose documents: NARA says to air dry them flat in small piles or one at a time, changing the blotting paper underneath as it gets soaked.

Photos need gentler handling than paper.

• Don't touch the image. The NPS says do not touch the image surface of a wet photo until it is dry.
• Dry face up. Lay photos flat and make sure the emulsion (the side with the image) is facing up.
• Rinse only if needed. The NPS allows rinsing photos one at a time in clean water only if they're visibly dirty and the image layer is intact. NARA is more cautious and warns rinsing or soaking some photos could cause irreversible damage. If in doubt, don't.
• Take them out of albums and frames where they aren't stuck.
• Be careful with freezing. The NPS says do not freeze older or valuable photos without first consulting a professional conservator.
• Stuck photos: for valuable photos stuck together or to glass, the NPS says do not pull them apart; consult a professional conservator.

Our mold after flood Texas guide covers the rest of the house after a flood.

• Control humidity. The NPS says spore germination is less likely if RH is controlled between 45 % and 55 %. For the whole house, the EPA recommends below 60 percent (ideally between 30 and 50 percent). A dehumidifier for mold helps in a damp study or storage room.
• Pick the right spot. The NPS advises avoiding storage in or near damp areas such as attics, basements, sinks, windows, or directly on floors, keeping items at least four inches above the floor, and away from outside walls.
• Keep air moving. NPS says a fan helps increase circulation.
• Keep it clean. Dust and dirt feed mold; NPS recommends keeping storage areas clean and using dust covers.
• Don't seal damp paper in plastic. Kentucky Extension says items should never be stored in airtight plastic.

If books on one wall keep molding, the wall or room is the problem. Look for leaks, condensation or a musty smell; our mold smell in house and signs of mold in house guides can help. An air purifier for mold won't fix a moisture source.

For hidden mold, a licensed mold testing company in Austin, Houston or another city on our Texas page can inspect. A separate mold removal company handles building cleanup, since Texas law says a license holder may not perform both mold assessment and mold remediation on the same project. Check licenses with our license check tool.

If you have symptoms you think come from mold, see a doctor; a mold test can't diagnose illness. The CDC says individuals with persistent symptoms should see their physician. See also our mold allergy guide.