How do I prevent mold on stored items in a damp NB garage during spring?

The key to preventing mould on stored items in a damp New Brunswick garage during spring is a three-part strategy: get everything off the concrete floor, control moisture at its source, and improve air circulation so humid air does not stagnate around your belongings. Spring is the worst season for garage mould in NB because snowmelt saturates the ground around your foundation, temperatures hover near the dew point, and months of accumulated winter moisture trapped inside the garage finally starts condensing on every cool surface.

The most important step is understanding why spring is so problematic in NB garages. During winter, your garage slab stays cold — often near or below freezing in an unheated garage. As spring air temperatures rise into the 5–15 degree Celsius range while the concrete slab remains cold from months of frost stored in the ground beneath it, warm humid air contacts the cold slab and condenses. This condensation — sometimes called sweating slab syndrome — makes the concrete floor visibly wet and creates ideal conditions for mould growth on anything sitting directly on or near the floor. In NB's Maritime climate, relative humidity regularly exceeds 70–80% during spring, which compounds the problem.

Get everything off the floor. This is the single most effective mould prevention measure. Store all boxes, soft goods, seasonal items, and equipment on shelving units at least 6–8 inches above the concrete slab. Wire shelving is preferable to solid shelving because it allows air to circulate around stored items. Heavy-duty wire shelving units capable of holding 200+ pounds per shelf run $80–$200 at NB building supply stores. For items that must sit on the floor — heavy toolboxes, compressors, table saws — place them on wooden pallets, rubber mats, or plastic risers so they are not in direct contact with the damp concrete.

Replace cardboard boxes with sealed plastic bins. Cardboard is a mould magnet — it absorbs moisture from the humid spring air, holds it against whatever is packed inside, and provides cellulose for mould to feed on. Clear plastic bins with snap-on lids cost $8–$20 each depending on size and keep contents dry even in the dampest NB spring. You can see what is inside without opening them, and they stack securely on shelving units.

Control the moisture source. If your garage slab was poured without a vapour barrier underneath — common in older NB garages built before the 1990s — ground moisture wicks up through the concrete continuously. You cannot add a sub-slab vapour barrier after the fact, but you can apply a concrete densifier or penetrating sealer to the slab surface to reduce moisture transmission. Products like sodium silicate densifiers cost $50–$150 for a two-car garage and reduce slab moisture significantly. For exterior moisture, verify that the grade around your garage slopes away from the foundation at a minimum of 2% (1 inch per foot for the first 6 feet). Clean gutters and extend downspouts at least 4–6 feet from the foundation to keep roof water away from the slab perimeter.

Improve air circulation. Stagnant, humid air is mould's best friend. A simple through-wall exhaust fan — a $150–$400 installation — pulls moist air out and draws drier air in through natural infiltration points. Run it for a few hours each day during the damp spring weeks. If your garage is insulated and relatively airtight, a dehumidifier rated for at least 50 pints per day is highly effective — expect to pay $300–$600 for a unit with auto-drain capability so you do not have to empty a bucket daily. In an uninsulated, drafty garage, a dehumidifier fights a losing battle against outdoor air infiltration, so focus on ventilation and keeping items elevated and sealed instead.

For items particularly vulnerable to mould — leather goods, fabric, upholstered furniture, documents, and clothing — consider storing them inside the house during the spring transition or placing silica gel desiccant packets or moisture-absorbing products inside their storage bins. These steps are entirely DIY-friendly and most NB homeowners can implement them in a single weekend. If you discover existing mould on garage walls or structural framing, however, consult a professional to assess whether there is a deeper moisture intrusion problem that needs addressing before it damages the garage structure itself.