Old Stone Foundations: Mice, Damp Wood and the Pests That Follow

Older stone foundations attract mice, carpenter ants, camel crickets and sometimes termites for two reasons: they have gaps, and they hold moisture. A lot of the oldest buildings in Ellicott City are granite, quarried locally and set into the hillside, and older farmhouses from Woodstock to Catonsville sit on fieldstone. These walls have stood for a century or two, and they'll stand a lot longer. They just need a little help keeping pests out.

This guide walks through what tends to go wrong in a stone basement, the things you can do yourself, and when to have someone look.

Why stone basements stay damp

Stone walls don't have the waterproofing a modern poured foundation gets. Water moves through the mortar joints, especially on the uphill side of a house built into a slope, which describes a lot of Ellicott City. Many cellars were never meant to be living space, so there's no vapor barrier and little airflow. Add a gutter that overflows or a downspout that dumps at the foundation and the basement stays humid all summer.

Some homes and buildings along the Tiber and Hudson branches and lower Main Street went through the floods of 2016 and 2018. Most have been dried out and repaired, often with real care. Even so, it's worth keeping an eye on lower-level framing in a building that took on water. Wood that stayed wet for a long time, or that's still near a damp wall, is exactly what carpenter ants and termites look for.

What moves in: mice, carpenter ants, camel crickets

Mice come in through gaps where mortar has crumbled, around old coal chutes, under the bulkhead door, and through pipe holes drilled decades ago. A gap the size of a dime is enough. Mouse control in older Ellicott City homes is mostly about finding and sealing those openings, with traps or locked bait stations doing the rest.

Carpenter ants go for the sill plate and joist ends where wood sits on damp stone. Big black ants indoors in late winter, or little piles of sawdust under the trim, are the giveaway. Our page on finding the carpenter ant nest explains what a tech looks for. Termites can come up through the gaps between stones, building mud tubes that are easy to miss in a dim cellar, so a careful termite inspection takes a flashlight and patience.

Camel crickets, the humpbacked jumpers in the laundry room, are mostly a humidity sign. They're harmless, but lots of them mean the basement is wetter than it should be.

A walk-around you can do this weekend

Take a flashlight around the outside and then the inside of the foundation. Note anything you could fit a pencil into. Inside, look along the top of the wall where the floor joists sit, behind the furnace and water heater, and in the corners where boxes lean against the stone.

• Open mortar joints, especially low on the uphill wall
• Gaps around pipes, the gas line, the dryer vent and cable
• The bulkhead or cellar door, and any old coal chute
• Soft or dark wood where the sill sits on the stone
• Mud tubes on the stone or on wooden posts
• Downspouts that dump water against the foundation

Sealing, drying and when to call

Mice chew through foam and rubber, so pack steel or copper mesh into gaps and cover it with mortar or sealant. Repointing a whole stone wall is a job for a mason, and a pest tech can point out the worst spots first. Run a dehumidifier, extend downspouts, and keep firewood and boxes off the stone. If you find droppings, don't sweep or vacuum them dry. Wear gloves, wet them with disinfectant, let it soak, wipe up and bag it.

If you're still catching mice after sealing, finding sawdust, or seeing swarmers in spring, call and have someone look. Homes in the historic district, the older streets of Elkridge and farmhouses out in Woodstock and Marriottsville see this most.

See also: Mouse and Rat Control, Ant Control, Termite Control