How should I maintain the expansion joints and control joints in my Ottawa garage floor?

Expansion joints and control joints are among the most overlooked maintenance items in an Ottawa garage, and neglecting them leads to water infiltration, frost heave damage, and cracking that spreads into the slab. Understanding what these joints do and keeping them in good condition is straightforward and inexpensive compared to the repair bills that follow when they fail.

First, the distinction between the two types. Control joints (also called contraction joints) are the grooves cut or tooled into your garage slab in a grid pattern, typically dividing the floor into roughly equal panels. Their purpose is to create intentional weak points where the concrete cracks in a controlled, straight line as it shrinks during curing and as it expands and contracts with Ottawa's temperature swings. A properly jointed two-car garage slab typically has 4 to 6 control joints creating panels no larger than about 10 by 10 feet. Expansion joints are the wider gaps (usually 1/2 to 3/4 inch) filled with a compressible material where the garage slab meets the foundation walls, the driveway apron, or a column footing. These allow the slab to expand in summer heat without pushing against rigid structures.

In Ottawa's climate, these joints work hard. The temperature differential between a -25°C January night and a +35°C July afternoon causes your concrete slab to expand and contract by several millimetres across its full width. Road salt tracked in by vehicles dissolves into brine that flows into every joint and crack, then freezes and expands, widening the gaps further. Spring snowmelt floods the joints with water that carries more salt and debris deep into the openings.

Annual inspection and maintenance should happen each spring after the worst of winter is over, typically in April or May. Here is what to do. Start by cleaning out all joints thoroughly — use a pressure washer or a stiff wire brush and shop vacuum to remove dirt, salt residue, gravel, and any deteriorated old sealant. Compressed air works well for stubborn debris in narrow control joints.

For control joints, the best maintenance is filling them with a flexible polyurethane or silicone caulk rated for concrete and traffic. Do not use rigid fillers — they crack and pop out as the joint moves. Apply the sealant so it sits slightly below the surface of the slab (a technique called a concave bead) so tires do not pull it out. A tube of quality concrete joint sealant costs $8 to $15 and covers 20 to 40 linear feet, so sealing an entire garage runs $25 to $60 in materials for a DIY job. If you want it done professionally, expect $200 to $500 for a two-car garage.

For expansion joints, the compressible backer material (usually a foam strip) may have deteriorated over the years. If the foam is compressed flat, missing, or crumbling, replace it with new closed-cell foam backer rod sized to fit snugly in the joint, then apply a flexible sealant overtop. Backer rod is inexpensive (a few dollars for a 20-foot roll at any hardware store) and is essential for proper sealant performance — the sealant needs to bond to the two sides of the joint and flex between them, not bond to the bottom of the joint where it would tear.

Signs that your joints need attention include visible gaps with no sealant, sealant that has hardened and cracked, water pooling in or around the joints, and the edges of the joint chipping or spalling (called joint ravelling). If you notice the concrete on either side of a control joint is at different heights, that indicates the slab has settled or heaved unevenly — joint maintenance alone will not fix that, and you should consult a concrete professional.

Do not fill joints with rigid materials like mortar, concrete patch, or non-flexible caulk. These materials cannot accommodate movement and will crack out within one Ottawa winter, often taking chunks of the joint edge with them and making the damage worse.

Proper joint maintenance takes an hour or two once a year and costs almost nothing, but it prevents water and salt from undermining your slab from below — the same process that causes the frost heave and spalling damage that costs thousands to repair. Ottawa Garages can connect you with concrete maintenance professionals if you prefer to have it done right by an experienced hand.

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Looking for experienced contractors? The Ottawa Construction Network connects Ottawa homeowners with qualified professionals:

• Justyn Rook Contracting
• RenoMotion Inc.
• Titley Construction
• BFI Renovations
• Leeds Property Maintenance