How do I repair spalling concrete on a garage floor in the NB freeze-thaw climate?

Spalling concrete on a garage floor is a common problem in New Brunswick, and the freeze-thaw cycle is almost always the root cause — but the repair approach depends heavily on how deep the damage goes and whether you address the underlying moisture source.

Why NB Garage Floors Spall

Spalling happens when water penetrates the surface of the concrete, freezes, expands, and breaks the top layer apart from below. In New Brunswick, this cycle can repeat dozens of times in a single winter, and garage floors take a particularly brutal beating because vehicles track in road salt and slush — and road salt is one of the most aggressive accelerants of concrete spalling known to exist. The salt lowers the freezing point of water, which means freeze-thaw cycles happen at temperatures where you might not expect them, and the chloride ions in the salt chemically attack the concrete paste that holds the aggregate together.

The other major contributor in NB garages is deicers applied directly to the floor. Calcium chloride and sodium chloride products sold for walkways and driveways will destroy a concrete garage floor within a few seasons if used regularly. If you have been spreading deicer inside the garage to melt ice near the door, that is almost certainly making the spalling worse.

Assess the Damage Before You Repair

The depth and extent of the spalling determines what repair method will actually hold. Surface spalling (less than 6mm or about 1/4 inch deep) that affects the cream layer of the concrete can be addressed with a quality resurfacer. Deeper spalling (6-25mm) requires a polymer-modified repair mortar. Anything deeper than 25mm, or spalling that exposes the aggregate across large areas, or damage that includes cracking and shifting suggests a more serious problem — potentially a failed vapour barrier beneath the slab, a drainage issue, or concrete that was poured too wet or finished too early, trapping bleed water near the surface. That level of damage warrants a professional assessment before you spend money on repairs that will not last.

Also check whether the spalling is worse near the garage door. This is the most common pattern in NB garages because that zone receives the most salt-laden slush, experiences the most dramatic temperature swings, and is often where water pools if the floor does not slope properly toward a drain or toward the door opening.

The Repair Process

Start with aggressive surface preparation — this is where most DIY repairs fail. Loose, flaking, and delaminated concrete must be completely removed before any patch material is applied. Use a cold chisel and hammer or an angle grinder with a diamond cup wheel to remove all loose material back to sound concrete. Feathered edges do not hold — undercut the edges of the repair area slightly so the patch has mechanical grip. Vacuum out all dust and debris, then clean the area with a stiff brush and water. Allow it to dry completely, which in NB's humid climate may take 24-48 hours.

For surface repairs, a polymer-modified concrete resurfacer (Quikrete Concrete Resurfacer or equivalent) applied at 3-6mm thickness works well if the underlying concrete is sound. Mix to a pourable consistency, apply with a squeegee, and texture with a broom before it sets. These products bond well to clean, sound concrete and can handle NB's freeze-thaw cycles if the surface is properly prepared and the product is rated for exterior use.

For deeper repairs, use a polymer-modified repair mortar rather than plain concrete mix. Plain concrete mixed from a bag has poor adhesion to existing concrete and will pop off within a season. The polymer modifier — either pre-blended into the dry mix or added as a liquid bonding agent — is what makes the patch stay. Apply in layers no thicker than 25mm at a time, and dampen (not saturate) the existing concrete just before applying the patch so the base does not pull moisture out of the repair material too quickly.

Curing is critical. Cover the repair with plastic sheeting for at least 72 hours and keep it from freezing for a minimum of 7 days. In NB, this means timing your repairs carefully — late spring through early fall is the ideal window. Attempting concrete repairs when overnight temperatures are dropping below 5°C significantly reduces the chance of a durable result.

Preventing Future Spalling

Once the repair is complete and fully cured (28 days for full strength), apply a penetrating concrete sealer — silane or siloxane-based products are the best choice for NB garage floors because they penetrate into the concrete rather than forming a surface film that can peel. These sealers dramatically reduce water absorption and freeze-thaw damage. Reapply every 3-5 years.

Stop using salt-based deicers inside or near the garage door. Use sand for traction instead, or install a rubber threshold seal at the bottom of the garage door to keep slush and melt water from pooling on the floor.

If your garage floor lacks a vapour barrier beneath the slab, ground moisture will continue wicking up through the concrete and contributing to the problem from below. Unfortunately, this cannot be corrected without replacing the slab — but sealing the surface helps slow the moisture migration.

When to Call a Professional

If the spalling covers more than 30-40% of the floor, if the damage is deeper than 25mm across large areas, if you see cracks wider than 3mm or any vertical displacement between sections, or if the floor feels hollow when you tap it (indicating delamination below the surface), a professional assessment is the right call before investing in repairs. A contractor experienced with NB garage slabs can determine whether resurfacing is viable or whether a full slab replacement — with proper vapour barrier and air-entrained concrete this time — is the more cost-effective long-term solution.

For help finding concrete contractors or garage builders in your area, browse the New Brunswick Construction Network directory at newbrunswickconstructionnetwork.com.