Foundation Crack Filler: The Five DIY Products, Compared

The hardware-store aisle has five products that all claim to fix a foundation crack — a two-part epoxy kit, a polyurethane foam kit, a tub of hydraulic cement, a vinyl patching compound, and a flexible masonry caulk — and the right one depends entirely on the crack in front of you. But the first question isn't which product. It's whether your crack is a DIY job at all. The honest answer is that consumer crack fillers are for cosmetic hairlines and nothing more: they fix the crack, never the cause. A crack that's moving, leaking under pressure, offset, horizontal, or growing is a symptom of foundation movement, and no tube from the shelf addresses the soil doing the moving. This page sorts the five products — what each is actually for, when a homeowner can reasonably DIY, and the line where you should put the product down and call an engineer instead.

First, Is This a DIY Crack?

Before any product comparison, the gate question: is this crack cosmetic, or is it structural? Get this wrong and the most carefully chosen filler is the wrong purchase.

DIY product is reasonable only for a cosmetic hairline that meets all of these:

• Width under about ⅛ inch — a fine, even hairline, not a gap you can fit a coin into.
• No displacement — the two faces sit flush; run a fingernail across and feel no step out of plane.
• No active leak — it isn't weeping water, and there's no hydrostatic pressure pushing through it.
• No progression — it hasn't measurably widened, lengthened, or developed offset across a full wet-and-dry season.

A single thin vertical or hairline crack with none of those traits is almost always cosmetic shrinkage — the ordinary record of concrete curing — and sealing it is a legitimate weekend job. The full decision framework for telling cosmetic from structural lives on our normal vs. structural cracks guide, and the thinnest cracks specifically are covered on the hairline cracks page; this page won't re-derive that — it picks up after you've confirmed the crack is cosmetic.

The cracks that send you the other way — to stop, not to shop — are the ones with any structural tell: width over roughly ⅛ to ¼ inch, a horizontal direction across the wall, a stair-step pattern in brick or block, displacement between the faces, active growth, or a crack paired with sticking doors across multiple rooms or visibly sloping floors. Those are not product problems. They're engineering problems, and the next section's table won't help you with them — the engineer's report will.

The Five Products, Compared

This is the centerpiece. Five products, what each is built for, and where each fails. Read it as a matching exercise, not a ranking — there is no "best," only the right tool for a specific, correctly diagnosed crack.

Two distinctions in that table do most of the work. The first is moisture: epoxy needs a dry surface, while polyurethane tolerates — even requires — moisture, which is the whole reason they aren't interchangeable. The second is structural versus not: only epoxy restores strength; polyurethane, hydraulic cement, patching compound, and caulk all seal or cosmetically fill without making the concrete stronger. And one limitation applies to both injection kits: high-pressure injection only works on solid poured concrete — on hollow concrete block (CMU), the material just flows into the cores, so block walls need a different approach entirely.

Match the Product to the Crack

With the table in hand, the decision tree is short. Diagnose the crack's behavior, then pick:

• Dry and structural, in poured concrete → epoxy injection kit. A stable crack that needs its strength back. Epoxy welds it monolithically. The full step-by-step — port spacing, surface seal, low-pressure injection from the bottom up — lives on our epoxy injection guide; the short version is that the surface must be dry and clean, and patience during injection is everything.
• Leaking or slightly moving → polyurethane injection kit. Where water is coming through or the crack still cycles a little, polyurethane reacts with the moisture, expands to fill the void, and stays flexible. See the polyurethane injection guide for the install. (If the leak is a fast, plug-it-now emergency around a penetration, hydraulic cement is the faster patch — just treat it as temporary.)
• Cosmetic surface crack, spall, or divot → patching compound. Shallow, appearance-only damage on the face of the concrete. A vinyl or acrylic patcher fills and paints over it.
• Brick or mortar hairline → masonry caulk. A flexible elastomeric filler moves with the joint and seals out weather without pretending to be structural.

The throughline: you're matching the product to what the crack is doing — bearing load, leaking, or just showing. Get the behavior right and the product follows.

What to Buy at the Home Center (and the Brands You'll See)

In practical terms, here's what's actually on the shelf and the rough money involved. These are categories and well-known brand examples, not recommendations or rankings — and prices are estimates that vary by region and product size.

• Cosmetic patching and masonry fillers — vinyl concrete patchers, hydraulic cement, and masonry/elastomeric caulks. Quikrete-type products are the category you'll recognize here: a vinyl concrete patcher for surface cracks, a hydraulic cement (about $10–$15 per 10 lb) for active leaks and penetrations, and a masonry crack filler for brick and mortar. Budget roughly $15–$30 for cosmetic sealing.
• Injection kits — two-part epoxy or polyurethane systems with surface ports and a delivery method, sold as complete kits. Sika injection kits are a commonly seen example of this category. A DIY injection kit typically runs about $60–$150.

That's the entire honest price picture for a cosmetic job: tens of dollars for a tube, low hundreds for a kit. There is no affiliate angle here and no "best product" to crown — the kit you need is dictated by your crack, not by a label. If a crack genuinely warrants more than a $150 kit, that's usually the signal it's no longer a DIY crack. For what professional work costs by comparison, see the crack repair cost breakdown.

The DIY Mistakes That Cost You Later

Most DIY crack-repair regret traces to three avoidable errors — each one a case of using the right product on the wrong crack, or the wrong product on the right one.

1. Smearing a surface patch over a crack you might later need injected. This is the expensive one. If a crack turns out to be structural and needs professional injection, the resin has to penetrate through open ports along the crack. Old patching compound or hydraulic cement clogs that path, so the contractor must grind it out or work around it — and epoxy won't bond to previously patched concrete at all. A cosmetic cover-up on an undiagnosed crack can make the real repair harder and pricier.
2. Using epoxy on a wet crack. Epoxy needs a dry, clean surface; it will not adhere to damp or actively leaking concrete. Reach for epoxy on a weeping crack and it simply won't bond — that's the case for polyurethane or hydraulic cement instead.
3. Treating a structural crack as cosmetic. The costliest mistake of all isn't about product choice — it's skipping the diagnosis. Filling a horizontal, offset, or growing crack hides a symptom while the underlying movement continues, and you lose the early warning that something structural is in progress. The crack comes back, and so does the problem behind it.

The pattern behind all three: diagnose first, buy second.

When to Skip the Store

There's a clear line where the right move is to walk past the aisle entirely. Skip the store — and go to an engineer — when the crack is:

• Wider than about ⅛ inch, or wide enough to fit a coin edge into.
• Horizontal across a wall — the highest-urgency pattern, usually meaning soil or hydrostatic pressure is pushing the wall inward.
• Stair-stepped in brick or block and wider than about ¼ inch, or visibly progressing.
• Offset — one face shifted out of plane so you can feel a step across it.
• Growing — measurably widening or lengthening over time.
• Paired with other signs — sticking doors across multiple rooms, sloping floors, or a bowing or bulging wall.

Any one of these means you're looking at foundation movement, not a surface defect, and no consumer product fixes movement. The right next purchase is a diagnosis: an independent engineer quantifies what's actually happening and specifies the real repair, which on a moving foundation is usually about the soil and the load path — not about the crack at all.

FAQ Note

The FAQ below covers what homeowners ask most while standing in the aisle — which filler is "best," whether a Home Depot product can fix a foundation crack, which Quikrete-type product fits which situation, epoxy versus polyurethane, whether hydraulic cement and crack filler stop leaks, how big is too big for DIY, and whether DIY patching can cause problems later. For the upstream decision — is the crack even cosmetic? — start with normal vs. structural cracks; for the installs, see the epoxy injection and polyurethane injection guides; and for the broader picture, the crack repair hub.

Get Matched With a Vetted San Antonio Foundation Specialist

If you've confirmed your crack is cosmetic, a $15–$150 product and a careful afternoon are usually all it takes — no specialist required. But if the crack is wider than a hairline, offset, horizontal, stair-stepped, growing, or paired with sticking doors or sloping floors, that's foundation movement, and the right next step is a measurement, not a tube of filler. We'll match you with a vetted San Antonio foundation specialist — and point you to an independent engineer who can confirm whether the crack is cosmetic or structural before you spend anything. The match is free, the quote is no-obligation, and we don't take a fee from you. We screen for a sealed-engineer diagnosis done before any repair is quoted, the correct fix for the measured damage, and a clean Bexar County permit record. If a contractor wants to inject a crack that an engineer hasn't classified — or waves off a horizontal crack that warrants real attention — we'll tell you. That's the only way an editorial matching service should work.