While hairline fractures in your concrete countertop can give it character, some might prefer a sleeker surface. If you’re going for a pristine look, then look no further!

After all, these cracks can also make maintenance more complicated as dirt will accumulate inside them. In the following paragraphs, we will guide you through the necessary steps to fix those cracks.

How to fix cracks in concrete countertops

What causes hairline cracks in concrete?

Regardless of the size of the cracks in your concrete countertop, most of the time the cause of them can be summed up to stress. Yes, materials can get stressed out too. In fact, a hairline crack will form when tensile stress builds up in the concrete and is too much for the material to bear.

Another common reason why you may see hairline cracks in your concrete countertop is shrinking. In a similar fashion to stress, concrete can shrink down and crack.

Another note is that weaker parts of your countertop where the concrete is thinner, such as around the sink or edges of the counter, may be susceptible to cracks as well. If you’re noticing larger cracks, the cause of these could be “flexing” which can be caused by your house settling.

Other reasons you may have cracks in your concrete are as follows:

• heat and humidity in your interior space 

• a bad base for your countertop 

• overwatering, or water resting on and around the surface

Photo: Flickr- Jeremy Levine

How to repair cracks in concrete

Hairline cracks don’t have an impact on the structural integrity of your concrete countertop so sealing and concealing the hairline fracture are the main objectives of the restoration process.

The first thing to consider when repairing hairline cracks in your concrete countertop is that any attempts to fix fractures must be done with great precision, otherwise the repairs may look obvious and be a waste of effort. Essentially, it begins with choosing the correct filler. 

When filling the fracture, you must make sure the filler will bond adhesively to the concrete and refurbish the countertop's smooth surface, all while creating a liquid-proof barrier to stop liquids from penetrating. The ideal material for this project is both flexible and strong; using a sealer that’s stronger than concrete will help you avoid further issues with cracking.

When repairing hairline cracks, remember that it can be challenging. Both patience and a good eye are required to fix the crack so the colour matches, and so the crack essentially disappears. Hairline cracks haven’t fully opened which means there isn’t that much room to work with, so a liquid sealer of a very low viscosity will work best to penetrate the depth of the opening. 

Preparing the concrete for repair

The first essential step to repair the fracture is making sure the concrete is clean of any oil or other stains. If anything has penetrated the fracture, it can leave stains that need to be cleared away first.

If the crack has just appeared and doesn’t seem to be stained, you can proceed to work a fresh sealer into the fracture. Using gloves, you can rub the sealer to fill every nook and cranny.

For the crack to be effectively repaired, the sealer needs to be able to penetrate the opening and fill it completely. An ideal sealer will have low surface tension and a low viscosity since those two factors help the liquid sealer seep into the depths. 

While common concrete countertop topical sealers can be used, it's not recommended as they’re not formulated to penetrate a hairline crack and fill it completely. Many of these sealers have low solids content, however, when using a material with a high solids content, it will not shrink when curing. This is something to avoid at all costs because if the material shrinks while curing, it can pull away from the concrete and potentially leave an unsightly gap. 

Finding an epoxy that is very fluid will both fill and seal effectively, since these types of products wet the outside of the concrete countertop, which means that they can fill the crack more adequately. From an aesthetic standpoint, epoxies can give a darker appearance.

Concrete countertop fillers

The most common materials for crack repairs in concrete countertops are polymer-based cement grouts, silicone or latex caulking, or epoxies. While these can be colour matched to give a smooth and blended look to the countertop, they do have benefits and drawbacks.

Polymer-based ciment grout

When concrete countertops are being manufactured, polymer-based cement grout is typically used to fill any gaps in the surface. Cracks can appear before the concrete is properly sealed and if this is the case, polymer-based cement grout is often used. 

The major downside to polymer-based cement grout is that it can be hard to work into hairline cracks that are tight, which means that it only covers the surface and doesn't bond the concrete together. Of course, this material must be sealed to avoid staining and liquid penetration but considering that it is quite rigid, this could lead to future cracking.

Silicone and latex

Both types of caulking (silicone and latex) are quite easily worked into cracks but more effort will be needed for hairline cracks. A big problem with caulking is that it doesn’t penetrate cracks very deeply, making it more of a flexible covering than a filler. 

Because of the nature of caulk, it may react with the concrete and will degrade over time in areas that are in contact with water often. In such a case, it would be wise to seal the area with a low viscosity sealer before filling the sealed crack with caulking.

Epoxy

For a concrete countertop crack, epoxy made for laminating stone is a great choice for filling it in. This type of epoxy comes in two forms: knife grade and flowing grade. Knife grade epoxy is very thick, with a composition like petroleum jelly, while flowing grade is much thinner and will penetrate more easily without being worked in.

So, carrying out your own repairs on hairline cracks in your concrete countertop is far easier than most would initially think. Nevertheless, as with all home improvement projects, it is recommended to consult an expert to be certain your home improvement project goes off without a hitch.

Author: David Benzaken