Whenever you think your wall has been holding up well over the years, it can be a bummer to sometimes notice a few hairline cracks, especially in mortar joints. However, this can be quickly remedied with a mortar mix, but you must consider a few other things. 

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You will find in this article the causes of hairline cracks, how to prevent them, and a few tips & tricks on fixing these cracks.

What Causes Hairline Cracks In Masonry Mortar?

Hairline cracking within concrete block walls results from internal stresses resulting from shrinkage and thermal expansion & contraction, which are expected to happen as time passes.

These factors need to be considered in the design and construction of your house, especially your walls. Indicated below are incidents that could cause your mortar walls to crack.

Resettling Of Subgrade Or Foundations

Soil excavation is done to place the foundations of a building. As the ground settles down over time, the house’s foundation shifts slightly, causing small vertical cracks.

But depending on the kind of soil your house is built on, your house could experience more drastic movement that can greatly damage it.

Additionally, natural disasters like earthquakes, floods, and hurricanes can significantly damage your house’s foundation.

Environmental And Climatic Influences

An example would be a nearby tree growing. Its roots are invasive and can damage the foundation of your house.

The tree would start to have bigger and longer roots that could extend to the underside of your wall, causing it to crack. They also need a lot of water, affecting the soil’s moisture and causing cracks. In addition, water can damage both the walls and foundations over long periods of drought.

Natural Deterioration And Aging

The building’s beams, columns, and other reinforcements are prone to corrosion and wearing, especially if the concrete foundation is not done properly. Cracks in the foundations expose the steel reinforcement to moisture which can cause rusting and may lead to brick wall cracks.

Ground Vibration

As mentioned earlier, natural disasters also cause hairline cracks, especially earthquakes. The vibrations and movement of the ground can worsen even the slightest sag or play in any loose or poorly constructed part of your home.

Tips On Fixing Fix Hairline Cracks In Mortar Joints

So how do you fix hairline cracks in mortar joints? It’s a fairly simple and easy process, but it does require a bit of time. To start restoring your mortar joints, you’re going to need a few tools.

What You’ll Need

  • Clean Paint Brush or Any Brush With Soft Bristles
  • Chisel or Putty knife
  • Water Spray Bottle
  • Pointing Trowel
  • Mortar mix

Steps and Procedure

1. The first step in this procedure is to remove any loose mortar. Use a putty knife and scrape along the mortar joints. But if the cracks are severe, you might want to resort to removing the cracked mortar.

You can use a chisel or angle grinder to remove the cracked mortar. You’ll be filling them out later, so you have nothing to worry about. Just be careful not to damage the bricks.

2. After scraping out the loose mortar or chiseling out the damages, use a clean paintbrush to brush off any dust or flakes in the cavity joints to make the application process easier.

Prep the joints for the application. You’ll want to spray them with water lightly. Use a garden hose or a bucket of water, but don’t soak the wall. You only need the bricks to be misted or moist.

3. The next step is to mix the mortar mix. Use only the amount of water specified on the instructions that come with the mix. Add the water bit by bit to get a good consistency, which should feel like peanut butter and is thick enough to stick to the surface.

Let the mix rest for around 10 minutes to absorb the water. The mix should feel stiff but not crumbly. And if the mortar mix is drying, do not add water to try and revive it. Instead, make a new mixture.

4. Now, you can apply the mixture to the joints you’ve cleared. You can put some of the mixtures on a piece of wood or some platter to make the job easier. Use the pointed trowel to push the mortar mix into the joints and pack them down for maximum durability and waterproofing.

Ensure the mortar is not directly hit by the sun in hot weather. It’s a bad thing for it to dry too quickly. Make some shade or work on the shaded parts first.

5. Clean the bricks again with a brush. Using a brush with soft bristles should be best to keep the mortar from smearing. Remove any chunks on the brick face before the mortar hardens.

How To Prevent Hairline Cracks In Mortar Joints?

It would be best to do a few things to prevent these cracks from happening. These things may not apply to everyone, but it’s worth noting.

Proper Use Of Expansion Joints

Expansion joints will keep the wall from cracking when exposed to temperature changes and exposure to moisture.

Proper Work Execution

If the work is done right from the beginning, there won’t be a problem later on. Don’t forget to check instructions and follow proper procedures.

Removal Of Space Or Shims

You should remove all temporary shims used during building from the walls. Most of the shims are made of stainless steel, and removing them will prevent the wall from rusting and cracking.

Using the recommended materials that are also versatile can go a long way and help you avoid any damages to a point.

Fixing Hairline Cracks In Mortar Joints Can Be An Easy DIY

Repairing your mortar joints isn’t difficult. If you’re struggling, consult an expert in the field to advise or help you in the process.

Editorial Contributors
Matt Greenfield

Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

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