Polyurethane Crack Injection



Cracks in concrete are a common problem for homeowners. If you leave them alone they will only get worse and be more expensive to repair. Cracks happen because of one or more factors. Before you consider fixing a crack, you need to know why it happened and if underlying factors are still active.

Settling, excessive weight or stress, changes from hot to cold and back again, and just plain shrinkage all work together to cause and worsen cracks in concrete.

Causes of Cracks

If you are going to fix cracks in concrete, the first important thing is to understand why there are cracks in the first place. When a concrete mix loses water before it is completely hardened, it shrinks. This is technically known as plastic shrinkage cracking.

When the ground under the concrete or your home settles, cracks occur. This is especially common with settlement around openings and embeds and causes cracks at the corners of windows, doors, or beam pockets. The usual problem is that there was insufficient consolidation of the base, a dry concrete mix, or insufficient concrete covering steel rebar.

If a home’s foundation is not solid, you will see structural cracks. These are caused directly by either horizontal forces or settling. You will see these more commonly in the block walls of a basement. The issue here is commonly the hydrostatic pressure of water as more or less water will create lateral stresses and cracks.

When a crack runs the entire length of a wall, it is typically from settling. If you suspect that there are structural issues in such a case, do not just patch the crack. Contract a professional engineer to determine what measures need to be taken to prevent serious structural damage.


Dormant cracks are those that were caused by a process that is now done. Problems caused by improper cement mix, for example, are a one-time issue. The same may be true of settling if the cracks have not changed for years. However, when you have an active issue it does not make a lot of sense to patch it until you have gotten a handle on the underlying problem. If you have a crack that is active, not structurally dangerous and progressing very slowly, make sure to inject with a flexible sealant.


Before you choose a crack injection product for concrete cracks, consider these factors:

  • Crack depth and width
  • If you have an active or dormant crack
  • If appearance is important or not
  • If you will need to seal the crack against pressure or not
  • Walls are beginning to lean noticeably
  • Floors are starting to settle and become uneven
  • Chimneys are tilting or leaning cracks can be seen in foundations or basement walls


Epoxy grouts are more popular for these reasons:

  • Epoxy resin adheres more strongly to both hardened and fresh concrete
  • You can purchase products that adhere strongly to most types of surfaces, even when wet
  • Epoxy grout has low shrinkage and excellent mechanical strength
  • These products are chemical-resistant, including to alkalis

You will inject epoxy grouts under pressure. Fix and seal injection points or nipples along the crack line and then inject the epoxy under pressure. This requires specialized equipment. The process is sometimes referred to as concrete welding because the sealed section is often stronger than the original concrete.

If you are dealing with cracks wider than 1 mm, you can also seal these by epoxy resin injection. This is especially the case on vertical concrete surfaces. But, for horizontal cracks, you can often just pour the epoxy grout into the crack.


A better choice for fine cracks in walls can be a polyurethane resin. Because these products are thinner (lower viscosity), it is easier to get them to penetrate into really fine cracks. The down side of these products is that they do not have the same bond strength as epoxy.


Active cracks that are not structurally dangerous can be sealed, but you need to use a flexible material like polyurethane which will tolerate a small amount of movement. This is especially the case then the crack may widen and narrow in a cycle with changes in temperature or hydrostatic water pressure. You can get by with a flexible epoxy resin for tiny amounts of movement but the better choice is typically polyurethane that provides greater flexibility.


Improvements in crack injection technology have come with a reduced cost as well. The professionals who inject cracks for a business use specialized equipment and have specialized training. The most important part of this is the ability to promptly recognize the reasons for your cracks and know the best products and procedures you need to do the job at a low cost.

If you have concrete cracks, they will not fix themselves and may cause problems like water issues. Call the professionals at Seattle Foundation Repairs today to check out any potentially dangerous cracks in your home.


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Residential Applications

Homeowners choose them to prevent sagging foundations. If you are experiencing cracked foundations or drywall it may be signs that your foundation needs a permanent stability solution.

Commercial Applications

Contractors use our piering systems whenever the soil sample indicates a deep foundation solution. This is required when they want to avoid excavation expenses, such as tilt-up construction.

Industrial Applications

Plant managers love our anchors because of speed in which they are installed. With our system there is minimum impact to daily operations.