18.04 2025
Lights on: How does a wall signal "SOS" and what to do?
A crack in a wall is not cosmetic, but a warning letter from the structure. To “read” it correctly, it is important to understand where the gap originates, along what route it creeps and what to do to stop the process.
1. Where cracks most often originate
- Corners of openings. In the frame of a window or door, the flow of forces abruptly changes direction; tensile stress is concentrated at a point and “tears” the material diagonally.
- Joint of the foundation and the wall. If the soil subsides unevenly, the foundation “pulls” the wall from below; the gap starts literally at the base and gradually rises upward.
- Long walls not cut by expansion joints. During daily heating and cooling, the masonry expands and contracts, and at one point a vertical joint opens in the middle of the span.
- Ribs of monolithic elements. At the sharp “G” and “T” corners of the frame, the concrete experiences chips that turn into cracks, barely reaching the tensile strength limit.
2. Bottom-up or top-down?
- Soil problems (subsidence, heaving, erosion) almost always “draw” cracks from the bottom up: the first web appears at the base of the foundation, then moves to the plinth, and then to the brick or concrete of the wall.
- Overload of floors, shrinkage of fresh masonry or drying of the upper wooden crowns create tension at the top of the wall; the gap goes from top to bottom.
- Temperature difference can give rise to two counter cracks that converge closer to the middle of the span and look like an open “hourglass”.
3. What shape do different cracks take?
The crack profile is the “signature” of the cause.
- Vertical crack, wider at the top. Most often a sign of corner subsidence (structural split): opens up more in spring, tightens slightly in summer.
- Step at the seams. Brickwork gives a diagonal of horizontal and vertical sections if one corner of the building subsides faster.
- Diagonal 45° above the opening. Appears when the old frame was removed without supports or the lintel was overloaded.
- Horizontal every five to six rows. Often signals corrosion of metal connections: the outer row “comes unstuck” from the core.
Engineers additionally evaluate the width of the opening: microcracks up to 0.1 mm are almost invisible to the eye; 0.2-0.5 mm already require repair; anything wider than half a millimeter is considered an emergency according to European standards.
4. Live and “dormant” ruptures
- Active (live). The width changes noticeably from season to season over time; moisture and oxygen reach the reinforcement, accelerating corrosion in the case of reinforced concrete structures.
- Stable (dormant). They arose due to a one-time shrinkage or a single overload and no longer grow. They can be treated pointwise without touching the base, but it is very important to make sure that they have stabilized and do not grow over time. Temperature movement will still occur if the cracks are not “sewn up” with the right reinforcement or polymer materials.
To distinguish one from the other, beacons are placed on the crack (the type and type of beacon varies from a piece of tape to professional 3D beacons): if it identified movement over a couple of months, you have a live defect in front of you.
5. Four traditional repair methods
- Expansion and filling with mortar. Clean the joint, wet it, press in the lime-cement mixture. Suitable only for stable thin cracks; the main advantage is the price and half an hour of labor per meter.
- Metal “stitching”. Grouts are cut across the crack, reinforcement is laid and filled with mortar. The method restores the bearing capacity.
- Cement injection. Fine Portland cement is supplied under low pressure, filling the pores. The method is environmentally friendly and relatively inexpensive, but useless if water is leaking from the crack.
- Foundation sub-concrete. Pits are dug along the wall in a checkerboard pattern and concrete is poured, essentially building up the base. Radical, but time-consuming and expensive: a week of downtime is the norm.
6. Modern solutions
a) Polymer resins
- Epoxy injection. The two-component resin fills the gap entirely and, after curing, holds up to 40 MPa of shear — stronger than concrete itself. It will take about an hour of active labor per meter of seam.
- Polyurethane foam. Wet contact triggers a reaction: the composition foams 20-40 times in minutes, instantly stopping the leak. In terms of time, this is the fastest method: less than an hour per meter and no downtime.
b) Composite reinforcement (CFRP)
Carbon fiber tapes or a “cocoon” around the column are glued with epoxy or other special materials. The mass is almost zero, and the load-bearing capacity increases by 30-50% – confirmed by tests by scientific groups.
c) Micro- and geopolymer injections
Mineral or sol-gel based suspensions penetrate even 0.05 mm cracks, harden without shrinkage and reduce concrete permeability.
d) Self-healing concrete
Capsules with epoxy or bacteria Bacillus are introduced into the mixture at the plant. When a microcrack appears after years, the capsule will open and the polymer or calcium carbonate will “glue” the gap. At the construction site, this requires zero additional hours – the material works itself.
7. How to estimate labor costs
- Minimum time — polyurethane injection: one shift, the premises can be put into operation by the end of the day.
- Average volume — epoxy: more preparatory operations and curing time (up to a day), but the strength is fully restored.
- Maximum hours — concreting: excavation work, formwork, concrete strength gain — the count goes into tens of man-hours.
If the facility is important to the business (a store, a cafe) and every day of downtime means money, then polymer technologies pay for themselves even with a higher price for the material.
8. How to prevent new cracks
- Make proper drainage: water should flow away from the foundation, not wash away the soil underneath it.
- Cut expansion joints on long facades every 20–30 meters.
- Monitor the humidity of the basement level and the serviceability of the storm drain: dry concrete cracks less often.
- Unload the floors: heavy pallets cannot be stored on a slab designed for an office.
The main thing
A crack is not “cosmetics”, but a dialogue between the building and the owner. Bottom-up? — check the foundation and soil. Top-down? — look for overloads or shrinkage of the masonry. Choose a treatment method based on two criteria: whether the crack is active and when the object should be operational again. Traditional solutions are suitable for quiet, old cracks; modern polymers and composites allow you to restore strength and protect the building from water and corrosion in a day. The main thing is to eliminate the cause, then a new crack will not appear either from above or below.
