How to Repair Cracks in Concrete Floors
and Floor-to-Wall Joints These are the most common problems in basements. Almost all concrete slabs have some cracks. And many older basements develop a “leaky” floor-to-wall joint. Usually, water leaks in only occasionally during a major rainstorm or snow melt and such cracks can be repaired. However, if it becomes a regular problem, consider installing a sump pump to relieve the hydrostatic pressure on the foundation. Foundation slabs, concrete driveways, factory or warehouse floors have similar crack problems. How not to fix cracks Caulking over the cracks is useless. Water will fill up the crack and wick through the layer holding the caulk, which destroys the bond and the caulk gets loose. Hydraulic cement is a temporary fix only. It actually does not bond to concrete – that’s why you must make an inverted V-groove. And it is much more rigid than concrete, which continuously moves, shrinks and expands. This stiff “rod” will gradually get loose and water will start seeping around it. How to repair cracks in concrete slabs First, deep-seal the concrete with RadonSeal to strengthen the concrete and prevent further cracking. Any existing cracks will help the sealer penetrate into the concrete. RadonSeal also tends to close hairline cracks as it reacts and expands, particularly in concrete floors. But the crack may be wider below the surface. Self-leveling polyurethane caulk is available in stores. Route out the crack with a hand-held grinder at least ½” deep and fill with the caulk. The self-leveling caulk sinks into the narrow crack. Two passes may be required to make it level with the surface. If the crack is wider, say over ¼”, fill the routed crack with normal polyurethane caulk. But this allows water into the part of the crack not filled with caulk. Or avoid grinding by using our Easy-Peel Crack Injection Kit. The forceful expansion of polyurethane foam assures that the entire crack is filled, keeping water completely out permanently. If the crack is wider, say over 1/8”, push in some sand first to prevent the polyurethane from leaking out of the bottom and expanding below the slab. If you need also a strong surface of the repair, which will not wear out in traffic, use our Epoxy Crack Filler. It uses an advanced epoxy, much stronger than concrete but flexible to allow for its natural movement. Other epoxies are rigid, which can lead to new cracks developing parallel to the original crack. Route out hairline cracks with a hand-held grinder at least ½” deep and pour in pure epoxy, which will sink deep into the narrow crack. A second pass half an hour later will make the repair level with the surface. In case of wider cracks, insert first a foam backer rod of fill partially with sand and then, fill with the epoxy-sand mixture. For more information, visit Epoxy Crack Filler How to repair floor-to-wall joints Once the basement gets a bit older and the exterior waterproofing coating disintegrates, occasional water seepage apparently through the floor-to-wall joint becomes a very common problem. Why it happens:
- As water works its way through the concrete walls, it comes out at the bottom of the wall, making it look like it is coming up from the floor-to-wall joint.
- In case of concrete block walls, a water column builds up inside their unfilled hollow cores and the hydrostatic head pressure pushes the water out through the lowest blocks.
When there is not a significant gap, we find that in most cases it is enough to seal the walls (and floor) with RadonSeal. This stops the water migration or seepage coming out at the joint. If this is not enough, route out the joint with a hand-held grinder ½” deep and fill with polyurethane caulk or Epoxy Crack Filler. “Floating slab” construction allows the floor slab to move, shrink and expand, without imparting structural stresses on the foundation walls. There is often a visible gap between the floor and the walls. Sometimes, builders allow for a wide gap to drain any water that will seep through the walls in the future, which is a poor practice. An open floor-to-wall joint lets in soil gas carrying lots of water vapor and often, radon gas. You cannot finish the basement because the framed walls would trap all the vapor and cause molds. You have to repair the joint while still allowing the slab to move. The open joint can be repaired with self-leveling polyurethane caulk, Easy-Peel Crack Injection Kit, polyurethane caulk, or our Epoxy Crack Filler. The same procedure as for cracks in slabs as described above. Sometimes, water really comes up through the open joint. It could be caused by a once-in-a-decade rainstorm, plugged gutters or downspouts, and similar. You may repair the problem by diverting the rainwater away from the foundation. However, if this becomes a regular problem, you may need to install a sump pump to relieve the hydrostatic pressure from underneath the slab. For more information, visit Epoxy Crack Filler for Concrete or Do-It-Yourself Foundation Crack Repair.
Any questions? Please contact us by e-mail,
telephone (203) 225-0366 or toll-free 1-800-472-0603
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Products not sold through retail stores. Available exclusively from:
Radon Mitigation & Waterproofing Concrete Sealer Co.
Novion Inc., 18 L'Hermitage Drive, Shelton, CT 06484 USA
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