Foundation wall or slab crack repair using polyurethane foam injection: this article explains how to use injected polyurethane foam to repair a concrete basement (or crawl area) wall or slab crack in order to stop basement or crawl space water entry or air leakage.
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A variety of site conditions can lead to cracks in a concrete or other masonry foundation wall. Speaking generally, foundations may be damaged and cracks may appear from innocent causes unlikely to affect the structure such as shrinkage cracks, initial settlement, or from potentially more serious causes such as ongoing settlement, unusual pressures or loading, or from improper construction.
Before repairing a foundation crack by sealing it against water entry, it is important to diagnose the cause of the crack and its effects on the building structure. If there is an underlying ongoing problem causing foundation movement or damage, that problem should be corrected.
Cracks in concrete walls that are larger than 1/4", cracks which are increasing in size, or cracks which are indicative of foundation movement should be evaluated by a professional. The diagnosis and evaluation of foundation cracks and structural foundation damage and repair methods are discussed at FOUNDATION REPAIR METHODS
Shrinkage cracks and in some cases other foundation cracks such as those caused by minor initial settlement might not be a structural concern but may still form an opening leading to water leaks into the building. Concrete shrinks as a natural process of it curing. This shrinkage causes the concrete to develop stresses and to relieve it, the basement wall cracks.
Concrete shrinkage cracks are a common condition in a concrete foundation [or also in concrete slabs unless control joints were used in the wall or floor design] and occur when concrete shrinks as it dries and cures.
Shrinkage cracks are easy to recognize and to distinguish from cracks that occur later in the life of a foundation because [usually] the cracks are not continuous and tend to extend in a very irregular line through the concrete (as shown in the photo) range in length from a few inches to the entire height of the concrete wall, extending from wall top to bottom.
Concrete shrinkage cracks virtually always extend through the full thickness of the foundation wall, which means they can provide a ready path for water entry into the building.
Common areas for a shrinkage concrete crack to develop are under a basement window, above a doorway in the middle of a long wall or where the foundation "steps down." Shrinkage cracks also often occur near the middle of a large poured concrete wall [or floor] if no control joints were used. [Concrete control joints are very often omitted in residential construction. Shrinkage cracks and how to recognize and diagnose them are discussed further at SHRINKAGE vs EXPANSION vs SETTLEMENT.
Once concrete cracks in a basement or crawl space wall or floor slab, it is possible for water to leak into a building through the crack. There are several ways to repair a basement crack leak. An easy, quick, and effective measure to stop basement or crawl space water entry through a foundation crack is to perform an injection of polyurethane foam into the basement crack. [Also be sure to find and fix the sources of water outside.]
Both commercial and home-owner "do it yourself" kits and equipment are available to seal foundation cracks using this foam method. [Photograph of this foundation crack repair kit, courtesy of Applied Technologies].
Polyurethane foams are injected into the basement crack in a liquid form. This allows a gentle and slow filling process of the basement crack that will completely fill the crack. After a few minutes the polyurethane will begin to react with the water in the crack to begin foaming. Water is actually the catalyst that converts the liquid polyurethane into foam. This foaming action increases the volume of the polyurethane up to 30 times its liquid form.
As the polyurethane foam expands it fills the basement crack from bottom to top and front to back. The finished foam will be a closed cell structure that will not allow water to leak into the basement crack. In fact, if there are any voids in the soil outside of the basement- such as under a rock or if the foundation is backfilled with gravel-the polyurethane foam will expand and extend out into the void.
The polyurethane foam forms a strong bond to the concrete. This bond will be able to withstand the hydrostatic pressure that may develop from high subsurface water levels. High underground or "subsurface" water levels are typically caused by heavy rains and most-often by failure to direct roof runoff or nearby surface runoff away from the building.
This concrete crack repair process using polyurethane injection is likely to be more successful and more durable than other crack patching methods. Surface patching of the crack is just that. Only the inside of the basement wall is covered by a repair. Chiseling out the crack and filling it with hydraulic cement only fills a portion of the crack.
Water can still enter the basement crack and will eventually force out the patch or hydraulic cement. [Forces that tend to cause separation of poorly-bonded concrete surface patches include the molecular action of crystallizing mineral salts left behind as moisture passes through the masonry wall.]
Basement crack injection is a quick repair process that stops water leaks. The technician does not have to drill into the concrete to do it. For this reason the basement crack repair is a clean process. The technician will attach ports to the surface of the basement crack that allow the liquid polyurethane to enter the basement wall and stop the leak.
Once the basement wall crack is completed, water will not be able to leak into the basement. Now the homeowner's possessions will be safe. As will any insulation on the basement walls, the drywall or the framing used to finish the basement.
List of Polyurethane Crack Sealants Products, Sources, Brands, Manufacturers
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Frequently Asked Questions (FAQs)
Question: concrete slab roof leaks repair with polyurethane?
(Apr 22, 2011) judy said:
our roof is made of concrete slab instead of corrugated sheet? there is water leak everytime it rains because of the crack on the floor which results in messing my ceiling. Can this polyuretahne foam injection be applied to the crack to seal the crack on the roof?
The manufacturer of polyurethane foam describes the product as useful for sealing against water leaks through cracks in concrete. If the crack is cleaned and dry before applying the sealant you are likely to have a better result.
Watch out: it's always better to fix a roof leak from the outdoor or exposed side. Especially on low slope roofing, water that leaks in at a given point often travels to show up somewhere else in the roof system, making tracking down a leak source tricky. But once sealing the crack where water is presently leaking in you might find that because you never fixed the roof leak, water simply travels further to enter at another crack.
And if you live in a freezing climate, failing to fix the roof leak from outside means you are leaving the roof exposed to continued freeze-thaw cycle damage.
Question: unsuccessful prior crack repairs
(May 25, 2011) Dave said:
My leaks are coming from previously repaired cracks using hydraulic cement and I am going to inject poly foam should i chip out the cement or just put my ports over it. If I chip it I am worried it may open up a much bigger crack! Can someone advise me please?
The reason we sometimes chip out small cracks prior to repair is to permit a mechanically sound patch - we chip out the crack to form an inverted vee (the crack is wider inside the foundation wall than at the wall surface). But if you are sealing with poly foam injection, this may be less critical than vacuuming and cleaning out the crack. Take a look at what the poly foam crack sealant manufacturer recommends and do what they say - the manufacturer has a great interest in making sure that their product is used successfully.
Question: is water needed for crack repair catalyst
(Aug 30, 2011) Curt said:
What if water is not currently present in the crack you are filling? If water is the catalyst, should the walls be mositened somehow? How much moisture is really needed to craete a good bond? Thanks
Curt, in my experience moisture in air is usually enough to act as the needed foam catalyst. That's especially so during a humid summer or fall.
In very dry conditions I have lightly sprayed a water mist on or into cracks or where we were injecting foam. Don't overdo it.
Question: cracks in concrete floor - fill with sand first?
(Oct 11, 2011) Rosalie Willard said:
I have 1/2 inch wide cracks in a concrete floor. The cracks seem to be through the entire slab but are not long. Anything liquid just disappears down the crack. should I try to fill it with sand or something before putting the foam in the cracks?
Rosalie, that's a good question. Expanding foams usually expand quickly enough that one does not have to install a base gasket or filler in the crack bottom. But a 1/2" crack is pretty big and you describe what might be a fairly large cavity below it that could waste foam during the injection procedure.
I'd try injecting a few feet of crack, speeding the nozzle along the crack and watching the foam expand to just fill the thickness of the concrete itself. Stop, watch the sealant material. If it does not drop down through the crack and disappear you're ok.
Otherwise you may need to try pouring sand or stuffing a foam backer rod into the bottom of the crack before sealing it.
Finally: if you have a large cavity below a cracking concrete floor, I'm concerned that even after sealing the crack you'll see further cracking and settlement. Some diagnosis of the cause is in order so that we know what to expect.
Question: nails into block wall made holes that now leak
(Oct 21, 2011) Matt said:
I have had my basement waterproofed but the previous home owner nailed into the blocks so he could finish the basement. Water was coming through the holes and down the walls. I took hydraulic cement and filled the holes a couple of years ago. Now the water is seaping through again. What should I do?
The best repair would have been to get water away from the building walls outside - that's the place to start - check first roof drainage for clogged spilling gutters, and for surface runoff that is directed against the building foundation walls.
Repairing a leaky foundation wall from the inside sometimes sort of works ... like the little Dutch boy with his finger in the dike. It's the least reliable. A good hydraulic cement patching compound might work, but there is nothing better than relieving the water pressure from outside.
If you try patching again be sure that the surfaces are clean of debris. Even a hydraulic cement patching compound like Thoropatch that will permit application on a wet surface (or swimming pool patching compounds that will permit application even under water) still if the surface is loose, granular, and dirty the patch may have trouble bonding.
(Dec 1, 2011) Jason said:
Great article. The major home improvement stores do not carry polyurethane foam injection products. I'm trying not to use hydralic cement or caulk due to their often temporary fix. I don't have the resources to pay a professional to do the injection so I'm trying to purchase a poly injection kit. Where can this be purchased for the best price? Thanks
Jason if the manufacturer, contacted directly, is not willing to see their product sold directly to a homeowner, a second choice might be to purchase a caulk commonly used to seal cracks against radon entry.
Question: repair pool decking cracked through?
(Dec 26, 2011) Pamela said:
Can this procedure be used to repair cool decking that is cracked all the way through?
Pamela, I bet you meant "pool decking" ?? In any case, polurethane foam injection can be effective at sealing cracks in concrete against leakage, but it is by no means a structural repair. If you are talking about concrete walks or "decking" surrounding a swim pool, you'll want to watch out for settlement and trip hazards.
Question: repair cracks from outside?
(July 27, 2012) Brian said:
Thanks for the great information! Your website is extremely helpful for professionals and do it your selfers. If a basement is already drywalled and finished I suppose that excavation and outside filling of the crack would be the best method for this? Would outside filling with poly sealant be recommended over inside filling anyway? Also if I can reach the cracks by excavation outside should I just do the poly sealant, would that be enough to stop a leaking crack, or would some kind of waterproof coating be recommended as well?
thanks again for the help guys!
Brian, your supposition makes some sense, but every site and case can be different so the most economical repair choice (and most effective repair) between inside and outside repair also will vary.
Generally it's less expensive to repair a cracked wall from inside the building because of the cost of the excavation necessary outside; and there is risk of added foundation damage if the excavator is not expert.
In general I prefer to fix foundation leaks from outside by addressing roof and surface water and runoff first, but when we move on to digging up the whole foundation and installing drainage, those costs skyrocket -which is why there is a "little dutch boy at the dike" repair approach of fixing leaks from inside the wall.
Properly applied, pressure injection of a crack sealant such as the ones discussed here will flow through the thickenss of the foundation wall all the way to outside the building, fully filling the crack. So it is not necessary to excavate outside just to fill cracks and for that purpose alone I doubt it's cost effective compared even with tearing off inside drywall and then replacing it after the job.
If you are excavating outside a foundation it seems to me that job should include a complete footing drain system, including conducting the water away from the building to an acceptable destination.
At that point, sure, it's fine to coat a foundation wall: coatings reduce moisture movement, they don't guarantee against leaks. To make the basement into a boat - which is not normal construction - requires application of a waterproof plastic or vinyl or similar product sealed entirely around the entire foundation wall, usually combined with a geotextile to keep soil from clogging passages intended to let water outside the wall flow down into the footing drains and away.
Question: high water tables in Florida
(Aug 29, 2012) Simon Randle said:
The water table in Florida is high after Tropical Storms Debby & Isaac. I have a house on a monolithic slab with block walls. After high rain a "small" amount of water seeps through a gap where the wall meets concrete floor. It has obviously happened for years but I only noticed it when carpet became damp after Debby and I removed the baseboard. I am sure water is wicking up through foundation. It will be tough to reach the outsode wall/slab because my pool pump and air conditioner sit right outside wall and a concrete pad.
The inside floor is about 6 inches above grade and ground then slopes away at about 30 degrees. I plan to install gutters and catch basins to reduce swamp condition during summer. My question is will your Polyurethane foam have a chance of preventing the problem in conjunction with my attempt to get water away from the house. I fear involving a Structural Engineer who will sell me a full excavated project! In the worst case the carpets only got damp for say 40 ft3, hardly a flood!
26 Sept 2014 Denise Pine said:
How can a foundation wall be repaired that was hit by a dumpster when being backed into the driveway.
If it's just a gouge, concrete patching compound should work just fine.
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