The question “Is it better to fix a basement leak in a poured concrete foundation from the inside or the outside?” is one of the most common questions that homeowners with a wet basement ask. The reason the question is being asked is that, whether you research the subject on the internet or consult waterproofing contractors, a homeowner usually ends up getting conflicting advice.

Almost every basement leak repair, regardless of the foundation type, can be performed from inside the home or from the outside, with excellent results. Follow this link for concrete block foundations.

Exterior crack repair excavation in progress

Interior foundation crack repair by injection

Properly done, both exterior and interior waterproofing repairs will put an end to your wet basement problem. The decision to fix a leak from the inside by injection, or excavate and waterproof from the outside should be based on your circumstances; there is no “one size fits all” solution. The decision to repair a basement leak from either the inside or outside is not black and white; there are considerations…

What to consider when deciding to waterproof on the inside or the outside

In brief:

  1. Drywall has to be opened / removed to access the foundation for interior repairs;
  2. Interior injection repairs are a far cheaper way to fix a basement leak than excavating and waterproofing;
  3. Injection repairs eliminate voids in foundation walls while exterior repairs can only patch over voids;
  4. Warranties are the same, regardless of the approach used;
  5. Exterior waterproofing carries a great risk of damage and injury compared to interior injection repairs;
  6. Interior waterproofing is unaffected by weather delays; and
  7. Interior leak repairs provide confirmation of the source of the basement leak whereas exterior repairs do not.

In detail:

  1. Injection repairs require top to bottom exposure of the bare foundation wall where the leak is. In contrast, exterior excavation and waterproofing will invariably damage the landscaping in the vicinity of the repair as well as the areas wherever the soil has to be piled and where the excavator and crews will be travelling; additionally, fences and decks may have to be removed and rebuilt, and so on.
  2. An injection from the inside costs $100’s whereas an external excavation can easily cost several $1000’s (not including the cost of re-landscaping, rebuilding the fence, etc).
  3. Injections, which are always carried out from inside, will fill the crack or hole completely from the inside to the outside; an external crack repair involves patching over the crack on the outside.
  4. When excavating, it is possible to damage the weeping tile system such that you end up with greater problems after the repair than you had when you started.
  5. When excavating, there is always the risk of damage to gas lines, hydro lines, etc, even if the locates were done properly (assuming that the contractor has gone to the trouble of obtaining the locates). Compared to injection, there is a far greater risk of human error when excavating.
  6. With excavation there is always a risk of the earth caving in; if the proper safety procedures and excavation techniques are not being used, and the person in the pit is killed by a cave-in, you may end up being sued.
  7. The scheduling of excavation work is dependent upon the availability of crews and excavators; delays on other jobs due to rain or equipment maintenance can postpone your scheduled repair by days or weeks. Given that injections are typically completed within a few hours by a single technician with fewer equipment requirements, your wait in the event of a delay will be measured in hours, not days or weeks.
  8. If the cost of accessing the wall from inside is prohibitive, or if you have a custom built bar or shelving you might consider external excavation; however, if the problem has not been ascertained by examining the bare wall from inside, you cannot be 100% sure of what exactly needs to be repaired, if anything at all.
We’ve inspected many wet basements and have concluded that “where the water is, the problem is”, but this is not always the case; water will travel behind finished basement walls guided by the slope of the basement floor. If the exact location of whatever is leaking is unknown, imagine digging up your foundation in the wrong place to carry out the repair!
Before you sign a contract for any foundation repair, ensure that the cause of the problem is known with 100% certainty. In general, if you haven’t observed the problem on the bare walls from inside the home you can’t be absolutely certain as to the source of the water; from the outside, you can’t possibly tell whether a crack is leaking or whether there are 1 or 2 or 3 or even 10 rod holes leaking. All too often, homeowners agree to $1000’s of foundation excavation and waterproofing which is either done in the wrong location, for the wrong reasons, or to resolve a leaky basement problem that could have been fixed from the inside for far less money.

If drywall is cut open to expose the source of the basement leak then it will always be cheaper to fix the leak from the inside.

Are interior basement leak repairs as effective as exterior repairs?
From a warranty standpoint we offer the same warranty whether the leak repair is done from the inside or the outside. In terms of effectiveness, both injection repairs from the inside and exterior waterproofing repairs are commonplace in the industry so both approaches must be effective otherwise waterproofing contractors would go broke.

Like just about anything else, the quality of the leaky basement repair is probably the primary determinant of the success of a repair. Both interior and exterior waterproofing repairs can be done well and also poorly; shortcuts can be taken in both approaches. In our experience, improper installation procedures are the primary cause of failed basement leak repairs.

What is most important is the skill and attitude of the waterproofing technician fixing your basement leak – the man behind the tool. Find out who is going to do the work and use your gut to decide on which waterproofing contractor you’re going to hire.

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