How Do You Waterproof A Block Foundation From The Inside?

how do you waterproof a block foundation from the inside (2)

As an alternative to interior waterproofing by installing an interior weeping tile system, water leaking from the walls of a concrete block foundation can be repaired by excavating and waterproofing the exterior foundation walls. In this post, we cover the advantages and disadvantages and the detailed steps involved in waterproofing foundations.

 This method of waterproofing aims to stop the water from the inside. It involves installing an interior drain tile that directs the water along the drainage system installed below the floor and drained into a collection well. A sump pump then pumps the water out.

The bottom row of blocks in the basement is drilled, forming weep holes that allow water to drain out and into the drainage system. Looking for dual occupancy? Look no further! MJS Construction Group has you covered.

Allow considerable float time for waterproofing. If you’re using a waterproofing subcontractor, recognise that a good waterproofer can be in high demand during the busy season. Rain can also delay waterproofing work.

Plan the layout of waterproofing well ahead of time. The plan elevations will likely show the finish grade line on the foundation walls, but these lines should be confirmed with the architect, if necessary. You don’t want black, gooey waterproofing showing above grade. Watch for changes in the level of grade. A line of waterproofing descending at a diagonal from one level to another won’t work if the architect has decided to handle the change with a retaining wall.

Ideally, you should mark layout lines with a crayon or chalk line, especially on a complex foundation with varying grades. On a simple foundation, it might be safe to instruct the waterproofer to keep his work so many inches from the top of the foundation. I like to see waterproofing as close to the finishing grade as possible, but no lower than 6 inches in any case. 

Don’t leave form-tie holes that are below grade unprotected. Work out ahead of time what you’re going to do at basement windows and bulkheads, porch foundations, and intersecting walls that don’t have to be waterproofed.

When deciding what walls get waterproofed, follow this basic rule: Waterproof any foundation wall with earth on one side and usable space on the other, including crawl spaces. Extend waterproofing at least 12 inches onto intersecting walls that don’t have to be waterproofed. 

You might want to continue the waterproofing on other walls if it’s a very wet site. Under extreme conditions, water has been known to travel through the keyway along the footing and into occupied space. Consult with the architect if you have any doubts.

Check the waterproofing manufacturers literature for temperature limitations. You’re probably okay applying waterproofing on a cold day if you’re working with a solvent-based material. But watch out if your material is water-based. The lower limit for some products is 40F.

Concrete Block Foundation Waterproofing

how do you waterproof a block foundation from the inside (3)

A leaking concrete block/cinder block foundation is a challenging reality for many homeowners living in homes built between 1920 and 1980. On this page, we explain why block foundation walls leak and how these types of foundations are waterproofed. 

Can You Tell If Your Block Foundation Leaks

You can easily tell if a concrete block foundation leaks by observing the presence or absence of staining on the blocks.

There is no denying it. If your foundation walls appear in any way similar to the images above, you have visual confirmation that your concrete block/cinder block walls either have water trapped inside the blocks or moisture-wicking through them. 

If your walls do look like these images, likely, you have at least occasional basement leaks, with moisture-wicking through the blocks into the air in your basement, causing a damp basement and water entering your home beneath the basement floor slab. Unfortunately, these ideal conditions lead to the premature deterioration of your foundation walls. There is only one way to solve this problem: waterproof your foundation.

Concrete Block / Cinder Block Foundations Leak

Block foundation walls have an inherent weakness in that there are mortar joints on all sides of the blocks (the same as any brick wall). There is a general tendency for mortar joints to develop some hairline cracking over time, typically due to the swelling and shrinking (e.g. expansion and contraction of clay soils) of the soil in response to soil moisture levels. The more water there is in the soil, the more pressure is exerted onto the cracked mortar joints.

Note: A drop in the footing supporting the base of the foundation (settlement) also results in mortar joint and block cracking. Below-grade hairline cracks in the mortar joints, and cracks in the blocks themselves, are constantly subjected to hydro-static pressure from the water table surrounding the foundation, thus facilitating the entry of water into what are essentially hollow blocks.

Inject Leaking Concrete Block Walls

Homeowners are increasingly aware that pressurised injection (epoxy and polyurethane) is a very economical way to waterproof a leaking basement; consequently, we receive numerous requests to inject block walls. 

Unfortunately, pressurised injection is not a viable way to waterproof concrete block foundations because the blocks are hollow, thus making it impossible to contain the injected resins in the area(s) where water is penetrating the foundation.

Applying Interior Sealants On Leaking Concrete Block Walls Work

Some seemingly knowledgeable individuals and companies would have you believe that applying a waterproof sealant, or tar-based product, on the inside surface of a concrete block or cinder block wall will fix your leaky basement. 

While sealing a concrete block foundation wall from inside your basement may temporarily resolve a basement leak, this form of basement waterproofing will trap water within the foundation wall and effectively prevent any evaporation of the moisture trapped inside the blocks. 

As concrete is a porous material, the resultant pooling (entrapment) of water within the cinder-block wall will, eventually, accelerate the deterioration of the blocks to the point of failure and, with time, lead to far greater repair costs and potentially damage the structural integrity of sections of your foundation walls. Surface sealants must be applied on the exterior foundation wall surface for the foundation to be properly waterproofed.

There Are Only Two Professional Concrete Block Basement Waterproofing Methods Available.

Logically, foundation damage and water penetration of a block foundation would be averted by preventing water from entering the concrete blocks in the first place. 

This is accomplished by excavating and waterproofing (coating) the foundation wall. Alternatively, when destructive excavation is undesirable or money is to be saved, entrapped water in a concrete block wall can be purged, and your basement waterproofed by installing an interior weeping tile/perimeter drainage system. 

Both of these basement waterproofing methods will greatly decrease the rate of deterioration of your foundation.

Over the years, we have encountered numerous situations where foundation walls need to be rebuilt or reinforced to avoid foundation failure (often the result of years of neglect of a known problem). The cost to rebuild a wall or to reinforce it is significant; you want to avoid such a situation if at all possible, and block foundation waterproofing is the place to start. At MJS Construction Group, we offer a wide range of home builders Melbourne.

Select The Most Appropriate Repair Method For Your Leaking Block Foundation Walls

Fortunately, it is possible to fix concrete block/cinder block wall leaks permanently. To determine which waterproofing method is the most appropriate to your circumstances, either external waterproofing or installing an interior weeping tile system, some factors should be taken into consideration:

  • Whether the basement is finished or unfinished;
  • Whether there is visible mould inside the home;
  • The moisture levels detected behind finished basement walls (a high level indicates mould is likely to present);
  • The condition of the concrete blocks (level of deterioration visible externally and internally, if possible);
  • The accessibility of the areas that need to be waterproofed;
  • Whether or not the water on your basement floor is a result of a high water table;
  • The extent of the landscaping surrounding the home (concrete walkways, decks, fence locations, etc.,);
  • Your willingness to destroy the landscaping around your home or to fully remove finished basement walls;
  • Your level of concern for the existence of mould behind finished basement walls;
  • Your basement waterproofing budget;
  • Whether you are pragmatic or a purist;
  • Whether or not structural reinforcement of the wall is required;
  • The condition of the existing weeping tile and the efficiency of the existing city stormwater drainage infrastructure;
  • The extent to which basement waterproofing is required; and
  • The waterproofing contractor you choose.

As mentioned above, when dealing with a concrete block foundation, there are only two professional block foundation waterproofing repair methods.

History Of Concrete Block

Concrete has been used in construction since ancient times. It is made from a mixture of cement, aggregate and water. Poured concrete (the most common type of foundation in Chicagoland) is formed (cast) onsite. Concrete block is concrete formed and hardened offsite in a manufacturing plant. 

Sand and gravel aggregate is found in abundance throughout the Midwest. They are the raw materials needed to manufacture concrete blocks. Many people use the terms “concrete block” and “cinder block” interchangeably. It should be noted that there are distinct differences. Cinder block tends to be lighter because it uses remnants (ashes) from burned coal as the aggregate instead of heavier sand or gravel. 

In the early 1900s, mass production methods led to a proliferation of homes being built using concrete blocks. They became popular because they were easier to store and transport when compared to stone and brick. They were also advertised to be “fireproof and waterproof”. The great Chicago Fire is a testament to its fireproof qualities. We’ll tackle its “weatherproof” claims, however, later in this post! 

Blocks are used in both above and below-grade foundation construction and come in different forms. You might have heard of “split-faced block”, which is used in above-grade construction. Concrete blocks used to build foundations usually come in 16-inch x 8-inch x 8-inch units and weigh about 40 pounds each. They are stacked by a mason and held together using mortar.

Problems With Concrete Block Foundations

how do you waterproof a block foundation from the inside

Over time, soil and water pressure exerted against the foundation causes the mortar to break down and wear away. Consequently, water seeps through the exterior mortar joints and into the hollows of the block. The water trapped inside the block eventually leads to foundation seepage. It should be noted that concrete blocks are porous by nature. It easily absorbs moisture, which can contribute to mould problems. 

In some instances, the soil and water pressure is so great that it causes the wall to bow inward. We’ll discuss the structural concerns of this movement at another time, but we do have an answer.    

Ok, so now we have water coming into these hollow blocks and the basement. What to do? It’s very simple. We can either stop the water on the outside (Exterior Waterproofing) or capture it inside (Interior Waterproofing).

A concrete block foundation offers a home one of the most stable foundations available. However, it can succumb to the pressure of the water and soil that surrounds it. The high pressure exerted on the walls of the foundation results in the breaking down and wearing away of the mortar used to join the blocks of the foundation. Water is, therefore, able to seep through the spaces and cracks leading to water seepage.

Concrete is a porous material. It, therefore, absorbs moisture in time. This can lead to a mould or mildew problem.

There are some instances where the pressure on the wall from the soil and water is so great that it causes the concrete block wall to bow inward. If this problem is not corrected in good time, it can cause the wall to collapse.

It is important to ensure that a concrete block foundation has adequate waterproofing during the construction phase. If you are experiencing waterproofing problems with your home’s foundation, various solutions are available to help correct the problem.

There are two approaches to dealing with waterproofing of this type of foundation.

Positive Approach. This Involves applying a waterproofing solution from the exterior of the foundation walls. This approach involves little destruction of the interior of the home. It, however, costs much more as it is labour-intensive.

The Solutions applied will depend on the extent of damage observed. The contractor excavates the foundation and installs a waterproof membrane to the exterior of the foundation walls. Next is the addition of drain tiles to collect and drain any excess water near the foundation.

Concrete Block Waterproofing Solutions

Exterior Waterproofing:

Approaching the problem from the exterior (the “positive side”) seems to make the most sense to many people.  

We are all for it when applicable and necessary. One big drawback – COST! It takes a considerable amount of labour (money) to dig down to the base (footing) of your foundation wall.  

Once excavated, a waterproof membrane is applied to waterproof the foundation walls. A drain tile is added to collect and dispose of the excess water.  

If there are obstructions, such as a driveway, porch, or garage in the way, they would need to be removed and replaced. This also compounds the cost of the job. 

Interior Waterproofing:

There is another school of thought when it comes to waterproofing concrete block foundations. Rather than stopping the water from the “positive side”, the water can be directed into a drainage system below the floor on the inside.  

The process is known as Interior Drain Tile. As a part of the installation process, holes are drilled into the bottom row of blocks.  

These weep holes allow for water to drain out from the hollows and into the drain tile system beneath the floor. We can install Interior Drain Tile Systems in unfinished and finished basements, although the latter requires some prep work.

And that’s only the first reason to keep the foundation dry. Then there’s the little problem of wet, damp basements and crawl spaces that can breed mould and make below-ground interior spaces generally unpleasant. 

The problem is that typical concrete is not waterproof. Although uncracked (and what concrete is uncracked?), it will typically keep out liquid water, water vapour can still penetrate quite easily. Keeping water drained away from concrete foundations and preventing it from moving through the concrete are essential to a successful structure.

Accomplishing our goal, then, of draining any water away and ensuring a dry interior space below grade can be relatively simple or fairly involved depending on geographic location, climate, topography, soil/water table conditions, and depth of the foundation. There are three components of any system designed to keep water out. These are, from the bottom up:

  • Drains to move water away from the bottom of the foundation
  • Wall treatment to prevent moisture from moving through the wall and to route water down to the drains
  • Ground surface treatment adjacent to the building to direct surface water away

And remember that since this will mostly be underground when the building is complete, doing it right the first time is critical because coming back to fix it is an expensive undertaking. At MJS Construction Group, we have the best townhouse builders selection to make your house a dream come true.

A leaky foundation in a residential building can damage finishes and furnishings, even the structure itself. In a commercial building, water can ruin expensive equipment and disrupt vital work. It all adds up to lost money, wasted time, upset customers and sometimes litigation.

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