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Nearly every foundation wall is rolled or sprayed up to the grade line with a thin layer of an asphalt-based coating called dampproofing. Some people mistakenly think this is a waterproofing layer, but it is not designed to stop liquid water and will not bridge small cracks where water can enter.
For what it’s worth, the building code requires at least dampproofing on all foundations and waterproofing only on foundations exposed to hydrostatic pressure. When the foundation drainage system is working well and its capacity is not exceeded, all is fine. But if the system malfunctions or you are hit with an inch of rain in one hour, all bets are off, and you may wish you had paid extra for a fully waterproofed foundation.
Damproofing
The thin layer of asphalt applied to most foundations is called “dampproofing”. The purpose of dampproofing is to slow down the transmission of water vapor through the concrete walls into the house. If you backfill with a well-drained, granular material next to the foundation wall, or a drainage board that provides a capillary break, then dampproofing will do a reasonably good job of keeping water vapor from entering.
However dampproofing will not stop liquid water under pressure and it will not bridge the small shrinkage cracks that develop in concrete walls and slabs. In short, dampproofing helps keep basements a little drier, but does not prevent basement leakage or flooding.
Waterproofing
If you plan to use the below-ground construction as living space, or want to provide that option in the future, then you should consider upgrading from dampproofing to a full basement waterproofing system. There are many systems, but most start with a heavy spray-on elastomeric coating that can bridge cracks and keep out water under all but the most extreme conditions.
To work effectively, basement waterproofing coat must seal the joint between the foundation wall and the footing, as this is a common entry point for water. This requires attention to detail, such as cleaning the dirt out of this joint before applying the waterproof coating.
Most foundation waterproofing systems include a layer of “protective board” over the elastomeric coating to protect it from damage during backfilling and settling of the soil. The protective board can a dimpled mat or a foam or fibrous insulation board.
Some elastomeric coatings claim that they do not need a protective layer, and some dimpled mats are marketed as complete waterproofing system without a membrane, but I am skeptical. One test I apply is “If it sounds too good to be true, it probably is.”
Drainage Boards & Mats
There are a host of products designed to provide a capillary break and vertical drainage against the foundation wall. Most are designed to eliminate the need for granular backfill around the foundation. Some are used in conjunction with a spray-on waterproofing membrane, while are sold as standalone waterproofing without the elastomeric (synthetic rubber) coating.
To add to the mix, some products include exterior insulation – either foam made with vertical drainage grooves, or fibrous insulation boards that provide both drainage through the open matrix of the fibers.
Exterior foundation products do not have an easy life. Excavation contractors are not always precision craftsmen. The boards or membranes can be damaged or pushed around during backfilling, be dragged down as the soil, attacked by insects (in the case of foam board), and damaged at grade level. So pay attention to the attachment details and overall durability.
With any of these products, it’s important to pay attention to the termination at the top. Some are more secure than others and all run the risk of getting damaged here or buried during landscaping. With exterior foundation insulation that continues up to the wood frame, as it should, the termination is not a concern. However, protecting the exposed foam above grade can be problematic.
Some of the more popular drainage boards and sheet products include:
Dimpled membranes: These are plastic sheets with the dimples facing into the wall, creating about a ½ inch gap for drainage and a capillary break. Widely available products include Platon Air-Gap Waterproofing Membrane, Delta MS, and GeoMat. It’s important to select a product with adequate compressive strength to resist being crushed by the backfill.
Dimpled membranes with filter fabric: On these, the dimples face outward and are laminated to a layer of geotextile to protect against clogging. Products include: Platon DoubleDrain, Delta-Drain , and CCW Miradrai.
Matrix panels: These form the air gap by using a tangle of thick plastic fibers. The best known is Enkadrain, which is available with filter fabric on one or both sides and uses 40% to 50% post recycled material. This product has been around for decades, which is always a good sign.
Insulating drainage panels: These products provide both exterior insulation and drainage. Foamular’s Insul-Drain is XPS foam with vertical grooves for drainage with a bonded filter fabric. Warm-N-Dri and Drain & Dry are both semi-rigid fiberglass panels that insulate and drain, although Warm-N-Dri is no longer available as a standalone product (available only as part of the Tuff-N-Dri waterproofing system). The new kid on the block is Roxul Drainboard. This high-density mineral wool insulation board has good drainage characteristics and excellent compressive strength. Like fiberglass, mineral wool is impervious to water, insects, fire and pretty much anything else you can throw at it.
Some materials do double-duty as both a drainage layer and exterior basement insulation. Two I am familiar with are Insul-Drain Drainage Board (XPS foam with drainage grooves and filter fabric) and Roxul Drainboard (rigid rockwool panels). Rigid rockwool is currently marketed as a commercial product and is not available in all areas. But it has some advantages over foam – it drains water well and is impervious to water and insects. Foam below grade can get excavated by insects for a nice, warm home.
Drainage Mats. As mentioned above, a dimpled or matrix-type drainage mat can go over the waterproofing to create a drainage space and capillary break, which means that it is less important to use granular backfill. Some companies market these products as the primary waterproofing material. This can work with a well-functioning footing drain system. However, if the footing drains silt up over time or cannot drain fast enough, and water backs up around the foundation, the drainage mat may not be enough.
Foundation & Sitework Articles
Foundation Drainage: Below Grade
Managing Roof & Yard Runoff
Insulating Basement Walls
Site Evaluation
Basement Leakage FAQs
framistat says
Solutions for Wet Concrete Block Foundation
My 1960 ranch home has a brick front and concrete block foundation. About two feet of the brick ledge formed by the block was left uncovered and open, then backfilled with sandy soil. I removed as much of the soil from inside the block as possible before covering the openings with concrete bricks. Later I found a hole the size of a baseball in another block about two feet below the soil level. There is no coating of any kind on the outside of the block. Inside, the waterproofing paint is peeling from the wall, and there are stains and mold along the bottom and in two corners up to about four feet. There is efflorescence through cracks in the floor, but no flowing water and no dampness. Interestingly there is a vine growing up from the margin around the floor. My question is, what repairs would you suggest, and does the soil inside the blocks need to be removed? If so, how best to do that?
buildingadvisor says
There is rarely a quick fix for basement moisture problems. Waterproofing paint or sealers on the interior rarely last long if moisture is migrating inward, as is almost always the case.
Moisture is always moving from wetter areas to drier areas, which means from the soil into your basement. Even relatively dry soil has a lot of moisture in the entrapped air. The water is migrating into the house by diffusion through the block or concrete, air leakage into the basement due to the stack effect (in cold weather), and evaporation of moisture that has wicked into the block or concrete.
Concrete is very porous to moisture, and concrete block is worse due to the lower density, joints, and hollow cores. The problems will be worse with wet, dense soils, a high water table, or water build-up around the foundation walls due to poor drainage. Think of your basement as a big porous sponge surrounded by wet soil.
The optimal solution to your problem would depend on site conditions, the planned use of the space, and your budget. Effective moisture control is essential if you are planning to finish the space. Otherwise, you will have musty room and risk damage to framing and finish materials.
If you are just using the space for storage, you can tolerate more moisture. Concrete and block are not harmed by moisture, but finish materials will be. Also, moisture from a wet basement migrates upward in the winter due to the stack effect and can cause moisture problems throughout the house.
The cheapest repairs with the biggest impact often focus on surface drainage – mainly directing runoff from gutters and yard away from the house. If you have water coming up through the floor in wet weather, then a sump pump is needed. Next on the list would excavation around the foundation to improve drainage, dampproof or waterproof the walls, and repair or replace (or add) footing drains. While everything is open, you might also want to consider adding rigid foam insulation.
If excavation is not in the budget, then you might want to consider interior drainage systems around the perimeter of the basement slab. These usually involve cutting a trench around the edge of the basement slab and installing a manufactured channel or traditional French drain (perforated pipe in a bed of gravel), that drains to the exterior. Adding a layer of dimpled drainage mat and foam insulation would complete the project before finishing the space.
The soil inside the block would not be a concern. If it is wet, it will dry over time, and will not harm the block. But the fact that you have efflorescence and stains on the floor and walls is evidence of a high seasonal water table and excess moisture in the surrounding soil.
joseph says
Who Should I Hire To Waterproof New Foundation?
Hi,
My wife and I are building a home in southern Illinois within the next year. I am looking for a waterproofing service provider who provide your above described services in this area. We are in zipcode 62888 and approximately 35 minutes north of Carbondale, IL and 75 minutes SE of St. Louis, MO.
Thank you,
Dayasagar says
Can’t Stop Basement Leakage with Polyurethane Foam
What is to be done to avoid water leakage in three large basements in an old building. We are now using passive grouting with polyurethane foam but we cannot fully avoid leakage in each basement. Is there a better approach?
buildingadvisor says
Before undertaking any efforts to seal basement leaks, it’s best to start with an assessment of surface drainage. If you can redirect some or all of the surface water flowing toward the foundation, you can often reduce or eliminate leakage into the basement. Sometimes the solution is as simple as redirecting water from gutters and downspouts to a safe distance away from the building.
A high water table exerting hydrostatic pressure against the basement wall is more difficult to solve, but it will be difficult to stop leakage without addressing the source of the water.
Where sealing foundation cracks is necessary, it’s best to seal the exterior where that is an option. Typically, contractors will install an exterior waterproofing membrane and may install or repair the foundation footing drains to direct any subsurface water away from the foundation walls.
However, exterior excavation is often too expensive or may be impossible due to limited access – for example, adjacent properties are too close. Also the disruption to landscaping, planting, paving, and decks and porches can make exterior excavation expensive and unappealing.
The most common approach to interior sealing is injection with epoxy or polyurethane foam. The approach is determined by the size and characteristics of the crack, whether the crack is stable, and whether it is actively leaking.
If the foundation is unstable and still shifting, structural repairs will need to be done before any waterproofing. Where the sealed crack needs to be as strong or stronger than the surrounding concrete, epoxy is often the best option. Where the crack if fully stable and the only problem is water leakage, polyurethane foam can be very effective.
Where the leak is active with flowing water, contractors typically drill holes to inject polyurethane deep into the crack to stop the water flow. Otherwise, flowing water can dilute the sealant and impair its performance. Once the crack is dry, the contractor can use either polyurethane or epoxy. Some polyurethanes use moisture to cure, while others need a dry substrate. Modern dual-cartridge systems have made injection of epoxies and urethanes easier and more affordable.
Where the water flow cannot be stopped, hydraulic cement or similar fast-set grouts are sometimes used. Hydraulic cement expands as it sets, plugging difficult leaks. Ultra fast-set grouts are proprietary formulations that bond chemically to the concrete.
The specific product used will depend on the site conditions and preferences of the contractor. It sometimes pays to have an independent third-party – typically an engineer — spec out a solution.
Whatever approach you choose, always get a guarantee in writing that the leakage will be eliminated. The expertise of the contractor is usually more important than the specific product used. Look for someone with extensive experience with the type of leakage you are experiencing and check their references.
Donald says
Should I Apply Waterproof Paint Before Insulating Basement?
Should I apply waterproof masonry paint to the interiors walls as an extra moisture barrier step before applying the XPS insulation?
buildingadvisor says
Interior waterproof paints and coatings on block or concrete basement walls are, at best, a temporary fix. If there is any moisture coming through the wall, it will cause the paint to peel and blister, and may cause efflorescence as well.
The only place to effectively control moisture entry though a basement wall is on the exterior. Hopefully you have at least coating of asphalt dampproofing on the exterior. A drainage board on the exterior helps eliminate any hydrostatic pressure. A full waterproofing system, as described above, is the most foolproof solution and a good idea if you are planning prime living space below grade.
If you have any active leaks in the wall, you will need to deal with these before insulating the wall. In some cases, an interior drainage system is the most practical solution.
Once you’ve solved any water leaks, you can block any residual moisture on the interior by taping or sealing all joints and edges in the foam board. The easiest approach is to use contractor’s tape on the board-to-board joints and canned foam at the perimeter edges.
The foam will protect the interior finish from any moisture that builds up behind the foam. Some of the moisture will be reabsorbed by the masonry, which is unaffected by moisture. Over time, moisture can also slowly dry to the interior through the foam, as long as it is not foil-faced.
As shown in this illustration, you can also add a stud wall and unfaced batts on the interior side of the foam if you wish to have additional insulation and wood studs for easy nailing of finish materials.
Donald says
Thank you for the information. This is very helpful.
How about waterproofing the crawl space (crawl space encapsulation) and adding a vapor barrier on the walls and dirt floor of the crawlspace. Also, I was told it may be good to insulate the crawlspace walls and the ceiling of the crawl space with XPS foam insulation. I am currently planning to renovate my basement and any advice would be greatly appreciated.
buildingadvisor says
Not sure where you are located, but in all climates, it is advisable to add a heavy-duty vapor barrier over the dirt floor – even if the soil appears to be dry. In general, a lot of moisture enters a house from an unsealed dirt floor. You can use heavy-duty (minimum 10-mil) poly sheeting or a reinforced product such as Tu-Tuf.
The poly ground cover should be sealed at seams and turned up a minimum of 6 inches at the side walls and sealed. If you are not insulating the wall, run the poly all the way to the top, leaving a 3-inch inspection gap for termites where required. Some contractors cover the poly with an inch or two of clean sand or smooth rounded gravel to protect the ground cover from occasional traffic. Another option is to add a second layer of 6-mill poly to protect the main vapor barrier.
There are two approaches to insulating a crawl space.
1) Vented Crawl Space: Insulate the floor above the crawl space and ventilate the crawl space.
2) Unvented Crawl Space: Insulate the walls of the crawlspace and treat it like conditioned space – essentially like a basement with a very low ceiling.
The traditional vented approach too often results in a soggy, moldy, unpleasant space – or worse if there are serious moisture problems. The main problem is that the ventilation air often brings more moisture into the crawl space, where it condenses on cold surfaces (concrete, pipes, ducts), creating a breeding ground for mold and wood decay. This is especially true in warm, moist climates such as the Southeast.
The approach now favored by most energy experts is to seal the crawl space and insulate the walls. The easiest material to use is foam board or spray foam (a more expensive choice). Any type of foam will work, foil-faced polyiso board is the only type that you can leave uncovered in some areas, depending on local codes. Other types of foam must be covered with ½-in. drywall or another fire barrier.
In the band-joist area, you can cut foam board and seal it in place between the joists with canned foam.
To guard against moisture problems, make sure the ground is sloping away from the crawl space on the exterior. If there is water on the crawl space floor, you’ll need a sump pump to remove the water to a safe place outside the crawl space.
Finally, you’ll need to connect the new, conditioned crawl space to the rest of the house by adding a heating/cooling register. Or if you don’t want to heat and cool the space, the current version of the IRC allows you to install a small through-the-wall exhaust fan instead. The fan should provide 1.0 cfm for each 50 sq. ft. of crawl space floor area (IRC 2000/2003 Section R408.2, Exception 4; IRC 2006, Section R408.)
Not every code official is sold on the unvented crawl space idea, but it has been used successfully in many homes. However, it only works with effective drainage and a good ground cover. If you introduce standing water into a sealed crawlspace, in a warm climate, you can expect to find rotted floor joists in a few years. So take a peek at least once a year to make sure everything is working as planned.