Waterproofing & Drainage
Waterproofing Walls to Code
Once block or concrete walls are finished, they need to be waterproofed according to building code, at a minimum. In order to pass inspection, builders typically spray a 6-mil waterproof tar coating over a concrete wall; for a block wall, a builder will first parge the block. Parging (pargeting) is simply applying a coat or two of mortar over the block to create a contiguous surface, which can then accept a waterproof coating, the block being too porous as is. The typical parge coat is 1/32″-1/16″ in thickness. Once parged, the builder will then apply or spray the tar onto the parge coat. We use a 60-mil application of liquid rubber which lasts more than the 7-10 year shelf life of tar.
In the old days, tar was applied with brushes straight out of the bucket, towed by trucks, which heated the ingots or pigs of tar for ease of application. Today we have machines, which spray the tar, again paying attention to cost, as opposed to quality. Some custom home builders at this point actually install sophisticated waterproofing systems, incorporating advanced rubber liquids (as opposed to tar), drainage membranes, protection mats, and other innovative systems which are readily available, but cost much more than ‘builder grade.’ Pictured below is an advanced waterproof system. Notice the large bed of gravel at the base.
Drainage and Drain Tile
Next, because it is code, and should be done regardless, a drain tile system needs to be installed directly adjacent to the footer, never below the footer, and never above, where the bottom of the floor will be. Although drain tile should be laid outside the foundation walls according to all residential and commercial codes, building code in Maryland (and Virginia) now dictates inside drain tile leading to gravity (rare) or, in most cases, a sump pit and pump. Again, some custom or quality homebuilders will do both regardless of code – interior and exterior. Whether the drain tile is located inside or out, the drain tile should be totally surrounded with a bed of round washed gravel (river rock), and sloped 1″ for every 10’ – 20’, two other design specifications, which are usually ignored.
A Foundation Properly Waterproofed
Proper Exterior Waterproofing System
These are great examples of quality exterior waterproofed foundation walls. Notice that in the second picture, the gravel comes almost to the top of the excavation (2-4 feet of gravel. The wall is sheathed in a drainage membrane, which will not allow any water to sit against the wall, acting as not only a vapor and waterproof barrier, but also a wall drainage system so that water drains down the wall into the drain tile, which is located below the gravel next to the footing.
Pouring the Floor
Once the foundation walls are laid, the floor is poured. To do this, a blanket or layer of gravel is laid down, usually crushed blue stone #57, between the walls, and over top of the drain tile, which is next to the footings and the dirt. A cross-laminated polyethylene vapor barrier anywhere from 6-12 mils in thickness is then laid over top of the gravel. Next, rebar and reinforcing wire are laid out in grid like patterns, and the concrete is then poured to create a 4” thick floor slab, some builders installing an expansion joint around the perimeter, most just allowing the floor to shrink somewhat as it cures and loses moisture. In the past, when concrete was inexpensive, a few custom homebuilders poured floors which were anywhere from 6″ to 12″ thick. Code is 4″ which is usually adequate.
Once the walls are built and waterproofed, and the drain tile is placed next to the footing, the excavated soil (known as “backfill”) is usually added back into the empty space surrounding the walls. Waterproofing, wall cracks, and various structural problems in MD, VA, and D.C. are sometimes a direct result of the soil, which was placed in the backfill when the house was built. Current building code in Fairfax County, Virginia mandates that backfill consist of more than 50% sand and stone aggregate, but that isn’t always a code that is followed.
In any case, once the backfill is in place, the curing cement foundation walls are shocked by the backfilled soil in three different ways: temperature, weight/pressure, and impact. The soil pressing against the concrete can cause it to either shrink or expand with the change in temperature, The sudden weight of the backfilled soil, which adds sudden pressure to the walls, can be detrimental to the slowly curing cement and structure. In addition, builders traditionally throw all of their trash back into this void around the house, and as the soil, rocks, and debris are backfilled into this space – sometimes hastily or carelessly – this also can cause damage to the walls.
If that is not bad enough, during the construction phase, the foundation walls are generally exposed to variations in weather conditions, such as rain, heat, freezing cold, and humidity. All these factors can cause future problems with basements and foundation walls, which you are possibly experiencing. See Causes and Solutions.
Beautiful home, right? Notice the huge hill behind the house. Notice the Company / Developer’s Name on the sign. This home had water problems from the very beginning. Within 6 months, this home continually flooded and the builder came back 10 different times to correct the problem unsuccessfully. The Developer built this home over a spring that used to be there when this was farmland. The homeowners 3 years later contacted The Foundation Expert. We referred them to an attorney because they could not afford to have the work done that was needed to restore their home to an environment they could live in. In 3 years, they never used their back yard because it was a swamp.
Complete Care Solution
If you’re wondering about how to waterproof a basement, The Foundation Expert offers the best solution. We design a complex network for exterior drainage, as well as for interior drainage systems that not only keep the water flowing out of your house, but also add to the aesthetic appeal of your residence. Efficient, reliable and built to last, our drainage solutions are the best way to reduce your basement wall waterproofing costs.
Call The Foundation Expert today at (877) 344-1155 and allow us to resolve your basement and foundation problems. sam@theFoundationExpert.com