Building a slab foundation for a home takes more than just pouring concrete. It’s important to understand the composition of the ground upon which the foundation will sit. It’s also important to visit the proposed building site during all seasons before grading for the foundation begins. Through thoughtful site review and planning, avoid costly building mistakes such as leaky slabs.
Excessive Ground Water
Excessive ground water is one major cause of leaky slabs. Slab foundations poured without a decent underlayment of gravel, rock and a plastic water vapor can wick moisture from the ground. While in most cases this is not a bad thing, when the ground water is excessive, concrete will wick the moisture into the home and create mold.
If you don't consider the site during the rainy season and prepare for rainwater runoff, the house might find itself sitting in a pool of water during the winter. Concrete is porous and naturally absorbs water. Excessive drainage around a foundation without a safe outlet will cause a leaky slab. To avoid a leaky slab, provide proper drainage around the house, such as a French drain system dug down around the foundation’s edges. Place the french drain at the bottom of the foundation upon soil, cover it with washed gravel and filter fabric and backfill it with dirt.
Slab foundations often have plumbing running in the foundation itself. If the plumbing malfunctions during house settling, this can cause leaks in a slab. Worse yet, if the drain and waste system malfunctions, sewage disposal waste leaks through the foundation as well. Another cause of slab leaks are improperly wrapped copper water supply pipes. When the pipes are in contact with certain soils, electrolysis occurs and corrodes the pipes over time, eventually causing excessive water leaks in slabs.
In homes with basements, the slab foundation often connects to a brick or concrete wall set in the dirt. This requires sealing the foundation walls that connect to the slab. If the concrete blocks, concrete or brick foundation walls do not receive proper sealing with a waterproof material, and drainage is not adequately provided to wick water away from the foundation walls, water leaks to the lowest points and comes up through the slab.
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