Below Grade Waterproofing

Due to a range of environmental factors, protecting basements and other underground spaces is a complex challenge. The structure and the items stored within can be easily degraded and damaged if precautionary measures are not followed, as it is essential that water (standing water and driving rain especially) and moisture are kept out. Below we have written a brief introduction of the main methods of below grade waterproofing. If you have a below ground basement or garage, you should consider in investing in these methods.

One method of prevention is to use waterproof concrete. Water infiltration can be reduced if waterproofing admixtures are added to concrete. The drying shrinkage and permeability of the concrete are greatly reduced. This method of waterproofing is low cost and does not usually require any additional waterproofing step, but care should be taken in the placement and finishing of the concrete.

Another option would be to install a dewatering system. This system would collect and move the water away from the structure and can be used in conjunction with other below grade waterproofing options. Due to the need for regular maintenance, this can be expensive option.

A final option would be to use pre-applied membranes. These would be put in place before the concrete is poured. The concrete would then bond to the membrane as it sets. The membrane would prevent water infiltration and potential toxic gases. This is recommended if the blow ground basement is being used to store valuable items.

Pre-applied membranes can be installed in 3 different configurations: negative side, positive side, and blind side.

Negative side waterproofing is when the membrane is applied to the inner surfaces. The benefit of this method is that it is easy to apply and repair, but the drawback is that structure could move and crack over time, meaning that more waterproofing will be needed to repair the damage.

When the waterproof membrane is applied to the exterior of the structure, it is termed positive side waterproofing. The benefit is that it can be easily inspected but it is not always an option depending on the property’s location.

The final installation option is blind side waterproofing. This is when the membrane is applied to the underside of structural slabs. This option is normally only pursued where there are space limitations. If choosing this option, you should consider other draining options to help keep water away.

Ultimately, below grade waterproofing should be considered a “last line of defense”. It is better to prevent water reaching underground basements and garages. You should consider installing French drains or drainage boards to help remove rain and standing water. To prevent water entering, you should also install a garage door threshold seal. These act as a physical barrier to the water, and the MS polymer adhesive prevents water seeping underneath, whereas weather seals attached to the bottom of the door do not prevent all water from entering.

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