Waterproofing a Brick Basement Floor

Brick floor
velacreations/Flickr/CC By 2.0

Brick is a strong, durable, and easy to maintain material that has a rustic natural feel that is stylistically perfect for most finished and unfinished basements. However brick is also a particularly porous material, and when installed in moist, below grade basements there are certain precautions that need to be taken to ensure that moisture and mold do not spread.

Unfortunately, many older homes have basement floors where the brick was installed directly on ground soil in order to cut down on the spread of mud. Depending on the environment, and the level of the water table, these flooring installations will often be subject to water penetration and damage, as well as the growth of mold which can cause a health hazard for the entire home.

Condensation in Basement Brick Floors

Moisture damage from condensation is the least common and easiest to fix problem when it comes to a brick basement floor. It occurs mostly in humid environments, where the air is heavy with water that transmits down through the surface of the flooring material.

In order to determine whether the moisture is coming from the air above or the ground below, tape a piece of tinfoil to the surface of any areas that commonly become damp. Then leave it for a day or two. When you return, if moisture has accumulated on the top of the foil, you know you have a condensation problem.

The easiest solution to deal with this is to get a dehumidifier for the basement. Ideally, you will want one that pours water out directly into an existing drain. In very humid environments or large basements, you may want to get multiple dehumidifiers. Leaving a shop fan running in the space will also speed drying and help to keep the air circulated.

Runoff Moisture Damage

Runoff occurs when water from rain or melting ice penetrates the porous soil around a home. Over time it can move through the hard-packed dirt beneath a building's foundation and, through the power of both hydrostatic pressure and the capillary effect, make its way up to penetrate the brick flooring in your basement from below.

If a proper vapor barrier was not installed underneath a brick floor in the basement then the best way to handle runoff water problems is to try and divert the liquids away from the home:

  1. The ground around the building’s foundation should slope downward, one inch vertically for every one foot of horizontal distance covered.
  2. Install downspout extensions to direct gutter water away from the structure. Water should be deposited at least four feet from the outer foundation.
  3. Eliminate or limit any plants that you have growing directly around the perimeter of the building. Not only can their roots cause problems with the foundation but watering them may cause moisture to seep through the base of the structure.
  4. If there are paved surfaces around the perimeter that are cracked or damaged, they should be repaired to prevent further moisture from leaking through broken areas.

The Water Table

Most basement floors are built below grade, which means that they are under the natural level that water exists at in that environment. When a brick floor is installed in a below-grade area, moisture will move through the soil surrounding it and below it, pushed by hydrostatic pressure, forced up and through and into cracks that exist around the foundation, and ultimately up into your brick basement floor.

Unfortunately, if your brick floor was not installed with a proper vapor barrier layer and treated with waterproofing solution on its bottom and sides, then there is no easy solution for this problem. A sump pump can help to drain excess water but it will not keep the brick flooring dry or free of mold.

Important note: You cannot simply seal the interior surface side of a brick basement floor and hope for the water damage to stop. This is because the moisture will continue to seep up through the unsealed bottom and sides of the brick and then will be trapped there, unable to rise through the surface. In many cases sealing off a brick basement floor’s surface can actually make the problem worse.

Waterproofing a Brick Basement Floor

  1. If your basement brick flooring does not have a vapor barrier beneath it then it will need to be removed in order to properly waterproof the installation. This can be done by weakening the grout lines around individual bricks with a grout saw. You can also crack the grout using a screwdriver and a rubber mallet.
  2. Once the grout is removed, slide a putty knife in the gap, and then rock the brick to loosen it in its place. Next, a pry bar can be inserted into the gap in order to lift the individual paving brick out. If you are going to reuse the bricks then be careful as you extract them, taking care not to damage the surface or outer edges of each tile.
  3. Depending on the surface beneath the bricks you will have to take different actions. If it is concrete, then you can install a vapor barrier directly on the slab. If however it is packed soil underneath, then you need to install at least two inches of dry gravel to act as a natural barrier against water soil penetration.
  4. Before adding layers to the area beneath your floor you may want to dig down into the soil in order to ensure that you do not lower the eventual height of the room. If you do decide to dig down then you will probably want to consult with a professional engineer, to ensure that you don’t do any damage to the foundations of the house as you are excavating dirt.
  1. A one-inch sheet of polystyrene board will help to create an even surface over the gravel. Tape the joints, and then install a five-millimeter poly sheet to the surface of the board. Tape those joints as well using a seam sealing tape. This will create a vapor barrier that will resist the penetration of moisture. You may also want to consider running the poly sheets up along the side of the walls to create a barrier on the side of the outer bricks.
  2. Once you have the water barrier installed, a thin slab of self-leveling concrete can be poured to create a smooth underlayment for your bricks. The original paving tiles can then be installed over this without having to worry about further below surface penetration from soil water.