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Waterproofing a Basement From The Outside

By Edited Feb 13, 2016 0 0

Many homeowners who live in a wet area, near a river, stream or other water source often find it necessary to increase their waterproofing efforts to keep water and dampness out of their basements. Some homeowners may use a waterproofing paint or other waterproofing material and find some success, but not a complete stoppage of water entry. It’s not uncommon for those who live in a wet area with either sand or soil surrounding the foundation to experience a wet basement. The dampness or actual water trickling down the basement walls is due to hydrostatic pressure. Hydrostatic pressure forces water through the porous masonry materials when the ground becomes saturated and the water has nowhere else to go.

Exterior waterproofing is typically very successful and well worth the cost to stop the water from entering the basement. If the dampness or seepage is not stopped it can lead to mildew and toxic mold growth. Mold can cause several health problems from breathing problems to neurological issues. The basement will also take on a damp smell that may permeate through the house. The damp smell can leach onto any items stored in the basement and leave the basement virtually unusable. Getting rid of the damp smell can be challenging if the water problem isn’t identified and corrected. Excess water can also cause wood rot which threatens the structural integrity of the house. Creating a barrier between the water trying to make its way into the basement and the porous masonry walls saves the health of your family, provides you with a usable space and protects the structural health of the house.  

In most cases waterproofing the foundation is best left to a professional because of the work involved. This is how it’s done just in case you feel brave enough to take on the challenge.

You will need:

  • Washed coarse stone
  • Plywood
  • 2 by 4 inch pieces of lumber
  • Perforated pipe
  • Stiff brush
  • Hydraulic cement
  • Roofing cement
  • Polyethylene plastic sheets
  • Trowel

Preparing to Waterproof the Foundation

Use a shovel to begin digging a trench from the foundation out 36 inches.

As you dig and the trench gets about 3 to 4 feet deep, place a sheet of plywood up against the dirt and wedge a 2 by 4 inch piece of lumber from the plywood to the house’s foundation. Never skip shoring up the trench in any type of soil or sand. Soil and sand are both highly unstable and can shift, filling in the trench, which will cause entrapment for those inside the trench. Not shoring up a trench is not an option.

Continue to dig a trench along both sides, front and back of the house and shoring up the trench every 3 to 4 feet as you work your way down.

Dig until you are at least 6 inches below the foundation.

Tamp the base of the trench with a hand tamper to compact the dirt.

Pour approximately 2 inches of washed coarse gravel into the base of the trench.

Rake with a metal rake the gravel to make it level.

Preparing the Foundation

Attach a stiff brush to the end of a threaded broom handle and brush the foundation walls to remove excess dirt and debris.

Examine the exterior walls from cracks and holes.

Press hydraulic cement into the holes and cracks with a putty knife.

Let the hydraulic set and harden.

Applying Waterproofing Materials to the Foundation

Scoop up roofing cement on a trowel and trowel on a ½ to ¾ inch thick layer onto the foundation walls. Begin at the base of the foundation and work your way up in small, more manageable sections. Move the 2 by 4 inch pieces of lumber to the left or right as necessary to gain access to that particular section. Do not apply roofing cement in a large section because it will dry and be ineffective.

Place a sheet of polyethylene over the wet roofing cement and press it in place. Wrap a rag around a board and smooth the polyethylene to push out air bubbles and big wrinkles. It does not have to be perfectly wrinkle free.

Apply roofing cement with a trowel to the next section of foundation and about 10 to 12 inches onto the first sheet of polyethylene. Place the second sheet onto the foundation wall and overlapped onto the first sheet of polyethylene. Smooth the second sheet with a board wrapped in a rag. Continue to apply roofing cement to the foundation wall, previous polyethylene sheet and smoothing the next sheet until the polyethylene covers the foundation walls from bottom to top.

Scoop up more roofing cement on a trowel and apply a ¾ to 1 inch coating over the polyethylene sheets around the entire foundation.

Let the roofing cement dry for 4 to 6 hours to harden and set firmly.

Still More Waterproofing to Complete the Job

Lay perforated pipe on the coarse gravel around the entire foundation, extending it to a sewer pipe if your local codes and laws allow or run the pipe into a dry well away from the foundation.

Pour 6 to 8-inches of washed coarse gravel on top of the pipe, make sure you use coarse gravel that is larger than the holes in the perforated pipe.

Begin removing the plywood and 2 by 4 inch pieces from the bottom and back filling the trench as you work your way up.

Don’t compact the backfill with a tamper, allow the soil to settle naturally. As the dirt settles, add more soil to create a slight slope running away from the foundation to promote a water runoff.

Exterior Waterproofing Tips

Call your local utility companies before you dig so they can mark utility lines entering the house.

Obtain any necessary permits prior to beginning the project.

Do not attempt to waterproof the exterior without help, as it is a dangerous and back breaking job.

Never dig trenches without shoring them up as this is extremely dangerous and can lead to death.

Waterproofing a basement from the outside of the house is a very big project and typically requires a professional. If you plan to waterproof from the outside, professionals usually do it right the first time making them invaluable.

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