Waterproofing A Concrete Basement Wall

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Waterproofing concrete is the process of preventing water from passing through or seeping into the concrete. It is important for any structure that contains concrete, and it acts as a protective layer and enhances durability.

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Concrete absorbs water, which can cause any number of problems: if rust or mould starts to grow, it will damage the supporting beams; if groundwater seeps in and sits on top of the foundation, it could lead to structural instability; and before you know it your basement walls are sagging under the weight.

Waterproofing should be done while applying other treatments like cavity drainage systems, curing agents, control joints, etc., simultaneously for better results. Click here for some additional learnings. 

 The following steps can be used for waterproofing an existing concrete basement wall.   

Step 1) 

Drill holes in the floor about 3 inches away from the wall to let any water that seeps through the drain into the sump pit via a French drain.

If there is no sump pump it may be necessary to install one so you will need to install a 4 inch PVC pipe with elbow joints at strategic locations along its path down to the footing drain or daylight well.

This pipe should have 5-6 inch perforations every few feet on its bottom half that are opened by spacers about 6 inches apart, which allow water to pass into the pipe but keep out debris.

Step 2) 

Next lay 6-mil polyethylene sheeting (the kind that contractors use to line trench walls or trenches themselves) over the floor. Use 6-mil tie wires every 18 inches to secure it in place and make sure you overlap all seams by 6 inches.  

Step 3) 

Get some clean washed river rock (avoid sharp rocks like granite or limestone). Lay down about 8-12 inches of these rocks on top of the plastic sheeting, overlapping each rock with the one next to it.    

Step 4) 

Next, lay another piece of 6-mil sheeting over the top of this rock layer.   Make diagonal cuts about an inch apart in this upper sheeting so that water will be able to flow into the pipe without damaging the plastic.

Staple this to the first sheeting at each corner and use wire tie wraps about every 2 feet along its length.   

Step 5) 

Get some large pieces of angular shaped concrete blocks (preferably 4-8 inches wide).

Stack these up next to or on top of one another, using mortar to secure them in place, with their edges overhanging the trench edge by an inch or so. Fill in any voids between individual blocks with mortar.

Step 6) 

Place a wood beam across the tops of these blocks and stack more angular shaped stones on top of it.  You may need to use metal brackets or other support methods so that larger stones are supported. Continue this step until the wall is covered from top to bottom.

Step 7) 

Now add a second wood beam on top of these stones and do not use mortar between them. Add another layer of large angular shaped stones with an inch or so of space in between each one, but make sure that they are all touching the wood beams you have placed across their tops.

Step 8) 

To finish the topmost portion of this wall, install a piece of metal flashing about 4 feet long and run it along the top ridge or highest point of your stonewalling.  

Fold it over at 90-degree angles every few inches to secure it in place and connect it securely to itself using wire ties with about 18-24 inch long wire tails and bend them over to keep them in place.

Step 9) 

Tack a piece of 1/4-inch thick steel plate on top of the metal flashing using roofing nails so it is straight and slightly overlapping the edges of your stone wall.   Nail it at intervals of about 8 inches apart with nails that are between 6-8 inches long so they go all the way through this metal or stone layer.   

Step 10) 

Place the second piece of sheet metal above the first one, overlapping slightly and repeat this step until you have added 3-4 layers to this section of your waterproofing. This will help divert any runoff from getting into your basement even if some of the stones are dislodged.   

Step 11) 

Add a piece of 6-mil plastic sheeting over this top layer, making sure that it is not bunched up anywhere and cut 4-inch perforations every few feet in its bottom half where it will be overlapped by any pieces of your stonewalling. Secure it in place using heavy-duty staples about every foot along its length.

Step 12) 

Paint all exposed polyethylene sheeting with a coat of coal tar epoxy paint to protect it from UV light damage.  This can be purchased at most hardware stores.   

Finally, use a backhoe or digging machine to bury any exposed portions of your waterproofing system under several inches of soil.    

You can use cinder blocks or large rocks covered with grass to disguise these exposed parts if desired.

 

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