Block Basements: Part Six

Grade & Sump Pump

In part five we got the block foundation walls cleaned, covered in a waterproof coating and reset the drainage tiles, then installed a bed of washed stone. The stone acts as the clear base for the soil that will back fill against the house. Properly draining soil is the last step and can consume a large portion of the actual budget if it has to be removed and replaced. The soil that goes back into the hole has to be pushed in carefully; too much pressure can crack or bow the wall. I have seen a basement contractor do this in layers and slowly raise each level of soil. Once the trench is filled the soil should be set with an aggressive slope away from the building. This allows for the expected settlement.  The contractor our client selected made comment that they go back to a site some weeks later and check to see if the soil has settled more than expected and they have brought in additional soil in some cases so this all important drainage away from the building is maintained. They seed it down for grass and replaced the shrubs if requested.

The last step depends upon the water test that they do on the drain tile. If the water test shows good discharge or they know they have got a storm sewer hookup, then a sump may not be necessary.  The contractor noted that a high percentage of basement waterproofing jobs they do includes a sump pump if they are the least bit unsure of the drainage. There are two methods of installing a sump pump, internal or external. This trade commented that they prefer the internal pump for a couple of reasons. He has seen the external units freeze up if they are poorly installed and if a pump fails this is generally not covered by your homeowner’s insurance, an internal pump is.

When they know they need a sump pump they jack hammer out a spot in the basement floor, usually at a corner where they can loop in the drainage tile. Most pro’s use the manufactured plastic bucket designed for a sump installation. These buckets are about 18 inches deep and are usually set up on a base of washed gravel. A channel is dug under the footings to allow the plastic drain pipe to be discharged into the bucket. There are a number of punch out holes that can be opened to help with the under pad drainage too. They use a submersible sump pump manufactured by Hydramatic. I have also used this brand; they are known for long term reliability and are far better than the stem style of sump pump. Once this is all set in place a hard plastic discharge line should be installed along with a check valve fitted just above the base of the liner. This check valve stops the back flow of water reversing the pump; this will reduce its life span. Once outside the wall with the hard pipe you must carefully discharge this water, it can create some amount of erosion. If you are in the city you cannot discharge this water onto your neighbour’s property. It may take some thought, don’t bury this line however. I have seen more than one early spring thaw where the underground pipe froze and caused some considerable damage when the final spring thaw came.

Back inside the home this sump pit should be finished. Proper concrete poured around the top edge and the bucket cover fitted and twist locked into place. This is done for a couple of reasons. It helps reduce the evaporation of the water into the basement which only adds to extra humidity and the cover stops anything from falling into the sump hole and damaging the actual pump. If at all possible the pump should be on a designated electrical circuit so that no other tools or appliances could accidentally trip the power supply.

 External pumps are not as common, I know of only one basement contractor who uses this installation. I have seen these used where the basement is occupied and the owner wants access to the pump at any time. The contractor must excavate a pit about 20 inches below the footings, usually in a corner. They will install a culvert section as a chamber for the sump pump. Care must be taken to ensure the pump and float is not obstructed. The rigid plastic line should be discharged on the surface. In this type of installation, you do not use a check valve; the cover should be secure, water resistant and insulated to reduce the chance of freezing.

This block basement project is now complete. The contractor on site offered a 10 year warranty for his work, a strong indication they had faith in their workmanship and given this company was in its second generation, an excellent indication of quality workmanship. 

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