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THE FRENCH DRAIN SYSTEM
The French drain system is the most practical method of correcting a water problem in a wet basement. Such a system is low-tech, by modern standards, and in many cases it can be installed fairly quickly. In any waterproofing project, it’s important to complete the job as quickly as possible, especially when heavy rain or other sources of water damage are threatening.
A French drain is basically an underground passage made by filling a trench. With loose stones or rubble. For more than 55 years, the Maurice family has successfully adapted French drains to solve a variety of basement water problems. Three pieces of information are needed in order to assess any wet basement problem:
-- thickness of basement floor
-- type of soil under floor
-- height of water table
A test hole will determine the facts. Cut a test hole in the floor. With a stone drill or small jackhammer at the location where a sump pump holding chamber will be installed. In locating the sump pump, the most important consideration is to accommodate discharge piping outside the building.
Dig a Test Hale
The test hole procedure is worth the time involved. If the soil is sandy and wet, it’s best to repair your test hole and wait for a drier season. To fill in a sizable hole (about 12x12”), mix up two parts sand to one part cement; then put together a primer "paste" of cement and water and trowel it on the sides of the hole before filling it with the two-to-one patch material. If your test hole is small, it can be filled with a water plug or hydraulic cement.
If your test hole reveals dry soil, proceed by cutting the concrete floor with a concrete saw or 75- to 85-lbs. jackhammer near the foundation Walls that show water seepage. If your floor is thin and you are able to do the work, a sledgehammer can sometimes do the job.
Cut the concrete floor, measuring from the foundation wall onto the basement floor approximately 14”, or 16” if footing is in the way. It’s important to leave uncut sections of floor every 15 to 20’, to serve as wall supports for safety purposes. These uncut sections are known as contact points, and they are approximately 16” long uncut. Where wall cracks are evident, leave two wall supports on either side of the crack and cut out 48” between them.
After the concrete floor trench has been cut out and the concrete removed, deepen the trench to 12” from the top of the concrete floor. Remove small quantities of dirt with pails; a conveyor belt may be economical for big jobs.
If an excess amount of water flows into the basement after digging, install a temporary sump pump in the area where permanent sump pumps will be installed.
Sump Pumps: The trench you have created will cause water to enter at a lower level, resulting in more water entering into the sump pump chamber or chambers. Through the years, I have become a strong believer in installing two sump pumps side by side. In addition, a gasoline powered auxiliary generator is an essential investment for any building where flooding and power outages have occurred. I also recommend that you manually activate your sump pumps at least once a year to be sure they are in working order.
Your estimate of the amount of water coming in will determine the size of the chambers and the capacity of the pumps to be installed. When locating the pumps, consider where the sump pump water will he discharged. The water must flow away from the house on a downgrade slope, using plastic piping that will subsequently be laid. More information on chambers and pumps is provided later in this guide.
--- Contact Points--Cracked Wall
Laying PVC Pipe
When the digging is complete, including removal of din under the contact points, start laying 4” perforated plastic pipe, with the holes up. Begin from the sump pump chambers and continue around the basement, using elbows in the corners and returning into the other side of the pump chamber. Start filling the trench with clean crushed stone, from 0.5 to 1.5 inch in size, to a height enabling the replacement concrete floor to be level with the existing floor and of equal thickness. The top edge of the sump pump holding chamber should be lower than the existing concrete floor so that a %” plywood cover in stalled over the chamber can be flush with the existing floor This cover will prevent concrete from entering the chamber. After the concrete is poured, be sure that the cover has not bonded to the concrete and can be removed.
Preparing for New Concrete
The abutting concrete should have a clean surface to bond to. The cut concrete floor edge can be washed with a heavy spray and brushed before the new concrete trench is poured. Then cover the stone with concrete, flush to the existing floor.
--- French Drain with Holding Chambers
CONSTRUCTING THE SUMP PUMP HOLDING CHAMBER
Sump Pump Holding Chamber
Clay chimney flue liner, which can be purchased in a variety of sizes, makes good holding chambers for sump pumps. A flue liner 12x12” and 24” in depth can hold a dewatering submersible pump that will pump 60 gallons of water per minute and can lift the water to 25’ in height. It operates on a single phase alternating cur rent at 115 or 230 amps; the discharge opening of the pump is 1.5”.
A larger chamber of 12x18”, and 24” in depth, will hold a dewatering submersible pump that will pump ll0 gallons per minute and can raise water 50’ in height. This larger pump, placed in the larger chamber, will also operate on a single phase at 115 or 230 amps; its discharge opening is 2”. (In our own experience, the Hydromatic OSP33 and SPDSOH have been the most dependable, efficient, long-lasting, and troublefree sump pumps. However, at least 12 other pumps currently on the market can be used for this purpose.) --- illustrates a two-pump arrangement.
Installing the Chamber
For a two-pump system, dig to a depth of approximately 27” from the top of the concrete floor to the bottom of the sump pump hole, and place approximately 2” of crushed stones inside the hole. The length and width of the hole depend on the size of the holding chambers. Place the flue liners into the hole, seating them firmly onto the stone.
To make bases for the pumps, place a piece of 1.2 -1.5 inches thick precast patio block inside each chamber. The patio block slabs will prevent stones from entering the pump impellers and stopping the pumps' action. The imperfect ?t of the prefabricated slabs inside the chambers will allow water to enter or drain out of the chambers.
-- Dual Sump Pumps
Cut Holes in Chambers
If you are installing two pumps of different sizes, elevate the larger pump on two layers of patio block. The higher pump will work less often, leaving removal of smaller amounts of water to the smaller pump.
After the holding chambers are installed, fill around them with stone to the bottom of the existing drain trench.
After laying the PVC drain pipe, continue filling with stone to the bottom of the floor slab.
Before installing the sump pump holding chambers, cut a square hole 4x4” in two sides of each holding chamber. This is achieved by using a power saw With a concrete cutting blade. Measure down from the top of the holding chamber 11” to the bottom of the hole. When two holding chambers are used, two holes should be cut at the same level so that Water can enter from one chamber into the other. In this way either pump will help dissipate excessive water or kick in if the other should fail. Each sump pump has a check valve to prevent the water from back-flowing out of the discharge pipes. It’s important to install a separate electrical outlet and circuit breaker for each pump and for the :. All installation of wiring must be done by a qualified, licensed electrician. 2. All electrical codes should be followed by utilizing the most recent National Electrical Code (N .E.C.) and the Occupational Safety and Health Act (OSHA)-l I strongly recommend the two-pump system as a pre caution against any further basement flooding (in a few extreme cases, I have installed three pumps in one basement).
Depending upon the circumstances, any combination of pumps could be installed. The smaller pump can withstand the wear of more frequent operation, and it should be installed so that the depth of water before the pump starts working is 2” lower than the depth of water that activates the larger pump.
-- Holding Chamber
Be Ready for More Rain
Placing the larger pump on two layers of precast concrete patio block and putting the smaller pump on one layer of the concrete accomplishes this difference in activation levels very simply. Also, your sump pump installation instructions Will include information about setting the activation point of your pump. With this two-pump system, excessive water will be taken care of by the larger backup pump. and if one of the two pumps should fail, repairs can be made on the defective pump while the working pump continues to function properly.
Once the size of the dewatering submersible pumps has been determined and the appropriate chambers have been installed, discharge piping must be laid. Two pumps can usually tie into one 2” discharge line, but if there is a great deal of water you should provide a discharge line for each pump. Drill a hole through the foundation wall six” below the outside grade, and install 2” solid PVC piping through the foundation and along the base of an outside trench, keeping it on a downward slope. Normally discharge pipes are 4 to 10’ long.
If possible, end the pipe with an angled cut to match the slope of the yard or soil.
Always start a French drain system at the location of the sump pump hole or at the gravity flow outlet. These measures are important while the work is in progress be cause, if an unexpected rainstorm should occur, it would still be possible to install a pump that would keep the water table down. Where a sandy subgrade exists, the installer could excavate and install one section of pipe in the trench and cover it with stone to stop erosion caused by water shifting the sand.
--- Sump Pump Chambers (Side View)
If the situation involves a natural gravity flow system (which is just a natural downhill flow of water away from the house, unaided by a pump), dig a trench through the foundation wall or under the wall footings for holding the discharge pipe. The discharge pipe will connect with those laid on the downgrade flow.
If while installing the French drain system, you find that the footing under the basement floor is high (not leaving enough room to lay 2” of crushed stone over the foundation footing and under the concrete floor), cover the top of the footing with 3/8” crushed stone and pour a thin slab of concrete over the footing. This procedure allows the water that flows between the footing and the concrete floor to enter into the French drain system. If the concrete footing should be too high, cut the comer of the footing with a jackhammer blade as needed.
The French drain system can be adapted to help basements that show evidence of water entering around either a chimney base or a fireplace base. One sign may be efflorescence (deposits of salt crystals) on the fireplace base due to the evaporation of water. Because of capillary attraction, water will be drawn to the surface around the fireplace base, causing moisture on the basement floor. A solid chimney base or Lally column footings that are flush with the basement floor and much thicker than the floor will sometimes cause capillary attraction. Because the massive footings are deep, water moves to their outer and upper surfaces.
Start by cutting the concrete floor approximately 12” in width around the leaking chimney or fireplace base. Dig down 12” and cut a trench to the leaking base which should be the same depth as the existing perimeter drain. The system under construction should be drained. Lay pipe at the base of the trench connecting into the French drain system. Then, lay stone over the pipe and pour concrete over the stone.
-- High Foundation Footing
A FINISHED BASEMENT
When installing a French drain system in a finished basement with wall paneling or plasterboard-finished walls, cut a trench only on the sides that have the water problem. You must cut the concrete floor under the finished wall back to the foundation wall and remove the soil and concrete there. Next, dig the sump pump hole and lay the perforated pipe. Afterwards, fill the trench with crushed stone over the pipe and backfill with crushed stone to the foundation wall. Fill the trench with concrete but leave a space between the fresh concrete and the foundation wall.
It’s imperative to keep the concrete approximately 1 inch away from the foundation wall. This space or weep hole is necessary to allow water to enter the stone trench from any leaking wall ties, soil pipes, or cracks in the foundation Walls. If conditions involve a high water table and a fast Water recovery with sandy soil, omit the weep space behind the finished panel wall. Unlike the above Weep space system, be sure to push the concrete under the plate to make a seal against the foundation wall. lf the foundation wall leaks, this can be remedied by digging on the outside next to the foundation wall; cleaning the cracked surface area; and drying with a torch, if necessary, 6” on each side of the crack. Then apply a plastic roofing cement ½”:thick to cover the prepared surface. Protect the plastic cement from disturbance by covering it, from bottom to top, with a 6-mil sheet of polyethylene. Be sure to secure the polyethylene sheet with a strapping nailed to the house.
--- Drain System around Chimney Base to Floor Drain
LEAKING BASEMENT WINDOWS
Window Well or Areaway
Another condition that requires water control is where water enters through or around windows. There are two probable causes: (1) the foundation wall is too low or (2) the grading is inappropriate. Either way, the window is now situated below the existing grade. Efforts to divert the water by installing an areaway or window well may only attract and collect water if the drainage is not corrected, too.
The solution is to dig outside the house foundation around the full width of the window area. Dig to a depth of 18 to 24” below the bottom of the window. Drill a hole from the inside of the basement (centered under the window) 2” up from the bottom of the window well through to the outside wall. Install a 1.5” plastic pipe through the hole and cement the pipe on each side of the foundation wall.
Fill the areaway, or window well, with clean crushed stone to a level of 4 to 5” below the bottom of the window opening. Typically, a galvanized steel liner is in stalled; backfill around the outside of this unit with soil.
The drain pipe will connect with the French drain system under construction in the basement. If a French drain system is not being installed, the water will have to be piped into a sump pump hole located in the basement floor.
--- French Drain System with Weep Space
A HOUSE WITH A STONE FOUNDATION
When installing a French drain system in a basement that has a stone foundation, cut the concrete floor approximately 14” starting from the stone foundation on the sides that have a water problem. Dig the soil in the trench on a slope away from the base of the foundation wall. As stated earlier, always start a French drain system in the sump pump area and install the chamber and sump pump first to handle water that seeps into the trench. If water should enter faster than expected, 4” perforated pipe can be laid in the trench and covered with stones to sub grade. This is the best way to secure the existing condition overnight in case it should rain.
Weep Space: If the stone foundation wall leaks, lay a strip of ply wood on edge over the stone in the trench in the areas of leakage and pour concrete in the trench against the ply wood. When finishing the concrete, run a concrete edger against the plywood; remove the plywood the same day.
The slot will provide a weep space for water to enter the system. Eliminate the weep space where soil is very wet and sandy; it will provide an undesired en try for sand into the basement.
Don’t proceed with a French drain system if a test hole reveals a high water table. It’s best to wait for drier conditions.
-- Window Drain
A CONCRETE BLOCK FOUNDATION WALL
Water problems are often a result of downspout discharge Water which enters the basement through mortar joints of concrete block foundation walls. Water moves through the porous block from one chamber to another, raising the water table inside the block chambers. Eventually, water will seep onto the floor.
A method of releasing water from the cells of concrete block is to cut slots in the concrete footing that intersect the block. These slots allow water to flow freely out of the block and into the French drain system.
Every house with a basement should have gutters and downspouts that discharge water away from the foundation on a downgrade flow. Improper water drainage; Will cause dampness in the basement or will cause water to enter the basement from under the foundation wall and footing. This water will be noticed first where the basement floor abuts the foundation wall.
HYDROSTATIC PRESSURE UNDER CONCRETE FLOOR: WHERE HEAD ROOM IS AVAILABLE
Raise Floor when Feasible: In a Wet basement where hydrostatic pressure has raised the concrete floor, the best method of correction is to use the following procedures:
1. Cut the concrete floor next to the foundation wall approximately 12” in width on all sides, leaving uncut sections of floor as wall supports.
2. Dig a trench 7” deep.
3. Install two large sump pump chambers 7” above the old existing floor.
--- Drain Inside Stone Foundation
4. Using a jackhammer with a bull point pin, punch holes into the existing concrete floor approximately 48” apart. This releases hydrostatic pressure under the floor and allows the water to flow up into the stones and pipe system leading to the holding chambers.
5. Lay perforated pipe in the trench and cover the entire floor area over the pipes ill the trench with 3” of crushed stone.
6. Lay a 6-mil polyethylene sheet over the stones and pour a new 4”-thick concrete floor with a compressive strength of no less than 3500 psi with a 4” slump.
Water Is Powerful
Don’t underestimate hydrostatic pressure. I have seen houses where water pressure has raised a 12” thick concrete floor 3 to 5”, along with the main carrying timber and Lally columns with footings.
HYDROSTATIC PRESSURE UNDER CONCRETE FLOOR WITH SANDY SOIL and NO HEAD ROOM
When Floor Can't Be Raised: Sometimes soil under the concrete floor is sandy, having a fast water recovery which raises and cracks the concrete floor. Don’t attempt any repairs while the ground is wet.
When the soil is dry and the weather forecast is for fair conditions, use the following procedures:
1. Cut out the entire concrete floor and remove 4 to 5” of soil throughout the entire sub-floor area.
2. Dig next to the foundation wall, at a slope of 45 degrees away from the wall, a trench 14” wide and 12” deep from the top of the oncoming floor.
3. Lay plastic pipe in the bottom of the trench with the holes up to discharge into the two holding chambers, or the gravity flow system if conditions will allow.
--- Hydrostatic Pressure New Floor Poured Over Old Floor
Similar to Double Pump:
4. Place 4 to 5” of crushed stone over the pipes and entire floor to subgrade.
5. Lay a sheet of 6-mil polyethylene over the entire floor and pour the new concrete floor.
A SINGLE SUMP PUMP INSTALLATION
A sump pump is installed by cutting the concrete floor and digging a 27”-deep hole in a comer of the basement.
Cut out two 4x4 or 4.5x4.5” holes on the two sides of the holding chamber. Lay 2” of stone at the bottom of the hole. Place the chamber upright on the stones and fit galvanized wire mesh over the cutout holes to prevent the stones from entering the chamber. Fill around this chamber with stone to 4” below the floor, then place concrete around the chamber. Last, lay a 2” concrete slab at the bottom (precast patio block works well) of the holding chamber over the stones and install the sump pump on top of the slab. If a French drain system is installed later, the perforated pipes can enter the cutouts in the holding chambers.
Where dwellings are close together and the pitch of the land won’t allow the water to leave the sump pump with out causing damage to abutting properties, it’s best to discharge water into the nearest storm drain (if this is legal) or to install a dry well.
A HOUSE BUILT ON WET LAND
--- Single Sump Pump Chamber
When building a house where the water table is high, you can take certain steps to avoid water problems. First a basement concrete floor grade should be established. Mark a floor grade chalk line on the foundation wall, 5” above the footing. Install sump pump holding chambers with the cutouts in a comer of the basement floor. Lay 4” plastic piping continuous at the base of the footing to return into the chambers. Lay 3” of crushed stone over the entire floor area, and cover the stone with polyethylene sheeting. Wrap the bases of Lally columns with Styrofoam to separate the bases from the concrete floor to prevent cracking. Then pour a new concrete floor over the entire area.
A HOUSE BUILT ON A DOWNGRADE SLOPE
A house built on a downgrade slope will almost always have a water problem. To control the situation while the concrete foundation Walls are still exposed, apply a water proofing material that will fill the concrete pores. If such a product is not available, apply a plastic cement or roof coating with a plastering trowel and wrap the foundation walls with two layers of 6 mil polyethylene over the plastered surface.
After either of the above applications, lay 4” plastic perforated pipe with the holes up at the base of the footing, continuing around the three sides of the upper grade of the house. These drainage pipes will continue on to a gravity flow. Backfill over the pipe system with at least 30” of 1- or 2” crushed stone, and lay 6” of %” crushed stone over this system to restrict the oncoming top soil from filtering through the larger stone and entering into the pipe system. Next, lay rigid insulation against the foundation and continue backfilling to grade.
Downspouts Should Discharge Separately: Downspouts for the house, which often carry leaves and other debris, should always have their own solid-pipe drainage systems for discharging water away from the building.
WRAPPED AROUND FOUNDATION 4"P\/C PIPE
---The Outside System Concrete Foundation
INSTALLING A DRAIN SYSTEM OUTSIDE OF FOUNDATION WALLS
To Waterproof without disturbing a finished basement, an outside drainage system is preferred. First, dig outside on all sides of the foundation to 12” below the existing concrete floor. If the basement is concrete block, cover the foundation wall with a roofing plastic cement. Then lay two sheets of polyethylene over the plastered surface. To prevent the poly from sliding down when you backfill, se cure it with strapping nailed to the wall. Lay continuous perforated 4” PVC pipe which will enter two sump pump holding chambers inside the basement, perhaps in a furnace room or utility area.
Place panels of 2”-thick, 36”-wide rigid insulation against outside foundation Walls. If the foundation is concrete block, it’s important to insulate to at least 48” below grade; in very cold climates, insulating all the way down to footings is even better. Backfill the en tire trench with stone to grade, to prevent frost from exerting damaging lateral stress on the block foundation.
In the event of power failure it’s best to have an emergency generator that will continue to run the sump pumps, especially when you have a finished basement to protect.
A HOUSE BUILT ON A CONCRETE SLAB
Water in House
A house built entirely on a concrete slab may take in water because of improper landscaping, enabling water to flow toward the house slab, This problem can be corrected by digging outside next to the leaking side of the house slab to a depth of 12 to 16” and approximately 16” width, continuing to a downgrade slope for gravity flow. If a gravity flow does not exist, a dry well chamber or a lift chamber can be installed to dissipate the water or to pump the water away to another area. A 4” pipe is laid at the bottom of the trench that will pitch to discharge. Fill the entire trench with stone to grade.
---: The Outside System Concrete Block Foundation
ESTABLISH HOUSE GRADE
Avoid Lowest Point: When building a house on a downgrade slope, where a house foundation is built much lower than the existing road grade. you should first consider elevating the house foundation as much as necessary to overcome possible water problems. Grade from the house to the road with a reverse grade, forming a valley so water can flow away from the house. To avoid problems with water, lay perforated pipe along the perimeter at the base of the footing on the exterior of the foundation. Then backfill with crushed stone approximately 30 to 36” deep and follow.
A SUMP PUMP LIFT CHAMBER
Custom-built Well: In wet locations without the advantage of gravity-aided water discharge, a concrete block chamber may be constructed at the lower discharge end of an existing drainage system. A common size is 40x40” by 4’ deep, with a concrete slab at the bottom. Then set 8x8x16” concrete blocks in cement mortar around the inside walls of the chamber and fill the block cells solid with mortar as you build the chamber. (This custom-built concrete block chamber can be made as large or as small as required. Also, you may install sump pumps as necessary to dewater the chamber.)
--- Outside Drain System House on Slab
Create Good Drainage
Drains on It: Own
The sump pump is installed on the floor of the chamber.
The discharge water will be pumped through a plastic pipe with a check valve installed on the horizontal section at the top of the elbow leaving the chamber. The discharge pipe will leave the chamber on a downgrade slope so that water won’t remain ir1 the pipes and freeze. If the discharge water is pumped on an upgrade and not below the frost line, a small hole can be drilled in the center of the flap in the check valve to allow the water to return slowly into the sump pump chamber. This procedure will prevent water from freezing in the pipes. The cover for the chamber should be solid to keep out rainwater. Make it as strong and secure as necessary to prevent tampering or accidents.
The lift chamber can also be used to contain a new source of Water that might result when a new development abutting your land is graded to a higher elevation. First, dig a trench the length of the standing water approximately 16 to 20” deep and approximately 16” wide. Pitch the trench to the left or right, to assist drainage toward a gravity flow or a lift chamber. After 4” perforated plastic pipe has been laid in the bottom of the trench. fill the trench to existing grade with crushed stone.
A DRY WELL CHAMBER
A dry well chamber may be built when discharge water cannot be pumped into the backyard or where a storm drain does not exist. Locate the dry well chamber away from the house on a downgrade slope so the water won’t reenter the basement and the discharge pipe will have a pitch to the chamber. First, dig a hole approximately 6x6’ and 6’ deep. Place 4 to 5” of crushed stone into the hole.
Build a concrete block chamber by laying concrete blocks over the stones and filling the cells of the concrete block with crushed stone to prevent blocks from shifting. Next, lay a heavy plywood cover over the top course of block resting 3” on all sides. Then, build a form 5” high over the plywood cover. Lay #4 rebar 12” on center each way; then pour 3500 to 4000 psi concrete. Finish by filling around the chamber, to sub-grade, with crushed stone. Then cover with double polyethylene and, finally, existing soil to grade.
--- Sump Pump Lift Chamber
Channel Slope System
INSTALLING DRAINS IN FRONT OF GARAGE DOORS
Water problems often exist when a garage is built under the house and the driveway has a downgrade slope. Water naturally follows the surface of the driveway and enters the garage. A method of correcting the water entry is to dig a trench to a depth of 24 to 36” and approximately 16” wide across the entire frontage of the garage opening. Lay crushed stone in the trench and pour a 4” concrete slab over the stone before installing a prefabricated channel slope system with grates. These trough sections are laid in front of the garage doors with pipes to flow on a downgrade left or right if possible. If gravity drainage is not possible, you will need to install a lift chamber or a dry well.
Another method for collecting water in this situation is to install a concrete block manhole with an open grate top and a 6” plastic discharge pipe 16” below the top of the grate down to pipe invert, gravity flowing. This concrete manhole should be placed beneath the center of either a two-door garage or a single-door garage.
---: Dry Well Chamber
CONTROLLING DOWNSPOUT WATER
Sometimes water problems are created simply by the water discharging from downspouts next to the house foundation wall. In this case dig a trench from the base of the downspouts 10 to 12” deep continuous on a downgrade slope. Next, install a plastic downspout connector onto a"4” solid pipe and elbow to divert the water away from the house on a downgrade flow. This procedure may be all that is necessary to correct your water problem.
If a gravity flow is not possible, a dry well should be built no closer than 15’ away from the house.
USING A BLOW PIPE TO EXCAVATE UNDER OR AROUND OBSTRUCTIONS
The blow pipe is an improvised tool that can be very useful in removing soil from difficult places such as from underneath the concrete floor of a finished basement bath room. Note that additional lengths of blow pipe ends can be attached in order to reach the desired depth. The most popular lengths are 24”, 48”, and 72”. A small air compressor to power the blow pipe can be purchased or rented.
Divert Away from House
---: Downspout Extension
---: Downspout Extension to Dry Well
When installing a French drain system in a basement where an oil tank or furnace is an obstacle, cut the concrete floor and trench up to each end of the tank. (It’s important to dress with protective clothing, including a hood, while doing this procedure.) Turn the ball valve of the blow pipe to allow the compressed air to blow full blast through the pipe as it’s being thrust forward and backward against the soil that is being blown back. Continue on each end of the tank and remove loose soil With a hoe and shovel until the hole is the same size as the existing trench. Then, lay the perforated pipe continuous through the tunnel. Backfill the entire system with stone using the handle of a shovel to poke stone into the tunnel and around the pipe. Complete the project by pouring concrete over the stone-filled trench.
There are some instances where the blow pipe procedure cannot be used because the soil is composed mainly of clay or it contains too many large stones. In these cases it’s better to continue the trench around the oil tank or furnace, always providing a weep space along the uncut section of the tank base to collect any water coming up from the rear of the tank.
Around If Not Under
LEDGE ROCK IN THE BASEMENT
Hard to Remove
In the northeastern United States, where I live, ledge rock is commonly encountered when basements are excavated. Water may flow through or around ledge rock, contributing to moisture problems. Because of the difficulty of removing ledge rock, builders of many older basements poured around or barely over ledge rock outcroppings. To correct such situations, take the following measures:
1. Establish a sump pump hole location.
2. Dig a trench from the sump pump hole to sections of the wet basement by cutting the floor next to the ledge rock and digging a 12”-deep trench on all wet sides.
3. Lay 4” perforated pipe and crushed stone, providing a weep space (a very important feature) to collect the flow of water from the ledge that will enter the French drain system.
4. Fill the trench with concrete, removing the weep space material at the same time.
A HOUSE FOUNDATION WALL WITH NO FOOTING
Angle Away from Wall
Keeping in mind all procedures connected with the installation of the French drain system, special attention should be given to leaving enough contacts to secure the house foundation wall. If the foundation wall is not 12 inches below the existing concrete floor, the remaining depth of the trench should be dug at a 45-degree angle away from the wall. Next, lay the perforated pipe, and the stone, and continue by resurfacing the trench .
--- Exposed Ledge Rock
HIGH HUMIDITY IN BASEMENT
For Serious Humidity and Dampness: The most practical way to prevent damp basement walls is to apply a damp-proofer such as Xypex to exterior foundation walls while the building is under construction.
Follow the manufacturer's instructions and finish with a layer of 2” insulation board to grade. (Xypex is described under Supplies, at the end of this guide).
If the builders failed to provide effective dampproofing, a damp basement in an existing house can be corrected by digging outside the foundation walls to the top of the footing. Clean the wall surface and apply plastic roofing cement up to the grade line. Cover the walls with two layers of 6-mil polyethylene and place 2”-thick insulation board over the poly. If the problem is only dampness, finish the work by backfilling with the same soil you removed. If major water threat and flooding are likely, install perforated pipe and stones as discussed for block foundation walls.
If these procedures are not possible, the following suggestions could help: (1) Keep open all basement windows for cross-ventilation to help reduce dampness. (2) Purchase a heavy-duty dehumidifier, which will help enormously in keeping the basement dry. The water collected by the de humidifier can be drained into the existing system by attaching a hose to the back of the dehumidifier (the water holding pan) and allowing the water to drain into a sleeve pipe preinstalled to receive discharge water.
A COLD WALL
Especially during a series of cold spells in Winter months, one or two basement Walls will receive less sunshine. Water may condense on these colder Walls and run down the surface. If this condition is noticed while waterproofing the basement, install a weep space on the sides that have wet walls.
Another method of correcting the dampness of cold walls is to dig on the outside of the house foundation wall and install 2 inch rigid insulation board to a depth of at least 48”. This Will prevent coldness from penetrating the concrete walls.
LEAKING CRACKS --OUTSIDE REPAIR
Plastic Roofing Cement and Poly: To prevent water from entering through cracks in the foundation walls, consider the following procedures for re pairing from the outside:
1. Dig from the outside of the foundation wall down to the top of the footing.
2. Dry the concrete surface 6” from each side of the crack with a blow torch or heat gun.
3. Brush the areas clean and apply a 1/2”-thick layer of plastic roofing cement over the crack, 6” on each side, from the top of the concrete footing to the top of the surface grade.
4. Lay a 6-mil polyethylene sheet (16” in width) over the crack, starting from the bottom of the wall, including the top of the footing, and continuing to the top of the foundation wall. Be sure to secure the polyethylene sheet by nailing it, together with a strip of Wood, onto the house. This procedure is necessary to prevent the polyethylene sheet from sliding down and disturbing the tarred crack during trench backfilling.
LEAKING CRACKS -- INSIDE REPAIR
Over the years we have developed a very successful method for repairing a cracked foundation wall, leaking wall, and leaks around pipes by applying a flexible rubberized patching material. The steps for application of a waterp1oof mg material must be followed carefully. First, the area must be absolutely dry and warm (at least 50 degrees F) before it can be repaired. Remove all laitance, efflorescence, paint, whitewash, and foreign within 3” of either side of the crack. After stirring well, apply the patching material over the prepared surface with a brush, working from the bottom of the crack up, covering all the prepared surface follow the manufacturer directions to complete the work.
Sometimes water on the basement floor especially in a deep basement, is the result of a diffusion of fluid coming through a semi-permeable membrane (the concrete floor) that has been caused by the temperature difference between the room and the concrete floor. These different temps can form a vacuum and draw water onto the surface of the floor. Very helpful measures in these circumstances are the creation of cross-ventilation plus the use of a heavy-duty dehumidifier.
FERRIC OXIDE CLINGING to Stones and SUMP PUMP
Prevent Clogging: Ferric oxide or hydrated oxide of iron, is sometimes encountered installing drain system. It’s easily identified because of its combination of red brown black orange, and yellow colors. If you should find this substance while installing a French drain system, it’s important to in stall a 12x12x24” or larger sump pump holding chamber in each inside corner of the basement. Next, lay a continuous 4” plastic pipe around the perimeter of the basement to discharge the ferric oxide into each sump pump holding chamber. This procedure will remove the ferric oxide as it flows through the pipe and will prevent clogging of the sump pump.
Two Pumps Important: After the pipe is laid in the trench with the holes up, place 1%” crushed stones over the pipe to subgrade. This larger stone will allow the water to flow faster, thus helping pre vent the ferric oxide from restricting Water flow. Be sure to install a two - sump pump system in conditions like these.
In situations where ferric oxide is present, it’s important to clean and service sump pumps on a yearly basis.
Sealing Soft Brick: Sometimes brick chimneys and brick veneer walls contain a high percentage of soft brick, which have a tendency to absorb more water than hard baked brick. Soft brick can sometimes be identified by a residue of paint from their earlier use on the inside of a factory building, or by the light color caused by their being placed in the back of the oven, where they received less heat in the baking process.
After a rainstorm, soft masonry not treated with a good water repellent agent may transmit Water to the inside Walls of the house. In cold weather, the water in excessively soft brick Will freeze and expand, causing fractures in the masonry.
Before sealing masonry, check for defective pointing and joints, and remove and replace them. After the new mortar has cured, apply a double coverage of masonry coating according to the manufacturer's specifications, which will be determined by the rate of masonry absorption.
SHORTCUTS TO TROUBLE
Prevention Pays: Some contractors believe they can avoid water problems by simply laying 6- to 12” crushed stone under the concrete floor and: (1) not laying perforated pipe around the perimeter of the basement; (2) not providing a sump pump and holding chamber; and (3) not providing a discharge gravity flow pipe from the system. Without the above pre cautions, water can enter under the floor, creating hydrostatic pressure and causing the floor to rise. To avoid wet basement headaches and expenses, don't take shortcuts. Crushed stone alone is not enough to prevent serious water problems.
The following tools are suggested:
stone drill hammer drill pointed shovel garden hoe ' jackhammer push broom power saw clay spade abrasive masonry blade pipe wrench Wheelbarrow 5-gallon pails concrete wood float concrete finishing trowel edger An air compressor for the blow pipe and other tools can be rented. Sizes from 85 to 185 ft^3/min. are available. Consult with your supplier to match the size of the air compressor with the tools you are using.
Easy Sealing is a product developed as a bonding agent and sealer especially useful for repairing leaking cracks and tie holes.
Xypex is a Canadian product comprised of portland cement, very fine treated silica sand, and active proprietary chemicals. When mixed with Water and applied to concrete, a catalytic reaction seals concrete against penetration of water.