SEARCH FOR PATH OF FOUNDATION WATER 3

[RFKim]

I'm hoping to help a client who has water passing through concrete blocks into his basement. The surface water outside the wall appears to flow away from the building. Are testing methods available such as dye testing to determine if the water is flowing down the walls from the gutters, or ground water flowing below the surface, or other paths?

 

[bimr]

New construction or existing? Foundation drain or not?

Water may be coming up from an aquifer. Water may be following the utility pipes.

Dyes for testing can be obtained here:

http://www.pollardwater.com/pages_product/dyesdata.asp

 

[racookpe1978]

What we had:

(1) Water was overflowing the gutters - sometimes - during heavy rains.
(2) Water was - light and medium rains - not overflowing gutters, but WAS collecting into the open dirt area just uphill of the concrete blocks. So, dirt got water-soaked, water soaked down deeper, water laid against concrete blocks and soaked in after many hours of wet soil. NOT udner light rains, but only after soil was saturated for a time.

 

[cvg]

dye testing is possible, but might be very difficult to confirm by visual methods. water quality analysis might also work, but it is a bit pricey and also not guaranteed to give you a solid confirmation of the source.

if you suspect gutters and downspouts, which is a good assumption, then just fix the problem.

if you suspect groundwater, geologic mapping, borings or nearby wells might help to confirm it.

a leaky water, sewer or drainage pipe could also be causing the problem

 

[Ron]

Local experience and geotechnical awareness will help you more than most other methods. Nothing wrong with trying groundwater mapping, dye testing, etc.

 

[oldestguy]

When building foundations are built and then backfilled, the usual procedure is to shove earth into that area from nearby. That results in lines of soil deposition inclined towards the wall. So when water hits any part of that backfill surface and soaks in, it has a tendency to follow the weaker inclined planes. So, just because the surface is sloped, does not mean you won't have a wet basement. Do a search in this forum for "waterproofing ground surface" or similar. I have written a few places about this using powdered bentonite to quite effectively seal that ground surface. You need to treat the entire backfill surface.

 

[oldestguy]

I did a quick search and no luck. Anyhow you strip sod from the whole backfill, re-grade if you can, and then spread 3 to 4 pounds per square foot on the surface with powdered bentonite and work it in thoroughly about 3 inches with a roto tiller. Work around plants, but remember those are then untreated areas. Replace sod. This bentonite is available at plumber supply houses for well drillers to use as drilling mud. Do not use the granulated stuff, since it does not thoroughly mix. A common trade name is Volclay, a natural volcanic clay. Do not go with higher concentrations, since this likes to take on water and swell to fill voids and too much results in a greasy mess. Do the work only on calm days to avoid it blowing around. If you are not sure of the mix, do a test with a mix in a wheel barrow, then put some in a #10 tin can with the bottom punched full of holes and see how fast water seeps out, comparing untreated to treated soil. Run the test after water has swelled the bentonite. Ideally a 2" thick layer will be practically waterproof.

 

[civilman72]

OG - Geotech engineers that I have spoken with avoid putting an impervious surface next to the building because they say it prevents subsurface water from reaching the surface (through capillary action) and evaporating. By trapping this subsurface water they say it can make a basement even wetter. I've specifically heard this conversation about impervious liners that homeowners have placed around their house with hopes of keeping surface water out of the subsurface and the geotechs tell them to take it out. I'm assuming a bentonite layer would have the same characteristics as an impervious liner.

Your opinion is highly regarded around here - what are your thoughts on the potential negative affects of the impervious layer?

 

[oldestguy]

Well that is an interesting facet about this general subject. Really the treated surface is very similar to using a tight clay layer there. We are adding roughly 10 to 15 percent clay to what ever soil is there. Water from below will move via capillary action, but slowly, especially to plant roots. However, the low permeability keeps most of the surface water out during those times when water in on the ground surface. Speaking from my experiences, I have treated two of my houses that way. Also I'd estimate the number of such treatments, including one earth enclosed type school, at a dozen or thereabouts. Never has there been a complaint to me. However, one home owner decided that if a little is good, more is better. The excess bentonite attracted much water and then sod actually slid down a slope in front of the house (the greasy mess mentioned). Bentonite is a mineral made up of sheets, similar to mica. The attraction of water to those intersheet spaces, will cause bentonite to swell 16 times its original volume, given the water available and no loading on the clay. It is that tendency that cause it to fill the voids. The use of landscaping plastic sheets under bark and wood chips may be what you heard. I know you will find water droplets on the underside of plastic laid on the ground due probably to the vapor pressure effects. In the jobs I am familiar with the culprit was surface water entering, not ground water. At my current house it is that use also, but the ground water table is only a foot or so below basement. The only problem event requiring the treatment was from heavy rains. With the treatment, the sump pump does not run now at those rainfall times. No excess moisture noted inside in the four years I have been here. I can only say all the jobs, except the "grease", have worked. Just before I moved here I "supervised" a job of volunteers for a country church on a ridge. Later they installed an elevator by excavating from the outside. Wouldn't you know it, they destroyed that "seal" there and in came the rainwater in that area later. A comment about dumb landscaping. Many 10 -15 yer old houses here (including mine before I fixed it) have a 6 inch deep trench of about 2 ft. width around the house walls filled with clear pebbles. That is to keep weeds from growing there. They are laid on a "landscaping fabric". I know that was part of my problem of sump pump running a lot. However, the poor gal across the street has lived in her house 10 years and in almost every rain that trench fed water to two window wells. The sump pump ran, but no help for those windows. I put her and her daughter to work mixing sand with bentonite, a 1 to 5 mix and that was packed in the trench at and on either side of the windows. Needless to say now no window troubles, but the sump pump seems to handle the water that otherwise came from the trench and bckfill. At my house no trench now but one inch of pebbles on treated soil.

 

[civilman72]

Good stuff. Thank you for the explanation.