I live in NC with clay soil. A problem area for me is under my deck
where the soil NEVER seems to drain. I've removed the mulch installed
by the builder. :-( to try and help to no avail. I don't want the deck
supports to prematurely rot out from underneath us!
Is it possible/adviseable to install a membrane/barrier on top of the
soil to only permit evaporation and no further water uptake?
Could/should I also add crushed rock to assist in draining the water
away from this area?
If you have positive drainage topographically away from that space, then the
problem lies in both the moisture retentive qualities of the below deck
soil, as well as the inability of the surrounding soil to translocate the
water away below ground. Many different possibilities exist for why exactly
that's happening, but the solution you propose is not a good idea.
Are you familiar with how to identify what types of soil you have? (sandy,
silty, loamy, etc?)
David J. Bockman, Fairfax, VA (USDA Hardiness Zone 7)
I really can't suggest solutions without knowing more about the soil
conditions. either the soil itself is suspect (marine clay, or something
similar) or there is some sort of physical barrier keeping that area from
draining. Other possibilites are leaky sewer lines or water lines...
If it were me, I'd get under the deck and shovel out a hole going about 2
feet down. I'd dump the soil onto a tarp and then drag it out into the sun
until it dries, then I would examine it. You can plot your results on a
three sided chart which I've posted to alt.binaries.pictures.gardens as
'soil makeup grid' which is widely used to classify soil types. The diagram
shows a three sided grid with each side representing the content of a
particular particle on a scale from 0% to 100%. The bottom line is the sand
content, starting at 0% at the bottom right hand corner, and rising to 100%
in the bottom left hand corner.
David J. Bockman, Fairfax, VA (USDA Hardiness Zone 7)
It sounds easy, but it isn't quite as easy as it sounds. The
differentiation of the soil components isn't just a matter of judgement.
Our local extension service charges around $50 for a soil
classification. However, I spotted a link that tells you in detail how
to do it yourself. I haven't tried it (New England soil is still fairly
solid at this time of year) so I don't know how easy or reliable it is.
But it's cheap, and therefore worth a shot.
In case you're not familiar with the soil triangle, an example can be
found at http://www.oneplan.org/Water/soil-triangle.shtml (There are
lots of them out there. Google it. The above link was the first one.)
On the subject of soil tests for the garden, I recommend that if you are
using a home soil test kit you spring for a professional test at least
once to compare their results against your kit. The home kit pH tests
are reasonable, and the potassium and phosphorous are probably not too
bad, but the nitrogen home test is not really very reliable.
You've gotten some great advice here, so I won't repeat that, but thes
sites show how to dig your trenches and do the piping. I would thin
that you might also be concerned about the water against th
foundation. The gnats are probably fungal gnats due to all tha
moisture. It could also become a mosquito problem with the war
I'm not a use.net poster, but posting from a forum, so forgive me fo
not knowing how to snip and paste all the conversations.
The deck supports should be sitting on top of concrete footings or,
possibly, embedded in concrete. If they are just buried in the soil,
you may have problems with settling, as well as water.
It's a little odd that the builder would put mulch under the deck. Is
this a raised deck that you can walk underneath?
First, make sure your gutters aren't draining anywhere near the deck.
If there is a lower region of your yard in easy reach, I would dig a
trench and line the bottom with plastic sheeting. Put in a length of
corrugated, perforated pipe, and fill the trench with crushed rock.
The water will now drain from under your deck to the lower area.
If trenching isn't feasible, you may be able to dig a pit, install a
sump pump, and pump the water away.
Any covering, whether a membrane or crushed rock, will reduce
evaporation unless you deal with the underlying drainage problem first.
Yes, it is tall enough to walk under but, when it warms up the gnats
tend to keep one away.
Luckily, they aren't.
I like the trench idea. Would this solution also help drain the
exsisting water-logged soil or just help shedding when it rains?
Should I slope the earth towards the trench in the middle or, dig
As long as you don't line the sides of the trench with plastic all the
way to the top, it should drain the existing water logged soil as well
as catching surface runoff. It may not even be necessary to line the
bottom with plastic sheeting, but I think it would help direct any
water that doesn't enter the pipe. The water will seek the lowest
point, so it will seep through the walls of the trench and flow away
through the pipe. Eventually, the water table should be level with the
bottom of the trench, instead of at the surface.
If you can find the lowest point under the deck, I'd start the trench
there. It may not be necessary to dig multiple trenches. Make sure
the trench always runs downhill until you get to the place where you
want the water to drain out. Don't forget to put a nylon "sock" around
the perforated pipe (available along with the pipe at Home Despot or
Lowes) so that silt doesn't clog the pipe in a couple of years.
Once the trench is away from the waterlogged area, you could convert
from perforated to solid pipe and bury it under soil and plantings
instead of having a gravel filled trench.
I live in NC, too, and I've been digging similar trenches to drain
water away from the back of our house. I've also connected the gutters
to solid-walled pipe that runs through the same trench.
My only other piece of advice is to try to dig when the soil is damp
but not soaked (though that may not be possible in the waterlogged
area). When our clay is wet, it is incredibly sticky and permanently
stains clothes. When it is dry, it's like cement.
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