As I've mentioned previously in other threads, I'm in the process of
building a deck. At the moment, I've just dug holes 5 feet into the
ground in preparation for pouring concrete pier-columns (the
foundations which my deck will rest on). However, as soon as these
holes were dug I noticed they would partially fill up with water,
seeping in from the surrounding (clay) soil). I've drained them once
with a sump pump, and I thought the holes would stay dry until I could
pour the concrete into them, provided the weather remains dry til then.
However, despite continued dry weather conditions, this morning I
noticed that the holes have filled with water again. I surmise this to
be related to my neighbor leaving his lawn sprinkler on the night
previous, and that water seeping into the ground from that is what is
entering my holes. All this has got me thinking... Will my concrete
pier-columns be stable enough to hold my deck properly since the
surface soil they will be buried in is obviously prone to holding
water? Right now the weather is dry because it is summer. But most of
the year it rains a lot here (Vancouver). If water from a neighbor's
sprinkler can saturate my future foundation soil so readily, can I
expect it not to turn into an unstable, sinking, muck when the heavy
Responses please and thanks,
Concrete does just fine in wet conditions, It is not the presence of water
or not but if that water contributes to a weakening of the soil containing
it that is important. This I certainly cannot answer from here. Given that
a deck load is not very high, directed straight down and that clay us
usually very dense and stays put unless on a slope, MY gut feeling is that
5'deep by what 1.5' wide would probably be enough anchor. The depth of the
hole is mainly necessitated by the need to get well below the frost line to
prevent movement, otherwise, a shallow, broad support would work just as
well if you live in a no freeze zone.
If the deck is to be covered or used as an indoor space than you will want
to be more particular about the underpinnings and maybe worth consulting a
structural engineering firm for an evaluation. In fact a concrete
contractor may be able to advise you enough without expensive tests.
I have found that if I fit a plastic (garbage) bag in the hole and then
place the Sonotubes into the hole inside the bag, I can pour the concrete
without stirring up bottom mud and contaminating the concrete with the mud
and excessively diluting the concrete with excess water.
From Calgary. Concrete does not weakens in water. Think hydro dam built
with concrete. The question is whether your soil is stable to keep the
concrete post in place. Here usually we dig down to frost line minimum
for this kind of work. That is ~ 6 feet deep.
I think the main problem is the holes are to deep. You just need the
holes deep enough to get below the frost line. If I were you I would
find out what is recommended in your area and refill and pack the holes
to that depth.
If 5' is recommended then just go ahead and do like the other poster
said, drop your sonotubes in trash bags into the hole, fill with
concrete, and put the post anchors on top of the pillars while the
concrete is still wet. I wouldn't sink the posts in the ground in the
concrete as you have a lot of moisture in your area.
I'm going to be mixing my own concrete. (I already bought a dozen bags
of "Ready-Mix".) Guess I can buy a bag of cement and add extra just the
same as the concrete plant would do?
Is this additive also available for the 'mix-it-yourselfer'? If so,
what product do I look for?
Okay, I can live with that very small risk (for this part of the
country anyway, that is <g>).
BTW, I forgot to add another, related, query to do with my future
intention to build a large shed with a below-grade basement cellar.
Given my "wet clay soil", in addition to the inconvenient fact that
local bylaw states any foundation drainage flow into public sewer must
be by gravity only (i.e. no sump pumps, etc), is there anything special
I might need to be aware of here (considering that I intend to use my
cellar for storage and therefore needs to be dry)? For example, is
foundation drainage always a necessity (because this concrete
foundation will be too low to drain into my sewer connection under
bylaw constraints)? Should the concrete of the basement cellar walls
and floor-slab (my foundation, in other words) require any extra
measures be taken to make it sufficiently water-resistant and, if so,
how is this usually accomplished? (1) E.g. buying "waterproof" concrete
made from "epoxy cement"? Pre-installing a waterproof (e.g. "swimming
pool") membrane? Etc...
You're in for a shock. Our 7 4' deep holes took **42** 80 pound bags of
quickcrete. You don't say how many holes you have, but at 5' deep you'll
certainly need more than a dozen bags. That might get you a hole and a
You'll also likely want to rent a mixer. Our HD rents one for about $40 a
24 hour period. You dump in the mix, and some water, then wheel it right up
to the hole and dump it in (after mixing, of course). SO much easier than
mixing by hand, when you're mixing up 3500 pounds of the stuff... Even so,
you'll want help. 80 pound bags get heavier with every one you lift...
This is one of the many reasons to do the math ahead of time and get stuff
delivered. I've seen people nearly destroy their vehicle cramming a ton of
bricks into the trunk when they could've just gotten an entire palette
delivered for around $50. Likewise with concrete and gravel, check with a
local supplier. You can get gravel for about a THIRD of what bagged stuff
from the box stores would gouge you.
Renting a mixer for concrete is about the only way to go unless you've got
enough to justify ordering up some delivered by mixer truck. Then it's one
wheelbarrow at a time to offload it from the hopper to the holes. And
you're generally stuck with ALL that came in the load, not just the amount
you need. So unless you've got a lotta holes, patio and/or stairway
landings then mixing your own is the way to go. Just buy it from a bulk
source and have it delivered instead of overpaying the home despot and
wrecking the car.
Quickcrete's pretty cheap. I had all my deck supplies delivered for $35
(delivery charge) so didn't pay more for delivery. I can't imagine I could
have had "bulk pre mix" (does that even exist? I had no interest in trying
to mix my own concrete from its component parts) delivered for cheaper than
I paid for my Quickcrete, and then I would have had a big pileof dry powder
in the garage or wherever, making a huge mess...
I had 40 bags delivered, ended up needing a few more so I sent the wife down
to the local BORG to pick up six more while the rest of us worked on the
pour, of which we only used two. I'm from the "rather have too much on hand
than too little since you can always return it" camp but I guess my footing
holes were wider at the bottom than my calculations indicated...
Ours were 12" round, with 3 of them having a 17" base (the others roughly
12" -- the city's plan reviewer said those didn't need flareing).
We ended up needing about 6 bags/hole. I'm guessing you'll need more than
that, with the deeper depth and wider bottoms, and even with the narrower
I have direct, recent experience with this, as we're also building a deck
right now. Our 4' deep holes (7 of 'em) did the same thing. When I first
called the building department, they told me "the holes have to be dry and
no much for the footing inspection". When I pressed them for how exactly I
was to accomplish that when I was obviously below the water table, they
forwarded me to the inspector who would actually be coming over, and we came
up with a plan:
a) first I sucked the water out of each hole (with a shop vac) and removed
the loose muck caused by digging the hole.
b) Then the inspector came out to verify the footings, and verify that the
soil was indeed clay.
c) She then had me place about 3" of river rock in each hole, and tamp it
down good into the mucky clay. This didn't raise the level of the footings
much (we had plenty of depth anyway as I only need 42" for frost footings
and I had 48") but provided a very solid base for the concrete pour.
d) The next day when pouring the footings, they had of course filled with
water again. I sucked them out, one at a time, before doing each pour.
Can't say how well it will hold up as this was only last week -- but they
seem solid so far...
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.