Bit of a simple question, I hope:
I want to form for a 10x8' concrete pad for a shed. The spot I want the
shed in has a bit of a slope. I believe it to be about 4-5" over a 10' run.
The problem thus is how to build the forms to take out the slope in the
grade. I imagine a 2x4 in the back (high end) and a 2x6 in the front (low
end) but what is the best way to get the sides to go from 4" to 6". Of
course I may be way off in my thinking and would appreciate any other
I know the truth is out there, but I like to stay in...
If it was mine-- and I only wanted to do this job once. . . . I'd
scrape all the sod and crap off the site. Then I'd bring in a load
of #2 crushed stone for a base. Spread it on the site a couple
inches at a time. Tamp well. $75 to rent a compacter for a day is a
cheap investment. On the upper side I'd make sure it was at least 4"
thick [8 would be nice but it might involve digging]. Make it
level. use 2x4 to form your pad.
Once a shed is sitting on it [full of crap] is a poor time to try to
straighten up a pad that was poured on a sloppy base.
From my experience (and I'm no concrete expert) from building my forms
for my 18x22 workshop, the top of the forms have to be level at the
top. Drive two wooden stakes in each corner into the ground about 2
feet outside each corner. Each stake will be used to tie a string
line to show the inside top of each form. Tie strings from one
corner over to the adjacent corner. If done properly, all strings
should be level when done and will form the square of your proposed
slab. Once this is done, determine the distance between the string and
the ground and multiple points on each side. This will determine the
height of each form. you will need to dig a small trench 2" wide on
each side to put your lumber so that the top of the lumber is barely
touching your string. Make sure you brace the lumber with wooden
stakes on the outside, as concrete will pus the form out if
unsupported.. When everything is done, make sure the top of all the
lumber is level to each other as this will be the top of the slab.
I would also suggest following the previous suggestion about the base
preparation. a good base will keep the slab from cracking.
What I would do, as an old concrete formsetter would be this:
Think about how they make concrete foundations for houses. They make the
edges thicker than the rest so that the walls have extra support, and the
rest of the slab doesn't "walk", or shift. You don't want the slab to just
conform to the top of the landscape, but be fortified at the edges.
If it were me, I would dig down with 2 x 6's and 2 x 8's, BUT only making
the outside of the perimeter deeper than the center of the slab. Pack the
loose dirt before you pour. This would accomplish more than one thing.
First, should you want to drop some cheap cheap (did I mention cheap) rebar
around the deep footer part, that would assure, but not guarantee that the
slab would last longer than if just poured with plain concrete. Secondly,
with the perimeter dug as a footer, this would keep water from infiltrating
in and under and through the slab later, causing voids, hence weak spots.
Thirdly, you are talking about only a few more sacks of concrete, say $20
for the whole job. You do a little more digging, but you end up with a
level SOLID slab that you will probably never ever have to fool with again.
Don't forget to put the anchor bolts around the perimeter if you are going
to use a plate, or to match the pattern on the bottom channels of your shed.
So much can be done with these little slabs with a little forethought and a
few extra dollars, rather than writing back with, "HELP, MY SLAB IS
CRACKING!" An hour's more work and $20 more in cost.
As the man said, "You can pay me now, or you can pay me later."
Only if also is going to grade the area around the slab so it will drain
away; otherwise he'll have that end in a hole.
I'd suggest the building up of the low end as easier/simpler solution
altho definitely needs proper packing before pouring the slab.
Alternatively, split the difference and have less to landscape at the
upper end and less to fill at the lower...
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