I am curious why so thick? You are holding up a bit more than 30
pounds/SF. Hand batching that much sack goods will have you worn
out. 15-20 bags of 80 #. Normal sack goods makes about 2500 PSF
concrete if you don't add excess water (most people do).
Keep the whole world singing . . . .
DanG (remove the sevens)
I need to lift surface high enough so that it won't flood during heavy
rains. putting it 6" above ground level will insure that. The most I've
seen in that area is 2" of water during an extremely heavy downpour bfore
the water had a chance to drain off.
Just want to be safe.
I will rent a mixer for this job for sure!
Before you mix all that concrete, look at some alternatives.
Can there be a platform on blocks? 500 pounds is not much so building a
wood platform with a 2 x 4 frame and decking boards on top it will be
sufficient. I'd use four concrete blocks to support it all. Once the
concrete is in place, you have a very permanent slab. With wood and block,
you can move, modify, eliminate, add height, as needed.
The concrete slab will weigh about 1600 pounds. Do you really want to
handle that when something a couple hundred will do the job just as good?
I'd use welded wire grid, an inch and a half from the bottom and top.
Either that, or place about half the concrete, and then dump rocks
in to bulk it up, and then another layer of concrete.
(Always assuming I could resist the temptation to cast
a storage vault under the damn thing.)
I'm w/ Dan--why in the world use an 8" pour for such a small load?
What is the footprint of the object(s) to be mounted on the slab? If
the purpose of the thickness is to get the height above surrounding
grade, I'd recommend strongly considering accomplishing that by grade
adjustment and a resulting thinner slab. A standard nominal 4" slab
would easily support the load unless it is a very small footprint (and
in that case it would make a lot more sense to make local mounting
piers thicker rather than the whole slab).
As for the bar, I wouldn't worry about bar, but I'd probably use 6"
square mesh just for doing it (and because I've got a roll remnant
around :) ).
HTH, and better or more specific answers would undoubtedly be
forthcoming w/ some more info on what the objective actually is...
BTW, iirc (and I think I do) the 80-lb Quikrete sack is 2/3 cu-ft so
your proposal would be a roughly 3x5x(2/3) cu-ft * (3/2) bags/cu-ft -->
15 bags. That's a lot of hand mixing considering the time element
since you presumably want a continuous pour.
OK teach me something about slab building as I am a rookie.
The object is a 500bs box that is 2' x 4'. It is fairly evenly distributed
over the box so load is not a problem.
Like I said in a previous post I'd like the surface of the slab to be 5" -
6" above the current ground level. This is in south texas so frost line is
not a major problem.
how would you recommend constructing this slab?
Would it be fine if the grass formed a little hill with this slab
on top? Never pour concrete on grass. Remove sod as required.
Use gravel, fill sand, broken cement blocks, old bricks, rocks, or
select fill (compactable sand/gravel). Set a 2x4 edge form at the
height and slope that you want to end up with. Pack the bottom
edge with dirt or whatever so the concrete can't run out. Pour
and finish. Strip forms and add back top soil and sod.
If you want it high above the grass with nicely finished 6-8"
face. Set an edge form (2x8?) around the intended slab. You
still need to have removed the sod. Raise as much of the center
with rubble or select fill as possible, leaving the top and sides
at least 2" thick. Think about the finished concrete looking a
bit like an upside down cake pan.
Keep the whole world singing . . . .
DanG (remove the sevens)
I'd do one of several things, assuming you don't want a wooden deck
type solution (which, in So TX I can certainly see) which as someone
else mentioned would certainly not be difficult to make to support the
I'll outline basic choices/alternatives to consider--what, specifically
works for you depends on factors I don't have any way of knowing--where
you are, what sort of tools you have or have access to, etc., etc., ...
First choice would be to simply make a small "hill" to place the slab
on top of...will need some fill material from somewhere which can be a
pain if you're in a large metro area and don't have any hauling
capabilities. If you're lucky you've got enough of a lot you can
scrounge enough soil from one place to make the area you need large
enough high enough above the surrounding area. Assuming it's a yard,
ideally you would want it graded enough to plant back to grass and mow
along w/ the rest of the yard.
Next would be variations of the "wall and slab" method...rather than a
slab this thick all the way through, go ahead and form the full height
around the outer edge but fill in the center portion except for an area
around 4-6" wide (say) w/ fill material so that the bulk of the pour is
only 3-4" thick. Again, need something for some fill--can be old
brick, rock, clean dirt (not mixed w/ sod, sticks, etc.) or whatever
else you can find. Need it to be good enough that it can be packed
solidly, so settling isn't an issue later.
More sophisticated versions of the above include laying an outer wall
of block or brick, etc., and essentially proceeding as above from
there. Really all the point is is that there should be far less
labor-intensive and expensive ways to get the end result w/o pouring
such a huge block of solid concrete.
Second alternative would be to
No, you shouldn't need rebar, but as someone else suggested wire mesh
instead. The rebar is there for bending stress, it won't stop it from
Besides you didn't specify which gauge rebar you wanted to use, there's only
about 50 different types (well actually that's an exaggeration). Anyway if
it were me, I'd go with the other suggestions of pillar and post.
You guessed it. Its a Generac 15kW unit and it will be a perminant addition
to the house and won't move.
I thought about a wood solution but I don't like the idea of hot generator
on wood. Wood rot and termites are also issues to deal with.
Tell me about building a block foundation?
Pour a standard 4" slab. Get 4 precast concrete deck anchor blocks. Drill 4
holes in alignment with the anchor holes in your genny's bottom/frame. Use
threaded anchors to mount about 1 foot lengths of 1/2" or 5/8" threaded rod.
Fit the four blocks over the threaded rods and mortar the blocks to the slab
and fill the center hole in the blocks around the threaded rods with morter.
Set your genny on top of the blocks with the threaded rods through the
mounting holes in the bottom of the genny and tighten into place with some
washers and nuts. This will provide an air space under the genny to keep it
dry reducing corrosion, help it cool with in operation and high enough to
prevent minor flooding from touching it. I did a similar installation in my
garage for a diesel generator.
What about motor mounts or similar things? I'm thinking rubber mounts or
polyurethane mounts - last for decades even under harsh conditions - like
the kind in your engine compartment.
Say split the difference, 4" concrete slab with diesel engine mounts -
should put it well over 10" total height.
Consider a few 4x4s, a decking of 2x6s, four (maybe six) concrete blocks for
support. You'll need a saw, a tape measure, and some nails. Total time of
construction for one person: 2 hours.
It'll take two hours just to MIX twenty 80-pound bags of concrete.
Also, consider what you'll have to do when the wife says: "It would look
better over there."
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