Hello all. Am finally moving forward with my garage/shop rejuve. It's a
2.5 car detached garage built c.1920. At some point in the past, a very
thick (10"-12") slab was poured in the car parking section - leaving a
wood floor over joist over dirt (24'x11') shop area to the side.
Needless to say, the floor had rotted away, along with the sill plates
on the foundation that sits about 4" below ground level on 2 sides.
My plan is to pour the shop slab and then use that to support the walls
and roof so that I can cut away the lower 2' or so of the rotted sills
and studs. Ending up with pouring a cap over the existing foundation and
sistering in new lower studs.
I certainly don't need to pour in 10" of concrete for my woodworking
tools. Heaviest tool is a cast iron band saw weighing in at about 800
lbs. How thick would you recommend I begin considering? (There's not
much likelihood any type of vehicle could be parked on this section as
there is a ceiling joist post in the way which leaves little room to
maneuver anything of size into this area. Perhaps a tent trailer, ATV or
boat any future owner may have.)
I also plan on pouring the shop floor about 2" lower than the car floor
and installing a 2x sleeper/ 3/4" plywood floor for foot comfort/dropped
tool survival with beveling the ply at the car floor edge to make a
smooth transition. Vapor barrier? If so, should it go under the slab or
under the sleepers?
Lastly, with the "sunken" shop slab... What considerations should I
think about in case any water might end up under the wood floor? Do you
think simple vents in the plywood in various places along the edges
would offer enough ventilation to evaporate any standing water? (The top
of the new slab will sit about 2" above all exterior surfaces.)
Thanks for the feedback on what I should consider as I make plans for
Here're a couple quick pics of what I've got going on:
Owen, If it were mine, I would fill the floor flat (level with the existing
concrete floor) with 3/4" gravel base mix (gravel & sand), wet then compact.
Drill 6"- 8" into existing foundation and epoxy 2' rebar rod into holes.
After the epoxy cures, bend them so they are in the middle of your new slab
and tied to a 12"x12" grid of rebar. Pour a uniformly thick 5" slab and
finish. You never know what you may use this floor for latter or the next
occupants use may be.
As for the workshop floor, use a vapor barrier over the concrete slab then
add sleepers and floor. However, I would just use the concrete and use mats
for comfort and drop tool protection.
Isn't that Oneway heavier than that bandsaw :)?
First, a 4" 4000psi floor without mesh or rebar is sufficient to use anchors
and hold a 8,000# capacity above-ground auto service lift. This is my
business. So, that's all you need to put cars and pickups on without
problem. Definitely suggest the 4000psi vs common 3000 and even used 6000 in
my garage. The cost is only a couple dollars more and well worth it.
I'm concerned about a "slab" then using it to support the roof and then a
"cap". Your strength comes from a continuous pour and if you section it then
it becomes an island. The edges will not hold a good load and your walls are
free to float without the bond to the floor slab. Depending on the
foundation you could do the back drilling and epoxy in rebar to connect to
your slab. Never seen it done quite this way and would be wary. If I
understand your description then I'd use the dirt floor to support and do
the work and pour accordingly.
I'd spend my plywood money on good floor mats. Far more cushion and it
eliminates maintenance issues and those you brought up.
The AAW Symposium was cool. Crowded, yes, but great artists and
demonstrators. Neat to meet some of the names.
What a chuckle. Don't get me started.
First of all, thank you, Tom, (and Karl) for the help. The demolition
for this project was started almost a year ago - then after a $16,000
estimate for the job, it sat over the winter and spring while I turned
it over and over in my mind trying to figure out how to do it myself.
That's in the basement. Cooler down there in summer and warmer down
there in winter. You shoulda seen a friend and me getting that thing
down the c.1920 basement steps. We could certainly have used your help!
OK, I'll go with the 4k psi - when you say 4", do you mean a real,
honest to God/Allah/Vishnu 4" or a 2x4's 4"?
I understand what you're saying, but... The existing 2-car area was
poured inside the existing foundation and stud walls - they nailed sheet
metal to the lower 4" of studs & sill and poured the floor level higher
than the surrounding foundation. I figured I could follow a similar path
on the shop area and then pour a cap over the old foundation to bring
the sills above ground level. Do the foundation walls need to be tied to
the floor slabs? I was going to drill vertically into the top of the
foundation and epoxy in rebar to tie the cap to the existing - as well
as put in anchor bolts for the sill.
Mark your calendar for next summer - it's here in Portland!
Fly-by-Night CC wrote:
> First of all, thank you, Tom, (and Karl) for the help. The demolition
> for this project was started almost a year ago - then after a $16,000
> estimate for the job, it sat over the winter and spring while I turned
> it over and over in my mind trying to figure out how to do it myself.
Many years ago decided to add a slab patio addition to a small
Skinned off the sod, set the forms, had a couple of truck loads of
foundry sand delivered to the curb, then one by one, moved all that
fill , one wheelbarrow load at a time, back behind the house where the
patio would be built.
Leveled out the fill, and decided it was time for some concrete quotes.
Quotes clearly threw up a red flag of warning.
Thought about it for at least a couple of weeks, then remembered my
daughter, who was in the first grade, had a classmate who's father was
a concrete contractor.
Gave him a call and explained what I had done.
Reluctantly he stopped by and took a look, indicating that my work,
while maybe not up to his specs, was acceptable, and gave me a price.
The next door neighbor who indicated that if it was a fair deal, they
would also get a patio poured.
We struck a deal and work began the following week.
I took a day's vacation to properly behave as a sidewalk superintendent.
As I stood there watching this crew working, I made a mental note.
At that time in my life I was willing to try almost anything except
practicing brain surgery and now after seeing it done, laying concrete.
Properly laying concrete is definitely an art form, IMHO.
... and it's amazing how many it takes to do the job today.
I remember when I had more youth than sense, and, willing to try anything,
including brain surgery given the necessity, I single-handedly built the
forms and poured the footings and grade beams for a 40' x 70' building.
Why it is still standing, tall and straight, some 32 years later is
apparently a mystery considering the 20 man crews I pay to do the flatwork
on a new house these days, not to mention the paperwork, permitting and
inspection fees the city requires for their blessing/grace.
That's amazing. My 3520B was a handful without those steps.
Probably true 4" since the slab is normally tied to a footer as in a
But I'd consider a GOOD 2x4 (no humps in center thinning the floor) and I'd
the man who sets little metal stakes at the correct depth so that as he
he knows for sure he's maintaining the correct depth. If you buy the
insist on a copy of the concrete company's load ticket it's less likely to
problem. Otherwise the contractor may calculate/price by measurements but
buy that much and save by sagging a little in the center (or humping the
Do the foundation walls need to be tied to
Not my expertise but sounds workable. Consider the wall foundations are free
to float and buckle without a "connector" to the opposite wall foundation.
on the anchor bolts. You haven't cited the wall/foundation thickness but,
if a block foundation, you'll blow out the wall with the stress the anchors
work as an anchor. Better to continue with the epoxy approach I would think.
I may have to mortgage the house to pay for fuel at 8-9mpg diesel for my
But I love your country and consider the symposium an excuse to visit again.
We rode our Harleys down the coast and over to Vancouver Island in 2002.
God's country. Promise me an Orca sighting and I'll carry the dually on my
Tom, I too have installed hundreds of hoists - both inground and above
ground. While I agree with the higher PSI suggestion, suggesting that Owen
not use rebar/wire in the floor will only result in cracks and posible lift
edges. Maybe its just a California thing but I could not imange not using
Probably that's exactly what it is. After all, that's the earthquake world
and your point's well taken.
Rebar around here just causes unnecessary problems drilling for the anchors.
Wire's no big deal and common.
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