Workshop concrete

[Fly-by-Night CC]

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 the pour.

Owen

Here're a couple quick pics of what I've got going on:

[Karl B]

Fly-by-Night CC wrote in news: [e-mail]:

Use a minimum of 4" of 3,000lb. concrete and you should be just fine. 4" is the standard for commercial floors. If you were going to put cars and light trucks onit, then use a 5" slab.

[Teamcasa]

"Fly-by-Night CC"

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.

Dave

[Tom Nie]

Owen 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.

TomNie

[Fly-by-Night CC]

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!

[Lew Hodgett]

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 existing patio.

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.

YMMV

Lew

[Swingman]

... 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.

[Tom Nie]

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 monolithic pour. But I'd consider a GOOD 2x4 (no humps in center thinning the floor) and I'd love the man who sets little metal stakes at the correct depth so that as he pours he knows for sure he's maintaining the correct depth. If you buy the concrete or insist on a copy of the concrete company's load ticket it's less likely to be a problem. Otherwise the contractor may calculate/price by measurements but not buy that much and save by sagging a little in the center (or humping the dirt).

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. Careful on the anchor bolts. You haven't cited the wall/foundation thickness but, especially if a block foundation, you'll blow out the wall with the stress the anchors use to 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 dually. 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 back.

TomNie

[Tom Nie]

Sorry about the formatting. I'm still learning this internet stuff.

TomNie

[Teamcasa]

"Tom Nie"

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 something.

Dave

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[Tom Nie]

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.

TomNie