concrete slab for workshop

Page 1 of 3  
Hello
My neighbor wants me to help build the forms & pour a concrete slab for his work shop. Any assistance would be greatly appreciated. From your own experience. Things to consider. Things to do & things not to do. Maybe a How To website Is it necessary to pour a footing or just pour the concrete on the gravel bed. Any re-bar necessary? The building is 16' X 20' Thanks. ron
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Ronald Murray" writes:

his
<snip>
Many years ago, I tackled this same task.
Got as far as building forms and getting pricing on concrete and rental equipment such as a powered buggy to get the concrete from the curb to the back yard.
There was a concrete contractor in the neighborhood who reluctantly agreed to look at the job site and give me a price.
Needless to say, he got the job.
Stayed home and watched the day the contractor did the work.
Smartest decision I ever made was not to lay concrete.
After watching the job, I could have written a book about what I didn't know about laying concrete.
I'll try most anything, but two (2) things I won't do:
1) Brain Surgery. 2) Lay concrete.
HTH
--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<snip>
Hmmm, are you saying you wouldn't lay concrete?!?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Just ran this one by my resident neurosurgeon. The opinion was "brain surgery is easier than plumbing and much easier than concrete work.";-)
RB
Lew Hodgett wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I guess that is reflected in their pay.
There are guys who do nothing but concrete finishing. When I poured my garage floor the guy showed up with his windmill buffer deal after the concrete was screeded. He just "owns" the final finish. He floated it out and when it was set he power troweled it.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ronald Murray wrote:

Been there. Done that. For a 20' X 24' shop.
1. I suggest footings and re-bar in the perimeter footings. 2. Consider having termite protection applied just before the concrete is poured. 3. Embed J bolts into the wet concrete to provide attachments for the tubah base of the walls.
Hoyt W.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
16x20 should be poured in 2 sections with an expansion joint in the middle to minimize cracking. Put 6x6 #6 or #8 wire in it and be sure to pull the wire up into the slab. Even if you use "chairs" it can still sag but once pulled up into the concrete it will stay put. Pros will usually snap tie #3 rebar to the wire, just to keep it flat. Generally you will want to use a "bell footer" where the edges are 4-8" deeper than the slab. Run some rebar around that perimeter. Two #4 or #5 (1/2" or 5/8") will usually do. Get an "acorn" clamp, connect to the rebar and stub up 10' or so of #4 solid copper wire at the point where your electric will enter. That will be your "Ufer" grounding electrode. This not only provides a good connection to earth, it also creates a good ground plane in your shop. When you place the plastic sheet under the slab do not put it under the deeper footer part. The plastic is to slow the curing of the slab. After it sets (hard to the touch) cover the top with plastic and wet it down by spraying water under the plastic. Keep the slab covered and wet for at least a week. You don't want concrete to "dry" you need it to stay wet and "cure". This allows the small bonds between the cement and the aggregate to continue to form. This really goes on for a month or more if it stays wet but a week is usually enough to prevent surface spalling and mitigate the tendency to crack. If you are in no hurry to build, longer is always better. If you are building to the southern building code you will also want hurricane straps embedded in the slab to tie your walls to, for you folks in the great white north you can probably disregard this.
This is also the time to think about things like water lines and electric raceways. It is legal to run electrical type ENT "smurf tube" (the blue flex stuff) in a slab. That is cheap insurance for ideas you might have later. I would be pretty generous with it. For plumbing we use CPVC here but YMMV. The plumbing should be underground but the smurf tube can be on the ground, under the 6x6 wire.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Where to start!
Lots of great info already, and perhaps you're beginning to see how much knowledge is needed. Well guess what, it's not just knowledge, but skill as well.
16X20 is a large project to do as a first timer. Breaking it into to two 16X10's is an execellent suggestion. Piece of cake if you're a finisher by trade, but a sizeable job for a newbie.
So far no one has mentioned the fact that you will need to screed the concrete, use a jitterbug to press the aggregate down, float the surface, edge the corners, joint it, and smooth it out. Oh yeah, all the while fighting to keep the surface flat and level.
Around my neck of the woods (CA,) I wouldn't consider anything less than joints 6' on center. Don't let anybody fool you. Concrete is hard and it will eventually crack. Better to direct those cracks into a joint than have them go where ever they want to go.
Even with the wire mesh, I would consider #3 rebar or better every 30" oc in a grid pattern. That will keep any cracks from lifting, and rebar is just not that expensive.
I'm a farm boy who has poured concrete at least 30 times over the last fifteen years. I'm now at a point where I could do the job you've described with another person of the my caliber.
My tenth job (by myself) was a 10 x 12 shed poured in much the same way as described below. It was a hot day, and the concrete ran about two cu.ft. short. I busted my butt on that job -- mixing the needed 2 feet by hand when I should have been screeding and floating. By the time I finished mixing and pouring, the concrete was firming up, and there was very little I could do to salvage the project. It is ugly, and if it hadn't been a shed, I would have ripped it out.
The best suggestion I can give you is to try a small sidewalk first. For once thing, you don't have to finish on knee boards, and if you don't like it, it's easier to rip out.

to
wire up

up
the
deeper
up
enter.
good
When
(hard
don't
enough
in
hurricane
great
in a

pretty
ground,
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Salthead"

Yes - and while you are busy learning to do all this stuff for the first time ever, the concrete will be getting very hard and completely unreworkable.
- Nate
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Top on the list of "things not to do" is to try to pour a 16x20 slab yourself, unless you have previous experience working with concrete.
About eight years ago, we needed to have our front porch repaired, to the tune of about $2500 to cut out an repour a 7x8' section that had badly cracked.
As I watched the workmen cutting out the cracked section, I said to myself "I could do that. Why am I paying these guys twenty-five hundred bucks?"
And as I watched them break up the old concrete and dispose of it, I said to myself "I could do that. Why am I paying these guys twenty-five hundred bucks?"
And as I watched them build the forms, and lay in the remesh, I said to myself "I could do that. Why am I paying these guys twenty-five hundred bucks?"
And again, as I watched them pour the concrete into the forms and shovel it around into all the corners, I said to myself again "I could do that. Why am I paying these guys _twenty-five_hundred_bucks_?"
Then the head of the crew got down on his hands and knees and floated the whole thing beautifully smooth in about ten minutes.
And I said to myself, "THAT'S why I'm paying these guys."
IMHO... if you've never floated concrete before, a 16x20 slab is NOT the place to begin practicing. OTOH, if you have, then go for it.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
For a copy of my TrollFilter for NewsProxy/Nfilter, send email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
After 37 years as a Concrete Contractor I have seen it all when it comes to Do-it-Yourselfers. Have no idea how many times over the years I have been called to fix someones mess. This isn't just a sidewalk that can be brushed to hide the imperfections, a shop floor must be level, very flat and smooth. You don't want your TS (etc) rocking on an uneven floor. The smoother the better, should be like glass, making cleanup much easier. The best advice you got here was from Doug and Lew. Hire a licenced, bonded contractor. Get bids from at least 3 and check out thier work references. Low bid is not always the best choice if you want a perfect job. When the slab is finished be sure they spray on a good coat of Sealing Curing Compound, which is better then covering with plastic sheeting. If you are in hot climate, keep it watered down for several days.
My 2 cents, Al in WA

his
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
No disrespect intended here, honestly trying to help, but if you have to ask those questions you had best hire a contractor. Concentrate your efforts on what to tell the contractor you want from him.
-- ******** Bill Pounds http://www.billpounds.com

his
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ron;     I agree with the Miller brothers (?) Doug and Al. I thought about doing my own sidewalk a couple of years ago, but decided that the finish work was not for me. I am now in the process of building a garage and home and concrete work is something I refuse to do. Do it wrong and you will be reminded of it for the rest of your life and you may loose the freindship of a good neighbor to boot. DO it right (especially foundations) and the rest of the job goes a lot smoother. Leave this one to the pros.
JAW
Ronald Murray wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Naw we aren't brothers but I do have 2 younger brothers that were smart enough to stay away from concrete. One retired from Motorola and other from UPS. Al

his
to
gravel
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Wow, I can't help observing at this point how utterly rare it is to see this kind of unanimity in response to a question on the wreck. Not a single person, in a group that is sometimes absurdly optimistic about our ability (yes I include myself) to do ANYTHING around a house, thinks this would be a good idea. Of course now that I've said it someone will step in to say, "No problem at all, maybe go to the library and take out a book on it, it ain't rocket science..." Personally this would scare the bejesus out of me. At least when I screw up a woodworking project I have some hope of undoing the thing, or REdoing it, or at least being able to get RID of it.... A 16 x 20 concrete slab...

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"brad" writes: <snip>

<snip>
Perhaps I can put it in a little different perspective.
Concrete, lots of it, gets very heavy, very fast.
First is an observation that is to say the least, a little crude.
Don't f**k with the truck unless you are prepared to get run over.
The other comes from my background in sailing.
A small sailboat, fully in the right of way, according to the "rules of the road", got on the radio and asked a 1,000 ft ore boat, carrying 60,000 tons of iron ore while making about 25 knots on one of the Great Lakes which shall remain nameless.
Back came a one word response, TONNAGE!
Dealing with concrete is like wrestling a bear.
You keep wrestling until the bear wants to stop.
Same thing with concrete.
HTH
--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
http://pages.cthome.net/edhome
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
brad wrote:

Nope.
I paid someone $750 (plus materials) to pour ~ 1400 square feet of floor, it's a little high here, a little low there.
It's one helluva site better than I could have done, and it's better than some commercially done floors I've walked on.
--
Mark

N.E. Ohio
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bradnh responds:

I had a friend once who decided to add a small extension to his house, with a concrete slab floor. In that area, 32" deep footings were needed. He went 42" for security (he said). He set up the forms and was all ready for the concrete truck. I got my rake and walked over. I noticed that bracing was maybe 5' apart and said something. He said it would be fine.
Every brace bowed, ends of forms separated, concrete filled the entire trench. Nothing to do but yank the forms entirely, rake and level at the trench tops after ordering in more concrete on an emergency basis.
What a mess!
I had little desire to work with large amounts of concrete before that, but now...NO desire, and that was 30 years ago.
Charlie Self "Wars spring from unseen and generally insignificant causes, the first outbreak being often but an explosion of anger." Thucydides
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yep it's a pain. The codes will eat you up, unless you are in an area that's lax or can claim to be a farm or such. Around here, major footers are required all round, and some inside too. Go to your pplanning office first! Get at least three bids before deciding. You can do it, but the forms have to be strong, well braced, and square. It's a bitch to be running around trying to brive stakes and install braces while the mud is being poured. Wilson

his
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Related Threads

    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.