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EJB
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Cement floor into existing workshop question
08/11/03 05:33 AM
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I know variations of this question have been discussed here and over at TBN, but never really got consensus on my particular situation so I'll throw it out here.
I have an existing 32x26 shop building with a dirt/gravel floor. The building has been up for about 40 years and has been used to store tractors etc for most of that time (point being the floor is pretty well compacted I would think).
The foundation is cinder-block, and I assume, but am not positive, that it extends all the way down to the frost line and most likely has footers in place.
I want to pour a cement floor into this building by fall (I am in New England), and here is what I am thinking I should do:
Use 2x6 (or 2x8) boards laid on edge(and secured) in front of the doorways to hold in the pour. (i.e. a form). I was hoping I could use the existing cinder-block walls as the rest of the "form"...any reasons I can't pour right up against the wall? or do I need to put in a form and remove it later so that I have an expansion joint between the existing wall and floor around the whole outside perimeter?
Also, I'd like to pour directly onto the existing floor without excavating down...I was thinking 4-6 inches thick with proper amounts of wiremesh in place...raising the floor this way would solve two problems: first make it less work  and two, it would leave the finish grade high enough to prevent water from running in the front; keeping all my tools nice and dry.
Is there any need to "subdivide" the floor? i.e. leave expansion joints thru the middle? I am hoping not, so that I end up with a smooth 32x26 slab w/no obstructions...
Lastly, I have done small amounts of cemet work myself, but his would be the largest pour by far...how much skill is required to end up with a nice smooth finished surface?...I'll only get one try to get it right and don't want a real irregular surface when I am done..
ANy other suggestions?
Thanks all in advance for the help.
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egon
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Re: Cement floor into existing workshop question
[re: EJB]
08/11/03 05:48 AM
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How much help will you have ?
What do you have for concrete finishing tools ?
Egon
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EJB
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Re: Cement floor into existing workshop question
[re: egon]
08/11/03 06:25 AM
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Don't have much in the way of cement specific tools, but might be able to borrow (or rent) some. The cement would come on a truck (I figure about 10 yards for a 4inch slab)
Was planning on one other helper, with about the same skill level as me (i.e. not a pro).
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egon
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Re: Cement floor into existing workshop question
[re: EJB]
08/11/03 06:59 AM
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Thoughts as I'm not a pro.
If you have a pro available they can pretty much get a level floor by evenly spreading the concrete with the chute. Otherwise I would suggest some forms to allow you to screed the concrete in place. These can be removed after they have served their purpose and the space filled with concrete. Eight to 10 foot width is about nice to work with.
You should have a large wooden bull float for the initial finishing. Try not to work it to much. A long plank to place on the fresh pour to stand on. You move this around as required. then for the finish a metal bull float or a motorized float with metal paddles. This will do the best job. After the final floating and the concrete has set up a little keeping it damp will make for a stronger floor.
Rubber boots, gloves and some square nosed shovels. Leave the rakes and hoes somewhere else as they will segregate the mix.
Be pepared for lots of backbreaking work. If the weather is hot time is important and you may want to order a concrete with a higher slump.
Insure the cement truck has enough chute to reach to the back. They can bring extra if needed.
Your original plan sounds okay to me but others will suggest the expansion joints.
Three people on site would make life much easier.
Egon
Edited by egon (08/11/03 07:17 AM)
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Re: Cement floor into existing workshop question
[re: egon]
08/11/03 07:23 AM
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Should he put plastic down first as a vapor barrier??
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egon
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Re: Cement floor into existing workshop question
[re: Justaplain]
08/11/03 03:48 PM
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wouldn't hurt.
Egon
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EJB
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Re: Cement floor into existing workshop question
[re: egon]
08/11/03 04:33 PM
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I'll wait and see if anyone else chimes in with other tips, but thanks so far for the advice. Plastic is probably a good idea, I'll add that to the list. Also may try to drum up another helper or two...
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rlw
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Re: Cement floor into existing workshop question
[re: EJB]
08/12/03 06:59 AM
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I'd use a fiber reinforced concrete it you want to try it without joints. But you'll probably want to come back and put a couple saw cuts in.
Better rent a power trowel (if you're wanting a smooth surface) - that's a lot of area to hand trowel for 2 guys.
When I had my 20 x 36 floor poured, they set a laser level at one end of the building and checked several times/places to ensure the center was level.
I put down plastic as well.
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dummy
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Re: Cement floor into existing workshop question
[re: egon]
08/12/03 11:11 AM
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Dig a test hole next to your block wall to see if you have footers or not. Is the block mortared in place? My thoughts are leaning towards whether or not you would have to backfill to keep the concrete from blowing out your "forms". Of course, Egon hit all of the other high points. Ask around about finishing work. I know 2 local guys that do pour and finish only work on Saturdays charging ~$0.65/sf. Yes, that would be an extra $550. but get them to show you how while they are there.
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Gary_in_Indiana
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Re: Cement floor into existing workshop question
[re: EJB]
08/12/03 01:59 PM
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If you want to be 'hands on" yet still be assured of a good finished product since concrete isn't very forgiving and doesn't wait for anyone, you might want to consider hiring some people who know what they're doing to run and manage the job while you and your buddy act as "labor" for the job.
You'll do a lot of the work yourselves and also know when everything's done, the job will be what you want.
I've used this method a lot of time on all sorts of tasks. I always tease about being the "owner/lotboy" at my business. The fact of the matter is that if you get someone who'll work a deal like this with you you'll not only save some money but also learn how to do it yourself the next time.
Good luck with whatever you decide. I hope this helps.
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Autotech
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Re: Cement floor into existing workshop question
[re: EJB]
08/13/03 12:12 AM
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One thing no one mentioned - Is 4" thick going to be sufficient for the loads you intend to put on the slab? You said you store tractors, and that the dirt "should be pretty well compacted" - both of those make me think that even with reinforcement you might be much better off with 6 inches as a minimum. I may be wrong but your local concrete supplier can tell you for sure. Also, with no gravel under the pad I'd be worried about water intrusion and frost heave, unless your shop is on high ground and well drained. Just a thought. Oh, and be careful not to get that surface TOO smooth - with snow and such really smooth concrete gets really slick in a big hurry. I know a smooth surface looks nicer, and cleans up easier, but just don't go for that glassy smooth surface.
Gregg
Remember - If I sound like I know nothing about farming it's because I really don't!
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EJB
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Re: Cement floor into existing workshop question
[re: Autotech]
08/13/03 04:38 AM
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>>I know a smooth surface looks nicer, and cleans up easier, but just don't go for that glassy smooth surfa
Not to worry..if I do the work myself, the chances of getting a "glassy smooth surface" are pretty remote 
I had wondered about the 4 inch thickness myself. At 4 inches I figured I need about 10.3 yards of concrete. At 6 inches I figure I will need 15 yards. The cost difference would be about $350 at $70 yard, so not huge, but still a chunk of change.
Any other opinions on this? What would be a typical thickness in my situation?
Also, given that I would like to do the work myself, and that I have no concrete finishing experience...
What about subdiving the floor into 3(or more) sections and doing 3 seperate pours on different days? Seems that doing 3, 26x10 pours may make it a lot easier for me to control, and then a single 26x32 pour and then I would end up with expansion joints too...opinions?
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egon
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Re: Cement floor into existing workshop question
[re: EJB]
08/13/03 06:53 AM
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The three pours are a very good idea for your situation. You may have to pay extra if the concrete supplier has a minimum yardage charge.
For the last pour you may want to have someplace ready where you can place any excess concrete.
The four inches thickness should be adaquate.
Egon
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BrianP
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Re: Cement floor into existing workshop question
[re: EJB]
08/13/03 08:41 AM
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My understanding is that you are not supposed to have the slab directly tie to the concreat walls. The result is that is sort of float 1/4 to 1/2" away from the walls. This way, expansion & contraction, sinking (you are adding a lot of weight) and the like won't destroy your walls. I think they sell some sort of 4" cardboard strips for this. They are left in place, I believe.
Crack control is probably a good idea, but it can be done with a saw after the fact. You only have to cut a shallow line.
I have had a lot of luck with slabs, including my basement that has no crack control and ony a few small cracks in 4000 sq ft, by using 6" mesh reinforcement. It is quite cheap. Make sure you place a level of gravel - and a vapour barrier is a good idea if for no other reason that it helps retain moisture during the cure.
Good luck with the pour. I wouldn't try it myself. Even pros can get into problems: I had tp pay $12,000 to have my mainfloor resurfaced because a contractor screwed up the work. 
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kerr
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Re: Cement floor into existing workshop question
[re: EJB]
08/13/03 04:02 PM
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sounds like a plan ta me. Egon is right fer sure about the shoot man gettin er real cloce ta grade first thing or you two will be toast by the time you guys drag it all down. Im sure you know this already thow. I would put grade stakes in the ground taller than finished grade wiyh a nail drove in the side at grade ta rest your screed on. this will keep you on track. pull em as you go. Fibermesh is the only way ta go IMHO. 4" is O.K. With 6" you could put some lengths of chain 16" or so in the pad also with about 8" above grade for securing things to the floor. "bodywork" Kinda handy fer sure. Dont forget about a sunken safe. ? P.V.C. will work fer this. Big enough for guns would be ideal im thinkin or that pesky wad of cash! Fibermesh with a slick finish still aint real slick, the hairs still give good footing and you can get your creeper ta roll when you want it to! Good luck ,
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GERARD
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Re: Cement floor into existing workshop question
[re: kerr]
08/14/03 02:00 PM
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I helped a friend with a 40 x 40 4 inch continuous pour on a garage. We had 7 guys and needed them all. (You need two to screed and at least 2 or three more to pull away excess from the screed board with shovels. Finish to need the right tools. we had a long magnesium bull float and a power trowel. Dittos on the plastic underneath and the fiber mesh. We cut in expansion joints after it had set but within the first week. Concrete saw, cut in less than half the depth of the concrete and fill the crack with some goop made for that application. (Kind of a calk that never really hardens?) He has a nice finish, no cracks, and it wasn't too hard but you do need the righ tools and some bodies.
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DUMBDOG
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Re: Cement floor into existing workshop question
[re: EJB]
08/14/03 03:36 PM
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When I had my shop poured, they used fiberglass of some sort, instead of wire mesh, with the cement at four inches thick, then cut lines in with a saw. Around the poles, they used some type of fiber product, about a half inch thick.
There are a few minor hairline fractures coming out from where the saw cuts end and the edge, one small raised portion where the two pours met, about a quarter inch is all.
This is on an area that was filled six feet and compacted with a payloader and then a foot of sand was spread and compacted by my compact tractor.
In my humble opinion, unless you are going to put really heavy equipment in there four inches of cement will be just fine. I plan on parking my 18,000# backhoe beside a 15,000# motor home which has been parked on this cement for the last three years, without any problems.
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egon
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Re: Cement floor into existing workshop question
[re: GERARD]
08/14/03 05:47 PM
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When your finishing the pad you can trowell in some grooves that will do the same thing as cutting it later with the saw. There is even a trowell made for this.
Egon
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dummy
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Re: Cement floor into existing workshop question
[re: egon]
08/15/03 06:28 AM Attachment
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One of these? 
Edited by dummy (08/15/03 06:30 AM)
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egon
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Re: Cement floor into existing workshop question
[re: dummy]
08/15/03 06:32 AM
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That's the one.
Egon
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MelonHead
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Re: Cement floor into existing workshop question
[re: DUMBDOG]
10/01/03 11:51 AM
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In reply to:
Around the poles, they used some type of fiber product, about a half inch thick.
Dumb question: Why is this necessary?
Would it also be a good thing with metal posts?
Thanks
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DUMBDOG
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Re: Cement floor into existing workshop question
[re: MelonHead]
10/01/03 12:50 PM
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Not being an engineer, as you can tell by me not even knowing what the product is called, my best guess is to provide a buffer between the post and cement floor in case of some shifting of either of the two. This would prevent cracking of the floor. I would believe that this would be a good thing to use no matter what type of post that you are using.
I will repeat that I am extremely happy with the way that the floor has stood up, considering the fill that it was placed upon and that the building is partly heated.
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