I originally posted this on the tail end of my post "poured concrete with grade, but decided to create a new post instead to potentially generate more replies. Sorry for any inconvenience.

So I finally got this slab poured yesterday, by the guy who is my contractor friend. Let me preface my question(s) with the disclaimer that he had put an addition on my barn which included pouring a slab for the floor that turned out just fine.

He used rebar for this job. The slab was ~six in., ~35X30 (I made it bigger than originally planned, I mean really, you can't have too big a slab in front of the house). The slab is in four "squares." As regarding the rebar, he laid it out in a grid which extended under the cross forms (not the perimeter). That is, each square did not have its own grid and the bar was laying on the ground. I brought to his attention that there wouldn't be much reinforcement that way and he assured me that they would lift it up during the pour so it would end up in the bulk of the concrete. Seeing as how the grid was on the ground under the cross forms I didn't really see how that was going to work so well. And in fact I don't think it did.

While pouring the second square they had too much concrete and so shoveled the excess into what turned out to be square four. In the mean time it was walked on, a lot, and by the time square four was poured it was pretty hard. Is that concrete now part of the slab, or is the slab thinner in those areas by the thickness of the hardened material?

In two of the squares they didn't do such a good job screeding and there are undulations. I mean, put a level across the top and there is an 1/2 - 3/4 in. space underneath. Is this something I should make an issue of? I really don't consider this to be acceptable but if it sounds like it's within some industry acceptable standard I can live with it. If it isn't, how can it be made reasonably flat?

He used pressure treated 2X4 for the cross frame, which means there is concrete beneath the wood. Is that an issue, like is that now a two inch slab with a piece of wood on top of it? The wood was left in place as the expansion joints. Also, the wood sits proud of the concrete surface for some lengths depending on how well they screed. Should I ask that it be knocked down? It looks to me that it's going to be a problem the first time I plow this winter.

I'd like to hear some comments, mainly constructive in nature if possible.

Thanks,

G

 

bridge ? have at it, my friend

 

I'm not quite sure I understand. As in, do I want to buy the Brooklyn bridge?

 

not at all altho if you've got a blank check handy bridgeman will be along shortly & will edumacate you,,, you're right to be skeptical

 

I get it. Looking forward to hearing back. The reason I am asking for feedback is to show he who poured the slab. After all, I'm just the dumb homeowner.......

Also, I haven't paid him the balance yet....

 

at least you're smarter than the avg h/o since you haven't pd yet,,, i think bdge is still sleeping & we're off to china so let me jot down a few thoughts,,,,,,,,,,,,,,,,


rebar bent under a form ? you're kidding, right ? not in anyone's idea of a good practice,,, you've probably lost 50% of whatever flexural strength the steel would've provided [ unsure why you needed steel in the 1st place but that's a different subject ]

the shoveled excess concrete now part of the slab ? probably not UNLESS it was vibrated into the shovel'd conc,,, no, the depth is not thinner BUT there may be a horizontal cold jnt UNLESS they moved quickly

even IF you have a 12' strait-edge, 1/2 - 3/4" isn't acceptable - just wait til it rains & watch the birdbaths appear

as conc cures, it shrinks - there's probably not a problem w/2" of conc beneath the 2x4 slot buy WHY such a large joint space ? 'proud' means higher than the surrounding adjoining conc ? - not good practice,,, expansion jnt material is what it is,,, wood isn't exactly,,, sure, plane it down OR jam it w/your plow

i'm sure bdge will give you book & page later - i gotta run - nagzilla's calling

 

I responded to his other post and I wanted to pass it along!

Where do you start? Don't be upset with Stadry when he replies. He'll ream someones A$$ for that job. Wood should never be used as an expansion joint PT or not! New concrete should never be placed over harden concrete! Flatness of a slab should never exceed 1/8"! Rebar should have been set on chairs! I'll let someone else give you the lo down on what else is wrong!

Read more: http://www.doityourself.com/forum/br...#ixzz3Bh4qGOdC

 

As I see it, you have 2 choices: You can live with it, pay your buddy the balance due, and keep him as your friend. Or, tell him the job is unacceptable, for the reasons listed (horizontal cold joint, rebar resting on grade instead of in slab, uneven surface finish, embedded wood, etc., and you want him to tear it out and start over. If he's successful the second time around, you can then pay him the balance due, and be happy with the finished product. Should he refuse to make it right, you then still have the option of living with it, or paying someone else to rip it out and repour it, correctly. If you go that route, I'd at least try to get all of your money back from your so-called "friend." It would make a nice down payment on the new contractor's charges, since he'll need at least $3000 just to yank the junk concrete and haul it away.

Any time anyone says he can lay rebar on grade (for a large pour the size of yours) and then lift it as the pour proceeds is either ignorant, or foolish, or both. Real concrete people use bar chairs and/or dobies to hold rebar in position, but your buddy probably didn't want to spend the extra $$$ to do so. Also, an area that's 30' x 35' needs more control joints than those provided by just "quartering" it--if they aren't already there, cracking will soon show up between the existing 2 x 4 joints. If you decide keeping your friend as your friend is more important than getting the substandard work corrected, keep in mind that if you ever plan to sell the place, future buyers are likely to reduce their offering price if they feel replacement of the sloppy slab needs to be done.

Is there any chance you could include a few pix, so we could see what you're seeing?

 

I spoke with my guy yesterday and voiced my displeasure. His response to the 2X4's is that if there is going to be any cracking it will be there. More or less a stress relief type of thing. I decided against telling him about martensitic phase transformation toughened zirconia.

His response to the rebar was that doing it that way would prevent differential heaving of the squares, and stands by the lift as you pour. The slab was poured on top of the existing hard pan, there's no layer of crushed stone underneath, which was my decision. I also mentioned it being inadvisable to leave ferrous metals in contact with the ground.

My main concern here is to what extent has the structural integrity been compromised. We didn't get too deep into the cosmetic issues which, to the extent that they can, will be fairly easy to remediate.

BTW, I have a M.S. in ceramic engineering and intuitively know the answers to my questions but I need to hear it from those who can provide informed opinion. That way I have reinforcement for my argument and be better educated, both as a dumb homeowner and a dedicated DIY'er

I left it that I would get back to him next week after having had a chance to consult with my go-to concrete guys, namely, you guys.

I'm still a film guy but my sister in law is here with a digital camera and I'll get some photos.

G

 

I posted photos here:
https://www.flickr.com/photos/toogbr...7646652446120/

My friend further states that expansion joints accommodate expansion/contraction through the thickness, not horizontally. Is that true?

His solution is to remove the wood and replace with appropriate expansion joint material, cut the slabs loose from one another and grind out the surface discontinuities with one of those grinders that looks like a floor polisher. And provide a five year warranty that if it fails he'll then remove the slabs and redo the job correctly.

 

Regarding concrete's expansion and contraction, your friend does not know what he's talking about. A mass of concrete will expand/contract equally (at a rate of 0.0000055 ft./ft./degree Fahrenheit) in all dimensions, but is always more evident across the length of a slab than its thickness, typically being many times larger--the factor for a 15' run of 4" slab will be 15 divided by 0.3333 = 45.

The photos depict done work by someone who urgently needs to find a different occupation. The forming, placement and finishing are all considerably substandard, with the visible lack of consolidation (honey-combing) at the form lines being some of the worst I've ever seen. And although skate boarders would enjoy the unique "roller-coaster" finish, keep in mind that extensive grinding will lower the overall grade line in those areas.