Replies

1. 
   mark_cadioli | Jan 31, 2002 11:23pm | #1

   *
   Tear out and use reinforcing this time. ( min 4" slab, 3 1/2" is too light . )

1. 
   jcallahan | Feb 01, 2002 03:23am | #2

   *Ditto mark's comments..... You'd be throwing money away by going over the old driveway imho. Any patches would be temporary at best and with some good rains ( I hear you get a little rain in Oregon), the cracks would most likely reappear in short order.

1. 
   bckelly1 | Feb 01, 2002 03:58am | #3

   *Karl,I'll make it three. Tear out and cast it again w/ reinforcing. One reason not to place a new conc. slab over an older, heavily cracked one is "reflection cracking". You've probably seen this on highways where they've placed asphalt over conc. You could see it on your dad's driveway too if you try to place a second layer.

1. 
   Gabe_Martel | Feb 01, 2002 04:02am | #4

   *Obviously the driveway wasn't designed for tandem truck traffic.Hardly the contractors fault if anyone allowed truck traffic on the laneway.If the cracks are as numerous and intense as you describe, you now have a base for the next driveway and wouldn't be repairable.Gabe

1. 
   Randy_Rogers | Feb 06, 2002 07:38am | #5

   *If height is not a problem and existing cracked drive is structurally sound (on firm sub-base), I've gone over with new concrete using 1" of sand as bond breaker in between so no reflective cracking. I suspect that there are membranes available serving same purpose as sand but probably not cheap. 3-1/2" a bit light for a driveway - is it cracked for entire distance or can sections be removed and replaced ? Randy

2. 
   Karl_Nisbet | Feb 06, 2002 10:37am | #6

   *Thanks Randy, the idea of the sand is a good one, I have not actually seen the driveway, it is in Hawaii on the island of Kaui where materials are very expensive to say the least and from what I have gathered there are not many contractors using any of the new membranes or polymer products which may be available here. I was hoping that it would be possible to pour over the old driveway, I don't think height would be a problem. How deep has your new lift been when you have done this in the past? Thanks for all the suggestions!

3. 
   Luka_ | Feb 06, 2002 04:14pm | #7

   *Randy's post jogged a brain cell or two, I think.Where are the cracks ? What kind of pattern ? Where I'd like to get to is this... Maybe the concrete can be cut, and only what desperatly needs to be replaced, replaced. In other words, incorporate as much of the cracks as possible into 'expansion joints', maybe even create some sort of pattern, then replace or repair as little as possible. What does your car care whether it is driving over decorative cracks, expansion joints, or whatever ? As long as the drive holds up, does the job a driveway is supposed to do, and can be made to look intentional...

4. 
   Cliff._Johnston | Feb 06, 2002 05:12pm | #8

   *Karl,If you're looking for a slab that will hold up then the following specs. were posted sometime ago on the concrete network as a synopsis of an engineer's findings and recommendations after a 6 or 8 year study of failed slabs in North America - they are very close to what I was taught as a union finisher back in 1965.The base should be compacted sand/gravel (depth and size depending upon freeze/thaw cycles in your region). The minimum slab thickness should be 5" of 3,500 psi concrete with mixed aggregate (max. size 1-1/2"). The reinforcing recommendation was 3/8" rebar on 18" centers with the rebar placed 1/3 of the way up from the ground (just below the center thickness of the slab for practical purposes). The engineer's extensive study indicated that although welded wire reinforcing may have been proven to be equivalent to some rebar specs., in practice the welded wire mesh was difficult to place near the center of the slab thickness and most (like nearly all) failed slabs had the welded wire mesh on or close to the bottom of the slab. In addition expansion joints with an expansion joint material (I use redwood - found it holds up the best, in my experience) should be placed every 8'-14' (I've typically used 10'-12' as often as possible). Without expansion joints (as opposed to control joints which should be defined as a cut 1/4 the thickness of the slab) the slab will dry and crack - essentially forming its own expansion joints and usually not as attractive to the eye. The other major factor is curing the slab - try to keep it damp for a minimum of 24-72 hours - the longer the better.A good slab costs only a little more than an "el cheapo" that will start failing quickly. I used the above specs. to pour my patio and pool deck slabs over 8 years ago after listening to 3 contractors give me a line that all concrete cracks in this area (I was injured and my wife thought that she had talked me into letting someone else do it). The concrete in this area probably does all crack as the contractors obviously don't know what they are doing. We designed, poured and finished close to 1,400 sq. ft. for the job and after 8 years have 0 (zero) cracks. So much for the local yokel experts. I still get "ticked off" thinking about them.Good luck,Cliff.

5. 
   Karl_Nisbet | Feb 06, 2002 08:10pm | #9

   *Thanks for all the info guys, I am going to give all these suggestions to my Dad and help him make a good decision. I will be going over there soon to and will see firsthand what the condition is and attempt to help him make a good choice. New concrete is apparently around $175.00 per yard for product only which makes it an expensive issue. Plus he tells me that disposal costs are really high over there as well so I don't know what he will decide. I think he is going to sell the house and move back to the mainland after the repairs are made!Thanks again, this site is a great resource since I find that the older I get the less I know!

6. 
   Randy_Rogers | Feb 06, 2002 10:02pm | #10

   *Karl: I placed concrete over existing slab with bond-breaker between and approached it very conservatively, in that I used existing slab as "mud mat" (work surface)only. Newer concrete was designed as stand alone even though I knew existing concrete would provide some degree of structural support. Someone at your site may attest to strength and stability of existing concrete drive, then you may opt for thinner profile - but I'd make sure that "someone" is willing to bear the burden of later failure, should it happen. Good luck in whatever you decide. Sounds like nice trip. Randy, again.

7. 
   Mike_Shultz | Feb 06, 2002 11:18pm | #11

   *Karl,I also live in PDX. (It's too bad that we only tied the record of 33 days of continuous rain.) If you pony-up a round trip ticket I might be tempted to give this project a closer inspection.

8. 
   Karl_Nisbet | Feb 07, 2002 07:40am | #12

   *I am thinking about becoming a slug farmer and giving up the heartache of building! MAybe I could afford two tickets then!

2. 
   Karl_Nisbet | Feb 07, 2002 07:40am | #13

   *
   Hi, I am general contractor in Portland Oregon and have a concrete question, not a new one I am sure but need some help! My dad has about a 200 foot driveway which is set on a steep slope (7%+) with a switchback about halfway up. The slab is 3 1/2 inches thick with no screen or rebar in it. He recently had a pond built which involved hauling loads of rock up the driveway by dump truck and resulted in severe cracks all the way through the driveway. The contractor was a friend of his (not me!) and he does not want to seek any redress from him. My question is what can I do to repair the problem short of tearing out and pouring a new pad? Can I pour over the old pad? I know this would result in a cold joint and would be no more stable then the pad underneath it. I also have read of products which can be topcoated over concrete for things like this, do they work? He lives in a warm climate so frost/cold is not an issue. Any ideas? Thanks guys!