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My contractor poured 4 1/2″ over 40′ x 48′ in a half day over panning … It was a hot day and the mix looked a little dry to me … I watered the pad down pretty well that night, and every night since … After four days, I noticed 7 spots of about 24″ diameter where a thin void had formed just about 1/16″ below the skin … You can chip it off with a screwdriver …A friend who does concrete work says a) Dried out too fast, or b) too much fly ash in the mix … The contractor says its not a structural issue, plans to patch it with some grout .. Not sure I buy it … What do you guys think? Is it core sample and testing lab time?
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John
"I watered the pad down pretty well that night, and every night since"
How much water did you put down? Too much water in the mix will cause what you are describing. A light mist of water with a some sort of covering would have been better to prevent evaporation.
As for the patch method, there are concrete patch mixes available for problems such as this. Just make sure that it is feathered nicely so that there are no ridges or bumps. Once the flooring material (carpet, vinyl, etc) is installled, you won't know it's there.
Vince
*What is the future use of the pad going to be? If nothing super heavy is going to be put down, it should be okay.I have often used "ponding" to cure slabs. Doesn't hurt them a bit. (As long as the crete has hit it's initial set and you can walk on it leaving no marks)
*The condition you describe sounds like blistering. The most likely cause is that the surface dried while the concrete below was still bleeding water. Troweling seals the surface. The result can be poor adhesion of the upper grout cap caused by the trapped water. Was the concrete placed on a poly vapor barrier? Bleed water can not escape at the bottom when a vapor barrier is present. From your description of the pour and site conditions there maybe another culprit. If the concrete was placed at a low slump and the contractor had to spray a lot of water on the surface to allow troweling the bond between the surface grout and the concrete below may have been broken. This makes for an ugly looking slab. It may need to be capped. Contact Master Builders. They have a large line of quality products to help solve this problem.
*Just to confirm what someone else has said: when I first got my union ticket back in 1965 I was working on missile sites in North Dakota. There was a little Italian finisher who took me under his wing (a little irony here as I'm 6'3"+ and he was about 4'10" and 100# dripping wet). The condition that you have is the result of over working with the trowel and too rapid drying of the surface during and shortly after the troweling - that's why flooding won't help. I can still remember our little paisano watching the power trowel operators like a hawk to avoid that problem and showing me what to look for, ie: watching for surface color changes (darkening) and avoiding a "glassy" finish - nice on cool, slow drying days, but, well, you found out what happens on fast drying days. This is a particular problem when conditions are right for rapid drying of the concrete surface. For the most part it is more cosmetic than structural and can be repaired; however, a large caveat - it also depends on what you are going to use the finished surface for. Some of the suggestions made by others here are excellent.Good luck,Cliff.
*John,In an effort to "stay ahead of the pour" your finishers closed (steel troweled) the surface before the bleed water had time to rise and evaporate. Since the surface was closed, the bleed water was trapped below the surface and caused the delamination spalls you describe. It is a common mistake among DIYers but from professionals is unacceptable. So your concrete guy will "patch the spalls with grout". How many times? Once, twice or every year? You'll probably need to use an epoxy base compound to assure permanent adhesion and also make sure the surface is cleaned well. In addition to Master, check out Sika and Ardex products. Your choices will depend on whether the slab is indoors or out and whether it will be visible or covered.Since your concrete guy is at fault here, he should kick back at least 50% of his labor cost and do the patching for free. Hope you're still holding the check.Eric
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Eric:
Thanks to you and all your colleagues for the information ... Based on what I have learned from my neighbor (who observed the pour) I believe your analysis is most on target ... You can see my project at http://www.evansville.net/~imc ... The pad is indoors, but the clincher is that this error blows my intent to use the pad as a finish floor after acid staining and topping with sealer ... I will visit the topping product vendors you mentioned ... JGD
*John:Definitely sounds like a workmanship issue to me.Here's another idea though: Around where I live concrete suppliers guarantee their product. Although it is probably not a material defect, you could call the supplier and say that there is a problem with the slab. My concrete supplier would send out a rep. The rep, would give a qualified b on siteopinion as to what the problem is. A concrete rep isn't going to give you anything in writing, as they don't want to "shaft" their best customers, the concrete subs who sell lots of their product, but still the concrete company isn't going to take responsibility for a workmanship issue.
*Hello to the Masonry Experts from a lumber guy. I'm looking for a product, probably two, that can clean concrete without hurting glass, and then seal it well. A friend of mine has a commercial customer who is experiencing a problem with their windows. It seems that something in the concrete wall, lime I'm guessing, is causing pitting in the glass. He believes if he can first clean it well, without harming the glass, and then seal it well, it will alleviate this problem. This project is in the Portland, Oregon, metropolitan area. Any suggestions on products or other ideas to help with this situation?Thanks, Jim
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Sounds like the main problem is that they've used Portland Cement!!
*You'll get more posts if you start your own thread instead of hijacking somebody elses.
*if your concrete is still green.. you have a better chance of a bond with your patch and the existing pour..don't let it dry out and get on it now instead of later...you will also have a better blend.. some of the paste will mix with the patch and you may be able to go with your original plans ..in this case.. haste may save waste..b but hey, whadda i no ?
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I may be an amatuer to concrete, but isn't it possible to do a thin pour over a new slab? The entire pour could be dyed at a much lower cost than otherwise, or dry-dyed and sealed as you planned, and the best part is, the contractor will help defray to cost in lieu of patching the old one.
The catch would be, will it bond? And are doorsills Etc, at critical height?
Good luck. Just thought I'd mention before the patching goes on.
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My contractor poured 4 1/2" over 40' x 48' in a half day over panning ... It was a hot day and the mix looked a little dry to me ... I watered the pad down pretty well that night, and every night since ... After four days, I noticed 7 spots of about 24" diameter where a thin void had formed just about 1/16" below the skin ... You can chip it off with a screwdriver ...A friend who does concrete work says a) Dried out too fast, or b) too much fly ash in the mix ... The contractor says its not a structural issue, plans to patch it with some grout .. Not sure I buy it ... What do you guys think? Is it core sample and testing lab time?