[ARCHIVED THREAD] - concrete curing question (Page 1 of 2)
Posted: 9/19/2014 11:14:34 AM EDT
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I am having a 12X14x4" slab poured for my reloading/gun room next week and I was wondering how long I need to wait for the concrete to cure enough to safely build on it. My building will be a 2x4 framed structure anchored with the cast in j bolts. Thanks, MonkTx |
A suggestion--don't use J-bolts. You can build a wall and use wedge anchors MUCH easier than trying to drill holes in the sill plate to line up with J-bolts. 
Also--patience is good. I always wet it, then cover with visqueen, then let it sit for at least a week. This forces the drying to occur form the bottom, which slows it down. The slower concrete dries the harder it will be. If you can get an opaque cover (canvass tarp maybe) over the visqueen that will further slow the process by blocking the sun. 
One last thing is to use a sealer on it after you uncover it. That will retard curing, and produce a little more hardness/strength. Edit: Forgot one last thing--I'd put bubble wrap for insulation UNDER it if it's going to be heated and cooled. It also acts as a vapor barrier. They make big rolls of it just for that purpose. |
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How much of a hurry are you in to start building? If your in a big hurry have them add 1 to 2% non-calcium chloride or just up the bag mix to 7 sack (5000 psi). Water curing is not a bad idea either. The design mixes i use in an industrial setting usually achieves 2/3 of the total compressive strength in 5 to 7 days. I'd have zero issues with framing that thing out a couple days after it's poured.
I'll ditto the drop in wedge anchors. J-bolts are not needed for this application. Any other questions, feel free to message me. |
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No. Tarps/visqueen and straw in cold conditions is to keep the concrete from freezing by utilizing the heat created during the setting phase. Concrete can freeze just like anything else in cold conditions. Frozen concrete = junk concrete. Yea I thought it was to keep in the heat |
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is that the reason for tarps in the cold  Quoted:
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Concrete cures by hydration, not by drying. is that the reason for tarps in the cold Freezing destroys concrete if it hasn't cured sufficiently. Nebraska DOR poured an overpass near me a couple of years ago, subzero temps the following days ruined it. Total tear out and rebuild for them. Still haven't heard how many much money they pissed away on that bonehead move. Have they not seen weather forecasts? |
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You want to keep the moisture in the concrete so it can hydrate. Exposed to sun and winds it will evaporate the water leaving less for hydration. Worse, it will cure unevenly from topside to bottom side and you could get curl. I've seen slabs lift a couple of inches when the moisture and hydration weren't controlled properly. Keep it moist as long as you can and covered if possible at least for a few days.
If the framing anchors are going to be close to the slab edges consider epoxy anchors instead of expansion anchors. Expansion anchors can blow out edges. Check the literature on the anchors about the recommended edge distances. |
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Freezing destroys concrete if it hasn't cured sufficiently. Nebraska DOR poured an overpass near me a couple of years ago, subzero temps the following days ruined it. Total tear out and rebuild for them. Still haven't heard how many much money they pissed away on that bonehead move. Have they not seen weather forecasts? Quoted:
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Concrete cures by hydration, not by drying. is that the reason for tarps in the cold Freezing destroys concrete if it hasn't cured sufficiently. Nebraska DOR poured an overpass near me a couple of years ago, subzero temps the following days ruined it. Total tear out and rebuild for them. Still haven't heard how many much money they pissed away on that bonehead move. Have they not seen weather forecasts? We would batch out loads that were "dry as a popcorn fart" with calcium chloride to accelerate the cure and super plasticizer so it would flow for winter jobs. |
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I was on a high rise a few years ago, they had a shit load of furnaces? burning coke underneath the deck. I did not know you could buy coke in this day and age. http://www.ar15.com/media/viewFile.html?i=29441  
day was shot if you hanged with them guys
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A suggestion--don't use J-bolts. You can build a wall and use wedge anchors MUCH easier than trying to drill holes in the sill plate to line up with J-bolts.
Also--patience is good. I always wet it, then cover with visqueen, then let it sit for at least a week. This forces the drying to occur form the bottom, which slows it down. The slower concrete dries the harder it will be. If you can get an opaque cover (canvass tarp maybe) over the visqueen that will further slow the process by blocking the sun.
One last thing is to use a sealer on it after you uncover it. That will retard curing, and produce a little more hardness/strength. Edit: Forgot one last thing--I'd put bubble wrap for insulation UNDER it if it's going to be heated and cooled. It also acts as a vapor barrier. They make big rolls of it just for that purpose. Lining up and drilling for j-bolts is super easy. Just cut the sole plates and put them up against the j-bolts. Mark and drill. Put them all in place for fit and then remove to frame. J-bolts are much cheaper than anchors. I used Rustoleum primer and garage floor paint in my shed. I don't have a single chip. I also sprayed my concrete in the AZ heat for a couple days, no plastic cover and have zero cracks--standard aggregate 6 sack ready mix. I built an 8x16 shed on a three day weekend, siding, roofing, etc. I painted it and my patio cover the following weekend in a couple hours with a rented paint sprayer. |
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yea drill now shit be soft, I've probably cored 10'000 holes Cast in j-bolts. No concrete drilling required, only need to bore the sole plates before framing the wall. All I had to do was mark the concrete forms and the finishers put the j-bolts in were I wanted them. When I built my second shed, I drew up the frame on a pencil drawing to scale and then put all of the materials on an Excel spreadsheet.--hinges, nails, and all materials in order to see costs and only make one trip to the store. The only thing I forgot is that a square of singles is three bundles. I had to make a second trip.
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You can frame it up the next day. Edit: Above advice about safe is sound. It's not uncommon for concrete to reach 75% of 28 day strength at 7 days so you should be GTG in a week to place that safe in there. Fixed it for you. It also depends on the strength of concrete ordered, most slabs should be at least a 4000psi. but there are some funky admixes you can add to get 4000 in 14 hours. |
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I remember from the Hover Dam tour that the concrete is still curing in that place from when it was originally poured. Must have been a long time ago. I've always understood concrete gets harder for 50 years, then gradually deteriorates and gets softer for the next 50. Anyone know for sure? |
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Must have been a long time ago. I've always understood concrete gets harder for 50 years, then gradually deteriorates and gets softer for the next 50. Anyone know for sure? Quoted:
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I remember from the Hover Dam tour that the concrete is still curing in that place from when it was originally poured. Must have been a long time ago. I've always understood concrete gets harder for 50 years, then gradually deteriorates and gets softer for the next 50. Anyone know for sure? Depends on the mix. That is close to the rule of thumb. |
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A suggestion--don't use J-bolts. You can build a wall and use wedge anchors MUCH easier than trying to drill holes in the sill plate to line up with J-bolts.
Also--patience is good. I always wet it, then cover with visqueen, then let it sit for at least a week. This forces the drying to occur form the bottom, which slows it down. The slower concrete dries the harder it will be. If you can get an opaque cover (canvass tarp maybe) over the visqueen that will further slow the process by blocking the sun.
One last thing is to use a sealer on it after you uncover it. That will retard curing, and produce a little more hardness/strength. Edit: Forgot one last thing--I'd put bubble wrap for insulation UNDER it if it's going to be heated and cooled. It also acts as a vapor barrier. They make big rolls of it just for that purpose. Tightening wedge anchors in green concrete will blow the sides of the slab out. With a 4" wall, he'll be drilling 2" from the edge of he slab. I would not use wedge anchors in concrete within 30 days of the pour. |
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Within 30 days or 30 hours? I'm a big believer in high-bag mixes and plenty of time. It has worked well for me with a number of pours.  30 Days. The concrete needs to harden up for quite a bit before the wedge anchors are tightened. You can drill a slab after a day or two if you are slow and careful, and can install the anchors, just don't tighten them right away. |
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Concrete guys can probably provide some Kure N Seal 30, or other acceptable wax based curing compound. This should dissipate withing 30 days for the most part. If not it can be removed with a citrus based cleaner or powerwasher for the most part.
If not, keep it damp and cover w/ Visqueen or damp heavy cloth. I would say in this climate that you should be able to do whatever you want on it within 5-7 days for the most part. A Quick unscientific way to check hydration is to find a spot early in the morning and fully tape down a 1'' square of heavy dark plastic onto the slab in a couple of places, and then come back around lunch and pull it up. If there is condensation on the back = still needs to cure. |
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Must have been a long time ago. I've always understood concrete gets harder for 50 years, then gradually deteriorates and gets softer for the next 50. Anyone know for sure? Quoted:
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I remember from the Hover Dam tour that the concrete is still curing in that place from when it was originally poured. Must have been a long time ago. I've always understood concrete gets harder for 50 years, then gradually deteriorates and gets softer for the next 50. Anyone know for sure? I heard something similar. A rule of thumb I heard was walk on it after 8 hours, drive on it after 8 days. You want to keep the surface wet and covered with plastic so there is enough water to allow for complete hydration of the surface. If the mix is dry, the cream not fully developed during finishing, and the weather such that the water evaporates, there won't be enough water to allow for complete hydration of the cement. |
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I'd go 2X6" walls, more insulation = easier to cool/heat= more comfort= more reloading= more shooting 2x6 would be a small up charge but you could use a thicker insulation for a higher R-value. Cast in place j-bolts are the way to go. Second best would be epoxy anchors, but more work and $$. Remember to protect the threads from concrete spatter, aluminum foil is cheap. Space at 16" OC and plan your layout to avoid stud interference. You could "juice" the mix with some polarset to get a rapid acceleration or use a <3000 psi mix design. Build on it the next day. (Commercial PM). I'd also consider treating the soil for termites prior to placing the slab and adding a vapor barrier. |
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Most mixes have excess water, more water will not impede cure or ultimate strength. Concrete will cure under water. True concrete will harden under water, but too much water in the mix will weaken it. I've seen loads refused by engineers for failing the slump test. |
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True concrete will harden under water, but too much water in the mix will weaken it. I've seen loads refused by engineers for failing the slump test. Quoted:
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Most mixes have excess water, more water will not impede cure or ultimate strength. Concrete will cure under water. True concrete will harden under water, but too much water in the mix will weaken it. I've seen loads refused by engineers for failing the slump test. Plus that, the crew will have to stand around for a couple of hours before they can float it. When I was a Millwright, we poured some big machine foundations, several feet thick, with conc. specs that called for almost zero slump, and we had to knock the concrete through the rebar with vibrators. |
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.......Cast in j-bolts. No concrete drilling required, only need to bore the sole plates before framing the wall. All I had to do was mark the concrete forms and the finishers put the j-bolts in were I wanted them....... This guy understands how to do it. Just drill the holes in the sole plate--go a little over size on the holes, there's no reason for it to be a tight fit here. Drop the sole plate on to make sure of alignment. Pull them off, frame the wall and set in place. If you use green treated wood for the sole plates (you should) make sure to use corrosion resistant nails or the green wood will rot them in short order. Any fasteners that go into green treated wood must be corrosion resistant and designed for this purpose. |