Replies

1. 
   Piffin | Nov 15, 2004 01:08am | #1

   http://forums.taunton.com/tp-breaktime/messages?msg=50185.1

    

    

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2. 
   WayneL5 | Nov 15, 2004 04:13am | #2

   The two most important things for getting a good strong floor are a good, solid, thoroughly compacted base, and not adding excess water to the mix.

   You'll be able to walk on it the next day.

   For a good hard surface it must be properly tooled, then cannot dry out for a week or so, and not go below 40°F for 14 days.  Concrete generates its own heat when it cures, but that tapers off after a few days.  I'd recommend nailing up plywood or plastic over the openings to retain as much heat as possible and reduce drying, and adding supplemental heat occasionally if needed so it doesn't drop below 40°.  Avoid large temperature swings such as warming the slab up to 70° in the day and dropping to 30° at night.

   To retain moisture on the surface, the traditional way is to cover the slab.  An excellent way is to lay wet burlap then cover it with plastic.  Or you could lightly sprinkle it with a hose each day.  Or just plastic would probably be fine in an enclosed structure.  Some contractors have insulating blankets that retain both moisture and heat.

   There are spray moisture retarders you can apply, but I'd avoid them because they make it difficult to paint the floor if you decide in the next few years you'd like to.

3. 
   davidmeiland | Nov 15, 2004 04:57am | #3

   As discussed in the other thread... I would lay out poly immediately after finishing the slab, then spread some blankets on top of that. I don't think you need to add moisture under the plastic, there will be plenty in the mix already and all you need to do is prevent overly fast evaporation. Covering the windows to retain heat is a good idea, but you probably have a huge hole where the garage door will go so that might be difficult. Some electric heat might be good. I would not use propane heat inside any building shell.

   If your jobsite is civilized, you can rent some moving pads from a rental place and use those as the blankets... maybe keep them clean with another sheet of plastic over the top. Leave that stack in place for 3-5 days and you probably have a winner. If you have a crew of animals on the job, forget it, you'll be paying full retail for those pads.

   Getting a mix without excess water is important. Hopefully your finishers are knowledgeable about that and will not order it sloppy to make it easier to move around. And... control joints.

   The main problems I have seen with slab cracks is in the summer in California. 80 or 90 degrees, a crew finishes a slab before lunch and heads home, leaving the dang thing baking in the sun with nothing on it. Cracks appear the next day and by afternoon the owner is calling everyone's cell phone every 5 minutes.

4. 
   slykarma | Nov 15, 2004 08:41am | #4

   • keep slab temperature above freezing for 5-7 days or all other precautions are pointless.
   • ask batch plant for 1% calcium addition to speed hardening after placing.
   • place the slab early in the day to allow maximum finishing time.
   • resist the temptation to tool in bleed water. It will decrease cement:water ratio at the surface and cause powdery, weak slab surface prone to crazing.
   • first thing next day, use a diamond blade to cut control joints to a depth of one third the slab thickness. Hose it clean, allow it to dry, then spray the slab with a curing compound like Cure 'n' Seal or Xypex.
   • maintain temperature above freezing. Doesn't have to be warm, just prevent freezing.

   Wally

   Lignum est bonum.
1. 
   Piffin | Nov 15, 2004 02:13pm | #5

   Preventing freezing is the most important, but it is the minimum only.

   Curing a slab under plastic and insulating blankets to retain the cure heat will result in a far harder surface.

   For instance, at the other extreme, if you cure crete under plastic, at eighty degrees or so, for ten days, and did not use excessive water in the mix, you will have a slab surface you can ring a hammer off ofwithout chipping it.

   Cure the same slab at 38°F with no cover, and you can drive a sixteen penny nail into it still after that time, or leave marks from a hammer striking it, or even chip some off. 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   slykarma | Nov 15, 2004 04:31pm | #6

   True enough, but if you don't prevent freezing then you have nothing at all. The 38 degree slab will still achieve full strength over time. Having said that, this doesn't seem too bad of a situation if walls and roof are in place. I would hoard door and window openings and use fan heaters. Insulated blankets have their place, but they can only retain the concrete's own heat of hydration. Once that has dissipated they don't do much. You will need an external heat source.

   What is a 16 penny nail anyway? Always meant to ask how that system works. Does it correspond to length or gauge?Lignum est bonum.

1. 
   Piffin | Nov 16, 2004 05:54am | #8

   Yes. a framing nail, about 3-1/4" long 

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2. 
   SamT | Nov 16, 2004 07:02am | #9

   ..What is a 16 penny nail anyway? Always meant to ask how that system works. Does it correspond to length or gauge?

   Represents cost. 100 16d nails usta cost $.16, just as 100 8d nails cost . . . wait fer it. . .$.08.

   ' Course that was when nails were hand made.

   SamT

1. 
   slykarma | Nov 16, 2004 04:43pm | #10

   Yes but what does it mean now? Does it correspond to length? Here we just order nails by length: 2" common, 3-1/4" duplex, 2-1/2" finish, 1" roofing, etc. Same as screws. How big is a 16 penny nail?

   WallyLignum est bonum.

2. 
   UncleDunc | Nov 16, 2004 09:58pm | #11

   Google is your friend.http://www.engineersedge.com/nail_size_chart.htm

2. 
   brownbagg | Nov 15, 2004 05:04pm | #7

   only differents, I would cut as soon as you can walk on it, cut 1/4 the thickness of slab