Pouring concrete in crawlspace

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  #1  
Old 01-03-15, 06:34 PM
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Pouring concrete in crawlspace

Hi, newbie to this website with a few questions for you pros. I have been working a few weeks on the unfinished basement of my 70 yr old two story house doing insulating(rim joists and sill plates)and I have a small crawlspace I want to open to the rest of the basement. It was previously semi closed off. It measures 10x4, it has a dirt floor and no outside vent. The floor and walls are very dry, in fact its sandy soil. So I sealed the rim joists in that area and plan to put rigid foam board on the walls. Should I put a vapor barrier down on the dirt even if its not damp? Or should I pour bagged concrete and finish the floor to make extra storage room? I was reading somewhere that a lot of moisture would lift from the fresh poured concrete when its curing into the house but I don't think its a big enough area for that concern although it is below our kitchen. How thick do I need to pour it if Im only using it for storage because the space sits waist high compared to the rest of the basement so it would not be walked on. Thanks for the reply's.
 
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Old 01-03-15, 07:01 PM
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You could just do the vapor retarder but I would normally recommend doing the concrete over the barrier as well. You could go with 2" especially if you use the fiber reinforcement tossed into the mix.

If the ground is sandy as you describe then you could also roll out a piece of 40 mil rubber roofing which will serve as a great vapor retarder and give you a heavy duty surface to store items on. You could lay a few pieces of pressure treated plywood on top of it to simplify sliding items around.
 
  #3  
Old 01-04-15, 01:25 AM
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i like cal's recommendation, too, other than the 40mm barrier,,, apron/vest stores sell 19mm pond liner,,, we use it all the time for just your purpose,,, think what you need's about $70 10' x 4' = 20 80# bags + 1 to drop imn-s-hfo, fiber's a waste - just put a header 1/2way thru & make 2 pours - 5' x 4' ea,,, place the furthest the 1st day & finish to the header,,, 2nd day, remove header & place the rest

IF you're doing it all in 1 day, you need a joint so pour against the header - have lunch - remove header & place wax'd paper against 1st pour no sawing/grooving of jnt needed that way
 
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Old 01-04-15, 08:27 AM
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I prefer not to buy 40 mil rubber liner or 20 mil pond liner if possible. I already have 6 mil white plastic sheeting if thats ok, or should I double it over if 12 mil is better? Also, if Im adding foam board in the future to the walls, should I attempt to make one continuous sheet run to the top of the walls and would that sheet go over or under the foam board? Again, it appears to be a dry crawl space with about 3 ft walls. While Im here also, do they sell mechanical fasteners at local box stores specifically for attaching foam board to cinder block? I checked HD and one guy knew nothing of the sort.
 
  #5  
Old 01-04-15, 01:48 PM
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If you are doing the concrete and the foam board I would run the poly up onto the wall a few inches and place the foam down to the ground level. You could adhere the foam with an appropriate adhesive, if you can get modified contact adhesive in cartridge form you can make pretty quick work of installation. You might put a few masonry fasteners in. If your top sill plate extends close to the edge of your foundation you could also put a few screws with fender washers in through the foam. Using the adhesive you won't need too many fasteners. You could use tap cons or anchor rivets to hold the foam to the masonry.

I suggested the 40 mil rubber if you were not using concrete, it flops out into place and stays very nicely flat to the ground and gives you a durable surface which is very easy to maneuver over when you have to. If you check a few roofing installers you could probably get a piece as large as you need from one of their rip-off jobs for very little $ if not free.
 
  #6  
Old 01-04-15, 05:55 PM
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2 layers of 6 mil doesn't make a 12mil thick layer as ea is still too *&[email protected]$^ flimsy for my taste we do this work for a living & choose 19mm for best bang for the $,,, we also have 15, 20,35 & 40mm mtls - 19mm works best
 
  #7  
Old 01-11-15, 04:11 PM
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Ok, Im back on this thread with another question about pouring concrete in this small crawlspace. The area is a bit smaller then I thought. It measures 8 x 3' 4". So I'm estimating (15) 80# bags of mix. Do any of you pros have any tips about mixing this cement up in my basement? Besides preparing it to pour, the crawl space access is 5 feet off the basement floor(the dirt floor of the crawl is 5 feet high too) and there is only a 2x2 access hole. I would prefer the easiest method if there is one for pouring this slab. 5 gal plastic buckets? I don't even have a mixing pan, and I have no Bilco doors for basement access so I have to bring everything down the regular house stairs. I can get the tap water for mixing it from a spigot off my furnace but the rest of this might be too much for me by myself.
 
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