does anyone have an opinion on how safe it is to work with cement as it is being poured in a shallow house crawlspace? Will I be in any danger from chemicals released from cement as it sets? Our crawlspace is wet (groundwater from cracks in bedrock and from under footing on bedrock). I would like to pour a 4″ cement slab over top a heavy duty vapour barrier to seal out ground water. any thoughts or ideas are always appreciated.
p.s. I realize it is then important that the footing drains are working and laid properly.
Replies
No danger of chemical outgas from concrete hydration. If doing it yourself you might be susceptible to contact dermatitis from unavoidable high exposure to wet concrete from working in such tight quarters. Some people are extremely sensitive to wet concrete. Hope you are not one of them.
thank you for your reply, Dave. Looks like I might have over-estimated the amount of concrete needed and the danger of any fumes. I will be certain to protect exposed skin, and I may just look into the pea gravel & TuTuff/vapour barrier option as well.
Doing this yourself, consider working in small batches, and not doing the whole thing in one day. That way you don't have the moisture of all the concrete down there at once. It's a crawl space, so the appearance of cold joints shouldn't be a problem.
You'll have time to get the hang of it and refine your methods. Consider building a very low cart that you can use to push two or three 5 gallon buckets around on. It'll roll real nice on the finished part of your concrete. Having a rat slab makes all your future crawl space work a whole lot cleaner and easier. Do, though, consider whether you might want to leave some small areas -- a couple feet square -- for access to dig and run utilities under the footing in the future.
-- J.S.
My hands get kinda dry and cracked when I work with concrete (which I do as seldom as possible, by the way - lol), but that's about it.
Are you sure you really want to pour 4" of concrete in your crawlspace?? It's gonna be a real messy job, and your moisture levels will increase while it cures.
Personally, I would try laying some heavy plastic sheeting to see if that solves the problem. That's also a hassle, but it's sure easier (and cheaper) than messing with concrete.
I'll assume that you've already looked into the usual suspects.....blocked foundation vents, poor gutter drainage, insuffucuent "fall" in the grade around the house, etc, etc, etc.
Can you use flowable fill for something like this.I am really not sure what it is, but I think that is low strenght concrete with lots of water so that it flows into place.Don't need any real strenght for an application like this.
Flowable fill varies from suppliers. Basic mix is sand with a bit of portland cement and lots of water. Yields about 300 psi strength.
Be careful when placing and floating the wet concrete.
A friend of mine, a very serious DIY guy, did exactly what you want to do, and he crawled all around in it to rake it, screed it, and float it. He failed to realize that you need skin protection, and ended up in the hospital with third degree burns on his knees and shins.
If it were me, I would get outfitted with fishing waders, and good rubber gloves.
Don't worry at all about any gaseous emissions. There are none.
So, is this a good way to fix a wet crawlspace?
Covering the ground with a cross-laminated vapor barrier, bringing the barrier up the foundation walls, and covering the vapor barrier with a thin layer of concrete?
IMO the only reason to cover with concrete is if you expect a good amount of foot traffic, like if it is a storage area. Even then, the more expensive polys hold up OK.
Really though, the best way to fix a wet crawlspace is to stop the water before it gets in there... granted - sometimes this is not possible.
Yes, 6 mil vapor barrier, and I usually spec out a 2" fiberglass reinforced mud slab. You can pour a 4" reinforced slab if you want and don't mind the extra cost.
It sux when it splashes in an eye.
Do you really need 4"? 2" would do the same job, the only prob is that you have to do a really good job on the subgrade... A spinning laser works great for this.
Of course, this would have best been poured while the house was being built. If it is that difficult to move around under there then the area will make a poor storage place. Four inches is very thick for what really requires a "rat slab" or thin slab.
What will be easier to do and just as effective at blocking moisture (I think the cement alone will not block moisture), would be laying down 6-mil sheeting or TuTuff and sealing all edges and run the sheeting up the foundation walls. Then spread washed pea gravel over it just to hold it down. You wont need much.
My $0.02