I am in the process of building an outdoor concrete slab.
The area I live is rocky and generally has good drainage.
Is a vapor barrier between the sub grade and compacted grade necessary in my case?
outdoor slab:to vapor barrier or not
I am in the process of building an outdoor concrete slab.
The area I live is rocky and generally has good drainage.
Is a vapor barrier between the sub grade and compacted grade necessary in my case?
No, it's just going to dry rot and leave a void. Just make sure your pour surface is dry and properly tamped
>make sure your pour surface is dry
so it sucks all the water out of the concrete? dont listen to this guy
>I want my concrete to stay wet
Is there going to be a structure on top of it or is it going to be a patio or something?
If it's outside you don't need a vapor barrier.
Also
excuse me, but it's not a stupid question, sir
moisture can diffuse from the sub-grade, can it not?
how can 10 mil plastic rot?
You've never heard of dry rot?
I have not
wait on
Are you saying that heat can cause thermal degradation in the plastic? Interesting
there will be a water tank on top of the structure
I've never seen plastic sheeting used underneath an exterior concrete slab. I don't see what benefit that would provide.
can't moisture seep in from the sub-grade? a thick plastic sheet can prevent it from getting it into the slab
Once concrete is cured, which it can cure underwater, it is impermeable. Where is the plastic wrap on the hoover dam?
concrete by nature is porus
hoover dam is 600 feet thick and they used additives to make the concrete less permeable to water
I did municipal construction for 4 years. I put in countless manholes. We used untreated concrete pipe, in untreated concrete man holes, and poured in untreated concrete slurry to finish the bottoms after installation. The only place treated concrete is used is sewage because hydrogen sulfide eats concrete. Every pipe we put in was connected with a thick rubber gasket, do you know why? Because the pipe is then water tight. You're a fricking moron.
ok, why do you think, by code, basements and garages require a layer of plastic between the compacted grade and concrete then?
Big Barrier™
ever been in damp basement? I have. landlord required me to run the dehumidifier 24/7
because its a fricking building and not outside?
Every manhole I've ever been in has been doaking wet weather there's a rubber or not.
Maybe they're just dry because your an engineer nerd
>can't moisture seep in from the sub-grade?
Well first the concrete should be installed over a gravel base, and water doesn't seep upwards through gravel very much due to the large granularity, at least nowhere near as much as it does through dirt. However if it did, it wouldn't hurt anything. It's an exterior concrete slab, it's going to get wet every time it rains. The top of the slab doesn't give a frick about getting wet, and the bottom of the slab is no different. The only reason plastic sheeting is used in interior slabs is because you don't want humidity wicking through the slab into interior living space, it's got nothing to do with protecting the concrete itself from moisture.
thanks for the reasonable answer
>The top of the slab doesn't give a frick about getting wet, and the bottom of the slab is no different.
so why do concrete sealants and additives exist? aren't they supposed to protect the concrete from water damage?
One reason to seal it is when concrete gets wet, and then freezes, the water seeps into the pores will expand and it will get spalling, pits and chip-outs wherever that happens.
Those pits hold more water, and it’s worse on the next freeze/thaw cycle.
Sealing it prevents the water from getting into the pores to some degree.
Also, you generally have aerated concrete (it’s got tiny bubbles in it) to help prevent this—the air allows the expansion without stressing the concrete, like a gas shock absorber.
There’s no perfect method, but it probably helps.
it's a problem if the slab is under a house
outside...if the ground underneath is wet, it's very likely wet on the surface too and the barrier isnt doing shit
Open up the wall. Or remove one of the P traps and push a snake in. If you are lucky you'll dislodge the clog. Or you could try some sodium hydroxide aka liquid-plumbr or drano or your regional equivalent.