[Eddie Bear]

I just bought my first house. (FYI)
Its a single level ranch with a crawl space.
The crawl space has some type of clay.
No signs of mold. The crawl space has two outside wall vents.
The A/C drains in to the clay so I plan to install a condensation pump.

There is a plastic vapor barrier down there but it has many holes and covers about 60-70% of the soil/clay. (the crawl space is about 26'x41')

I want to install a new vapor barrier.
Here is the question, Can I install the NEW vapor barrier OVER the OLD one?

My thinking is that moisture will get trapped in between the layers THEN cause mold.

The photo shows the condition.

 

[Ron6519]

I'd clean out all the garbage(old barrier included) and put down a new barrier that covers the whole floor.

 

[Eddie Bear]

Thanks Ron.
That's what I though. There is garbage down there (old shoes, tile, pipes).

Is it bad to have the barrier over the cast iron drain pipe?
That's how it is now. I a little worried about tampering with pipes that old. (I have that kind of luck)

 

[Eddie Bear]

OK, then about the mil of the plastic. Between 4, 6 and 10 mil, 10 would be best right?
I see 20'x100' 10 mil online for $119 (Home Depot its $199).
Is the higher the mil, the thicker the plastic?

 

[AGWhitehouse]

You can cover the pipe and yes the higher the mil, the thicker it is.

 

[Ron6519]

Six mil is the standard in vapor barrier thickness.

 

[jklingel]

I'd only spend the money on 10 mil if you were planning on using the crawl space frequently. Be sure to run it up the walls, secure it, and caulk it w/ a compatible caulk, something like Tremco acoustical caulk.

 

[Gary in WA]

As we don't know your location, only run the plastic up the concrete walls 6", to inspect for termites.http://www.termiteinstitute.com/content/map-of-hot-zones.asp
You may need to take special precautions if in a radon zone: http://energy.cr.usgs.gov/radon/rnus.html

Gary

 

[John_W]

Clean it out for sure. You are breathing air that comes from your crawl space.

Gary has a good point about radon. If you have to mitigate for that, the quality of the plastic and the way it is installed will be more important.