If you are trying to keep radon gas out of your crawl space and all
you need is a passive radon reduction system (only a radon specialist
will be able to tell you if you need an active system) I’d suggest
that you upgrade to a crawlspace liner that's 20 mil, puncture proof,
and has a UV protected liner.
6 mil liners are known to rip quite easily, and since you mentioned
that there is a water pump and a water heater there, you can count on
some rips and tears every time someone crawls in to maintain these
utilities unless you protect the liner somehow.
I am not a radon specialist, but I understand that it is a gas and, as
such, it will penetrate any barrier that is not completely, tightly
sealed and puncture proof. And once it is inside your crawlspace, the
very idea of providing a vent to let it escape, in my opinion, defeats
the purpose of having your crawl space encapsulated to begin with.
(If there is a hole for something to get out, something else can get
in through it, right?)
I'd recommend Clean Space, which is a thick UV protected 20 mil liner.
It can be installed almost seamlessly over the concrete, and can be
tightly sealed to control not only radon gas but also moisture..The
manufacturer (also a developer of a number of other crawlspace
solutions), offers a 25 years warranty against rips and tears, and
their dealers offer free consultations. It might be a good idea to get
one in your area to take a look at your crawlspace.
Have the radon levels tested after installing the liner and, should
you need an active reduction system, such as a fan and exhauster, it
is not difficult to have one installed below the CleanSpace.
If you ultimately decide to use the standard 6mil, I suggest you find
a way to protect or reinforce it, especially around the ground areas
that will be frequently accessed for maintenance. Beware of using
anything organic to protect the traffic areas or to hold down the
liner; for those are known to favor the growth of mold.
Also, use mechanic fasteners in addition to the adhesive because the
glue alone may not hold it properly. Duct mastic with fiberglass mesh
tape is recommended to seal the seams.



On May 22, 9:42 am, Pat wrote:
On May 20, 7:06 pm, "john"
wrote:

I just had laminated flooring installed in my entire basement. They used 6
mil plastic as well to help block the radon. Everything is pretty nicely
sealed. But they were only able to partially do my crawlspace. (obviously
because of the water pump , water heater in the way) Plus the area
underneath my stairs inside the crawlspace is exposed. (poured concrete)

I'd say theres about 40 to 50 square feet of crawl space thats expose.

Before I get my radon levels tested again, I'd like to sheet off the
crawlspace with 6 mm plastic. Im just not sure how to keep it a tight seal
down there. Taping the plastic to the sheetrock should be no problem, but
there are sections where i'd have to tape it down on the concrete as well,
and im sure that wont stick for long. any ideas ?

You have a few options. First off, you could just close off the area
of the crawls space. Then put in some vents and let the gas vent out
by itself. Simple and low tech.

You could also lay down plastic and put pea-stone over it to hold it
down. Again, simple and tech.

I wouldn't tape the plastic to sheetrock. You may eliminate radon but
you'll just be trading it for mold.

For the poured concrete area, you might be able to get away with any
of the numerous paint-on concrete sealers that are on the market.