Best Tape And Sealant For 6 Mil Plastic Sheeting In Crawl Space... - Insulation - DIY Chatroom Home Improvement Forum

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Old 04-24-2011, 07:59 PM   #1
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Best tape and sealant for 6 mil plastic sheeting in crawl space...


I plan on using the Blue Hawk 6 mil plastic sheeting that Lowe's sells as a vapor barrier in my crawl space.

I was wondering what is the best kind to tape to use for it to tape together the seams on the floor?

Also what is the best kind of caulk or glue I can use to attach the edges of the sheeeting to either my concrete block foundation walls, or to Dow Foamular insulation along the foundation walls.



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Old 04-26-2011, 10:59 AM   #2
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Tyvek tape from home depot...about 10 bucks a roll. There are people that will suggest UL181? tape, but i have been told that even a rated tape doesn't necessarily guarantee quality/longevity

As I am currently in the middle of finishing my basement, I have been doing a ton of research on what to seal the poly with as well...Here is my current notes/ideas that i have seen floating around...

1. Holmes on Holmes = Acoustic Sealant (stays flexible, and sticky after dry)

2. duct-mastic (stays flexible) - Holmes on Homes has suggested this, but not as highly

3. contact cement

4. rubber cement

5. 3m super 7 spray (I don't think that this would stay sticky after a while, especially with a bit of moisture/temp differential)

6. Butyl rubber caulk

7. Polyurethane based adhesive (probably P&L premium, my guess is long time to dry, probably doesn't bond very well to the plastic...i'll test this to see)

8. 3M Scotch-Weld High Performance Industrial Plastic Adhesive 4693H Clear

I would be very interested if someone would chime in with their two cents...


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Old 04-26-2011, 11:34 AM   #3
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I would recommend that you look at other sources of a vapor barrier. Anything sold at a box store may not be the best for long term durability. Do a search for Tu-tuf, dryspace, raven industries, stego, etc. The main reason why is that unless you know your crawlspace soil conditions (assuming dirt floor here) and that they won't react with the plastic, then you need something better. it is not as cheap as the $50 roll at HD or lowes but you get what you pay for. If you do a search on tu-tuf and the others, the sites usually have the tape that goes with the plastic. And yes, it will be more expensive than tyvek tape. The cheap stuff may work for you. Just offering potentially better products.

When you fasten to the walls, it needs to be a mechanical seal as well as caulk. Could use a piece of 1X material, wrap around the wood with the plastic, then anchor it into the wall with the correct screws. Before you drive it home, you could apply caulk (silicone or acoustical) behind the plastic/wood combo. You want a complete perimeter seal around the whole area.

If you use XPS foam, chances are you will need to cover it with drywall. Figure that out before doing it. This means you will need a way to construct a stud wall.

Some sites claim that you need to run the vapor barrier all the way up the wall. If you use XPS, then I see no point. Six inches would seem good.
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Old 04-26-2011, 12:23 PM   #4
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My poly application was to well drained basement floor. I have seen many recommendations that do support your "higher than 6 mil" idea. 6 mil is considered a class 1 vapor barrier, but i have seen that if you go 10mil, 15 mil... or higher, the length of time the plastic lasts gets quite a bit longer. But again, i would only say to use the thicker quality if directly on dirt, under slab...

the problem of using tape to secure vapor barrier is that the constant moisture does kill the tape first, so a second sealing is always recommended. tyvek is guaranteed for 10 years (whatever that means).

for my walls (again, very dry basement and pured rippled texture walls)...Concrete sealant on all small cracks...i pl'ed 2 inch 15PSI xps (vapor rating .7) to the walls, and used tapcons/washers every 2 feet to mechanically connect. You never want to run poly on walls that are partially above grade (largest danger of moisture and deterioration). You always want to verify that all edges and voids are filled behind and around the edges of the xps (great stuff foam works well). Great stuff foam is an air barrier but has never been tested for vapor barrier (directly from dow). Tape all joints with tyvek tape.

For joists, spray foam all openings to the outside world, 2 inch 15PSI xps (can use polyiso), spray foam all edges. I also put 2 inch over my rim, to make a total temp break. I also spray foamed/taped that rim xps to the wall xps to make a completely perfect seal.

The floors (very dry) 6 mil on floor, tyvek and probably pl'ed seams, wrapped up 6 inches and connected to wall xps. 2 inch 25PSI xps on floor foamed and taped. Wall base (untreated) on top of xps, tapconed through to concrete. 3/4" T&G plywood floor (never OSB). No sleepers down to the concrete. No 2x4's or 2x2's on top of the xps for floating sleepers.

People say that this floor should be tapcon'd to the concrete floor, but after a lengthy discussion with dow, and seeing that the foam's crush rating is rated at 10% crush, screwing the plywood down would cause the screws to eventually be the tall point of the floor (large floor warps over time). It also would put holes throughout my vapor barrier (virtually eliminating its purpose).

The walls will be finished with 2x4 studs and 5/8 drywall (probably green) and R13 unfaced in the voids.

The ceiling will probably be R19 unfaced prior to finishing.

silicone caulk does not stick to poly (tested, does stick well to concrete). acoustical sealant sticks only a little just because it stays a little more sticky. I have researched a bit on the difference and most accusticians are taught that silicone is almost identical to acoustical sealant (with the exception being price and marketing).

I currently am testing if rubber cement or pl (says it supports poly) works best.
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Old 04-29-2011, 12:26 PM   #5
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PL does not stick to 6mil at all.

Rubber cement sticks pretty well (few lbs of peel force). but it seems that it does not stick uniformly enough to make it water tight.

I had contacted 3m to inquire about their 3M Scotch-Weld Plastic Adhesive 4693 & Scotch-Weld Plastic Adhesive 4693H and they are actually sending me a quart of the 4693 and a 5oz of the pasty 4693H for to try out with my application at no cost! I will let everyone know the results of the adherance...

The product info sheet shows that there should be a 11lb peel force necessary.

Something worth doing is worth overdoing.
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Old 04-29-2011, 10:12 PM   #6
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I've read no plastic v.b. needed under foam board on slabs........

Air seal the foam boards on walls against any indoor moisture, even the glue....

Have you tried duct joint caulking on concrete/plastic yet?

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Old 04-29-2011, 11:18 PM   #7
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I've read pretty much everything relevant on the building science website...I don't think I've seen where they tell you not to put vapor barrier on the slab, they just leave it out.

The times in my research that i have seen vapor barrier between the slab and the xps (2" xps is only .7 vapor barrier, and does breath) is when the plywood is applied with no sleepers of any kind.
I am putting the plywood directly on the xps and basically allowing the entire floor to float on the xps (no tapcons through the subfloor to cause high points in the flooring after xps crush).
XPS crush rating is measured at 10% crushed. If you have 10% of 2" XPS, that means that the XPS will crush almost a quarter of an inch. granted 25psi (foamular 250) is quite hard to obtain (even for pool tables and pianos), but with the plywood directly on the xps, the floor will feel super solid and warm.

I did foam any slight gaps between xps sheets, as well as tyvek taped over them all the way up the wall even tying in with the foam in the joists.

I'm guessing by "duct joint caulking" you are referring to duct mastic? I believe i listed this on one of the sealing materials, but because of the very poor attachment of other caulk to poly, I would guess that it is along the line of pl, but will stay a bit more flexible (similar to acoustic sealant).

I received my 3m plastic adhesives in the mail today. This stuff IS THE BEST OPTION for attaching poly to poly. The tests I have tried:

poly to poly - almost ripping the poly to seperate the two layers
poly to xps - tears pieces off of the xps
xps to xps - you will break the xps first
poly to floor concrete - 20lbs ish of force necessary to peel off

the poly to poly stays just as flexible as rubber cement, but the connection between the two layers is massive and definitely air tight. The bond for all of the materials only took about an hour or so to fully cure, even the poly to poly.

from these tests, I will never do anything else besides this adhesive. I am even leaning towards making this the only connection between sheets (no tyvek tape).


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