[67drake]

I put 6mil plastic down in my crawl space as a moisture barrier beneath my project house. Before I started laying my subfloor I figured I’d glue the plastic around the perimeter of the crawl space to the cinder block foundation to help further seal out moisture.
I bought some water based indoor/outdoor construction adhesive that the label says bonds just about anything to anything. I put a bead down yesterday on a section as a trial run. I went back today and a can easily pull the plastic off of the adhesive. Adhesive sticks to the cinder block just fine.
I went back to the hardware store to find an alternative. All the non water based ones say specifically NOT to use on plastic. So I need ideas on what to use
I was thinking maybe a silicone type caulk as that seems to stick to anything, but don’t know how durable it would be in an unheated crawl space. Or if it sticks to cinder block?
The crawl space area will be unused for storage, so the plastic won’t really get disturbed or pulled on, so it doesn’t really have to be a STRONG bond, just durable.
Also, I know there are some super glue type products that will stick to plastic, but I need to run about 160’, so little tubes of glue isn’t ideal. I was hoping something to use in a caulk gun.

Thanks for any ideas.

[Jack Gifford]

I'm curious how old the house is, with a cinder block foundation? Is the crawl space vented?

[dataway]

When I rebuilt the floor/crawl space under my 90 year old kitchen that has concrete/stone foundation and a dirt floor, I put down the heavy plastic over the dirt, then shoveled in a few tons of clean crushed stone, small stuff .... it pressed the plastic down against the ground and the inner walls of the foundation. Seems to have worked great, musty smells totally disappeared, the gravel doesn't present a good habitat for critters or insects and it adds some thermal mass. Looks neat and clean too.

However at the time we had the entire floor torn up, joists, beams, everything ... so we just carried the gravel with buckets and dumped it in. Would be a pain if you had to crawl in there with the buckets.

[67drake]

Originally Posted by Jack Gifford

I'm curious how old the house is, with a cinder block foundation? Is the crawl space vented?

It’s not vented, but is open to the basement area, which has some air flow. It was built in the 1970’s or so.

Originally Posted by dataway

When I rebuilt the floor/crawl space under my 90 year old kitchen that has concrete/stone foundation and a dirt floor, I put down the heavy plastic over the dirt, then shoveled in a few tons of clean crushed stone, small stuff .... it pressed the plastic down against the ground and the inner walls of the foundation. Seems to have worked great, musty smells totally disappeared, the gravel doesn't present a good habitat for critters or insects and it adds some thermal mass. Looks neat and clean too.

However at the time we had the entire floor torn up, joists, beams, everything ... so we just carried the gravel with buckets and dumped it in. Would be a pain if you had to crawl in there with the buckets.

That’s a good idea, but budget is pretty tight right now. It’s about 600’ sq ft of crawl space.

[dataway]

If you have enough room to get in there .... just pour gravel or even sand around the perimeter to hold the plastic down and against the foundation wall. It's surprising how well the mass of the gravel/sand will hold down the plastic, and of course it presses it against every different shape very easily. No need to cover the entire thing from the get go.

Or ... make yourself some skinny "tube sand" ... find some kind of cloth or plastic tube .... like a long sock, fill them with sand, tie off the ends, place them all around the edges of the plastic.

[John V.]

I like gravel. Have gravel over plastic in the partial crawl area in my present house. I actually had a partial full basement and partial crawl in my 1st house built in the '70s. The crawl had a concrete slab floor and access from the basement so that I could use it for storage (Xmas tree, etc.). We added on to the room above the crawl and built the new crawl under it the same way with an opening between the 2 spaces.

Anyway, just spit ballin' but I'm reminded of the mastic used to "glue" the heavy plastic water shield to the inner door panel of late model cars.

I think it is nothing more than a non-hardening urethane product so that you can pull the shield off (like for power window motor replacement as I've done many times) and then restick the shield to the door panel. The trick is to keep the sealer from getting all over your hands or having the shield fold over and glue to itself.

Pretty sure that stuff would adhere pretty well to cinder block.

Not sure if it applies from a gun or if you buy it in a roll of tape with a removable backing. And not sure where you'd buy it either.

I do have experience with urethane in a caulking tube that cures but you might have trouble getting it to hold the plastic to the wall until it cures. Plenty of adherence at that point but not sure how you would hold the plastic in place waiting for it to cure enough to hold. Might do for a water shield but a big sheet of plastic would have too much weight.

Like I said, just spit ballin' but might give you some ideas.

[Stuart]

Maybe try some of that rubber flashing tape, like they use for sealing around windows and building penetrations. Here's one example but there are a number of brands and types. https://www.homedepot.com/p/Quick-Ro...T910/202267106

[Jack Gifford]

I haven't seen cinder blocks sold in this area since the early fifties.

[stags]

Moisture coming through the block will eventually loosen any adhesive and poly sheeting doesn't take adhesives well anyway. Check with a local roofing supplier for aluminum termination bar. Used to secure roofing/waterproofing membranes to foundations, walls, etc. A 10' x 1 1/2" length with prepunched holes on 8" centers is around $5.50. You can hand nail it (ugh), tech screw it or rent/ borrow a nailer for block and be done quickly. Could also use strips of pressure treated wood ripped from 2 x's if you have access to a table saw.

[dataway]

My main house, built in 1990 has a 10" block foundation. since I wanted to use the basement (open in rear) as a shop I had it built special for a 6" slab and 10' ceiling height to get me a full 8' head room after joists, beams and ductwork installed. Sealed with tar on the outside and insulated on the outside with 2" rigid insulation below ground level. Held up beautifully the last 30 years. In my case there was something about the added height that made a poured concrete foundation extremely expensive. Because of the height they did have to put in some Pilasters, areas of extra courses of block filled with cement.

Some of the construction tapes out there are incredible, but yeah I think when the block "powders" from moisture leeching through it might not stick very well.

Gravel seems great for keeping the typical basement dust down, and because of it's mass it tends to be a "sacrificial anode" for moisture ... vapor condenses on the gravel first where it does no harm and keeps it off the wood, then because of the tons of surface area it gives up the moisture very quickly when the humidity level goes down. Every time I have to go down into the crawl space I tell my wife I could live down there. When we rebuilt it I installed lights, raked out the gravel nice, it's really quite pleasant down there now.

[67drake]

Thanks for all the info and ideas guys!
I can still by cinder block locally btw. Maybe it’s a regional thing?
An idea that someone came up with was spray foam insulation in a can. I have quite a bit of it on hand for doing my window installs anyway. I’m going to try it out today.
Problem with gravel or pea gravel is the cost. Even in bulk it is expensive around here. I think it would work fine though. Money is just getting spread thin these days as I have multiple projects going on and planned for my houses and cars!

[Stuart]

Cinder block is an old name; these days they're generally called concrete blocks or CMUs (concrete masonry units), but everyone knows what you mean.

Home Depot still calls them cinder blocks: https://www.homedepot.com/b/Building...s/N-5yc1vZcdpe

[Lemans64]

How about vapour barrier sealer, they use it to seal vapour barrier on inside walls over top of insualtion. It's almost like urethane windshield stuff. Black super sticky stuff.

[tooski]

Acoustical sealant. Tar like substance. Sticks to everything. Needs solvent to remove. Apply with caulking gun.

[Lemans64]

That's the stuff.

[Jack Gifford]

Originally Posted by Stuart

... Cinder block is an old name ...

Old type of block, not old name. They used cinders as the aggregate instead of ground stone.

[dataway]

Asphalt roof sealant would probably work, that stuff sticks to anything.

And yep the expanding foam, as much as I hate the stuff, would stick to the block well I think ... not so sure about the plastic.

To bad you are not my neighbor ... I have 20 tons of 1/2" crushed stone in a pile on the property, got for a project and never used it.

Heck, one simple solution would simply be rocks or bricks along the perimeter, it would take care of 90% of the problem. Put them as close to the inside of the block wall as you can. I don't think the amount of vapor escaping around the edges would be an issue, the vast majority will be coming from the 600 square feet of dirt. It's not like the vapor is under pressure and will seek out the edges.

[turbo69bird]

I’d use the plastic and crushed stone method that is what we use around here the. We pour concrete over it. If I was just gonna put the plastic down and wanted to glue it down I’d probably use roofing tar sticky as a biotch and stays pretty tacky for a good while. .

[67drake]

Thanks, this house is long gone done and rented.
I never could get that stuff to stick too well, but most people I talked to told me it’s overkill and a waste of time anyway to try to get it that airtight. I just put it down to cover the ground, and stuck it to the foundation. It pulled away in a lot of places, but I’m not losing sleep over it.