Securing Vapor Barrier to a Fieldstone Crawlspace?
I recently bought a house that was built in 1850, and we’ve got the foundation variety pack: 1/3rd slab, 1/3rd full height basement with concrete floors, and 1/3rd half height crawlspace with dirt floor.
The crawlspace stunk mightily this summer, so we had some basement crews come look at it. Everyone advised a full encapsulation of the crawlspace dirt floor and stone walls. The prices were more than our budget, so I sourced high quality materials so that I can do it myself. But the one thing I can’t find an answer to is: how do I secure the top of the vapor barrier to the fieldstone walls?
This wall is the opposite of flat. The walls are round and the variance from stone to stone is large. No matter how clean I get it, I can’t imagine that butyl tape and construction adhesive would actually give me a good seal against this jagged surface.
I got clever and attempted to make a runner a few inches down from the top out of long pressure treated boards. My plan was to screw them into the wall with tapcons in the flattest possible configuration and then spray foam from the top to make a seal, and then use the tape to secure the vapor barrier to this.
Good idea? Terrible idea? My first obstacle has been that my 18v hammer drill isn’t even putting a dent into these stones, so I can’t even get the tapcons in. It’s giving me pause. Advice is most welcome.
Please note – the plastic in the pic is not a vapor barrier, it’s just some temporary sheeting so I get less messy when I’m working in there.
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Tuck the plastic up behind the board as you fasten it to act like a termination bar.
https://shop.stegoindustries.com/stegocrawl-term-bar-secures-barrier-to-concrete-masonry-42-x-1-125-case-pack-50/?utm_term=&utm_campaign=StegoCrawl+%7C+Test+%7C+Performance+Max&utm_source=google&utm_medium=ppc&hsa_cam=21691473039&hsa_ad=&hsa_mt=&hsa_src=x&hsa_ver=3&hsa_kw=&hsa_acc=3219239854&hsa_net=adwords&hsa_tgt=&hsa_grp=&gad_source=1&gbraid=0AAAAADRY2X_uC7tiIqP0TLE5sloORItfG&gclid=EAIaIQobChMIupuei-3IiQMVSBOtBh0tLzNyEAQYASABEgIxXPD_BwE
Then spray foam and/or tape behind to masonry
Usually with fieldstone the easiest things are either to spray something on it, or build a flat wall in front of it. Closed cell spray foam works as a vapor barrier, air barrier, insulation and also blocks minor water leaks.
If you want to do just a sheeting vapor barrier, one way is to run a piece of treated 1x4 or 2x4 screwed to the bottom of the joists as close to the wall as you can get it and still have it run straight. The sheeting gets stapled to this, ideally wrapped around before being screwed in place.
This needs to be sealed at the top. Typically what you'll have is a 6" or bigger timber resting on the foundation and the joists are mortised into it. If the sheeting runs along the bottom of the joists and to the timber and is fastened with staples it would seal the top.
I don't love this idea because stapled poly is somewhat fragile, but this will be able to prove to you that a vapor barrier solves your problem and there aren't other issues. A permanent solution should include insulation, for that I would recommend either spray foam or building a stud wall out from the fieldstone.
You need a rotary hammer instead of a hammer drill. Even a smaller class size SDS-Plus rotary hammer (9/16, 5/8, 3/4, 7/8 max rated hole size, etc.), should work much better than a hammer drill, and there's no reason to buy anything big for Tapcon-sized holes.
You may want to leave an exposed strip between the top of the membrane and the mudsill for things like termite tunnel inspection, if you're sealing the membrane directly to the wall.. I think I remember that being normal practice.
You could also parge a stripe of the wall with lime mortar to smooth out a spot for the membrane, but that's probably a lot of work.
I really think closed cell spray foam spray directly against the fieldstone wall is your best/only option here. I suppose if you have no bulk water issues, you could put a board across the top, seal it to the wall with canned foam, then use HEAVY poly (10+ mil) hanging from that to your floor layer. I think you'll have issues with critters over time doing that though.
I second the rotary hammer idea. Get an SDS-plus drill, use the GOOD bits that Bosch makes. This has several advantages: 1- the rotary hammer is the right tool here, 2- the good bit will last a LOT longer while also doing a better job, and 3- the SDS-plus chuck won't constantly be loosening and needing you to stop to tighten it the way a regular chuck will when hammering away.
BTW, the larger tapcons (bigger than 1/4") give much less trouble when securing things. Even if you don't need the strength here, I'd go 5/16"+ just to avoid issues with the tapcons stripping out in the holes.
Bill