I recently purchased a house, built in 1969, with a 2,000 sf unventilated crawl space. The floor is sandy gravel, and the perimeter walls are 3′ ht conc block. No standing water anywhere, no water marks on the stemwalls, but enough ambient moisture for a dehumidifier to need emptying more than 3 times daily, and (of course) there are signs of dry rot on the floor structure above.
The house was designed for a handicapped man (needing a wheelchair) and so the floor structure was pocketed inside the stemwalls to keep the floor level close to outside grade. The result is no place for crawl space vents and now no way to add them. I’ve decided to fix the moisture problem by turning the crawl space into a 3 foot ht ‘basement’, by which I mean an unheated space where radiant heat loss from the house above keeps it (relatively) dry. I will be moving the floor insulation to the perimeter wall and sealing the dirt floor and stemwalls against vapor infiltration.
Pouring a slab is just too dang tough, costly and not a great vapor barrier, so I plan on using “Stego Wrap” on the ground since Stego Wrap is a true water barrier and has a companion mastic for sealing around the interior spread footings. Stego’s suggestion is to seal the stemwall with Stego Mastic, then anchor rigid insulation over that and then carry the stego wrap up the stemwall 6″ +/- and fasten with termination bars. My question is about using the Stego mastic for waterproofing the conc block stemwall from the inside. It’ll cost $700 in materials alone, and so I’m wondering what other products are out there for damproofing the inside of a CMU stemwall? Suggestions & your experiences are appreciated.
Thanks,
Andrew Gil
Architect/ Builder
Edited 9/20/2005 12:44 pm ET by AndrewG
Edited 9/20/2005 3:25 pm ET by AndrewG
Edited 9/20/2005 3:30 pm ET by AndrewG
Replies
I like the idea, but why put the VB on the bottom of the floor.
All of the reports that I have seen about (JLC, FHB, http://www.buildingscience.com) have the vapor barrier on the ground and the crawlspace part of the "conditioned space".
Thanks Bill,
Good catch. That is what I planned and what I thought I said (hence the use of Stego mastic to seal around spread footings). I just edited the posting to make this correction.
So Bill,.......any other products jump to mind?
Andrew
I am really not that familar with the different types of products.I think that the FHB and two JLC articles did mention them.
a bit more costly but check out a company by the name of neutocrete. http://www.neutocrete.com
Bill,
Yes. I had already downloaded with my JLC on-line subscription "1986_Waterproofing Choices", "July 1999_ Spray-Applied Foundation Waterproofing" and "Sept02_Waterproofing Basement Walls". But, there's nothing that compares to someone out there who's gone the distance with a product or technique, especially when it costs a lot and product failure is not acceptable.
Andrew
Have you read:
SEALING A CRAWLSPACEby Larry JaneskyClose the vents and let a heavy-duty vapor barrier keep moisture, mold and radon out of the living space
in FHB #153?
Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
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Andy,
THe article you mentioned rings a strong bell. Problem is - as I said, I just moved and had to relinquish lots of older FHB and JLC magazines (to a close friend, who hapens to be on vacation). Do you know how I could get a copy? (I don't imagine that it si down-loadable for free)
Thanks,
Andrew
FOLLOW-UP:
Any tried and true mathods for fastening the VB to the conc block stemwall? I'll be fastening through 4" foil-faced rigid. The manufacturer recommends "conc nails", but I'd expect a power-actuated fastener to blow a hole right through the side of the block (yes? no?). Nailing to the sill with strapping would be easy, but that's 2 1/2 feet higher (and a whole lot more material to buy) than needed.
Thanks again,
Andrew
Edited 9/20/2005 4:34 pm ET by AndrewG
This may not be what you have in mind but a good VB material that can be glued is Tu-Tuff. (sp?) Do a web search, as I think it is only available from the manaf. It is just a hybrid poly but construction mastic, etc does stick to it so it can be glued to your block walls. I have done this and it works fine, although I have never done a sealed crawl space. I used PL premium const adhesive.
Thanks Matt, I've heard of it - in fact, it was mentioned in the FHB article that Andy Engel referred to above. I'll have to do a cost comparison between that custom-fabricated poly with a ribbon of off-the-shelf adhesive along the top of the block walls vs. Stego Wrap on the crawl dirt with a coating of Stego mastic on the block walls. (Stego's detail has the StegoWrap turning up the block walls only 6" +/- . The problem with less expensive poly's, as I understand it, is that they use a high content of recycled plastic which changes a physical property of the poly that results in a higher permeability adn shorter life. And so any poly htat isn't formulated for this appliacitron is a questionable expenditure of time, so it boils down to the cost of coverign the stemwall walls with custom poly or a moisture-tight mastic.
Thanks again,
Andrew
Edited 9/21/2005 10:13 am ET by AndrewG
The other thing about the cheap poly is that it seems almost greasy and most tape/mastic will not stick to it reliably.
My guess would be a few hundred for the Tu-tuff
I wonder if you could just use Dryloc on the walls?
I don't think there's an easy way to get that article. It seems that you have the gist of it in hand, anyway.
I'd use TuTuf, housewrap tape, and pressure treated battens with Tapcons and silicone caulk. Andy Engel
Senior editor, Fine Woodworking magazine
An updated profile is a happy profile.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
Andy,
Thanks again. I tried to email directly to your email address a few days ago. I went on-line to FHB and purchased the article (which I remembered well as soon as I saw the cover photo). I'm going to have to price out the difference between covering the stemwalls with the custom poly vs. with Stego mastic. There's also the VERY important consideration that I will already have Stego mastic on-site for sealing their fiber-reinforced vapor barrier around every spread footing in the crawl space (the detail that tips the scales for me on which way to start off on).
Thanks again,
Andrew Gil
Architect/ Builder
Larry Janesky's article is available for purchase in the Fine Homebuilding Archive.
Go to http://www.taunton.com/store/fharchive/index.asp and search for "crawlspace. Ruth DobsevageTaunton New Media
That is is the secret #153 issue.It is every going to be put on the back-issue list.http://www.taunton.com/store/pages/backissue_fh.asp