Vapour barrier and water proof paint in insulated basement walls?

[Harry Muscle]

I have a couple quick questions about my basement walls.

My original plan was to paint the concrete basement walls with DryLok paint or something similar to keep moisture levels down and to eliminate any possibilites of water leaking in (there's one spot where there was leakage before, but I haven't noticed any for about a year now). After painting with DryLok I would insulated all the walls, add vapour barrier, then add drywall. However, I got thinking ... wouldn't the DryLok paint and vapour barrier both act as vapour barriers? And isn't a vapour barrier supposed to be only on the warm side of the wall? So wouldn't using both cause condensation problems? Actually wouldn't using the DryLok itself in an insulated wall cause condensation problems since in effect you have a vapour barrier on the cold side? Or am I just not understanding this correctly?

Thanks, Harry

[Sev]

It's still correct to use the vapor barrier- which is to block moisture from warm, heated space penetrating and condensing in cold, unheated space, causing problems there. However, you still need to solve your moisture intrusion problem from outside, which is not always easy, or cheap. First, though, be very scrupulous in making sure all drainage is directed away from foundation. Take a look outside that area of previous leak and see if you can't improve things somehow, alter slope, extend leader, etc.

[DT]

It's a complex subject. For a lot of actual performance tested results, try the Building Science Corporation at:

There is a section on basement insulation methods. The bottom line is that the only insulation type that works is rigid insulating board, but you need to study the issues on vapor barriers and moisture dynamics in the reports to see how it applies to your situation

Dennis

[Joseph Meehan]

I would suggest doing the DryLok first then waiting until you have had a very wet year without any leaks before proceeding. DryLok does a very poor job of blocking moisture. If you have moisture problems you need to address the problem not the symptom (the leak). You need to work outside to stop leaks not inside.

I would not put that kind of work into a basement until I was sure all moisture problems were resolved.

[Dick Russell]

Joseph Meehan is right about solving any outside water entry problems first. If outside water isn't allowed to drain away from the footings to lower ground, it will find its way into any crack and force its way past any covering on the inner wall of the concrete. You haven't said how you would apply insulation to the inside. A common way is to mount studs and put insulation batts between, then the vapor barrier and drywall. Structurally that's fine, but if you don't provide a very tight seal around the edges of the wall, humidity will diffuse into the air spaces of the insulation and, in humid summer days, condense on the cold concrete surface. That could give you a musty smelling cellar or mold. This is another reason for building new houses with extruded polystyrene boards on the outside of the foundation walls, from footing up to the sill (protected above grade, of course). This puts the concrete mass on the warm side of the insulation, helps keep out water from passing through the walls from the ground, and prevents condensation on those humid summer days. Retrofits to do it this way aren't easy, so applying the insulation inside must be done so as to keep the air from contacting the cold concrete.

[Al Bundy]

"Harry Muscle" wrote in news: [e-mail]:

Harry:

The cart goes beh You need to work outside to stop leaks not inside.

Exactly. Assum .... be very scrupulous in making sure all drainage is directed away from foundation.

I'm sure there are many schools of thought on what it should be. Of course you can do a bang-up job with new construction. With a pickup, wheelbarrow, shovel and tamp, how good a job you can do depends on how bad the drainage issue is. Anything is better than flat except a pit of course.

[Harry Muscle]

Actually I believe I have solved the issue on the outside. As mentioned in the first post, I used to have water seeping in, but I haven't had any since last year when I redirected my downspouts away from the house. There's been several very heavy down pours since then and nothing seeped in, so I'm pretty confident in that, however, I always have a habit of going overboard so that's why I was thinking of painting the walls with DryLok.

That link posted by DT looks really interested though, and I'm thinking I'm going to pursue what it says there by using the extruded polystyrene. I haven't gotten thru the whole article yet though, so I'm not sure if that would make the DryLok uneccessary or what?

Thanks for all the responses so far, Harry

[Peter Shepherd]

One engineer's basement I put 2" extruded styrofoam on using Bailey retainer tee's instead of studs, and tapcons into the block wall. Acoustic sealant in the styrofoam joints to complete v. barrier.

If you want to go all out on preventing mold on drywall, as I think you're close to Toronto, you could also try

DensArmour Plus Paperless Drywall [avoids future rot] available at:

Patene - Hornby, 401 & Trafalgar - 4 x 8 - 1/2", 19.65 / sheet, vs regular white = 13.00/sheet, green drywall = 19.84, agent says DesArmour may altogether supplant green drywall soon, except if older is heavily discounted to builders, has exactly same finish as regular drywall, no charge for >/= 20 sheets, but if only 5 or 10 $40 or 50 to Oakville. Do ship to Toronto, have bundle with another order, no charge if able to schedule with other orders. (Feb 06 $)

If you're retrofitting higher than basement & want the ultimate in vapour barrier [though I'm not sure how much use it is in retrofit without being able to join around top plates etc]

- Certainteed "MemBrain" nylon vapour barrier with variable perm rating.

MultiGlass in Toronto has new nylon vapour retarder :

Price of Membrain, 8' (100") = 800' sq $147.00/roll + tax 9' (again + 4" overlap) = 900' sq $166.00 10' (again + 4" overlap) 185.00 12' (again + 4" overlap) 222.00

Peter Shepherd