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Re: GBlist: Questions on concrete sealant & vapor barriers for a below grade living space

Joseph Charlson wrote:
> 
> Questions on concrete sealant & vapor barriers for a below grade
> living space:
> 
> I have an unfinished basement that I'm finishing in the Boston area.
> The
> structure is all uninsulated cast concrete.  Its approximately 5 feet
> below
> grade and 2.5 feet above grade.  There doesn't appear to be any
> foundation
> drainage.  

Hi Joseph

You should check a few things before finishing a basement i.e. height of
water table and exterior drainage meaning not just if there is perimeter
drainage but also where the gutters drain, if the land slopes toward the
basement, etc. Look for signs of flooding or areas of excessive dampness
in the basement itself. Insurance companies don't always cover damage
from flooding.
 
Exterior damp or waterproofing and drainage is really the best option
(but not that useful if there is hydrostatic pressure from high water
table). If it is not possible to do the exterior work interior
waterproofing can be done with cementious products such
as Zypec (discussed earlier check archives for address). Other concrete
waterproofers
(such as the Olympia you mentioned) use percentages of silicone for
waterproofing. Most use a solvent base but there are friendly
alternatives - one is called Enviroseal by Thoro which is a water based
silicone top sealer and is quite effective. These products are generally
used to provide a clear coating on cement or stucco where you want to
preserve the appearance of the concrete. Use the cementious product if
you can as it has more integrity for its purpose.
I would not use fiberglass insulation as its effectiveness is
compromised by any moisture (in other words useless). Foam (EPS) in
higher densities would both insulate more effectively and provide the
moisture barrier. You could use a foamed adhesive such as enerbond to
attach the panels to the concrete and the drywall to the foam (no wood
involved - fewer materials for mold growth etc.

Finished basements such as you describe are not the healthiest places
and do not work well with conventional finishing materials (potential
for mold growth etc.) 
If I was to create specifications for finishing that area I would:
- excavate perimeter to footing
- slope the footing (applying mortar or cement)
- apply zypec to 8" above grade
- drain rock and perimeter drainage at footing (do not tie gutter drains
into perimeter drainage)
- apply foam insulation boards against exterior foundation walls from 2'
below
grade to top of foundation wall (you can use stucco or zypec over the
foam)
- use drainage board or backfill with gravel/sand
- create a free draining path area around the house rather than
plantings
INTERIOR SPECIFICATIONS: the interior should now be dry and insulated
- drywall can be directly laminated to the conc. walls but it would be
preferable to avoid paper faced and gypsum products - cleaning and
smoothing the exist conc. or going to a smooth stucco finish might be
preferable.
- flooring (if you need to install an additional heat source you might
want to think of running radiant floor tubing to take advantage of the
existing mass and pour a 1.5" slab over and either colouring the conc.
or installing tile, etc.

Sorry if this is more info than you wanted but it struck me that the
system you were describing was not taking advantage of or working to
improve what you already have. Its generally been my opinion that a
healthy house is not just a question of using the least dangerous
materials but more of balancing the inherent properties of materials -
so that they work together, e.g.. taking advantage of the fact that the
area is already ground insulated so insulating only the exterior portion
above grade, using the mass as a heat sink, improving the existing mold
resistant walls rather than adding a new, potentially contaminating
layer, etc.

Better stop now. Good luck
John Salmen
TERRAIN E.D.S.
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