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spray foam basement - any benefit to fill cracks and waterproof?

Posted by mpower (My Page) on
Sun, Jun 8, 08 at 21:13

Hi. I'm getting ready to have the unfinished basement in my 1970's home insulated with spray-on polyurethane foam. I plan to do the entire perimeter of the basement and have been told to space the interior walls in about an inch away from the concrete walls. I understand the foam is closed-cell and effectively works as a vapor barrier while providing insulation. There are a few cracks in the basement block wall foundation and I've seen some areas of the walls damp after very heavy rains or primarily when the gutters have unknowingly backed-up. Part of my remolding will include new gutters and improved exterior drainage. My question is regarding waterproofing and weather or not it is worthwhile to do when the polyurethane foam is waterproof and might provide the same function. Does anyone see a benefit of filling the cracks with polyurethane foam or epoxy and/or painting the walls with a product like Drylok? I've been leaning towards doing the extra work, but I'm second guessing myself and my foam contractor isn't recommending the extra work.

Follow-Up Postings:

RE: spray foam basement - any benefit to fill cracks and waterpro

I can't see the foaming dealing long term with the water issue. It's job is insulation, not waterproofing. Do what's needed to be done with the water, before the insulation is put in.

RE: spray foam basement - any benefit to fill cracks and waterpro


I ran across your post and was wondering if you had gone ahead with this. I was considering something similar but don't have much data to go off of. Anything you could offer would be greatly appreciated.


RE: spray foam basement - any benefit to fill cracks and waterpro

I went to an energy fair and there were several vendors there representing spray foam products. Some advertised that theirs was waterproof and could waterproof your roof, floors and basement walls and some stated theirs did not. There was a distinctive difference in the two.

I have only appraised one house that had it sprayed in their basement and besides noticing the wonderful job it did in controlling the temperature and being hideous looking, I did not notice any water as compared to some of the neighboring properties who did not have the foam. What the long term effects are, I don't know.

The "great stuff" that you buy in the store also states it is waterproof.

I think you will save in energy costs by using it but I would also make sure I have adequate drainage on the outside of my foundation.

RE: spray foam basement - any benefit to fill cracks and waterpro

Spray foam certainly appears to be a wonder product but it's no substitute for adequate drainage and repairs. Patch, fix and waterproof first, providing the waterproofing is compatible chemically with the sprayfoam.

RE: spray foam basement - any benefit to fill cracks and waterpro

Exterior foam insulation is great in theory. But as Building Science Corp. says in "Understanding Foundations,"

"Unfortunately, exterior foundation insulation
can have significant application problems that
often make it impractical to employ. The first
is the difficulty in protecting the insulation
layer during the construction process and
subsequently during its useful service life. The
cost of a protection layer often is more
expensive than the insulation itself. The
second is insect control. Exterior insulation
can be an "insect interstate" that provides a
direct pathway into the structure. Poisoning
the insulation or the soil is often the only
viable approach with exterior insulation as
barriers ("termite shields") have proven
problematic (Lstiburek, 2004). Third is the
problem of thermal bridging when brick
veneers are used (Figure 5). There is no
known practical cost effective solution to the
thermal bridging brick veneer problem when
exterior basement insulation is used. The heat
loss is so severe as to almost negate the
insulation layer (Timusk, 1981)"

It's essential to fix leaks before insulating. Just what is "excessive hydrostatic pressure"? Basement leaks usually don't get better; they get worse.

That said, ccspf is a great product for insulating the inside of the foundation. I've used Walltite by BASF on basements, as well as garage ceilings and other hard-to-reach spots.

There is no logic to spacing the basement framing an inch away from the wall. I have the walls sprayed, then the carpenters build the wall as tight to the insulation as they can. You can add fibrous insulation between the studs if you want to increase the R Value at a lower cost than using more ccspf.

RE: spray foam basement - any benefit to fill cracks and waterpro

I just had my basement spray foamed in the hopes of both improved insulation and help with the water that comes in around the sill. It didn't touch the water problem overall. One spot was a bit better, the other was like it always has been.

At best it might be a bonus if the installers can really get into the particularly leaky spots. We obviously didn't get so lucky.

RE: spray foam basement - any benefit to fill cracks and waterpro

You need to find the source of that water around the sill or you're going to end up with rotted wood. Check everything above the sill, including the roof line. Some possibilities: Clogged gutters, gutters pulling away from the house, no drip edge behind gutters, etc.

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