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Community and Q&A

What is a capillary break between the footing and foundation wall?

Arthur Ratner, AIA | Posted in GBA Pro Help on

Your details show a caplillary break between the footing and foundation walls. What is it? Is it continuous?

Replies

  1. GBA Editor
    Martin Holladay | | #1

    Arthur,
    A variety of materials can be as capillary break in this location. According to Joseph Lstiburek, these materials include "dampproofing, low-permeability paint, or elastomeric paint." Some builders have used 6-mil poly, although poly isn't easy to work with in this location. Then again, asphaltic dampproofing isn't easy to work with either.

  2. Riversong | | #2

    Whatever is used between footing and foundation must not compromise the mechanical connection that resists lateral displacement, or - for practical reasons - not interfere with the subcontractors setting the foundation forms. The material should also be able to resist some hydraulic pressure.

    Neither plastic sheeting nor asphaltic damp-proofing is acceptable. I use UGL DryLock latex masonry paint for this capillary break, as I do for general foundation waterproofing.

  3. Dick Russell | | #3

    Robert, what's your reasoning on the unacceptability of plastic sheeting or asphaltic amp-proofing for the capillary break?

  4. Expert Member
  5. Riversong | | #5

    Dick,

    As I already stated, the capillary break must not compromise the physical connection between footing and wall, which typically relies on a keyway and the friction of the concrete. If rebar pins are used, they will compromise the integrity of the plastic. A coat of hydraulic paint, like UGL Drylock will not change the bond of the wall to the footing or lose integrity with either keyway or pins.

    Asphaltic damp-proofing is exactly what it claims to be, which is not water-proof.

  6. Kurt Samson | | #6

    To follow up with this, should a capillary break be used when Concrete block is being used and not poured concrete? All the pictures I see have a Key and lock approach, that seems to me it keeps the wall from moving. But in the case of a concrete block, both surfaces (the poured foundation) and the block are flat. What would keep the wall from moving?

    Thanks in advance.

  7. GBA Editor
    Martin Holladay | | #7

    Kurt,
    Vertical rebar embedded in the footing. The rebar extends into block cores which are later filled with grout or concrete.

  8. Riversong | | #8

    Kurt,

    A concrete block foundation is no different from a poured concrete foundation in terms of wicking ability. If there is any possibility of moisture in the ground and you want a dry basement, then a capillary break should be installed between footings and walls, on the outside of foundation walls, at the wall/sill interface, and between the walls/footings and the slab (in addition to a thermal break).

  9. John Klingel | | #9

    Very interesting, and new to me. Robert: I assume these are the steps: After footers are poured and are dry, the paint is applied. You apply the paint to the footers well before you pour the foundation wall, so the paint is dry. Yes? thanks. john

  10. Riversong | | #10

    John,

    UGL Drylock Latex Masonry Waterproofing dries in less than an hour, can be second coated in three hours and is ready for foundation in 24 hours.

    Concrete has a theoretical capillary limit of about 6 vertical miles. In other words, it has a high propensity for wicking moisture and requires a capillary break at each junction to prevent "rising damp".

  11. Eric Stear | | #11

    I spoke to Drylok's technical support, and they said the only one of their products suitable for this horizontal application is Drylok Clear. They recommended 2 coats and said to allow it to dry for 2 weeks before pouring the wall on top of the footing. The two week delay is obviously a problem for most construction sequences. Does anybody know of a brush/roll/spray applied product that has the manufacturer's and support for this application?

  12. E C | | #12

    Eric - what did you end up using? I'm considering the use of Thoroseal (or Super Thoroseal) on the footings after a 7-day wait, 2 coats with 24 hours between coats and before the foundation wall is poured. I confirmed Thoroseal can be used on green concrete. Is there anything better that would keep the schedule moving and be suitable for a footing with a lot of vertical rebar (no key)?
    Would using HYDRALASTIC 836 (also ok on green concrete) be worth the extra cost vs Thoroseal?
    Is everyone else who uses Drylock really waiting 28 days before applying?

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