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Design Question: Existing Exterior CMU/CIP Stemwall

Discussion in 'Building Designers' started by Papio Bldg Dept, Oct 20, 2011.

  1. Papio Bldg Dept

    Papio Bldg Dept Platinum Member

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    I have been asked to inspect/review an existing building that is experiencing moisture issues at an exterior CMU wall that sits on a 4' AFF Cast in Place stemwall. The wall has been painted on both the exterior and interior surfaces, and shows signs that moisture is penetrating through the CMU and grout joints (i.e., bubbling and pealing paint, water streaks/staining, crumbling grout, discolouration in exposed CMU, etc.). The interior space is now being conditioned by a radiant heat system in the winter and a window box a/c during the summer and there is no interior or exterior insulation. Flashing and gutter systems at roof line appear to be in good condition and installed correctly, but I have not confirmed or tested them.

    Has anyone had experience with these types of issues in CMU walls? My initial thoughts are that the moisture is not (only) passing through the wall cracks and grout lines as first suspected, but perhaps there is also a temperature differential issue which is resulting in condensation at the interior side of the wall too. I am thinking I need to create a thermal barrier for the interior before addressing the exterior issues. Any advice would be greatly appreciated.

    Thanks in advance.
     
  2. north star

    north star Sawhorse

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    & & & &

    Papio,

    If it were me, I would probably investigate the exterior side first.

    What type of "paint" has been applied to the exterior?....Is it a

    type of paint that actually seals the CMU, or is it just paint?....

    Also, check all of the joints, cmu's, etc. for any cracks or points

    of penetration.

    * * * *
     
  3. Papio Bldg Dept

    Papio Bldg Dept Platinum Member

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    Joints were tucked and pointed about 3 years ago, and it appears to have had two layers of latex paint applied directly to the exterior surface. Interviewed the tenant today. Tenant stated moisture is only visible when it rains, and efflorescence is visible behind the paint at both the interior and exterior of the walls. No control joints provided in walls (walls over 20' long). Expansion & contraction cracks have formed in the walls along mortar joint lines, but no visible cracks appear in CIP stem wall.

    Am I correct in assuming the moisture is penetrating at the cracks/mortar joints and then getting trapped behind the paint?

    I wonder if a fluid-applied elastomeric air/moisture/vapor barrier system applied to the exterior would help.
     
  4. north star

    north star Sawhorse

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    * * = = * *

    Papio,

    I would apply [ or have applied ] a good quality system such as you

    are referring to, to the exterior.

    Mike Holmes did one of these on one of his shows.......Pointed &

    repaired all cracks and openings in the cmu / concrete wall, then

    applied [ completely ] a wateproof vapor barrier, ...then applied

    at least 2 separate layers of the elastomeric sealant......You're

    on the right track!.......Of course, you will have to fully expose

    the entire height and length of the wall areas.

    * * = = * *
     
  5. codeworks

    codeworks Gold Member

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    TNEMEC PRODUCTS. work great, as you can see, it's"cement" spelled backwards. good stuff
     
  6. jeffc

    jeffc Bronze Member

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    If this condition only occurs in the summer after a rainstorm, this help to address the cause and solutions :www.buildingscience.com/documents/reports/rr-0104-solar-driven-moisture-in-brick-veneer .PDF

    The bricks get wet from the rain and when the sun comes out, vapor pressure pushes the water into the wall assembly. The paint on the inside may be acting like a vapor retarder and stopping the moisture from just passing through. Installing a vapor rated paint on the outside would help and removing any vapor retarder on the inside would allow the water to defuse to the inside of the building as a vapor.
     
  7. JBI

    JBI Sawhorse

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    Almost sounds as though the mortar and block never bonded properly... if that's the case, the bond between the CMU wall and the CIP wall may be questionable as well. What portion is above exterior grade?
     
  8. Mark K

    Mark K Platinum Member

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    The heat and air conditioning creates situations where the moisture content on the inside is different from the outside. The differenc in the vapour pressure will drive the moisture through the wall.

    Suggest that you consult with an expert in moisture problems. A mechanical engineer might have insights. You could find that paint would peal due to the differences n vapor pressure.
     

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