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  1. #1
    Join Date
    Mar 2008
    Posts
    39

    Default Portland cement for repointing brick exterior

    I'm a bit confused here. People say Portland cement caused deterioration in 5-20 years. Are not modern brick structures built using Portland cement brick walls?

    Also, when repointing an older structure that has lime mortar (white, chaulkish) is it permissible to use Portand cement when PAINTING the outside afterwards? Or will the Portland cement destroy the lime mortar around it anyway? I thought perhaps the paint would prevent any moisture issues regardless of mixing lime joints with new, repaired, Portland joints.

    I'm not a mason!

    Thanks for help!


  2. #2
    Join Date
    Jun 2009
    Posts
    303

    Default Re: Portland cement for repointing brick exterior

    The repointing mortar should always match the existing mortar in strenght. ( PSI )
    If portland was the orginal mortar than it is ok to use OPC.
    If it is a soffter mortar than you should use portland.
    Alway use a mortar that is weaker than the weakest brick.
    Some lime mortars you could check on are
    NHL ( Natural Hydraulic Lime )
    NHL 2
    NHL 3.5
    NHL 5
    You can also get the NHL per mixed with sand.
    Another type would be a mix of one part cement Two Lime & 9 Sand this is sold as a 1-2-9 mix.
    In my opinion this mix PSI is to high for old lime structure repairs.
    Also in my opinion painting brick does more harm than good as for moisture exiting the mortar joints.

  3. #3
    Join Date
    Mar 2008
    Posts
    39

    Arrow Re: Portland cement for repointing brick exterior

    If it is a soffter mortar than you should use portland.

    I thought Portland cement was the no no, too hard, impervious to water, decays older softer bricks?

    On painting, I realize masons hate paint, painters love it, and generally a lot of brick homes are painted. In the case of lime mortar, soft bricks, 1920s period masonry, does paint absolutely ruin it? Most modern exterior latex/acrylic paints will breathe, so if moisture goes in, it has a way out. On a house where the brick is not structural and the house is framed with wood with finished plaster interior walls, seems the unit can breathe...even if painted.

    ?

  4. #4
    Join Date
    Jun 2009
    Posts
    303

    Default Re: Portland cement for repointing brick exterior

    Sorry i left out the word Should NOT use OPC

  5. #5
    Join Date
    Mar 2008
    Posts
    39

    Arrow Re: Portland cement for repointing brick exterior

    I see, thanks for confirming. It sounds like modern mortar OPC is a nightmare for soft masonry bricks from days gone by. I have seen some beautiful, still sound, brick 1920s homes that appear to have OPC (color is neutral gray, larger aggregates in the mix, no indication of white lime) . . . I suppose it matters on who built it. In any case, repointing of the soft lime mortar needs lime mortar...

    Back to painting, can anyone clarify? I still believe good paints will reduce moisture going into the wall, thereby reducing the issue of mortar damage. I suppose even if one made the mistake of using OPC to repoint, then painting could salvage the situation by blocking moisture that would otherwise create damage from freeze/thaw. ?


  6. #6
    Join Date
    Dec 2013
    Location
    Montreal Canada
    Posts
    183

    Default Re: Portland cement for repointing brick exterior

    I have seen a lot of masonry wall ruined by someone painting them with paint. Yes it can be done right but all to often it is done wrong. What happens is called spalding. Water moisture moves from inside the house to outside and is trapped by the paint on the outside where it freezes and breaks of the outside edge. I remember a architects office was painted with the wrong paint and in 1-2 years the outside brick wall had to be removed and new brick installed.
    I would point this out to people as the worse advertising that a architect could have. (we are so bad we screwed up our office brick wall, we have no idea how to do anything). It serves them right. They know about color ect but not about paint types. Karma

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