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Chimney top parging

Post in 'DIY and General non-hearth advice' started by 72Rover, Jan 4, 2012.

  1. 72Rover

    72Rover Member

    Joined:
    Dec 29, 2011
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    Loc:
    East VA
    Sweeping the flue a while back, I decided it was time to renew/recoat the cement parging on the top of the chimney. It's done pretty well (since 1938), but it gonna need work soon.

    The neighborhood hardware store must have nearly a dozen 'flavors' of cement and mortar mix. I was going to use a bonding adhesive first to prep the old cement, but didn't know if I should add a chopped reinforcing fiber to the mix to keep it from spalling in the future. It's going to be a thin coat.... Concrete needs to cure as opposed to drying, so what about covering w/ plastic so it won't dry out?

    My wife says I tend to over-analyze everything....

    Cheers

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  2. semipro

    semipro Minister of Fire

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    Jan 12, 2009
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    SW Virginia
    I did this a few years ago on my stone chimney. I cleaned the old masonry with a steel brush and muriatic acid then let it dry. I then coated it with the adhesive agent and applied the mortar. I can't recall which type but Type S comes to mind.

    I'm not sure that the addition of plastic fibers will prevent spalling but they will strengthen the mortar and prevent cracking. I like fibers and use them in most concrete applications. You may want to consider an air entraining agent if you're worried about spalling. In general, air entrainment helps with concrete that's exposed to extreme temps, salt, or movement.

    Keeping concrete moist after placement can do nothing but increase its strength and prevent "dusting". Its a great idea. You can put a blanket or burlap over it and spray it with water every so often to keep it wet.
  3. 72Rover

    72Rover Member

    Joined:
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    Loc:
    East VA
    Thanks. A couple of years back, I came across this fiberglas additive that could be added to most mortars and even some paints. At the building supply place, they had dry-stacked six or eight CMUs, then 'painted' both sides with this mixture. The finished unit was placed horizontally on two sawhorses as a display for the product. I was impressed, and "impressed" is a word I don't use very often....

    Cheers
  4. backpack09

    backpack09 Minister of Fire

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    Loc:
    Rochester, Mass
    I would wait for warmer weather.

    I redid my cap with the same mortar I was using to repoint with.

    Bonding agents are tricky, too little or too much cure time and you get a worse bond than without it.

    I simple used a spray bottle to keep the bricks and clay wet so the mortar would stick and went at it.
  5. ironpony

    ironpony Minister of Fire

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    as old as it is it might not be a true mortar
    some of the old stuff was a different mix, which was softer
    and its not a good idea to mix them
    might want to get some local advice
  6. 72Rover

    72Rover Member

    Joined:
    Dec 29, 2011
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    East VA
    Stopped by the local brickyard to ask them what mortar mix (S, M, N, O or perhaps other stuff) to use in this app. The old guy behind the counter recommended a Quickrete product called Quikwall. It's a surface bonding cement already reinforced with chopped fiberglass. It's for bonding and waterproofing dry-stacked masonry, so it sounds perfect for this application. He further recommended a thin, slurry application followed by a typical, mortar-type thickness. The only drawback is it's only available in 50# sacks, probably enough for a half-dozen chimneys, but it's only $16.

    It was T-shirt weather a week ago...supposed to be back in the mid-60's this weekend. I really haven't used much wood these last few winters. Stuff I'm burning now is five years old....

    Cheers
  7. semipro

    semipro Minister of Fire

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    That's great info. I'll bet I'll have a use for that stuff. Thanks for sharing.
  8. Beardog

    Beardog Member

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    Loc:
    NW CT
    When I was doing masonry, we would use Portland cement with acrylic added in for the wash (cap). If I had to redo mine, I'd chip the old one off and use that combo.
  9. Singed Eyebrows

    Singed Eyebrows New Member

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    Home Depot has a product called Rapid Set Mortar. This is really good stuff. It's a hydraulic morter that comes in 55 lb bags. You don't need any fiberglass with this stuff. It bonds the best to a latex bonder such as Quickkrite although spraying a mist of water on will also work. You will have about 15 minutes to work it at 50 to 60 degrees. At 90 degrees you are lucky if you have 2 minutes. Once you get used to this you will be hooked, it has tremendous strength & bonding ability. You can use this for patching walls sidewalks etc. It's about $15.00 a bag. Randy

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