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  1. #1
    Join Date
    Sep 2004
    Location
    Raleigh, NC
    Posts
    477

    Default Caulking a large gap

    Doing an exterior paint job with quite a few windows on brick walls to do. The place is 40-ish and much of the glazing and caulk is shot, so I'm digging out old caulk along the brick moulds. What I'm faced with is often 1/2 - 5/8 inch gaps where the points of the moulding and bricks don't meet. There's no way to put a backer rod in there because it'll just fall into the cavity behind the brick veneer.


    Somewhere along the line I came up with the idea (or learned from someone) to build up the caulk across a crack like this by running a bead on each surface, allowing those to dry and continuing until the gap is bridged. I've done this in the past and don't recall it failing on anything I've checked on later, but I feel quite sure that this is a dumb move and I'm looking for suggestions on how to do this better. I'll be doing 20 windows and I don't want a big liability.

    Thanks,
    rP

  2. #2
    Join Date
    Jan 2007
    Location
    Louisville, KY
    Posts
    3,771

    Default Re: Caulking a large gap

    They make some pretty big backer rods that won't fall into the cavity. I've used some up to 1.5" round. They compress pretty good and you can work them into deep areas like you need.

    Some sort of backer is the only way imo. What about some spray foam?
    Louisville Exteriors
    Professional Installers of:
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  3. #3
    Join Date
    Jun 2004
    Location
    Martinez, California
    Posts
    14,887

    Default Re: Caulking a large gap

    They make backer rod in lots of different sizes, it takes a lot of knowledge to know how to size the sealant factoring in the width and depth of the gap to be sealed, the dissimilar materials come into play as well in sizing sealant. Don't touch this, hire a professional sealant contractor, I've testified against a lot of contractors who have tried to apply their own sealants causing leakage, mold etc.
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    “It is not an endlessly expanding list of rights —the “right” to an education; the “right” to health care; the “right” to food and housing. That is not freedom. That is dependency. Those are not rights. Those are the rations of slavery – hay and a barn for human cattle.” - Alexis de Tocqueville

  4. #4
    Join Date
    Dec 2006
    Location
    CA
    Posts
    1,971

    Default Re: Caulking a large gap

    low expansion foam then caulk

  5. #5
    Join Date
    Jun 2004
    Location
    St Louis, Mo for the past 25 years
    Posts
    7,490

    Default Re: Caulking a large gap

    I run into that often on all the brick home we have here in St Louis. I have resorted to doing like you said with multiple passes of caulk. I often use a variety of backer rods to do the jobs. On my ladders I may have a bucket with a couple of diffent sizes because one size may fit one spot but not the next. Even with the backer rod you may still have to do a multiple pass on the caulk.

    For me the backer rod really just does as you say. Keeps me from trying to fill up the entire area with caulk.

    Have tried the foam gun approach but you still need to let it cure before you can caulk so it is another trip up the ladder to do the work.

  6. #6
    Join Date
    Mar 2006
    Location
    Seattle, WA
    Posts
    11,339

    Default Re: Caulking a large gap

    This is another case of needing to know your sealant and your tools. Backer rod is, I think, pretty necessary- multiple pass winds up with very different thicknesses of caulk that can fail for a number of reasons. There's also the question of whether the caulk you're planning on using will work for that wide of an application.

    There are a number of good primers on caulks, and the manufacturers give recommendations on the use of their caulks (that also tend to be part of their warranty requirements).
    http://www.lavrans.com

    "He uses statistics as a drunken man uses lamp posts; for support rather than illumination." -Andrew Lang

  7. #7
    Join Date
    Mar 2005
    Location
    Montreal
    Posts
    328

    Default Re: Caulking a large gap

    A couple of suggestions.

    Bridge the gap with 3/4" J-trim. The short leg sits on the brick mold, the long rests against the brick.

    If you have a bender that can bend down to half inch ( the lower limit for my Tapco) bend some
    profiles that look like an upside down lower case "h" or a high back chair. The back of the "chair"
    rests against the brick mold with the legs on the brick. I like to use double sided tape to hold things in place.

    In both case you end up with no gaps, therefore no need for backing rod, and with two thin caulk
    joints. IMO, the joint looks neater and is more durable.



    Mark

  8. #8
    Join Date
    May 2009
    Location
    Kent UK
    Posts
    3,152

    Default Re: Caulking a large gap

    a few notes of caution regarding risk

    low expansion foam is a good suggestion. high expansion foam can cause window casements and doors to bind.

    fire foam MIGHT be required if your codes demand it. fire foam is generally high expansion, so build it up in layers

    foam isnt waterproof, dont leave any part of it exposed
    Limey Carpenter

  9. #9
    Join Date
    Jun 2004
    Location
    Bellbrook. Ohio
    Posts
    1,741

    Default Re: Caulking a large gap

    I will occasionally hire a caulker to come in and caulk brick to Dryvit or gaps in general over 3/4", they always use backer rod and urethane caulks. When it gets to that level it can get messy if someone did not know what they were doing.

    Its really something that someone could earn a living just doing caulking but they can.
    -Dan

  10. #10
    Join Date
    May 2009
    Location
    Kent UK
    Posts
    3,152

    Default Re: Caulking a large gap

    on civil engineering works here, bridges, sea walls and ultility works, caulking is always done by subbies

    mainly because this type of work requires the structures to have 30+ years maintainance cycles

    back to building, like ohio says there are a smattering of firms who do caulking as their core business
    Limey Carpenter

  11. #11
    Join Date
    Jun 2008
    Location
    Montana
    Posts
    187

    Default Re: Caulking a large gap

    Quote Originally Posted by retro-patrick View Post
    Doing an exterior paint job with quite a few windows on brick walls to do. The place is 40-ish and much of the glazing and caulk is shot, so I'm digging out old caulk along the brick moulds. What I'm faced with is often 1/2 - 5/8 inch gaps where the points of the moulding and bricks don't meet. There's no way to put a backer rod in there because it'll just fall into the cavity behind the brick veneer.


    Somewhere along the line I came up with the idea (or learned from someone) to build up the caulk across a crack like this by running a bead on each surface, allowing those to dry and continuing until the gap is bridged. I've done this in the past and don't recall it failing on anything I've checked on later, but I feel quite sure that this is a dumb move and I'm looking for suggestions on how to do this better. I'll be doing 20 windows and I don't want a big liability.

    Thanks,
    rP
    Retro,
    Just thinking outside the box here and genuinely trying to help. What about the many chinking products typically used on log homes? Worked on several of these structures with their unique finish dilemmas the last couple years and was amazed at what the chinkers could do. Log chinking could span at least an inch and a half when well troweled and seemed to stay in place despite seasonal change and log shrinkage/expansion.
    Namaste'
    sawick

  12. #12
    Join Date
    Sep 2004
    Posts
    5,889

    Default Re: Caulking a large gap

    Quote Originally Posted by Ohiobuilder View Post

    Its really something that someone could earn a living just doing caulking but they can.
    We have at least one caulking specialist that specializes in caulking houses to commercial standards. He's always busy. Lots of commercial guys doing it, it's a good business.

  13. #13
    Join Date
    Aug 2009
    Location
    PCFCA, NorCal
    Posts
    79

    Default Re: Caulking a large gap

    Gary Katz covered this in his roadshow that I attended last Saturday. You definitely want to use backer rod behind the caulk with any gap and especially a large one. The thicker part of the caulk should be where it adheres the other materials and where it needs to stretch should be thinner.
    Not sure if my description makes sense but I'm sure someone can provide an example. Dick's picture shows how it's done right.

    -Steve

  14. #14
    Join Date
    Sep 2004
    Location
    Raleigh, NC
    Posts
    477

    Default Re: Caulking a large gap

    The problem I have is that the shortest distance is between the point of a brick and the outer edge of a brick mould. In order to get a backer rod in there to stay in place it would have to as big around as a tennis ball. but fit through a 1/2 crack.
    I talked to the owner about adding a bit of aluminum, and even discussed getting the mouldings wrapped by a metal man, that way it's out of my hands... also going to ask around about a caulking specialist in the area. I assume we have many of them, just never met one. Regardless, considering the warnings, I will see about getting this thing out of my hand.

    rP

  15. #15
    Join Date
    Sep 2004
    Location
    Raleigh, NC
    Posts
    477

    Default Re: Caulking a large gap

    On the other hand, I rather like caulking - maybe I should study and specialize???

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