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  1. #1
    Join Date
    Feb 2013
    Location
    The thumb, MI
    Posts
    54

    Default Do/Don't caulk cedar siding installed over rainscreen mat?

    I recently had my 1940's cottage sided with 3/4" white cedar lap siding (no taper) over Keene "DryWall" 3/8" rainscreen mat, which in turn is over housewrap. This type of siding & rainscreen was a first for my contractor but he seemed to enjoy the challenge & working with thick boards & fat trim pieces. He suggests not caulking the ends where the siding abuts the corner posts & window trim. His reasoning is that the breathable mat underneath gives the water a channel to escape, so caulk isn't necessary. Finish will be a penetrating oil (Sikkens SRD). This is a lakefront cottage in northern Michigan so weather can be harsh.

    What do you guys think about this line of reason? Naturally I want to believe since it takes a LOT of caulk to seal up all the edges. I'm just a little worried because "everyone else" has miles of caulk.
    In-process, showing layers:


    Done:

  2. #2
    Join Date
    Jul 2013
    Posts
    31

    Default Re: Do/Don't caulk cedar siding installed over rainscreen mat?

    Were the installation instructions for the siding?

    Gotta be careful with caulk and siding. Usually the manufacturer has specific places where it should or should not be caulked. Caulk is not a water proofing material and is never meant to be a first line of defense against significant amounts of moisture intrusion. It seals out wind and minor amounts of wind-driven rain, that's it. Siding and roofing should be put together in such a way that the structure sheds most water naturally even when no sealant is used. If your contractor said it didn't need to be caulked the only way I'd go against that is if I found installation instructions that said differently. Otherwise yo ucan indeed trap moisture that would otherwise escape naturally.

  3. #3
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,730

    Default Re: Do/Don't caulk cedar siding installed over rainscreen mat?

    I agree with your contractor. That wood is going to expand and contract with the weather, it is best to let it breath.

  4. #4
    Join Date
    Oct 2012
    Location
    Houston, TX
    Posts
    295

    Default Re: Do/Don't caulk cedar siding installed over rainscreen mat?

    Houston Remodeler has some pretty well formed opinions on this. I think he would say not to caulk, but I don't want to put words in his mouth.
    It's this old house, not this built after your dad was born house.

  5. #5
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,969

    Default Re: Do/Don't caulk cedar siding installed over rainscreen mat?

    When we do lap siding (usually ceement siding) we always place the corner trim boards over the siding and don't caulk the gaps. Houses were built 300 years ago this way long before caulking and are still standing. Dryness is the key. If the siding is butted to the corner boards you are depending on the caulking as your waterproofing. Caulking up against wood is a constant maintenance item to be avoided. The tar paper or tyvek under the siding is NOT your primary waterproofing and neither product are sold as such. That's what the siding is for, isn't it?

    With your thicker siding, I'd consider notching (on the face of the siding) in the corner boards to get a tighter fit.

  6. #6
    Join Date
    Feb 2013
    Location
    The thumb, MI
    Posts
    54

    Default Re: Do/Don't caulk cedar siding installed over rainscreen mat?

    It's also been done this way for 300+ years and caulk is relatively new--but not all new things are good.
    The cottage is done, the thick siding covers and hides the nails & trim screws used to secure the 2-3/8" thick corner posts so notching isn't possible. Maybe the corners should have been rabbeted from the start but the decision was made to avoid the dozens of spider & wasp pockets that creates.

    I don't need to ask how it's largely been the past 30 years--there are plenty of cottages around mine with cracked & peeling caulk. I guess the pertinent question for this forum would be--using the best available knowledge, do restoration contractors apply caulk to vertical butts on lapped wood siding today?

    I do know what Tom Silva would say. That man must own stock in DAP

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