+ Reply to Thread
Page 1 of 2 12 LastLast
Results 1 to 10 of 14
  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
    30

    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
    1,418

    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
    249

    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
    2,503

    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

  7. #7
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,503

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

    Butted seams get caulked. Not much other way around that.

    Well actually the parts should not be touching, but instead leave enough of a gap to get a decent bead of caulk in there and not just on top.

    Expect to repair the caulking on a regular basis, with the side of the house with the most sun and weather taking the brunt and needing more attention than the shady side.

  8. #8
    Join Date
    Jan 2008
    Posts
    1,327

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

    Butt joints caulk unless they have something waterproof behind them which will carry the water that gets on back out safely below. This includes butted corners. Houston is right in that there needs to be space for that caulking, but you also need to take into account that caulking loses it's elasticity when it's too thick- instead it will pull loose under material contraction because it won't stretch as easily as it is supposed to. For that specification you need to read what your caulking manufacturer says about it, which may mean that you need backer rod to maintain the specified thinness.

    Were this my project, I would use 60# felt tabs under the running (wall) joints with no caulk, the same material about a foot each way at the corners, both just under the siding, and I'd caulk the corners just for safe measure. This will allow for breathing as well as water repulsion with as minimal caulking as I'd feel good having in place- the best of all worlds. It seems that this would be a retro-fit at this point so there may not be much point in our responses. It does look good anyway, and lake-front property is always in short supply!

    Phil

  9. #9
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,418

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

    I am going to be a little more emphatic this time, ABSOLUTELY NO CAULK. Sorry about the yelling, but no one seems to understand how the underlayments on this cabin work. The rainscreen product vents the back side of the siding and the tyvec under that is to prevent water from getting into the framing. See this link on the rainscreen:

    http://www.keenebuilding.com/residen...een-020-1.aspx

    If you put any caulk on the wood, you will inhibit the woods ability to breath. You can stain the wood, but use a product that allows the wood to breath, yet still shed water as much as possible. You could also treat the wood with a sodium borate solution such as Timbor or Boracare. You would have to treat it annually but it is easy enough to do, mix it up and spray it on with a garden sprayer.

    If you caulk the wood, then moisture could build up behind the siding and start to rot it out. Then the caulk will split and crack creating gaps for water to get in and little pools to hold that water in.

    Your contractor appears to have done a great job on the exterior of your cabin, listen to his advice. He know what he is doing.

  10. #10
    Join Date
    Jan 2008
    Posts
    1,327

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

    Keith I DO understand how rainscreen works, but I also know that the siding is there to keep the water out, and that small areas of waterproofing behind it and on the endgrain will not substantially inhibit the ability of the wood to breathe. If this were not true, then all of the traditional wood sided homes would not exist today, and since they obviously do there can be no wrong in my approach. And while Tyvek is waterproof, it is not designed to be the primary water barrier on a home and it is not rated for such use- that's what siding is for and that can't happen if the siding installation is not in itself reasonably waterproof. You are intentionally allowing water under the siding and I don't think that is a good idea at all.

    You're sold on something with a much shorter track record and quite frankly I am a hard sell on anything lacking a track record which is not 100 years old because I expect the homes I build to last at least that long. Come back around in another 3/4 century and then let's see what has happened in the interim. Till then you're buying into what I feel is another engineered unproven product which has more than one important aspect of it's purpose totally overlooked in it's design. I'd bet you don't see that other ones. Newer is not always better, and as often as not it turns out to be worse than the well-proven traditional ways.

    Phil

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •