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  1. #1

    Default OSI caulking....to strike or not to strike, that is the question...

    Good evening,

    I've been siding some houses for a guy up here in the PNW, fiber cement horizontal lap siding. Long story short is he wanted all the caulking to be struck to smooth it out. When I caulked the siding it really looked great, but the house sat for awhile before paint and we had an interesting summer with some very hot days and then some pretty rainy/cooler days. So although the original installation of caulking looked perfect when the painter rolled through some of the joints had cracked out. I make a point of not just running the caulking over the surface of the crack but actually pumping the caulk down into joints and seams. We're using the OSI "pro series" caulking, a little bit thicker than Quad. So I've worked with crews that don't strike their caulking and I think it looks alright but striking does make it look cleaner I think. So does anyone here pre-caulk seams and joints before installing the siding so it "oozes" out from behind to be sure its filling the whole crack? Also I noticed some excessive shrinkage on field joints too. They call out for 1/8" gaps in the field and yet even when you pump the joint w/ caulking and smooth it flush with the face of the siding, give it a week and it has shrunk to an 1/8" below the original level. I like my stuff looking sharp and clean..but is the only way to avoid this by basically caulking the entire house twice basically? Perhaps if he hadn't let the house sit so long before paint would it had helped out by protecting the caulk from weather? I'm interested in some ideas on this one boys...thanks for the help!

    -Joe
    Last edited by Joester_03; 09-17-2010 at 10:53 PM.

  2. #2
    Join Date
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    I'd say that if you've got cracking happening, the FC siding was dusty or dirty when caulked. Or you got it too deep into the crack- caulk wants to be thinner in depth than width. OSI should be ok for small gaps like that though- there's a good chance that it got too much UV.

    Caulk is elastic (or, it's supposed to be). FC is going to move a lot in length- it's not like wood that doesn't expand & contract much with the grain (ie, along it's length for siding). Depending on the temperature and humidity, the cracks in the field might be flat, concave or convex.

    According to OSI: OSI Quad isn't recommended for gaps more than 3/8" deep without backer rod or less than 1/4" in thickness. Not recommended for expansion joints, including butt joints.

    Reading through their documentation, the only one recommended for butt joints and around trim, windows, doors, etc., is their EP-1000. The rest aren't recommended for butt joints.

    They do say that their sealant doesn't need to be tooled, and tooling isn't recommended. It doesn't say that you shouldn't tool it, but...
    http://www.lavrans.com

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

  3. #3
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    No, the house sitting unpainted has nothing to do with it. I resided a house with Hardie late last fall and couldn't paint it before spring. It's fine. Caulk was Quad. No issues.

    Last time I looked Hardie doesn't want you to caulk the butts in the field. Has that changed?

    I can't say I've ever seen Quad crack unless it was badly applied.

  4. #4
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    Our summer was weird this year. Unusually wet. (Probably wetter than a Michigan winter, which I assume is mostly snow) And I'm guessing the wet/dry cycling on unpainted FC DID cause more movement that "usual".

    That said, your sealant technique described is faulty. Too much sealant, and bonded on the back side (although that latter is hard to avoid in FC detailing - its more "painter's caulk, than sealant work)

  5. #5
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    If the sealant you used was one with something less than 100% solids you will get some shrinkage, that could be some part of the problem. I recommend you do not strike sealant joints which are skimpy and are subject to shrinkage. Or size the tooled joint to accept the expected movement.

    Where does the cracking occur?

    At the sealant siding interface or in the middle of the sealant?

    One is adhesion to the siding and one is cohesion as in how it sticks together.

    Then there is the issue of sealant geometry and three sided adhesion.

    Do you have any photos and a sketch of the section failure?

    BR

  6. #6
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    I use OSI Quad all the time when putting on steel siding with no problems,The guys around here are all using butt joint connectors on Hardi Plank and where they do caulk I have not seen any cracking. Some guys will finger wipe it and others will let it be a natural bead, Personally I prefer the natural bead , Quad will smooth itself out a lot if left alone.
    Randy
    ________________________________________________

    The bitterness of poor quality lingers long after the sweetness of a cheap price is forgotten

  7. #7
    Join Date
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    KY
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    I always tool caulk, I feel just a bead (not tooled) has a good chance of not bonding to the material. In the past, on repair work, a bead is always easier to remove than tooled caulk

  8. #8

    Default Re: OSI caulking....to strike or not to strike, that is the question...

    Hello,

    Thanks for your guys' reply. I have some photos of the the job, but haven't taken anything of close up caulking joints...I can do that here early this coming week. The cracking was happening in the middle of the caulking, not between the FC and the caulking. I watched this little tutorial on OSI's website about how to install FC w/ their caulking...There was 3 methods, one was w/ no caulk or flashing behind joint, one was with flashing and caulking applied to one side before the other piece of siding was installed, thus "oozing" the caulk a bit out the front of the joint. They said,"be sure not to smooth out the caulking, let it dry and then cut it flush." I think that's a little much but you know, everyone has their two cents I suppose. And lastly, it was just flashing behind the field joint. Throughout the whole house I'd say less than 10-15 field joints had cracked, and then a few places in direct sunlight/extended weather exposure sides had cracks along the seams between the corner board and FC. I've seen a lot of guys not tool their caulking, and most of it looks alright but at times in certain areas it can look lumpy, i.e. transitioning from one piece of siding to the next down a rake on the roof just for one example. So to say that the caulking was poor installation wouldn't be accurate, but I do appreciate dgbldr's comment on that one ;). I'll try out the different sealant for the field joints---this guy doesn't do the flashed field joints so they'll be caulked. Other than that, thank you for your guys' responses! Have a good night!

    -Joe

    --Oh and here are the pics, I framed this house too! :)
    Attached Images Attached Images
    Last edited by Joester_03; 09-18-2010 at 06:54 PM.

  9. #9
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    Quote Originally Posted by Lavrans View Post
    FC is going to move a lot in length- it's not like wood that doesn't expand & contract much with the grain (ie, along it's length for siding).
    Do you have any data to support that statement? About the FC I mean, not the wood.

  10. #10
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    Did you read this before installing?:
    http://www.jameshardie.com/pdf/insta...eplank-hz5.pdf

    Quote: James Hardie does not recommend the use of caulk at field butt joints. Install factory finished edges together at butt joints.

    Is any part of that statement unclear to you?

    And fill your profile so we know where you are.

  11. #11
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    Quote Originally Posted by charles View Post
    Do you have any data to support that statement? About the FC I mean, not the wood.
    Well, the simplest data proving that is the gap specified by all the various FC manufacturers.

    The next is merely rational- FC siding is a (relatively) grain-less composite product, as such it will move with heat or moisture (whichever affects it most) more along the long axis of the material than the short. This is true of most plastics and metals that don't have a grain. Grain starts to affect how a material moves- it won't all work like wood (wood is interesting in that some species move less than almost any other product, natural or man-made, that we know of; that's one reason why the better architect's & draftsman's rules have a bamboo or wood core- it moves less than any comparably priced plastic).

    I can't cite a paper off the top of my head, but if you really want it I'm quite sure I can search a few out for ya.
    http://www.lavrans.com

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

  12. #12
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    http://www.lavrans.com

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

  13. #13
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    Lavrans, I don't disagree with you but you lost me with that link. All I see there is a table that DOESN"T have fiber cement. The closest I can find is "cement" and the coeff they give calculates to 0.09" for a 12 ft length (length of a Hardie board) over 100F. Not sure that proves your point.

  14. #14

    Default Re: OSI caulking....to strike or not to strike, that is the question...

    dgbldr,

    I read the hardi specs and I appreciate the link, still I'd say here in the greater seattle area I haven't seen very many jobs done w/ hardi or any other mfg. without caulking on the field joints. I'm sure that they may work in eastern washington (desert climate) but obviously over here on the west side of the mountains we get quite a bit of rainfall. Also, on the house we're installing Nichiha fiber cement. They're specs show you do caulk the field joint. Thanks for the help though with the link, I'm going to show the head guy out here that additional information and then we could avoid the field joint caulking all together....in theory :) he tends to be pretty picky about his way, or no way :)

    http://nichiha.com/pdf/Installation%...Guidelines.pdf

    Check out Fig 4.3

    Goodnight all!

  15. #15
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    Default Re: OSI caulking....to strike or not to strike, that is the question...

    Joint Treatment
    Joint Installation Using Flashing (recommended) (Fig. 4.2)
    • The use of a joint flashing behind the butt joints is recommended.
    • Suitable materials for joint flashing include anodized or PVC coated
    coilstock and code approved weather resistive barriers.
    • The joint flashing should be at least 3” in width and long enough to extend
    above the board width a minimum of 1-1/2”.
    • Install NichiBoard™ boards over joint flashing with moderate contact.
    This is from the link you posted _03.

    Caulking the but joints is so yesterday.

    BR

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