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  • Caulking Hardiplank

    I have a follow-up question to an earlier post which sparked an interesting debate (see link below) on Hardiplank installation techniques. I'd already specified 100% acrylic caulk per instructions from the Hardie rep, but was thrown for a loop when the painter came by the other day to check out the job and asked me if I wanted him to caulk the underside of every board, as he said he often does that with fiber cement.

    I knew the gaps at corner boards and at butt joints should be caulked but was not anticipating caulking below as well, although there are some boards here and there that don't lay tight to the ones underneath that might benefit from some caulk. But aside from aesthetic considerations and possibly a need to keep the ladybugs(more every year in these parts) from cramming themselves into every gap during their annual autumn homecoming, is it necessary to caulk those areas? Seems to me that caulking under every single plank would trap any water that happened to get behind the siding and keep it from draining out.

    Much obliged for any comments on this.

  • #2
    Re: Caulking Hardiplank


    I remember going to a lecture sometime ago where Joe Lstibrek from Building Science Corp. was presenting a study that was looking into whether or not retrofitting insulation into a wall cavity could cause the paint on the siding to fail.

    You maybe wondering what this has to do with caulking the underside of clapboard as you describe above...let see if I can help.

    One of the important dynamics (the other being the sun)that I remember him describing of how moisture gets into and behind cladding is what he called "capillary suction". Water is literally wicked/sucked up (defying gravity) between the overlapping siding because the gap between the clapboards was too tight!

    A little illustration - if you put a drop of water between two pieces of plexiglass and slowly pull the two pieces apart you get to a point where the drop cannot span the gap between the two pieces because the surface tension is not great enough to hold.

    The gap is not very big but significant in your case because the painter is suggesting trying to close it. Maybe for asthetic reasons, maybe to keep out ladybugs or maybe to try to keep out water (that is the purpose of cladding right - to shed water?) What I learned from Joe many years ago is that there are always a couple of ways to attack a problem. In this case you can try to keep out water by perfectly sealing the outside surface (are we ever perfect - forever?) or you can build some resiliency into the cladding system by designing a ventilated rainscreen or the cheaper version - (Hardie is going to love this!) use round headed blind nails like they did in the old days which keeps the clapboards a sufficient distance apart to negate capillary suction.

    In the paint peeling situation Joe L. suggested going to an old time paint store and asking for "painter's wedges" (I think that's what they were called) and sure enough I did and they had them. He said to drive them up between the claps on the south side of the house and the paint would stop peeling (after we changed the drying potential of the wall by adding insulation) - I did and it worked beautifully.

    Another example is all this debate about "vapor barriers" (I have posted recently on this). In some situations Joe L. would suggest instead of trying to keep moisture out of a wall asembly just change the temperature of the first condensing surface so that it always above the dew point - no condensation - no water - no problem!

    Hope this is helpful. I am interested in what others will say...


    • #3
      Re: Caulking Hardiplank

      I believe the answer is that you should NOT caulk the planks along the horizontal edge.

      Actually, you should probably follow manufacturer's recommendations but its been my expereince in the last several years that the manufacturers either don't know anything about their product performance or are too scared of getting sued to say anything.

      I recently chastised someone on this forum for driving nail heads flush because the manufacturer recommned that the bottom of the nail head only contact the surface so as to not fracture the outer surface of the cement board.

      I have since come to the realization that this contractor's method was probably superior to manufacturer's recommendation. In such cases where I believe the manufacturer's recommendations are not good, I have always advised contractors to seek out the other suppliers and find one with recommendations that you can live with. In my own personal experience of late, that is difficult too.

      Not following manufactueres recommendations opens the contractor up to a lot more liability much like doctors when they decide to do what is best for you instead of what the AMA says is the proper protocol. You're out on a limb.

      It's a tough decision these days trying to decide what to do.

      To answer your question more specifically, I do not believe water can climb the 1 1/4 inches it would have to climb to rise up between the minimum overlap as recoommeded by the mfg.

      Also the September issue of Fine Homebuilding had some very nice details on how it is best to caulk corner boards.

      We also followed Harie's recommendation on caulk(one of them) and found the product to be unsuitable. We used a different product by the same manufacturer after some testing, which wasn't on their list but performed much better. We couldn't understand why. A few weeks later they added it to the list.

      In short they don't care how you caulk it or what you caulk it with, so long as you buy the planks and don't call them if you have a problem.

      You should also note that Hardie and others go out of there way, to be as vague as possible about installation requirements. They state that you should select and follow the sealant manufacturer's suggestions for caulking. This is to sidestep most of the liability exposure I believe. Problem is, it is not possible to follow the caulk mfg recommendations and caulk the butt joints of two planks on the same stud. Go figure.

      Nail guns are another issue.

      And all of the fastening issues take on a serious hue when you are building in 110 mph design wind like we have here.



      • #4
        Re: Caulking Hardiplank


        Why have you changed your opinion about flushing nail heads? There was a recent recommendation, somewhere on the forum, to use round head siding nails to hold the lap away from the lower plank for drainage. I see four problems with flushing the nail heads: 1) fracturing the skin on the planks, 2) Interfering with gravitational drainage, 3) creating a capillary pathway for water to wick up, and 4)(last and not least), the potential liability you incure when you do not follow manufacturers' installation instructions.

        Glenn, you surprise me -- please explain yourself.


        • #5
          Re: Caulking Hardiplank

          I really havn't changed my opinions. I've just become ambivalent and perhaps my eyes have been opened a little more. I'm still concerned about the liability. AS I said, It's hard to decide what to do.

          My last job with Hardie Plank was completed last week. I sat and watched a sub do part of the work for a day, then me and mine did the rest. Since we had just had a forum thread about it, I paid particular attention to every move during the entire three days, and worked with it myself. Here is my response in sequence.

          1. I have found that inspite of what you try to do someone is going to fracture the skin in a large number of places anyway. You can't repair it well unless you drive the nail below the surface. Also,think, about it - you fracture the skin on the butt end when you cut it off to the proper length. That is repaired with caulk. So that seems to be the appropriate way of fixing the nails when the skin is broken i.e. drive it in further and skim it over with caulk. Down side is the possible loss of fastener strength which can be countered by adding more fasteners.

          2. I don't believe that gravitational drainage is an issue at all. As hard as you can fasten it would not make a noticable difference in the drainage plane as long as its not caulked.

          3. As I stated before, I do not believe wicking can occur in this application over a distance of 1 1/4 inch minimum lap.

          4. You are wide open for liability. That's bad. But you're on your own anyway if the workers fracture the skin.

          One last comment. In the light of my own observations the last 25 years, I am forced to conclude that you cannot accept the recommendations of any manufacturer at face value.

          Are you familiar with the fiberboard case in Florida where the manufacturer blamed the contractor for the failures, then sent their own crews to reside a large number of homes (the right way) which failed again?

          ONe of my clients was a synthetic stucco manufacturer. We went back and repaired several failed homes the "proper way" and they failed again. Five years later, I know why.

          I have just completed two room additions. I believe my customers can do zero maintenance and not have any problems for 10 years. I say this inspite of the fact that the windows in one are real cheap (the customers choice) and going to leak like hell. I've made provisions for that. The same is true with the doors. Have you ever used the Sto Sill? What a great thing that is - basically a window/door pan with a false bottom so the frames don't sit in the water intercepted by the pan which drains out the front. (This creates a new problem though - potential for green stuff growing under the windows.)

          The quality of window and door manufacturer is in the toilet -- even some of the better ones. But that's another day. While it seems that all my workers think they are as good as any, I am shocked at what I have seen after a few years of actually working with them at ground zero. (Save this quote.)

          Your comments please.



          • #6
            Re: Caulking Hardiplank

            If you look closely at the Hardiplank literature, breaking the surface of the board with the nail head is acceptable. As I view their drawing, a little past flush with the nail head is still considered acceptable.

            Using the nail head to hold the next course away from the one below may be a workable concept for drainage, but the literature also indicates that face nailing of the boards is also an acceptable application method.

            I think I have to agree with Glen that the manufacturer's primary concern is to be sufficiently vague to cover their corporate asses. This becomes more clear when one contacts their "tech reps" with specific questions.

            Our practice here (S. Texas, where we don't have to consider the more serious environmental hazards as some of you must) is to not to blind nail at all, but to face nail and to set the nail head just deep enough for the painter to putty each hole. We do not ever caulk the horizontal joint. We do this nailing with nail guns using fasteners that meet all size and shape requirements, but not stainless nor hot dipped galvanized coatings.

            Personally have only a few years experience with this method, but know others with 6 - 7 years on some installations. Thus far no failures of any kind.

            Knock on cement/fiber?

            My opinion; worth price charged.


            • #7
              Re: Caulking Hardiplank


              It is undistputed, common knowledge in the Building Science field that water can easily (not even under extreme conditions) move 1 1/4" up the overlap. The raging housewrap and moisture penetration debate is based heavily on this fact. Here is what Paul Fisette from UMass's Building Material and Wood Technology recently writes about the issue (I have included a link to read):¿Capillary suction is a strong force. Even under conditions of light or no wind pressure, water can be sucked through seams, cracks, joints and upward behind the overlaps of horizontal siding. Add to that fact, most wood siding is not back primed, so its backside sucks water up like a sponge. The face of wood siding is usually painted. When painted wood absorbs water, it takes a long time to dry. Paint holds water in. As a result, wet siding is held tightly against housewrapped sheathing in most homes."

              Although the fiber cement product won't act like wood and soak up backside water like a sponge it certainly can act as a capillary to water with a pressure difference acting as the driving force and deposit water on to the housewrap/felt underlayment and/or exterior sheathing to cause problems. One must take a positive action to negate the pressure differential (like a ventilated rainscreen or increase the gap between the courses of siding) and it isn't caulking the joints which is moving in the wrong direction...

              IMHO - Voiding the warranty on your siding because you "broke the face of the siding with the nailhead" is much less of a concern then severe moisture problems behind you cladding system (remember the class action suits???)

              Would you agree?
              Thoughts anyone else?




              • #8
                Re: Caulking Hardiplank


                I do not believe that you are totally correct about the capillary action in the case of clapboard. Water can get past the wall at the seams but not on a wholesale basis - it might slip up through a discontinuity in some caulk at the corner of a window but you are not going to witness capillary action down the complete overlap of clapboard siding. It is not physically possible and I don't think that is what Paul meant.

                I believe that water can be sucked in by negative pressure under some circumstances (different than capillary action), but not between most of the overlap.

                Water can be blown up the overlap by wind but it would take a hurricane force wind to blow water up that high. We like to lap flashing etc at least 4 inches for this purpose but for siding we leave it at 1 1/4 or whatever the mfg recommends as a cost saving measure. Windspeeds above 70 mph are infrequent enough to not cause a problem.

                I believe that the facts would support that it is possible for water to climb more than 1 1/4 inches due to capillary action, but when you have a capillary 30 feet long, for example, its not going to happen. The water will go hozo before it goes up.

                The bottom line is that I can't think of a reason why one would caulk the overlap of clapboard siding. In fact, I think it would be detrimental to do so because it would limit drying of moisture that is going to leak in through smaller gaps.

                This has nothing to do with the debate on housewraps. Water is going to get through clapboard siding and a drainage plane is necessary. But water is not going to roll off the planks and roll up the inside of edge of the overlap on a wholesale basis.

                Actually I think we agree and at least come to the same conclusion, which is don't caulk the overlap.

                I think that Kelly may have the best approach from a technical point of view but he is wide open for a law suit if something actually does go wrong. It takes a lot of guts to do it different than the mfg recommends. I was also opposed to nail guns until I saw what happened all day with the hand drives.

                All said, I still do not recommend doing something different than the mfg suggests. Its too risky from a liability point of view. In this case, I'd have to say that if the mfg suggested methods do not work, another product should be used.

                Personally, I prefer brick and conventional stucco, or stone if available. My last two siding jobs were Hardie Panel, and Hardie Plank.

                Its better than Masonite, and T1-11, and LP Innerseal, but . . .



                • #9
                  Re: Caulking Hardiplank


                  What brought you from Brick and Conventional Stucco to fiber-cement anyway? Monetary constraints certainly can't be worth the liability exposure given the wholesale failures of fiber-cement roofing¹ (yes, I know -- HardiShake and HardieSlate seem to have been immune, but it really makes me wonder).

                  ¹ Permatek, Cemwood & Cal Shake (or were these just West Coast products and you "Right Coasters" haven't been affected?).


                  • #10
                    Re: Caulking Hardiplank

                    Thanks to all for the informative input. Based on your responses and my research I'll avoid caulking the overlap joints, though on large gaps under the porch where no water will ever get to the planks, I may allow them to caulk sparingly. Am even skeptical about caulking there, however, as it may look odd for some areas to look seamless if adjacent areas have the thin gap at the overlap.

                    You mentioned you found a caulk not on the "approved" list that worked better for you and which subsequently was added to the list...would you mind telling me what brand that was?



                    • #11
                      Re: Caulking Hardiplank

                      Having worked for CertainTeed (vinyl) and James Hardie, and now LP, all in R&D & applications, I found all your comments very interesting.
                      I don't recall JH recommending caulking the horizontal joint (and I did their current installation sheets). I know I received a call about it. Realistically, after applying the two coats of premium paint required you've effectively plugged some of the joint anyway. Now you're back to that capillary action issue, which I agree is a viable problem.
                      Speaking from the vinyl side, the vinyl industry has always maintained vinyl as not being a weather-resistant barrier. No siding really is - not even brick or stucco (EIFS anyone?). The best defense against infiltration of moisture to where it can do real damage (inside the wall) is good construction methods including flashing around openings in the wall, and inside/outside corners. Don't try to create the impervious wall, as many of you have already stated it won't last forever.


                      • #12
                        Re: Caulking Hardiplank


                        I don't think anyone in this thread stated that JH recommended horizontal caulking as you imply.

                        Glad to know who wrote the installation instructions at JH. There are a lot of problems with it, some of which I have mentioned.

                        Tell me, are mfg more interested in good practical application technicque, or supporting the marketing program, or protecting your legal rearends. What is the relative weight of these three when you are writing installation instructions??

                        When you call for technical information, you can never get a straight answer on anything. Yes, a generalization but largely the case.



                        • #13
                          Re: Caulking Hardiplank

                          Hi Glen,
                          Sorry for the misunderstanding - that I'm aware of, JH has never recommended caulking under the laps been a requirement to correct installation as to do so would be a product kiss-of-death in time consumption alone.
                          The verbage of the installation instructions themselves predated my time there, although I did try to clear them up. Unfortunately there were other branches involved with the final wording. Marketing groups do get their fingers in there. For the most part, they're flipping the bill for it, so they rightfully get some input. The ruling code person also gets heavily involved as the printed instructions are followed exactly during independent testing per ASTM. Legal confirms that.
                          Concerning the installation manuals I've been involved with past re-illustration, I've always pushed for the clearest, most common sense approach. I've seen countless field adaptations that work, but haven't gone through any ASTM testing for verification - protecting legal rearends applies here. I suspect you know, to do so would get quite expensive and take months per test.
                          Each company I've worked for has supplied inside training to the people answering the phones in basic techniques, but to really know application you need to spend time in the real world. Most won't take the time, nor are expected to.



                          • #14
                            Re: Caulking Hardiplank


                            The layout of the installing instruction is excellent. The copy is the problem.

                            Contractors use a lot of Hardie Plank here now. We were the geographical start of the EIFS problem, and brick is too expensive in many cases. I have had some recent/current experience with both hardie panel and hardie plank.

                            The biggest problem with the plank is that you must nail within 3/8" of the edge in order to have any hope of catching any stud. (On new cosntruction you can double every third stud or turn it sideways, on remodel you are stuck). Even then it defies most standards for fastening other materials that are even less brittle. Sealant mfg who are referenced in the caulking spec, usually require that the sealant joints be 3/16 - 1/2" to accomodate typical frame structure movement yet this is impossible with a panel on a single stud. In other words if you follow HP instructions you are either going to butt the panels together or leave an 1/8" gap depending upon whether you listen to the salesman or read the instructions. HP's sealant spec is a reference to the sealant mfg.. The sealant mfg requirement cannot possibly be met, so you are out on a limb. Then, HP rep comes by and says butter the joint with caulk and butt it up hard against the adjacent piece. A joint like that is doomed to fail although most remodelers think it is better (less gap to worry about sealing). So what do you do? (no need to answer)

                            We decided on 1/8" gap using OSI Quad, or NP-1 neither of which are latex which everyone seems to think is best. I find the shrinkage in the latex product to be excessive and less tolerant of movement.

                            Then there is the issue of breaking the skin with the nails. No matter what you do, somebody is going to do that. Kelly mentioned somewhere on this forum that he overdrives and caulks over the heads. I condemned that then later supported it after I did a little observing and testing on my own. But the mfg is not going to back that approach. They havn't tested it or a host of other possibilities because of the costs, as you say. All said, the bottom line is that the product is really not ready for market, and more capital is needed for testing.

                            Absent this a contractor can only do his best and hope and pray until the liability statutes play out. That is 6 years here on new construction. In some states, its as high as 20 years.

                            If you try to do good work as a contractor, you stay poor. If you don't care about quality and are willing to take chances, you can remove a lot of overhead and do pretty good until some lawyer finds a way to take money out of your pocket and put it into his which soemtimes is unfair.

                            These are the things that bother me about mfgs of building products - most of them. They take chances make money in high volumes and can afford better lawyers. A builder takes chances and either gets lucky or screwed. At my age, I'm am no longer willing to take the risk. I don't have time to start over.

                            Thanks for you input.



                            • #15
                              Re: Caulking Hardiplank

                              Hi Glen,
                              You hit it on the head! One of the main reasons I left JH was because I simply couldn't believe in the product. For one, cutting it creates silica dust, a known cancer causer. Then, as you mentioned, are the "proper procedures" that are practically impossible to achieve. F-c panels shrink with age in testing I've seen. Having to place a nail no closer than 3/8", but yet driven into the stud is virtually impossible. It’s just too easy to break out the ends.

                              I'm surprised at the caulk manufacturer's 1/2" outside gap tolerance. I never talked with them directly. They must really be trying to sell caulk.

                              Unfortunately those who rarely, if ever touch actual job sites make the decisions that make yours and my life most difficult. I blame the bean counters and legal departments for calculating "acceptable loss" vs doing the right thing from the start. The history of big business is full of examples of that.

                              Whereas shoddy installers shouldn't be allowed the luxury of making it big, quality installers shouldn't have to work so hard to make a living. I could never make a living being a contractor, buy I fully understand their plight (I have many friends that are). My whole focus on design is making products that help the installer. Unfortunately its sometimes hard to make Marketing, Sales, & Manufacturing understand that's what its all about.