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Curling at ends of fiber cement boards (C) InspectApedia EDFiber Cement Siding Curling or Lifting at Joints or Ends
Causes & prevention of fiber cement siding curl-up or lifting at board ends

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Curling or Lifting Fiber Cement Siding, Causes & Preventive Measures:

This field report of fiber cement siding lifting or curling complaints describes movement or curls observed at butt joints or at vertical trim abutments in Nichiha 1/2" thick fiber cement siding. The observation of this condition on several homes and in installations of various levels of workmanship and analysis of site and material conditions suggest that differential moisture in the material is an important factor in siding curl or lift problems.

This article series describes the types of problems that occur in fiber cement siding shingle & shake installations in North America, including fiber cement shingle shrinkage gaps at butt joints, cracks, breaks, and loose or buckling shakes. We describe various fiber cement siding complaints: open butt joint gaps, buckled siding, loose siding, nailing failures, moisture effects, and we include opinions, field observations, and research on the causes & effects of these conditions



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Curling at Butt Joint Gaps in Thick Fiber Cement Siding

Curling at ends of fiber cement boards (C) InspectApedia ED

Note: the reader-comments appearing at points in this article were provided by a reader whose siding is further illustrated and discussed at SIDING, FIBER CEMENT SHINGLE-BOARD DEFECTS - Troubleshooting gaps, breaks, peeling, bowing, loose fiber cement siding: causes, remedies. Nichiha Fiber Cement products, performance & warranty field report.

[Click to enlarge any image]

This looks a little like curling, as much as a 1/2" board could - but more definitely end effects rather than a whole board phenomena. I was only speculating -- attached are two photos [of 1/2" thick Nichiha Fiber Cement siding] that seem to lend some support the idea though.

Imagine two cement fiber boards with unprimed cut ends lying end to end on a floor in a lab. Make sure the ends "butt" up against each other -- touching with "moderate" contact. Say we put a few screws in the boards towards the middle to secure them in place to the floor. Through some magical laboratory radiation process we cause the butted ends of the boards to warp or bend upward. Say initially the first inch of the board(s) and then all the way to your 6 inches.

Looking down from above at the point where the boards meet a gap will appear and get larger. Its a visual gap from above -- but its not due to any "shrinkage" of the board.

The gap resulted from the "lifting" the ends in the Z axis, not due to separation in the Y axis. Anyway -- don't know anymore what my point here really was?

But if in the field this kind of thing is happening just on the ends over a whole lot of temp/moisture cycles who knows ... maybe phase one is unseen and expansionary in the y axis, there's board movement, pushing on adjacent boards, pushing on trim even, nails loosen ... and you end up with a permanent physical gap not a shrinkage gap -- or sometimes the stair step effect I've seen -- before moving on to the actual buckling phase which requires deeper saturation.

Note that my installer told me everything was "tight" at installation. And I believe him because the east and north sides are still tight with no gaps at all. -

E.D. 12/15/2014

Probable Explanation of Fiber Cement Board Siding Curling at Butt Joints

Curling at ends of fiber cement boards (C) InspectApedia EDYou are describing a gap that appears due to buckling or curling ends of the boards - limited perhaps at its upper end by the overlap of the next course of siding.

But in the photo at left there are wide open butt joints at board ends combined with a lifting or curling of the boards away from the building wall. There is also no visible compression damage at the board ends. This fiber cement board lifting and curling is almost certainly a different pheonomenon.

Indeed I can imagine that if the board ends are getting wet - you might see curling - this is a different phenomenon than the main butt joint gap shrinkage problem that I and everybody and his uncle usually talk about.

It's a new one to me, and surprising, more so in 1/2" thick FC material. I suspect this particular manifestation may be related to the thicker Nichiha Fiber Cement products and to a moisture differential across the board thickness, probably related to moisture uptake on the board's inner surface.

On the FC clad buildings I've examined the buckling was not focused on ends of boards and the gaps were between boards that more or less remained in the same plane.

Perhaps you've described a "new" product complaint. Certainly I"m doubtful that such a condition will ever heal itself.

Before moving on to examples in wood boards or wood flooring (given below), it's worth noting that these two roofing material "curls" have different etiologies and different manifestations. Indeed one can arrive at a credible explanation for the curling fiber cement board ends in your photos by study of causes and manifestations of curling on other building materials.
See FISHMOUTHING ASPHALT SHINGLES
and also
see CURLING ASPHALT SHINGLES for examples of moisture differential-related curling in other building materials.

OPINION: The cause of these curling ends of fiber cement boards seen at the butt joints is most likely the result of water passing behind the siding, entering at the butt joint gaps or water entering behind the siding at other building leak points such as improperly-flashed window or door tops.

Water entering at the butt joint where the curling is observed may be sufficient to cause this warping. But also, water entering the wall at butt joints or other openings higher on the wall may show up as a cumulative effect that would explain why there may be more curled or lifted siding at butt joints lower on the wall than higher on the same wall with the same exposure.

When the back side of a board is set and sun hits and dries the exposed side the board curls towards the dry side. This is true for wood products but also for some fiber cement products.

Where a fiber cement siding butt joint occurs the board ends are more exposed to wetting than along the un-cut length of the board. Possibly the combination of that increased water and the presence of the combined curling-lifting force of two open board ends is more able to overcome the resistance offered by the next lapped course of siding above. As well, the lower portions of these boards are more open to free movement.

In addition, the board ends are mechanically less-constrained against curling than the center portions of the same fiber cement board product.

Fiber Cement Board Curling due to Moisture Differential

Fiber cement siding with factory-primed ends curling (C) InspectAPedia E.D.

[Click to enlarge any image]

Above is a photo of curling extending back more than 1.5 feet at either end of the butt joints of an un-cut, factory-coated board all of whose surfaces were installed intact. This photo is discussed in more detail
at MOISTURE ABSORPTION into FIBER CEMENT SIDING

I've looked closely at uneven material drying and curling for other materials.

Additional forces at work here besides the sources of movement: differences in moisture and temperature across the board thickness, are the compressibility of the material and elasticity of the fiber cement siding material. Wood boards, once cupped due to moisture effects tend to retain that cupped set even after the boards are uniformly dry. That's because the wood cells in the concave side of the cupped board have been compressed.

We'd need to see material test data for fiber cement but it seems obvious that fiber cement, even products containing wood fibers, should be less compressible than wood. So one would expect to see the curling increase and decrease as wall moisture conditions vary. This is in fact what you reported.

See WOOD CUPPING vs WET SIDE
and
see BARK SIDE UP or DOWN on DECKS & STEPS?

I theorize further that this problem may actually be worse for thicker FC boards than for thinner products - surprising the manufacturer who thought that thicker boards would resist buckling or curling. The explanation is that in a thicker board there is more opportunity for a significant moisture gradient across the thickness of the board - it dries out more slowly and more unevenly than a thinner board. So the curling forces overwhelm the resistance of the thicker material.

Dargontina (2007) questions the benefits of going to a thicker fiber cement material.

Reader follow-up:

Look at the photo under the window -- of the short section of cut siding. A definite bowing up at both cut edges.

Looking at other boards, even whole boards with both ends factory finished -- they appear to be trying to do the same thing.

If they are well restrained at the corners, as they appear to be in the close up photo -- there appears to be curling up at the lower corner and/or possibly an upward slope to the whole bottom of the board. - E.D. 12/17/2014

Curling Nichiha Fiber Cement siding at butt  joints (C) InspectApedia E.D. Curling Nichiha Fiber Cement siding at butt  joints (C) InspectApedia E.D.

[Click to enlarge any image]

Reply:

Are you thinking, even slightly that since you see up-bends on factory primed un-cut ends that perhaps the water is entering through the board surface and that what I call curling is occuring more noticeably at the ends because they are less constrained?

To be clear we both want to find the best data rather than wanting to be the one who was right. - DF

Reader follow-up:

Yes - I am helping you win and me lose a case of cheap Mexican beer.

A small price to pay!

The bowing at the ends is seen again here in third board up. With more of a curl in the lower right corner if you see it from the side. - E.D. 12/17/2014

Curling Nichiha Fiber Cement siding at butt  joints (C) InspectApedia E.D.

Reader follow-up:

I propose this is simply mechanical bowing due to expansionary heat forces. Nothing to do with moisture.

Why this board and none of the others? All must have at least one cut ends. In this section there appear to be no butt joints. This board because he just cut it a little too big and jammed it in there. Nothing to do with water.

In fact, although it may be an optical illusion -- if you look closely at the board immediately above -- it appears to be bowed slightly in the opposite direction with the center rising a bit. Maybe. Although for the most part you might expect the confinement of the sheathing to always force the bowing at the ends outward. - E.D. 12/19/2014

Reply: comparing thermal expansion to moisture expansion in fiber cement siding

Curled or "buckled" fiber cement siding (C) InspectApedia ED

[Click to enlarge any image]

The effects of thermal expansion in FC siding are small in comparison with those attributed to moisture up-take.
See FIBER CEMENT COEFFICIENTS of EXPANSION

From the rather distant perspective of your photos (and still more distance as the crow flies), these instances look to me like curling up board ends that are not in contact with one another - they look very different from Doggett's expanded crushed FC panel sides that are visibly damaged and that remain either in contact or very close together, and not curl-lifted over the field of the product.

I think these are very different phenomena.

We could make a more reliable assessment of your siding by a very close examination of the board ends, both under a stereo microscope and a high powered microscope. (When you remove some siding save some of these for mailing to our forensic lab).

If the effects you see on your home were from expansion and compression we'll see that plainly at the board ends. One can see it in Doggett's photos even macroscopically. More sophisticated core cuts across the thickness of the curved or curled FC boards may also show, under the microscope, both the composite differences attributed to the Hatcheck machine production process, and possibly delamination and curling associated with moisture uptake.

Remember that the effects of moisture expansion are much greater than thermal expansion in FC products. And if a board is wet before installation it is in expanded condition and will principally shrink after installation - thus the butt joint gaps with ends showing no compression effects that one would have seen had there first been expansion.

Distinguish Fiber Cement Gapped & End-Lift or Curling Board Ends from Rippled Fiber Cement Siding

Other investigators and owners have reported rippling and uneven siding board lapping at fiber cement siding boards installed as a single board (no cuts) butted tightly beween vertical trim on buildings.

That rippled FC siding may be caused by board expansion from moisture, thermal effects, or both. A forensic examination of such walls would probably sort out the roles of leaks, mositure, tempearature, and installation nailing and board tightness against trim. - zumBrunnen (undated).

It appears to us [DF] that there are these distinctions between curled end-lift at fiber cement siding and rippled fiber cement siding

Curled Fiber Cement Board Ends vs. Rippled Fiber Cement Siding Boards [1]

Field Installation Observation Curled FC Board Ends Rippled
or Warped
FC Board lengths
Comments
Appearance on wall

Board ends curling, lifting away from wall sheathing, butt joints wide open, no visible compression damage at board ends,

Appears at both factory-sealed board ends and in un-primed board end cuts

Ripples throughout board length; appears in boards installed as single unit between vertical trim abutments and in wider wall expanses where siding was installed with no or too-tight butt joints.

 

  Curling at ends of fiber cement boards (C) InspectApedia ED [Photo requested] [Click to enlarge any image]
Defect visibility Varies depending on extent of board end lift or curl More apparent in oblique lighting, harder to see in shade  
Time first observed Undetermined Undetermined  
Butt joint gaps Open, often more than 1/8" Tight, closed, to opoen less than 1/8" Omission of gaps at or too-tight butt joint gaps is likely to contribute to buckling or damage when thermal or moisture-related expansion occurs in the product.
Butt joint flashing Absent Undetermined The omission of back-flashing at butt joints creates a high risk of water penetration into the building wall system and risks back-wetting of the fiber cement siding.
Butt joint sealant Absent Undetermined  
Vertical trim abutment Undetermined or varies Tight  
       
Geographic locale Coastal San Diego Atlanta GA Possibly other LOCALES
Location on building More apparent on sun-exposed sides All building sides  
       
Product properties 1/2" thick Nichiha Undetermined  
       
 
Suspected Cause(s)

Moisture differential across FC siding material

Moisture or water penetration in wall;

Thickness of the fiber cement material may be a factor.

Compression from thermal or thermal + moisture expansion.

Tightly-installed FC siding;
Under-sized or no but joint
gaps

Water penetration behind siding may be a contributor to both defects.

Improper nailing may be a contributor to both defects.

See SIDING FIBER CEMENT COEFFICIENTS of EXPANSION

Notes:

[1] Table development is in process. CONTACT US to comment or contribute. InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information provided free to the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website.

[2] Rippling fiber cement siding is described by

  • zumBrunnen (blog), "Fiber Cement Siding - Part 1", zumBrunnen Building Consultants, Inc., Plaza 400, 5881 Glenridge Drive, Suite 110, Atlanta, GA 30328
    Main: 404.601.4050 Email: info@zumbrunnen.com Tel: 404-601-4040 Website: http://zumbrunnen.com/

[3] Curling fiber cement siding board ends are described at SIDING, FIBER CEMENT CURL / LIFT DEFECTS

In explaining rippled FC siding zumBrunnen, an Atlanata GA (USA) building consultant offers:

Unpainted plank ends –cut ends need to be either painted or treated with caulking. The manufacturer’s written instructions call for painted ends. It is our opinion a bead of caulk is substandard to painted ends. Some of these caulked joints will fail and these unpainted planks will then be exposed to wind driven rain and ice, and can deteriorate from the moisture. If this occurs and causes material damage, we would expect the manufacturer to void his warranty.

1/8” gap not provided – the 1/8” gap is not a requirement for the material warranty but a best practice. This comment is contrary to manufacturer’s written instructions. We are concerned that if gaps are not provided, thermal expansion will contribute to the warping and rippling that we have observed around the site. If this occurs and causes material damage, we would expect the manufacturer to void his warranty.

Warping and rippling of planks – this issue remains unresolved and an answer is forthcoming - zumBrunnen Building Consultants, Atlanta GA, (undated) cited in detail at REFERENCES

Bottom line on causes of fiber cement curling or lifting at board ends

OPINION: We suspect that curling or lifting problems at the board-ends of fiber cement siding are the result of the combination of the following factors:

  1. Fiber Cement Siding Moisture Differential across the thickness of the fiber cement siding causing curling towards the dry or more warm side of the material. Expect to see differences in the extent of FC siding curling or lifting on building walls with different exposures, with more significant curling occurring on sun-exposed walls and on walls more exposed to driving rain or ocean spray.
  2. Fiber Cement Siding Moisture entry into the siding, probably from its back side, typically due to leaks into the wall system at open butt joint gaps, at improperly-flashed or un-flashed butt joint gaps over the field of the wall, at improperly flashed or sealed window or door head or side trim, or omission of sealant at vertical trim abutments
    See
  3. Fiber Cement Siding Nailing errors: failure to terminate butt joints over a wall stud may be a factor in explaining lifting or horizontal lapped board siding curling or lifting ends as the board ends are not asfirmly secured by nailing only into wall sheathing.
  4. Fiber Cement Siding Temperature effects may play a role in curling or cupping FC siding as well but we suspect this is a less significant factor.
  5. Fiber Cement SiIding thickness: because it is apparent that there is likely to be more moisture variation across the thickness of a thicker siding material this curling lifting effect in fiber cement siding may be more frequent where thicker siding materials are installed, such as Nichiha's 1/2" thick fiber cement horizontal board lap siding.

Minimize these effects by following the manufacturer's installation instructions with particular care in flashing, sealing, and in avoiding the installation of FC siding if it is wet or at high moisture content.

FIber Cement Siding Manufacturer Contact Information

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