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Caulking/Painting incorrect(?) Hardiplank Fiber Cement Siding Installation

Caulking/Painting incorrect(?) Hardiplank Fiber Cement Siding Installation


Old 09-13-08, 06:05 PM
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Caulking/Painting incorrect(?) Hardiplank Fiber Cement Siding Installation

Howdy, I'm a new homeowner trying to get a few things wrapped up before winter (coming soon in Vermont).

Our house is only a bit over a year old, but the previous owner never finished painting/caulking the Hardiplank Color Plus (pre-painted) fiber cement siding. Many of the field cut ends of the siding weren't primed or painted at all, both at butt joints between two pieces of siding, or where the siding butts up against window or corner trim. After a year of exposure (including a winter), there's slight deterioration of the Hardiplank at those untreated ends.

Also, the former owner did NOT add any sort of flashing behind each butt joint, as is recommended by James Hardie. The joints are spaced about 1/8" apart, rather than in direct contact (I know that's fine for caulking). Since there is no flashing behind, I'm assuming caulking is required to keep water from going through the cracks.

I'm trying to figure out the best way to finish up the job at this point. I was hoping to be able to get some primer and paint into all of those gaps, but I tried tonight with a very small brush and it seems pretty much impossible. Will caulk alone provide enough protection on those untreated Hardiplank ends? Anything else I can/should be doing?

Anything different I should do on the siding butt joints vs. the joints with trim pieces?

Is actually acceptable treatment to leave the field cuts unpainted and rely on the caulk to seal them? The install instructions do seem to leave that as a possibility:

"CUT EDGE TREATMENT: Caulk, paint or prime all field cut
edges." Also, under ColorPlus section: "Terminate non-factory cut edges into trim where possible, and caulk."

I know I may be over-thinking this, but I'm just hoping to do the job right to get the maximum durability I can out of the siding. Thanks much!
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Old 09-13-08, 06:15 PM
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Clarification: Is caulking-only on the joints okay?

Just to clarify, the primary question is whether just caulking those field-cut joints is sufficient, or if I really need to try to get some primer/paint in there. I talked to the local dealer today, who advised me to try to paint them before caulking. But... I'm getting all sorts of varying info from different sources.

At this point getting a sufficient amount of paint into all those 1/8" gaps to have much effect seems unlikely, so I'm hoping just caulk will do it.

By the way, the caulk I bought is DAP Dynaflex 230, which seems to meet the requirements James Hardie specifies (ASTM C920, elastomeric, permanently flexible).
Old 09-13-08, 07:13 PM
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Welcome to the forums!

I've not painted much hardie board but I would think just caulking the joints would be sufficent - it would certainly be easier

The advantage to priming a cut first and then caulking is the substrate won't try to suck out the liquid out of the caulking causing it to possibly fail sooner - not the best explanation but the best my feable mind can come up with
I would think it would be more of a problem with wood than with hardie board........ and it would be difficult to coat the entire cut edge once it's installed.
Old 09-15-08, 07:21 AM
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Am not relying on any but my own experience.....

Do not like DAP caulk for that purpose....

I have done bunches of hardi siding and found PolyseamSeal adhesive caulk works best, never have had any splitting or cracking with it unlike my experience with DAP products,,,paint any caulk......if you don't paint, dirt will collect on top of the caulk and it will eventually look "dirty" .......I think it just works itself in when you clean it periodically.

Do not spray to clean,,,,,,,use bleach or soap and auto brush..........

Good Luck

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