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I never seen such types of cracks online.

Is this particular post overloaded.

There is nothing on the deck.

Also another closest post set 10 feet away.

Any idea enter image description here

enter image description here enter image description here

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    Given its periodical exposure to the sun, have you considered given it a coat of paint or some other protection? Just to be on the safe side Commented Jun 11 at 15:53
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    @Gallifreyan good idea - perhaps an oil coating rather than paint? Maybe Boiled Linseed Oil or Tung oil or similar would help maintain the natural wood look. Another option would be a mesh frame, spaced off the wood by 50mm for ventilation, and encourage a tomato or grape vine to climb here, providing shade to the post.
    – Criggie
    Commented Jun 12 at 22:29
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    I was suggesting paint mostly to protect against the UV exposure; though there are a few transparent-ish oil coatings that protect against UV, I don't know which ones are good Commented Jun 13 at 3:31
  • Those cracks: w/e. But over-cutting the notch by like four inches is inexcusable. "DO NOT OVERCUT" chicago.gov/dam/city/depts/bldgs/general/EZPERMIT/…
    – Mazura
    Commented Jun 15 at 1:27

3 Answers 3

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Not concerning. Appears to be limited to a small section near the center (pith) of the tree that is exposed on this face of the post as cut. A side effect of the tendency to try to get the most post from the least tree in modern lumber production.

The wood on either side is solid, and this area will be shallow as well as not extending to the edges.

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  • The answer is correct, and note that these days 4x4 PT is almost exclusively made from the center of the tree, so cracks and checks are the norm, not the exception.
    – Cheery
    Commented Jun 11 at 17:44
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This is normal for wood that is exposed to the elements. The wood is constantly absorbing and releasing water. Over time, this will destroy pressure treated wood.

The pictures aren't concerning for two reasons:

  1. The wood still has some yellow to it. This deck looks to be maybe 3-5 years old. The wood likely still has lots of life to it
  2. The cracks aren't major. In fact I wouldn't even call these cracks. They appear to be surface only.

I wouldn't be concerned unless you see major cracks appear that run most of the length of the wood, or appear to be stress fractures near your fasteners (i.e. a crack surrounding a structural nail). Some cracking over time is normal. Cracks like the one below are the ones you should look out for (original source)

Cracked timber

If you want to limit this "cracking" (or prevent it on a new deck) wait until the wood is relatively dry, then apply a waterproofing material (water seal). Shouldn't deteriorate anywhere near as fast.

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    "wait until the wood is relatively dry" - not really - at this stage you want the wood to have as much natural moisture in it as possible (since lack of moisture is one of the main reasons for the cracking), so that the top coat seals that moisture in. All you really need is for the outside to be dry enough for the top coat to bond.
    – MikeB
    Commented Jun 12 at 12:49
  • @MikeB That doesn't mesh with actual instructions. Allow 30 days before applying on new pressure treated lumber. Water seal works by having the wood dry, then penetrating the pores of the dry wood that would fill with water, and filling them with the water sealer instead. Trying to use it on wet wood would result in little penetration.
    – Machavity
    Commented Jun 12 at 12:57
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    You are mis-understanding my comment. This is a very long way away from being new timber of any kind, and is severely lacking moisture to its core.
    – MikeB
    Commented Jun 12 at 13:37
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    @MikeB That's true. My point in mentioning it is you don't want to apply water seal after a recent rain (or the sprinklers ran)
    – Machavity
    Commented Jun 12 at 13:39
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The vertical cracks are absolutely no problem - they are a natural result of the wood drying out, a little too quickly. Proper treatment (eg painting) would have prevented/reduced it, but it's too late to tell you that now!

Note that this post is under a compressive load from above, so these will have reduced the strength of the post by about 0.0001% If it was under a tensile load that would be about 0.001%, and if there was a sideways/bending load it might have lost 0.1% of its strength. (Estimated figures only, obviously!)

The flaking is fractionally worse, and depends on the depth, but again, and as others have hinted, there is plenty of strength in the remaining wood - lose approx. one zero from each of the figures I just quoted.

Finally, I wouldn't expect the effects you've already seen to get significantly worse, and if the structure has been well built, you can afford to lose an entire post anyway.

EDIT: PPS I would worry if the crack has a significant diagonal component - ironically this is more likely in a better piece of timber that doesn't have heart-wood at its centre!

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    That last statement is bold. It's common for beam members to be joined over a post. Losing a post results in sag, typically, and a reduction in overall load capacity (such as in snowy regions). I get that you mean it won't fail in the short term, but that could be more clear in case someone comes along and decides they want a better view from the rocking chair.
    – isherwood
    Commented Jun 12 at 14:10
  • Given that there appear to be only two posts posts supporting that joist, I expect that losing one of them is pretty likely to be unaffordable. Commented Jun 13 at 13:29
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    Hence my final para was qualified by "if the structure has been well built". By my definition, if there is not enough redundancy to survive losing any one post, then the structure was NOT well built/designed.
    – MikeB
    Commented Jun 13 at 14:57
  • This is my definition: chicago.gov/dam/city/depts/bldgs/general/EZPERMIT/… - you could lose 3 out of 4 and it'd prob still be fine. - Problem here is the horizontal overcut for a notch that's just above a knot. Which can turn into a triangle that pops off and the thing falls down. There's also no bracket holding up the 3rd of 3 sisters which doesn't sit in the notch. And the only thing keeping it from racking is the one inch that's left of the post... Should be thru bolts x2 going into an uncut 6x6, sitting on a 1/2" thick bracket also w/ thru bolts
    – Mazura
    Commented Jun 15 at 1:35

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