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I'm making a spalted manitoba maple dining table. It ranges from 5 to 11 percent moisture so pretty dry.

Each slab is 5 1/2 feet long 2 1/2 inches thick and between 20 and 21 inches wide.

Now to the issue. I have noticed a lot of new cracks. And the slabs was completely smooth and flat. These cracks have now raised the wood on their edges.

What is causing all these cracks and is it likely to happen more?

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    Welcome to WSE. Pictures and dimensions of the individual boards and cracks would help us diagnose the problem. – Ashlar♦ Apr 17 at 2:13
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    Pics would definitely be a help, but even without them just remember this is spalted wood — the material is inherently undermined by the fungal attack. So what you get is always a bit of an unknown quantity. And for a dining table, if it'll be used much and not mostly a decorative showpiece, you want to carefully check for 'punky' areas in the pattern of spalting which are reasonably common, but not always present. If you have any these will need to be strengthened if the surface is going to be durable enough for a long service life. – Graphus Apr 17 at 7:05
  • Have added 2 pictures. – Greenwood worker Apr 17 at 12:51
  • Thanks for adding pics, they help a lot. I'll be interested to see if anyone else has a different take on this, but given the nature, severity and number of cracks here I suspect these slabs were not well dried through their thickness — these are classic, textbook, drying cracks. Now thick pieces of wood are never the same moisture level throughout, but these may have been damper than they should have been, i.e. there was a lot of moisture for the wood to lose while it approached equilibrium with its surroundings. [contd] – Graphus Apr 17 at 18:19
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    @AloysiusDefenestrate, slightly surprised? A stable 5% reading isn't possible except in very warm and/or dry conditions (like Phoenix in the summer). Basically, for any reasonable room temp the humidity has to be below 25%. The humidity can be a little above this (although not much) if the temperature is much higher. – Graphus Apr 19 at 3:00
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I'll collate the info from the Comments above into an Answer on what's causing this and what to do moving forward.

What is causing all these cracks and is it likely to happen more?

These look like classic, textbook in fact, drying cracks. As they've occurred after the wood was supposedly dried it seems likely it was poorly done, either too quickly (leaves the interior too damp), or incompletely (moisture content was left too high throughout).

Now this is spalted wood, spalting being staining/colour changes that occur due to fungal action. And it's important to realise that the material is inherently undermined because, not to put too fine a point on it, this is fungal decay. And each black boundary line surrounds a unique area of fungal attack; while the wood can be quite sound in some places — with no apparent change in strength, only in colour — in others it can be soft and 'punky' (sponge-like and crumbly). And everything in between.

So what you get with spalted wood is always a bit of an unknown quantity. However, cracks of this number and severity should still not occur if the wood has been dried to a decent standard, as of course it should be if offered for sale by any commercial source.

The OP has indicated that returning these slabs isn't an option, but for future readers do investigate this route. Many woodworkers, and at a guess the majority of pros, would seek to return wood that behaves like this, or get a complete refund!

What to do now
Because the cracking seems like it's ongoing it would not be advisable to flatten the surfaces or fill right now, but instead leave the wood to settle down as it reaches EMC (equilibrium moisture content) with its new surroundings.

How will you know the wood has settled? You'll get no new cracks. This may sound like a wisecrack but it really isn't, the wood will eventually stop cracking. And it should be left to get there at its own pace. Patience is key with this sort of thing, it's hard but don't be tempted to try to stick to an arbitrary timescale.

Normally, to allow new wood that you've bought to reach equilibrium with the conditions in a home or workshop you need to leave it a minimum of a fortnight. But that's for wood of typical thicknesses, slabs take longer naturally (not just because of their thickness but also the width and length... that's a lot of interior wood volume).

'Punky' wood, and what to do about it if you find it
For anything that'll be used much and not just a decorative item it's important to locate and deal with any punky areas. Apart from the importance of durability in something like a dining table, this can actually be needed just to achieve a uniform finish — the soft zones can be so soft they're impossible to machine, hand plane, scrape or even to sand properly, so hardening them up is frequently necessary.

It's reasonably common to use superglue for this purpose especially in wood turning and for small projects like jewellery boxes, but CPES (clear penetrating epoxy sealer) is also used, particularly on larger stuff as you might expect.

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  • Thank you for the help. One more question and probably the most important. How do I fix these cracks when the wood has settled? I have a very small single car garage that's full for the most part and the basement is also small. So not much room for a large scale operation. Would hand planing then resin work or glue? Any and all help is always welcome. Thank you again – Greenwood worker Apr 21 at 0:29
  • Welcome. Hand planing is arguably the ideal way to re-flatten any of the affected surfaces, although you could do it with just sanding if you chose to/had to personally I much prefer to make shavings than dust. Re. filling, as I mentioned above we have multiple previous Q&As on filling cracks and other defects in wood. – Graphus Apr 21 at 7:23
  • I just bought a pad moisture meter reading it's better than pin style. I'm getting readings between 40 and 80 emc. Where as pin is reading between 5 and 12 still. Which style of meter is more accurate – Greenwood worker Apr 25 at 2:08
  • I've read pin are most accurate (or to be more precise, only these can tell you what's happening inside and not merely on the surface). But the thing is the specific meter may be more important than the reputation of the type in general — easy to find good & poor example of reputable tools. Obviously here the 5% reading should is questioned just on principle, never mind that the wood is clearly behaving as though it is drying out.... this might suggest that you be more inclined to believe the new readings, but the new ones are v high, plus there being such a big variation is worrisome. – Graphus Apr 25 at 7:42
  • Can either meter be recalibrated? Are you confident you're using both metres as intended/directed by the instructions — correct species selected? Pinless pressed firmly onto the surface? Pins inserted deeply enough in all reading locations (and neither in a crack)? – Graphus Apr 25 at 7:44

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