I you soulcasted a tree into stone would it float

[Lesser spren]

Would air replace the matter of would there be microscopic hole in the stone

[Dunkum he/him]

short answer is it isn't clear from what I can see digging through the WoBs.  I did see this though:
 

Quote

Tortellini (paraphrased)

Since I started the thread about outposts and stone bridges, I felt like getting some input there.

Brandon Sanderson (paraphrased)

Brandon told me that single highprinces could not erect outposts because due to the superior mobility of the Parshendi—they would overwhelm any small outpost quickly. Soulcasting stone bridges is also not plausible. Apparently, they would need to first get the wooden bridge out there, then soulcast it and then, since the stone is heavier than the wood, they would have to reinforce it, e.g. with ropes. These could then be cut by the Parshendi, so it would not help at all. Dalinar with his mobile bridges is on a better track in his opinion. He did say however that several highprinces working together could easily establish outposts in the Plains. He said the competitive nature of the Alethi was doing them a huge disservice in the war and that if they would work together, they could have taken the Plains long ago.

Alloy of Law Manchester signing (Nov. 23, 2011)

 

which suggests that stone soulcast from wood is going to be heavier than the original wood was.  but there were also other WoBs that said soulcasting mostly conserves mass. and yet another suggesting that the process of soulcasting is a bit more complicated than it looks and potentially involves multiple reactions happening.  so just clear as mud

[Honorless he/him]

Reminds me of this video by Kurzgesagt:

But I don't think Soulcasting is a molecular transformation. It's part of the matter-energy-Investiture conversion. So the wood turns into perfectly normal stone with the same volume, maintaining the same shape (though the shape can also be changed)

Edited May 16, 2021 by Honorless

[Lesser spren]

10 hours ago, Honorless said:

Reminds me of this video by Kurzgesagt:

But I don't think Soulcasting is a molecular transformation. It's part of the matter-energy-Investiture conversion. So the wood turns into normal stone, maintaining the same shape (though that can also be changed)

That's why I wrote the question