sticky shell?

[Liquidpoop]

Hey i got a piece of wood from either an elm or sycamore tree(im told) and hollowed it out for my russian to live in. hes been in there for like 2 days and i took him out for feeding today and there was a patch on his shell that was all shiny and sticky it didnt smell tho. do you think it could be sap from the wood it seems to have wiped off. is elm or sycamore bad for a tortoise?

thanks
dean