sbuild for experimental

[Lorenzo <plorenzo@disroot.org>]

Hello mentors,

I would like to upload a package to mentors targeting experimental,
however:

my existing experimental chroot is broken beyond repair after
sbuild-update; when I try to create a new one I get

# # sbuild-createchroot  experimental
/target/dir/experimental-amd64-sbuild

[...]
I: Target architecture can be executed
I: Retrieving InRelease 
I: Checking Release signature
I: Valid Release signature (key id
4CB50190207B4758A3F73A796ED0E7B82643E131) I: Retrieving Packages 
I: Validating Packages 
I: Resolving dependencies of required packages...
I: Resolving dependencies of base packages...
I: Checking component main on http://deb.debian.org/debian...
E: Couldn't find these debs: build-essential apt usr-is-merged fakeroot
E: Error running debootstrap at /usr/bin/sbuild-createchroot line 438.

If I build on unstable chroot I get a lintian error
E: mplayer changes: distribution-and-experimental-mismatch

Suggestion? 
Is there a way to build in a sid chroot and upload to experimental?

Lorenzo