But isn't L1 on the left of the image and L2 on the right, then wrap the alu over the right half of the transformer.
Here's some food for thought, in Nuclear Acoustic Resonance during beta decay aluminium is used to shield against fast moving particles, but if heavier metals are used then it possible for the fast particles to cause Gamma radiation & xrays, i hope that's right anyway, Verpies warned against using heavier metals.
Also note that in the transformer picture that it appears that L1 looks thicker, this is not so, with L2 he has pulled the woven fiberglass sleeving tight to make it longer and have less diameter, he's probably done this to get more turns for L2
I would try to get some of that sleeving from an electrical shop because it will affect your windings spacing and therefore change the transformers operation quiet a bit. i think it's sold by the meter
, you will note on the diagram that both L1 & L2 are both using the same thickness wire.
It maybe worth videoing yourself building the transformer and put that up on youtube and post a link to it on Akula's feed, he may pipe in and say whats wrong.