Mnemonics - can they impede learning?

[Cortina]

We don't have spelling tests in school but when my son has had spellings he's brought home (mistakes he's made in his work) I've taught them to him via mnemonics. We use initial word mnemonics as they begin with the targeted word.

Wondering if I would be better off teaching 'spelling rules' if I know what those are?

Thing is we chant the following and once they are in his head they stay there. 100% success rate. He also draws pictures to help him remember:

house - house on upper slope explodes
thought - thought how old uncle got home tonight
through - through his roof old uncle goes home
there - there he enjoyed running everywhere
their - their houses end in rows

And so on..

[lovecheese]

We use some for "tricky" words which don't follow the rules of phonics eg. because; but I would think it , personally, important to know the rules of spelling as you say - ough, igh, ight etc because you can't remember a mnemonic for every word! That's just my thoughts as a mum, I'm not an expert!