Guys/Gals

I have an old pre-frabricated garage, which is made up from pieces of
concreate. Over the years, it's started to leak through the gaps in
the concreate slabs which make up the walls. Instead of forking out 5
grand plus for a new garage, I was going to attempt to seal the walls
using an external waterproof sealant (Thomson waterproof concreate
sealant, etc) and for the gaps, something like UNIBOND waterproof PVA.
I was going to attempt to use a foam product (don't know which one)
but I think the gaps are too small.

Does this sound plausible?

Any advice would be helpful.

Freddie