I find that my fundemental techniques are really bad. So I came up with an idea; to play nothing but exercises and scales for a period of time, say a week or so.
Is that a good or bad idea?
Ted is right.
It is a very bad idea.
First of all it is doubtful that “fundamental” techniques exist. Technique is ultimately specific to the piece you are learning. As you learn a piece you will find impossible spots. These are the spots for which you do not have the technique. You will acquire it by working on these spots and by working on specific studies/exercises that address that particular difficulty. So unless you can specify which part of a piece is causing you trouble, you (or your teacher) will not be able to select an appropriate etude/way of practising the piece that will assist you in conquering the technical difficulty.
Most etudes like Czerny, Cramer, Beyer, etc. target pieces of their period or before (e.g. Czerny targets Beethoven sonatas), and they will not assist you in developing technical facility for pieces composed afterwards.
Second, scales are pretty useless as technical exercises. For a start they use mostly fingers 1- 2 – 3, rarely 4, and most scales never use finger 5. Scales are important for two reasons: They teach you a way of fingering passages, and far more important they make you familiar with the concept of key (and with the geography of the keyboard). However to get familiar with the concept of key you need to know scales, not necessarily play them (that is, you need to know which notes make up which scales).
Finally, a week is too short a time for you to see any lasting results. It is like saying “I’m really unfit, I think I am going to run 5 miles everyday for one week.”
I suggest you decide on a couple of pieces you want to be able to play (within your level of playing) and start from there. Hopefully you have a teacher who will help and guide you.
Best wishes,
Bernhard.