I know the problem well. The problem comes because the dimond segments are glazing over in the harder material. You will find drilling through the breeze block (which is very abrasive) wears away the metal matrix that hold the diamond, exposing fresh diamonds to do the cutting (you can feel them). unfortunatly the bit wont last very long in really abrasive materials.
When you hit hard brick (which isn't very abrasive) the exposed diamonds wear down but the metal matrix doesn't so you don't have anything to do the cutting (the tips will be smooth and getting hot - if you carry on forcing it, the braze holding the tips on can melt or if welded, the steel can distort/crack).
Solution 1. When it stops cutting in the brick, re-dress the tips by making a cut in a spare breeze block, you will be able to feel, with your finger nail when the segments have "opened up". You'll be able to cut a bit more in the brick then. Cut a bit - re-dress, Cut a bit - re-dress, Cut a bit - re-dress, etc. you should get through it eventually.
Solution 2. Buy a more expensive bit with a greater cutting range, Abrasive - Hard. Cheap ones may say general purpose, but they wear out quickly in abrasive materials and won't cut hard materials well. They are useually good for cured limestone concrete in the middle of the range.
Solution 3. Buy one specificaly for Hard materials just to do the brick
If the segments are "opened up" you should be able to get through re-bar.
Hope this helps
Andy
I've just re-read, You are hiring? Go and test the HSS customer service, they should have info about diamond cutting in the shop, they should be trained to advise, they should give you the right tools for the job - but you have to tell them what the materials are.
