Too much expansive clay results in uneven drying through the brick, resulting in cracking, while too much kaolinite will make a weak brick.
tˈuː mʌtʃ ɛkspˈænsɪv klˈeɪ ɹɪzˈʌlts ɪn ʌnˈiːvən dɹˈaɪɪŋ θɹuː ðə bɹˈɪk, ɹɪzˈʌltɪŋ ɪn kɹˈækɪŋ, wˌaɪl tˈuː mʌtʃ kˈeɪəlˌɪnaɪt wɪl mˌeɪk ɐ wˈiːk bɹˈɪk.