When a SketchUp model has a lot of textures you want gone, use the textures tool to delete all textures in one pass — first install the 3dshouse dynamic plugin.
The important thing most users miss: SketchUp’s native cleanup (Window > Model Info > Statistics > Purge Unused, or Purge Unused in the Materials panel) only removes materials that are NOT assigned to any geometry. Any texture currently painted onto a face, group, or component is “in use” (marked with the small white triangle in the Materials panel) and Purge will simply skip it – so purging never gives you a truly clean, paint-free model. The textures tool is for exactly that case: it strips every material, applied or not, in one pass.
A related gotcha: deleting geometry does not delete its material. The definition stays in the file in case you reuse it, which is why a model that looks empty can still carry dozens of textures bloating the file size. And because purge cascades, removing unused components first frees the materials those components held – but applied materials still stay put until you clear them deliberately.

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