Thank you, that's it.
I should have come on this myself as I have already seen these images , when exporting to obj.

Sketch Up does not support the import of obj-files, not even the Pro-version. There is a plugin available, but it costs $79.

Hoped to find an alternative way.

By the way, I really would like to understand, why this method does not work always. Maybe I am doing something wrong.

Hello Hans,

unfortunately this is not always true. As you can see in the pictures above in my post at the top of the page, I did exactly this (assign texture in Sketchup to each surface, imported into SW3D, assign a new texture), but some textures are nevertheless distorted.

Thank you very much Ceciliabr,

I think, now I got the logic. If I am not wrong, I can es well explain the upscaling factor of 10 which I needed to get the stairs right with the red bricks. You scaled the box down to 0.2m (Factor 1/5) and used a 50% scale in the texture property (Factor 1/2). Makes ...

Hello Ceciliabr,

thank you for this explanation. I think I understood that I can not assign textures to an object with various areas, because they don't have the texture coordinates.

The workaround you proposed by building the object of many samll boxes and exporting to obj-file and importing ...

Hello Hansmex,

many thanks for your friendly offer. The point is that my model actually has 42 MB, which appears too big to send by mail.
I will have a look, whether an earlier (and smaller version) has as well that failure. Then I will come back to you.

Hello Ceciliabr,

Now I got it, very tricky [:D]

I played a little bit with your model with regard to customizing textures and additional questions came up. Hope you can answer them:

1. case:
Loading your model, marking all boxes and change texture of the selection (not with the material change ...

Many thanks for your helpful hint, Ceciliabr,

The boxes to circumvent issue 1 and 2 I already used before my post, but I must admit that I don't like this very much. If it would be only 1 or 2 times, ok, but more than 30 times is too much. I prefer to have objects (furniture and other stuff ...

any further ideas for this issue?