Weld Command and UV map

[gap]

The "problem" is the UV map coordinates is a vertices attribute, not a material one. So, by welding you are removing one of the two matched vertices from a face (like in my sample) - I think that could be the problem (but I can be wrong)

I see, it makes sense

You probably will not smooth the object, so if you don't mind to have some extra and tiny faces close to the weld region then you could try to extrude a short amount the face that will be welded. But, use the Weld [RMB] and set the tolerance to a shorter value.
I'm not sure it would work, but you could try.

No, I won't smooth it, it is a model I am creating for a videogame, but I want its geometry to be as clean and simple as possible. All in all, I think I will keep the duplicated polygons unwelded, or I will weld them using ModTool or MeshLab.

Here is a quick preview of the model I am working on by the way. It is the now destroyed old lighthouse of the Île de Sein, in France. My question applied to the railing and to lantern rooms's metal framework



Thank you for your feed-back anyway, I appreciate it