Best method to applying decals to materials, such as grime and 'leaks'

[FrankGehry]

I think adding a bit of grime to certain areas such as tops of walls, edges of slabs, etc. is a nice way to add a realistic nature to renderings. My issue has been trying to think of way to add only those decals in the chosen areas. I know the 'grime' could be part of the diffuse texture itself, but then it would repeat itself with the tiling.

Is there a way to add grime as a decal independent from the diffuse texture and specify in Sketchup which areas you wish for it to appear?

[Leslie_Stroobant]

I haven't tried it myself, but my first guess would be to draw a rectangle where you want your decal to be and texture that with the desired element. As long as you can get the opacity figured out so that only the "dirt" shows, I think should work. It's going to be a bit more work than just "stamping" it on though.
Perhaps you could do the work up front to save time later by making your own component database of grime components.

I'm curious how this will turn out, would you mind sharing a render if you try this? Good luck!

[andybot_cg]

FrankGehry Unfortunately, you're stuck with only 1 UV mapping channel in the SU model. You may be able to use a dirt map and add your grime texture there, but it won't get you the same result as manually mapping the grime texture. If you can map only the grime map and use that same UV for your texture, you can turn off repeating just for the grime and it would work as a decal. Wonder if you've made any progress since your post.

[Peter.Chaushev]

Actually, there is a a way to achieve 2 UV channels if you set up two different materials on the Back and Front geometry faces. Then you can switch the UVs of each texture between 1 and 2.

Kind regards,
Peter

[andybot_cg]

Actually, there is a a way to achieve 2 UV channels if you set up two different materials on the Back and Front geometry faces. Then you can switch the UVs of each texture between 1 and 2.

Kind regards,
Peter

Whoah!! Never thought of that, pretty clever...