Need tips to add dirt and weathering to a build

I mostly enjoy building houses and I can make some decent builds. Now I want to improve the realism of my builds with some additional touches, such as weathering and dirt. I want to take my texturing skills to the next level.

Let's say I have a house where I want to add some dirt and weathering to the external walls. I always build in-world, so I don't have a 3D model of the house. What I need is to have some map of the facade that I can use as a reference in Photoshop but I am not sure on how to proceed with this. Take a snapshot of the house? Then what? How do I keep things in scale?

Can anyone kindly share some tips? Thanks ...

hl2 textures have a few dirt and rust textures that are mostly transparent and widely spread fullperm insl.
i bet youtube has tutorials on how to add dirt to something.

What you'll generally have to do is export the textures that you intend to weather, add weathering effects externally in Photoshop or your favorite image editor, and then re-import and apply the altered textures. The big problems here are you end up either using a lot of textures, or having the same dirt patterns visibly repeating; and you have to be extra-careful about adding dirt at the edges of a seamless texture, so it remains seamless. But done right, the effect can be stunning.

Alternatively, if the walls are a 24-bit texture, you could put a 32-bit "dirt only" texture on a thin prim, with transparency over all of it except where the dirt is to be, and add that prim just in front of the "dirty" surface. Apply a 100% alpha texture to all sides of this 'dirt prim, other than the one that shows the dirt. This adds to prim count, but allows the "dirt" to be randomly placed and intermixed, and even to easily cross seams between prims. I use a similar technique to put "decals" of complex painted signs onto shiny surfaces of a build. For an example of this "decal" trick in use, go to the SE corner of the RUCE 1 sim, and look at the yellow food vending trailer, and the several food vending trucks nearby. A lot of the graffiti and painted-on signage on the sides of those vehicles are 'surface decals'.

Thanks for the answer, Ceera. Yes, this is what I try to do. What I am looking for are suggestions on how to have a visual reference of the building I want to weather so that the dirt goes under, say, the window sill and not applied randomly.

I have found some interesting suggestions posted, I believe, by Chosen Few or Robin Sojourner - can't remember - in another thread here in the forum. One suggestion was to recreate the model in 3D. I may explore that path but not for now.

Another suggestion is to apply a test pattern to all the prims that need to be weathered. So, this is what I am trying as I am typing this post:

I apply Chosen Few's test pattern texture to all the prims of the facade and align it with a texture alignment tool (not necessary but fast and practical). Then I take a snapshot of the facade, save it to the disk and open the file in PS.

I crop the image, use the vanishing point filter to correct the alignment and resize so that my reference map is of the exact size to accomodate the texture I want to use for the facade, repeated n times horizontally and vertically. In my case, that would be a 512x512 texture repeated 3 times horizontally and twice vertically.

That should make a pretty good reference map. At this point I just need to add the texture I want to use on x layers and start to work on each of them.

You are right about having to use a higher number of textures but that is also true if I had to use decals, with the aggravation that I'd have to use a higher number of prims too. I realize decals would be of a small image size, so there is a benefit with that.

On the other hand, having a reference map would help making me more aware of the exact size of the textures I need to use, rather than just randomly apply 512x512 textures as I do now.

Folks, please send further suggestions on how to improve the workflow. Thanks!

Thanks Ollj, I'll look into that.

I already see a benefit on using the test pattern texture. By more carefully looking at the size of the squares I have noticed that I can apply the texture twice both horizontally and vertically.

highrez snapshot to hard drive possible or snagit software. as far as weathered i use good old
gausian blur with transparency and then differing layers of colours on diff layers till it looks natural. i try and use a referance photo or picture and i always trust my eye rather than being to technical, i also only use my good old pen and pad with textures, not my mouse.

Rub snot on your monitor...

One way I like to do things like this:
Attach the job to your HUD. Build and texture there with many prims and shadow, dirt, whatever. Snap that. Small touchups and finishing, bump map some bits. re-import. They look like they grew in SL.