A couple of days ago I ballasted the "yard" area of the scrapyard on the layout.  Almost immediately that I started, I was not pleased with the result: 

It seemed to me that it was going to be a lot of work, waiting for the ballast to dry, painting - more drying, then weathering... So, after a bit of weathering, I decided that when the glue dried I would simply tear up the ballast and start again (this is where using latex glue saves the day once more, folks!)

It took just a few seconds to peel off the ballast the next day and then a quick brush around with an old toothbrush, followed by a blast with the vac and, like an archaeologist, I'd revealed something hidden under the yard!

The card that I'd used to nicely level the surface of the yard had remained in situ, and due to the seeping through of watered down black paint, had taken on a murky, splotchy, grimy - scrapyard appearance!

Unfortunately, I couldn't actually use said card.  The corrugated metal fences around the yard were fixed using a right angled strip about 1mm, so I originally added the card to level up the ground to the same height as this plastic trim, with the ballast gone the strip was visible again.

So today I added another (larger) section of the same card over the first, I weathered it simply by painting on watered down black paint and then adding random splodges of the same mixture - and I'm really pleased with the results, it looks just like mucky old concrete! 

The lesson I have taken from this is, if you have a nagging feeling that something isn't right - don't be afraid to literally "rip it up and start again!" (You never know what you might find!)