The one way that works for me is to paint the brick colour on with enamels, and let it dry nice and hard, a minimum of 48 hours, preferably longer.

The mortar is then added using water colour paints from a little jar, where the paint is a kind of slightly soft lump of solid matter, which dissolves into paint when a wet paintbrush is added. I normally mix white with umber and perhaps a bit of grey. The mortar mix is painted on all over the brick surface and allowed to dry. Because it's water-based, it can always be softened and removed with more water. I would never use acrylics for mortar in this way, as they dry too quickly.

To remove the mortar from the surface of the bricks, I get a nice, soft white linen handkerchief, wrap part of it around my index finger, and wet it from a pot of clean water. I then dab most of the moisture off the material again, and then using the damp end on my index finger, I wipe away the water-based mortar colour from the top face of the brick work. One thing I will say, is that you pretty much need to move your index finger to a clean part of the handkerchief each time.

A clean handkerchief (and, if applicable, an understanding partner!) is essential!

I'd add a photo of an example if I could, but I don't know how to do this on other people's blogs, sorry!

Personally I don't think you are too far off in the third photo. The mortar on the bricks is in my opinion not a problem but an advantage, because it tones down the red for convincing distance viewing.

Captain, to post an image here it has to be already on the web. If it is, then right click the image, click copy, and then go here and paste directly into the comment box.

Hi, thanks to Mikkel, I can now post photos in my reply to your blog entries!

Here is a photo of my scratchbuilt shunters cabin, made from Slaters embossed brick plasticard, painted using the methods I described in my earlier post, and using water colours for the mortar. The building is currently far too clean and will eventually get some weathering before being finally positioned on the layout.