Rattlecans. And get some decent caps for them from a graffiti supplier - the stock caps tend to be less than stellar.
If you don't go airbrush or rattlecans, it's a pickle. It's really important to get a good prime down before painting, and avoid primers that are watery as they will swell the mdf. Oh, and be prepared to kick yourself for not getting an airbrush sooner when you finally break down and buy it.
Definitely rattlecans, with good caps, as @chromedog says (the Citadel ones are already quite good in my view). You can get impressive gradients out of using a base color and white/black (or two other colors), by adjusting spray distance and doing short sideways sprays, from off-terrain to off-terrain. If you want to do multi-color terrain, also buy (Japanese) masking tape. But this you'd have to do with an airbrush also. Good luck! One thing to consider is that rattlecans can get expensive, if you do a lot of terrain. So if you plan to paint a lot of terrain, consider buying an airbrush nonetheless. Edit: For fine details or lines I can recommend acrylic pens. I hope I can post some pictures later.
As others have said, rattlecans are your friend. Here's a couple of Mel videos which will probably help some:
Just a few examples what you can do with only rattlecans (and acrylic pens): The japanese temple roof and wood I aged by spraying them from afar with white. Works quite well
Yes, it works well with Infinity models. It's for my Japanese table, and it's from Sarissa Precision: https://sarissa-precision.com/collections/japan-28mm/products/dojo. I may have bought it there or from my local shop. Also, just noticed that Mel is building the same temple in the first video that @jherazob posted above if you'd like some more examples. He's using a brush, though.
I also recommend rattlecans - they're easy to use and can give great results. Some additional markings with templates, some shading with washes, highlighting with drybrush, and some battle damage and you have nice buildings. I'm a minimalist when it comes to painting terrain and I usually go for easy and fast results, in contrary to painting miniatures ;) Thanks to this I have a set of painted terrain which gives me more than 1 full table with things such as this: Much more photos can be found here: https://forum.corvusbelli.com/threads/industrial-shipyard-table.552/ PozdRawiam / Greetings
Pigments can be used to shade in a gritty way. http://www.data-sphere.net/forum/viewtopic.php?p=9719 Tutorial http://web.archive.org/web/20150305...ilding-with-secret-weapon-weathering-pigments Oil or enamels if you prefer to avoid the dust. Some big flat brushes will help. Or if you go for "all concrete" look, acrylics and sponges will do. Tip 2B: cut the connection points with a chisel blade, flat or angled ("guillotine"); sometimes even the push trick can cause delamination. Tip 11: cover the tabs if the designer did not make them "part" of the model (brick ends vs a random rectangle in the middle of flat wall). Sometimes as simple as using textured paint.
