In the last couple months I've been creating custom molds from RTV Silicone.
I started with a small mold of shields, and then some custom bases.
Finally I progressed to larger molds of the HA fieldstone and cavern floors.
I've come to the conclusion that, if I didn't have kids, I would stick strictly to the HA materials because I like to custom-do most things to suit exactly what I want. However, with two kids under 5 running around there's just not enough time to devote to it (sucks that I'm also a perfectionist). So I'm going to buy a few sets of Dwarven Forge and see how that goes. I'll let you know how I make out.
Overall I love the HA molds , and building etc but part of my larger gripe is that they are too bloody small. It takes eons to have enough of anything to build your shit. That's just the reality. So, in order to change the situation I recommend learning about and creating your own molds (from the outset) from the HA blocks (Bruce Hirst doesn't have a problem with this) to increase your block production.
Also, I took a few of the single floor blocks and carved out some puddle pits - to later puts some drops of resin water after painting etc (pics shortly).
You can see from the pics below I used lego blocks with a bead of Aleene's Tacky glue along the edge. Don't chince or you will have leaks and waste material. I find that glue takes an overnight to dry. I also glue down the pieces with the same glue. I use the small lego blocks 1x2 or 1x4 to ensure equal spacing inbetween.
Before and after you mix and pour your RTV you need to make sure your surface is level or you will have a lopsided mold and that will mean headaches when you pour it later.
I use the motor from a baby bouncy chair to power my shaker table - works great. Leave that on until you don't see anymore bubbles rising. You can see a few bubbles in the next pic.
The last two pics are of my molds in action, one devoted to cavern floors and the other to fieldstone floors.
This is the basic process. If you have questions fire away. I use Mold Max 30 and Excalibur diestone plaster.