What is caulking?
Caulking is applying a texture called caulk (which is found in the common texture folder) to any faces that you cannot see. This means the game engine draws less which means higher fps and lower rspeeds (rspeeds are the number of tris on screen etc, the higher the worse) Some mappers make there maps out of caulk first entirely (I find this way easier and quicker too) and then put the texture they want to be seen on the faces. Remember that if a brush is entirely made of caulk (on all its faces) it will cause a leak. (Leak is where you havent sealed off your level from the void)
The caulk texture is found in "textures/common" — it looks like the picture in fig 1.0
Example Usage
Lets have a quick look at what I mean by caulking, lets start off by showing you a normal indoor bit of map, see fig 1.1
Here we have what the player can see, some steps a door, the walls etc. Now what he cant see is the sides of the steps and a lot more, so what we do is caulk everything he wont be able to see in game, like in fig 1.2.
I've hidden the brush on the right, (the large clipped one) we can now see where it has been caulked, anyplace the player cant see. The game engine by the way doesnt draw these parts but know they are there so to speak. And remember always caulk your maps! it means you can do more detail and means optimised maps, for optimum fps and compiles a lot faster