FYI Non-portalable textures
been meaning to post this.
from http://kenjara.wordpress.com/
Select the entity tool (Shift+E)
On the right in the entity object box scroll down to weapon_portalgun
Click in the map to place it!
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How to make walls unportalable: -
Create a new brush
open the texture browser and search for no draw
apply the no draw texture to the brush
select the brush and press ctrl + t
change its class to func_noportal_volume
place it in front of a wall that you dont want a portal to be made on.
This entry was posted on Saturday, October 13th, 2007 at 2:37 am and is filed under Computer Gaming. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
nice
I am convinced there is a way to make walls not portable without using the entity. And that doesn't include new tools being released.
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And some people are convinced that the world is run by a flying spaghetti monster who manipulates reality with His Noodly Appendage.
Just sayin' .... 
Well, considering I made a test map a few days ago with metal walls that I couldn't put portals onto, it's clear it atleast can be done.
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I know what you mean. In Hammer I managed to get some Portal textures to show up as not pink-checkers for a limited time, but now I find myself unable to repeat it under the same circumstances.
Clearly this form of mapmaking is equal parts voodoo and skill.
I use a different method, which desen't create that twirl when you try to make portals.
First, build your map. Then, group all the brushes which are non-portable. Turn them into a func_illusionary. Then, Shift+drag them to make a copy. Apply the glassbreak texture (filter glass + break), and turn it all into a func_brush. Choose the Texture render mode with Render amount 0. Place the new func_brush over the func_illusionary so what they are in the same spot.
You now have walls which, when attempted portaled, will make the falling particle effect like in the official game.
Now THAT'S thinking with portals!
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Nice 
I haven't done any maps yet as I don't have HL:DM, this is the first Steam game i've purchased so I think I need to wait for the official
SDK before I can actually map.
Unless someone has suggestions on what I can do without ever having
downloaded/purchased any other Steam games.
Looking at a portal materials .vma file, we find
{
"$basetexture" "Metal/metalwall_bts_002a"
"$surfaceprop" "metal"
"%keywords" "portal"
"%noportal" 1
...more stuff...
}
The line %noportal is either 1 or 0 depending on weather you can put a portal on the material. Reading Valve's development wiki, it says that lines starting with a % are directives for the tools only, and are not loaded by the game. From this we can assume that blocking portals is done somewhere in the toolchain, either in Hammer or most likely the new BSP program, once we have access to the updated SDK it should happen to our maps as well.