Thank you both for your answers Smile

I did some testing with the stewalin product...

Test 1:
  1. I mixed 100 g stewalin with 25 ml water (Like they suggest on the bag). It was thick as yoghurt.
  2. poured the mix in my 1:16 scale silicone brick mold (brick size 15x7x5 mm) while vibrating my casting table with a small sander without sanding paper on.
  3. waited 5 minutes, put a tissue on top of the mold to get rid of excess water.
  4. scraped the mold as gently as I could, but the mix thend to get dragged with the scraper leaving not entirely flat surfaces on the bricks
  5. waited ½ hour before I took the bricks out of the mold.
The result was a bit dark terracotta colored bricks, and a lot of them had uneven surface, some with small (bubble) holes - Not a successful casting compared to what I am used to with cheap danish plaster.
Weight of 1 brick after 24 hour: 1,05 g
Size: 15,4x7x5,5 mm


Test 2:
  1. I mixed 100 g stewalin with 40 ml water (Like I do with my danish plaster). It was a bit milk-like.
  2. poured the mix in my 1:16 scale silicone brick mold/mould (approx. brick size 15x7x5 mm) while vibrating my casting table with a small sander without sanding paper on.
  3. waited 5 minutes, put a tissue on top of the mold to get rid of excess water.
  4. scraped the mold as gently as I could, absolutely no dragging of the mix.
  5. waited 45 minutes before I took the bricks out of the mold (the bricks weren't quite dry after ½ hour)
The result was very close to terracotta colored brick, all bricks had very smooth and flat surface, not a single bubble hole, much more successful casting, infact better than with my cheap danish plaster.
Weight of 1 brick after 24 hour: 0,85 g
Size: 15,3x7x4,9mm

My conclusion:
The test results were based on 10 bricks from cast 1 and cast 2.
The master bricks that the mold is made from are approx. 15,3x7,1x5 mm (5 mm plastic board cut to brick size on a proxxon ks230 table saw).
Allthough I added 60% more water to the mix than stewalin suggest on the package, it seems to make more successful castings, at least with my bricks.
Test 1 does seems to be just a little bit stronger than test 2, but that may be due to an expected longer curing time for test 2.

Stewalin from Hobby Time (A swiss company called Glorex) seems to be a good alternative to plaster.
Allthough Glorex says nothing about slip casting, it may well be suited for it.
Infact Glorex doesn't really give much info about stewalin on their website or package, no technical, safety or datasheet, perhaps that's why it is impossible to find in Denmark since they would have to provide such information by law.
I did find another  product called Artelin that looks like stewalin in many ways, they provide technical information for the product.

I normally use white plaster coloring it with  concrete/cement/grout pigment powder or Tempera water colors, but could never really hit the right terracotta color, so being a perfectionist, I decided to give stewalin a shot when I found it Happy

Links:
Glorex website: http://www.glorex.com
Stewalin from Glorex product catalogue (pdf, page 111 from the index): http://www.glorex.com/Data/files/DFGB_02_technik.pdf