Thank you, I wasn't sure anyone was still interested about this topic after this time.
I grew up right next to the Dalen Portland Cement factory, and is now living next door to the remains of the Christiania Portland Cement factory, so the concrete ships have always interested me.
Anyway, I have another couple of bits of information I've uncovered - no concrete evidence, however.
I have providence placing PD93 Cretehive and PD45 Cretecamp firmly in Iceland in 1926.
In the book "Norske islandsfiskere på havet" (Norwegian icelandsfisherman at sea) by Kari Shetelig Hoveland - published 1985 the following is noted:
In 1925, after the death of Steffen Staalesen, his estate was sold out, including the herring factory at Hesteyri, Iceland. Included in that factory estate is :
"5 herring steamships, 2 barges made of iron and concrete. "Cretehive" 1000 tons and "cretecamp" 950 tons, with steam kettels and machines".
It's furthermore noted that the icelanding trawling company Kveldulfur (managed by Thor Jensen) bought everything, lock stock and barrel.
I haven't been able to follow up from there, though. My icelandic is not good enough to make progress.
That only leaves Creteground of the barges in iceland.
In the Lloyds registry of 1945, she's listed as the property of JW Robertson in Lerwik, Shetland. He's noted as a man of many talents, also for having bought two concrete barges from the admirality in 1920 - [www.scapaflowwrecks.com
On that very same list, Creterampart is also listed as his property.
He had at least one more concrete barge - The Naja, sold back to the admirality and used as a blockship at Scapa Flow in 1939. I had hoped this was Creterampart, but alas. Dimensions are listed as 35 x 10 m, which rules that out.
I also came across a line of crete colliers, most of whom went to Oran in Algerie - Cretetell, Cretecoal, cretecoke and Cretacite. Let me know if that's of interest.