Yes , as a boy I watched my uncle work on the shuttering of the Shirra.

The "jams" were wooden supports for the formwork which was also made of wood and filled with wet concrete.
Quite often the shutters would collapse under the pressure of the concrete as it was vibrated.
On the later dams, steel shuttering was used ...much safer.

On all the dams in Argyll ,the vast majority of the work force were Irish, hard men who lived in camps near the "job".

McAlpines Fusileers, give a good insight to the character of the men and the conditions they endured...Ake