In order to do the next pour, the first of the two big side pieces, I need to box the mold back up again. I didn’t get the pour spout flush with the sides, however, and the tight fit of the Lego box caused me some concern. I didn’t want to take a chance that the pressure might shift the original ever so slightly.
I decided old fashioned wooden mold boards, and a slightly looser fit, were a safer bet.
Here I have sealed any gaps with plasteline and poured the plaster.
With the plaster cured, I have unclamped the mold boards. On the top is my first large side piece, then the gusset, and then my remaining rubber side (with its plaster backing).