This paper describes recent research to evaluate Gypsum plaster seal designs in the full-scale pressure test facility at Londonderry, NSW. After the Moura Number 2 Mine explosion a review of the safety of coal mine operations resulted in changes to mining legislation where ventilation control devices (VCDs) were required to be tested in an internationally recognised mine testing explosion gallery to achieve over pressure ratings of 14, 35, 70, 140 or 345 kPa. Since this disaster, Minova has live tested all VCD designs to provide validation test data for design purposes. In recent years validation and certification of seal designs has been undertaken by Queensland Registered Professional Engineers (RPEQs) using laboratory measured seal material properties as input to 3-dimensional numerical models. As an engineering material, mining plaster has properties that approximate to those of a low-strength concrete. Unlike concrete, mining plaster gains strength extremely rapidly and this makes it ideal for constructing seals where downtime while waiting for material strength literally costs money. As a result of these properties, Sprayplast UW VCDs can be rapidly brought into service as explosion rated and/or water holding seals and stoppings. Previous full-scale explosion testing carried out in Australia at Testsafe’s Londonderry Explosion Gallery (Pearson, 1999) has shown that mining plaster stoppings can resist significant blast pressures. This paper describes a recent series of full-scale explosion tests carried out at the Londonderry Testing facility in NSW, which were intended to build on experience gained from earlier tests carried out at the Lake Lynn experimental mine in the USA and at Londonderry, NSW in 1999. The testing process and instrumentation layout will be described in which each seal design was subjected to a series of explosions progressively increasing in intensity until seal failure resulted. Two seal designs at 100 and 150 mm nominal thickness were constructed and instrumented to provide time-related overpressure and wall deflection response during the controlled series of explosions in separate test programs. Suppliers worked to develop reliable engineering designs, with results of the testing used to calibrate a numerical engineering model for Sprayplast UW mining plaster that can be used to design seals for overpressures up to the maximum currently legislated in Australia. The model can also be used to design bulkhead thicknesses for water retention. In addition to theoretical analysis, this paper also considers some of the practicalities of seal location, design, construction and maintenance.