Plaster of Paris - Basic Techniques


Plaster of Paris is hemihydrated calcium sulphate. On adding water it solidifies by an exothermic reaction into hydrated calcium sulphate. All patients placed in POP (including backslabs) should be given verbal and written advice about plaster care. Immobilization is used to : splint, provide analgesia and to prevent further injury. Please consider if POP is the best option (e.g. Futura splint or mobilisation) in each case.

  • All acute injuries (<48 hours post injury) must have fully padded casts, with no stockinette used, and full casts must be split.
    • The only exceptions are a scaphoid cast
  • Remove any rings from fingers or affected limbs
  • Use stockinette, padding and plaster appropriate to size of patient ( 10-15cm for arms, 15cm for legs, 20cm for below elbow and knee slabs.)
  • Do not use stockinette that is tight, when applied - Apply padding firmly but do not pull tightly
  • When wetting bandages, hold them vertically in the water till bubbles stop, (about 2 seconds), then squeeze very gently
  • Slabs should be dipped, squeezed, (concertinaed) when out of water, smoothed then applied with no wrinkles
  • All patients with first plasters post-injury must have circulation check the next day
  • All upper limb injuries should be treated with a triangular or high arm (hand injuries) sling
  • All patients should be issues with verbal and written POP instructions
  • Where used, patients must be given instructions on the safe use of crutches (particularly how to ascend / descend stairs)
  • All full casts must be split (if <48 hours post injury)
  • If splitting ("bivalving") a cast, avoid bony areas and split the flexor surface first
    • In the arm, split the palmer side, then the back of the forearm. In the leg, split behind the knee first but in front of the malleolus

Below elbow backslab

The plaster slab extends from a point about 5 cm below the top of the olecranon to the level just proximal to the knuckles in the dorsum of the hand and the distal crease in the palmar aspect.

  1. Measure the above distance with a gauze bandage strip and place it on the smooth table top
  2. 6 - 8 layers of 15cm PoP unrolled to the appropriate length
  3. Apply a layer of dry gauze bandage around the forearm to just below the elbow
  4. Hold the folded plaster slab in the folded position and immerse it in water for about 5 seconds (until bubbles stop)
  5. Take it out of the water and gently squeeze out the excess water
  6. Apply the slab on the dorsal aspect of the forearm and the dorsilateral aspect of the wrist and rub it smooth so that the lower end of the radius is gently gripped by the slab
  7. Take a roll of 10 cms broad gauze bandage, soak it well in water and squeeze out the excess water
  8. Apply 10cm diam wet bandage around the forearm, starting from the distal end to fix the slab
  9. The forearm is held with the elbow in a 900 flexed and the wrist in the position of function of 25° dorsiflexion
  10. The fingers should be free to move fully at the metacarpo-phalangeal joints

Above Elbow backslab

Extends from the middle of the upper arm to the point just proximal to the knuckles in the dorsum of the hand.

  1. A slab equal to the above length is prepared dry as described above, in 6 - 8 layers using a 15 cms POP roll
  2. The patient's forearm is held in mid prone position with the elbow in 90° flexed position
  3. A layer of soft cotton roll is applied around the elbow
  4. A layer of dry gauze bandage is applied from the hand up to the middle of the arm
  5. The slab is applied along the posterior aspect of the arm, elbow and the forearm down to the knuckles
  6. Make slits (about 5 cm) across the slab at the inner and outer aspects of the elbow joint crease. Overlap the cut edges and smooth out the bend without "dog ears"
  7. To strengthen the slab, at the elbow joint level, another slab of 5 layers is made and applied starting on the medial aspect at the top end of the first slab crossing around the point of the elbow and going upwards on the lateral aspect to the top end
  8. Smooth edges (particularly around joints) and place in triangular sling

Below Knee Backslab

  • The below knee plaster slab is applied in cases of injuries to the ankle and foot
  • Extends from the level of the tibial tubercle, posteriorly down the calf, ankle, heel and sole to the toes
  • Prepare a dry plaster slab of eight layers equal to the above length, using a 15 cms roll
  • Prepare two slabs each about 10 cm shorter, for use in the medial and lateral aspects of the leg
  • Apply the first slab from about 5 cm below the popliteal crease, along the back of the calf, heel and sole
  • Apply the side slabs on the medial and lateral sides
  • Fix the smoothed out slabs to the leg with a wet gauze bandage, keeping the foot in neutral position (ankle MUST be kept at 90°)

Above Knee Backslab

This type of plaster slab is applied in cases of injuries around the knee and fractures of the tibia and fibula. It extends from the middle of the thigh along the back of the leg and heel to the base of the toes.


  • Prepare a dry plaster slab to the above length (8 layers from a 15 cm PoP roll)
  • Prepare two side slabs of length 10 cm shorter than the posterior slab, each with 6 layers
  • The patient lies on his back. An assistant holds the leg about 25 cm above the couch with one palm under the knee and the other hand holding the toes. The knee is held in 5° flexion and the foot kept at neutral position
  • Cover the patient's knee with a layer of soft cotton roll; apply another pad around the ankle and heel.
  • Apply a layer of dry gauze bandage firmly from the base of the toes to the middle of the thigh
  • Apply the first slab after moistening, starting over the sole of the foot and along the posterior aspect of the leg and thigh and mould it to the leg by rubbing and smoothening it.
  • Slit the slab on either side at the heel and tuck the cut edges properly to avoid "dog ears"
  • Apply the side slabs on the medial and lateral sides of the limb and covering the heel. Mould the slabs over the leg by smoothing the slabs
  • Fix the slab with wet gauze bandage, holding the limb in the correct position described above
  • Rest the leg on two sand bags, one behind the knee and a smaller one behind the ankle

Content by Dr Íomhar O' Sullivan 19/09/2005.   Reviewed 11/02/2007.Last review Dr ÍOS 17/06/21. Patient advice sheet