Modroc for Plaster-of-Paris Projects, Pre-coated Plaster Bandage Instructions, Guidance... mod-roc For Use...

MARAGON - ARTS & CRAFTS

Casting, Moulding & Modelling - Materials & Kits

All About Modroc

Modroc is a plaster-coated bandage which is simply dipped in water and then used either as a covering, as a reinforcing layer, or to make a casing - which can be more or less rigid according to how much material is used. (The term modroc, or mod-roc, is a short form of "Plaster-of-Paris modelling rock", but it is now unusual to hear it called that). Modroc is almost indispensable in making body moulds and life casts:- it does away with all the inconvenience of finding material of the right thickness and size to make bandages each time, and eliminates the laborious process of soaking cloth in plaster. Modroc usually comes in 150mm wide rolls of 2.7m (6 inches x 9 feet), but dry rolls can be sawn with a bread-knife to make smaller widths or cut with scissors as work proceeds. The bandage is supplied in a sealed pack and should be kept dry until use - any unused lengths should be kept in a sealed plastic bag, or sandwich box, etc. Once dipped in water, the plaster residue becomes pasty and workable and the bandage can be wrapped around or applied rather like a poultice. Modroc is used routinely in hospitals for fracture plaster-casts.

Preparation
Take all the usual precautions with lots of sheeting and newspaper and the right tools to hand, and wear overalls or old clothes. Work with 2 buckets of water, one for dipping/soaking the modroc, and one for keeping yourself clean, or cleaning up if you need to interrupt operations; also have a towel or cloth to dry your hands and a pair of good kitchen scissors. A small soft paint brush, a dish-washing sponge, and something like a plastic payment card are also useful for body-mould work and - if you are working on a body-mould or life-cast - special considerations need to be made for the comfort and positioning of your subject, but see the specific pages for relevant notes.

Method
If you haven't used modroc before, do a few trial areas over a piece of wire mesh, the back of a plastic bowl, etc. - or on your own or your subject's foot if making a body-mould. A release agent is needed anywhere normal casting plaster would require it, so smooth down any hair and cover skin with petroleum jelly if working on people. Unless you know from similar work the sort of lengths of bandage you are likely to need, it is usually best to cut lengths of bandage as work proceeds, taking care not to wet or splash water on to bandage that you are not ready to use; work with lengths of no more than 80 - 90cm - longer than this can be unmanageable on small or medium-sized projects - although this doesn't matter too much if you are working on large areas, where the objective is to cover mesh or background quickly without too much concern for detail.

Working with one strip at a time, immerse the bandage for 3 or 4 seconds, making sure the water also gets to the points you are holding, but try not to let go of the edges because strips fold over and stick rather awkwardly; wait a couple of seconds for the excess water to soak in then apply the bandage to the subject. Generally speaking, work upwards on sloping or vertical surfaces, and don't feather out the bandaging at the edges of the mould - this is where it needs to be strongest. The first strips of modroc will set in 3 - 4 minutes, but this depends on the conditions, warmth of the background, number of layers used, etc. Provided they are overlapped, whether the strips are applied horizontally or vertically or criss-cross doesn't matter, and usually depends on the profile of the subject, or part of the subject. For detailed work such as a body mould where the 'vest' you are creating is the complete structure, it is important that the bandage strips are lapped so that there is always an unbroken thickness of at least 2 layers at any point - which effectively means applying 3 layers overall. The exception to this is areas where more than one or two layers would obscure the small details that you would like to preserve; provided these areas are quite small and not at the perimeter of the mould, they can easily be strengthened from behind after the mould has been released; stagger laps and joints by a couple of centimetres to avoid localised ridges and bumps emerging. Working with wet hands, the modroc should be gently pressed and smoothed on, drawing the wet plaster through/across the fabric until the mesh is blurred over - this process is essential with body moulds, and applies as much to the first layer as the last, although it becomes easier with more layers because of the presence of more paste. All the same, treat every layer as though it was the top layer, because faults will show through and be hard to correct within minutes. Note that kinks and folds in the bandage often show through where joint- and overlap lines would not - so use smaller pieces of modroc where curves, corners and recesses dictate. Avoid trying to snip through the wet modroc, it usually 'pulls' and leaves annoying and visible threads. The edge of the strips can be made imperceptible if the smoothing action is along and parallel to the edges, or slightly oblique - rather than across the edges.

Finishing
Having finished the bandaging, with wet fingers or a soft paint brush, manoeuvre surplus plaster paste across the surface of the mould - the edge of a plastic card can help in this process: combine this with a gentle, very light, damp-sponging/spraying and stroking with wet finger-tips over the plaster as it dries, but avoid rubbing across laps or the edges of strips - always move along or obliquely to the joints and laps - generally upwards and across the subject. The mesh of the gauze will be almost invisible if this is done well, so do a few trials beforehand. The mould can usually be separated from the subject a few minutes after the smoothing work has finished, but the de-moulding process should place more reliance on gravity and a gentle easing, rather than pulling away by force. To give the final piece extra rigidity it is a good idea to strengthen the perimeter at the back with a few extra strips. Avoid sanding the finished modroc surface as it will cause the gauze fibres to stand up. Trimming to the final shape can be done with a fret-saw etc., but if the final look and profile of the piece are critical - as with a body-mould - first make an imaginary border with a band of dark cloth, etc. to get an idea of what the piece would look like after trimming, or take a little off at a time, giving the piece plenty of support throughout.

Decoration
If you intend to decorate the finished mould, either paint or spray, let the mould dry for at leat 24 hours then seal the surface with a PVA adhesive diluted about 1:5 with clean water. Don't brush over the same area repeatedly, because the plaster will soon become pasty, so apply lightly and evenly, and avoid leaving brush marks. Seal the back also for extra strength. Leave the piece another 24 - 48 hours in a well-ventilated area before decorating.