Plaster for external use.. repairs to marble statues, church and cathedral repairs external waterproof or damp-proof plasters.... medical plaster casts,.. waterproof leg and arm plaster. Armature work with sculptors' tools and chisels... bas relief and intaglio work, usually suited to reproducing very high gloss or polished finish...
Casting Plaster Suppliers .. very good potters' plaster... slip-casts... rapid-drying slip-mould plaster... Critical table values and characteristics for standard mix all values at 7 days waterproof plaster density....plaster bending stress... tensile strength.... plaster release agent... soap wax or oil, price ... poly moulds ... mould box release oil such as WD40
Herculite No.2 1kg, 2kg, 3kg, 5kg, 10kg, 20kg, 25kg Fine casting plaster compressive strength... plaster porosity.. mould release time.... typical set up time at 20 degrees
Superfine Casting Plaster A white plaster suitable for fibrous plasterwork, general casting, modelling applications also suitable for carving.
Crystacal R & RS An extra hard white plaster for use where high strength and surface hardness are important in GRG, giftware and modelling applications.
Crystacal Lamina An extra hard plaster for the production of finely detailed decorative items which do not shrink on setting. Crystacast An exceptionally hard plaster for use in giftware and modelling applications where surface hardness and exceptional detail are important. Crystacal Alpha K A new ultra high strength casting plaster developed to replace resin in the production of fine detailed giftware. Ultramix A high strength, buff tinted plaster for the production of block and case moulds.
Cassini's plaster is a waterproof sculpting medium, superior to natural limestones because of its regularity... cassinite forms the perfect synthetic material for sculptures, alabaster.. great flexural strength makes it ideal for statues, particularly outdoor work, and water features, etc... superior to paverpol or other artificial meterials.
Plaster-of-paris suppliers.
external protection and weatherproof casting plaster products... outdoor water-resistant plaster-of-paris, ... internal and external walls,.. swimming pool and pond finish.. waterproof plaster cast, models.. high pH environments.. for drinking water.. waterproof plaster.. waterproof.. gypsum or casting plaster ... ..waterproof plaster of paris.. suitable for concrete brickwork, blockwork, all masonry, statuary... high chemical resistance.. €3.50/kg... waterproof finishing coat.. marine waterproof plaster.. more economic
General casting and moulding; suitable for a wide range of artistic applications and most large objects and impression work; also fibrous plasterwork, decorative mouldings, panels, etc.
Models, decorative items, occasional moulds, impressions, etc. Large items may need a framework or armature, etc.
Sculptures and casts requiring durability, reusable moulds, giftware and items likely to be handled frequently. Longer drying time in slip moulds but greater detail. Use Herculite No.2 for life-casts, etc.
Dense hard surface; large casts and projections may require the inclusion of mesh or fibre, etc.
Displayware, giftware, chess pieces, etc., reusable moulds; slower drying in slip moulds and slightly better definition than Herculite No.2, and also much used in life-casting.
Dense hard surface; very popular in exhibits, displayware and undecorated life-casting because of its whiteness.
Outdoor statuary, water features, sculptures, plaques, impression work, etc. Also marble/stone repair & restoration (cast or applied). Cassini's is unsuitable for slip moulds as it is extremely impervious.
Water/weather-resistant; dense surface; very high impact resistance; reinforcement is not usually required.
Plastercraft lends itself to improvisation both with materials and methods, and it is extremely satisfying to see a work-of-art evolve from what-starts-off-as just a white powder. All the materials mentioned below can be found in the drop-down menu, but you can also click here for the complete listing.
Technique
Method
Plaster-of-Paris Moulds & Casting
Although it can be sculpted as a 'negative', more usually a plaster mould is taken from some form of original or prototype. This may be part or all of an existing object, or a 'master' modelled for making one or more copies, and might be a pot, plate, figurine or even part of a car. Objects made of pliable materials such as plastic, rubber, silicone and plasticine do not normally require a release agent (e.g. vaseline), but heavily-detailed, rigid or shiny surfaces can be difficult to part - metal, glass and ceramics all need a release agent. New and existing plaster readily adhere, so a release agent is needed if the mould and the original are both plaster-of-paris, and the same applies if the subsequent casting is also plaster. Unless the original is flexible, undercut areas and deep recesses will require temporary filling. Intricate or hollow moulds can be formed in sections held together with rubber bands or springs, and the joint-lines levelled off after separation. The mould box can be a simple container or frame lined with a plastic sheet, etc. The original is fixed down or suspended in the box and the freshly-mixed plaster is gently poured in as near to the base as possible. Fine Casting plaster is suitable for most projects, and the mould can normally be released after 30 minutes. If encapsulation is not feasible - as with a large panel, plaque or other fixture - the mould box will have to be devised around or over the original ensuring that the junction with the sides of the box is completely sealed with plasticine, etc. Fabric or wire mesh may be needed to reinforce large areas. If the original is made of a soft substance such as paraffin wax which can be scooped or melted out of the mould, whole-object castings can be made (vents can be drilled into the mould to prevent air being trapped). Finished moulds must be completely dry if used for casting metals because the steam from trapped moisture can cause molten metal to be blown out - the mould may need drying in a low oven before use (not a microwave!). Any under-cut detail in the mould will prevent separation if the casting is plaster, metal, etc. - but this won't matter if the casting is a one-off and the mould can be broken away without damaging the finished item.
Impressions/
Imprints
Imprints are made by pressing the subject into the wet plaster, so that the mould itself is the finished item; a release agent such as an vaseline or a light oil may be needed depending on the material (see Casting above); this technique is popular with parents who want to keep a record of the size and shape of small hands and feet, and a kilo of plaster and some plastic flower-pot dishes is all that is needed for two hand and foot imprints. (Use Cassini's casting plaster for outdoor work).
Plaster Casts From Flexible Moulds
Alginate
can be used to make a mould as described in 'Life-casts' below or a permanent mould can be made either with latex
(by dipping or painting on to the subject in several coats), or with RTV silicone rubber (usually by immersion in a an appropriate container or box until the silicone has set). These moulds are easily separable and can cope with complicated and undercut detail in the original; a release agent is not usually needed when making the mould or when casting from it. Latex-rubber moulds are often seen in children's casting kits, but are used commercially in the production of a range of objects from garden ornaments to chess pieces.
Sculpting
A plaster 'block' can be made in a basic mould that slightly exceeds the model's shape and size; the block may be made partly hollow by including a light infill foam to save on plaster, and weight. Sculpting is usually carried out when the the plaster is quite dry otherwise tools and sandpaper, etc., will clog. Repairs are easily effected since new plaster readily adheres to existing.
Built-Up/ Armature Work
Plaster is built up around a hollow cage or framework (armature). Large pieces such as life-size figures will require wire and rods (not necessarily metal) to make up the frame, to which wire mesh, etc., can be attached. Small pieces can be made using mesh alone. canvas or cloth is then dipped in wet plaster* and then wrapped over the parts of this frame in successive layers until a sufficient covering and the right shape is achieved. (In the early stages any parts that protrude too much can usually be knocked back in - slightly too far - then filled out again). The final piece can be left natural, sculpted - or smoothed over with a final coat of plaster. *Modroc pre-coated plaster bandage is usually more convenient for small and medium-sized work.
Slip-Casting
Liquid clay (slip) is poured into a plaster-of-paris mould. The plaster rapidly absorbs the water from the clay, which then retreats/shrinks back from the mould surface as it dries; there is usually a residue/excess of liquid above the bottom layer of leather-hard clay which is poured off. The mould is simply turned upside down to release the clay object, with no need for a release agent. The mould is then dried and cleaned, and ready for re-use. This technique is often used in making ceramic tiles, or pot-halves, etc, but under fairly controlled conditions, and is not suitable for objects with heavy relief detail. To minimise the amount of water used while still ensuring that the clay has good flow across the mould surface, a deflocculant is often added to the slip.
Body Moulds
This single-stage technique is very popular with mothers-to-be who want a memento of their body shape during pregnancy. A pre-coated plaster-of-Paris bandage* is used to make the mould. Tummy and chest are first covered with petroleum jelly, then two or three layers of the moistened bandage are applied more-or-less as a thin poultice which sets very rapidly. The whole process takes 15 minutes-or-so and, although the result is a solid veil, it captures all the shape and holds a surprising amount of detail - and is great fun to decorate. Nursery scenes, cartoon and animal motifs are very popular, but in the right lighting and position, a plain, natural look can be very dramatic.
View the Mum-to-be body mould pack. There is more information about this simple moulding technique via the link at the bottom of the page. *Modroc bandage is a pre-coated plaster bandage which is dipped in water for 3 or 4 seconds - it then becomes quite 'pasty' and is applied/draped over the skin and then smoothed into the body's contours.
Life-Casting (Face, Body, Hands, Feet)
This involves making a flexible mould which is peeled away from the subject once set; the mould is formed in alginate gel which sets in 2 - 3 minutes and will even hold such detail as the pores of the skin. This is the negative which is then coated or filled on the inside with plaster-of-Paris; when the mould is removed the end-result is an exact plaster replica. The method is popular with parents who want to make a cast of their baby's foot or hand. The foot is either dipped or 'painted' with the alginate which can be peeled off once set (alginate is completely safe against the skin). The resulting 'sock' is firm and strong enough to then be filled with casting plaster. (A hard plaster such as Herculite No.2 is normally used for life-casting, but if the piece is to be left 'as-cast' a pure-white plaster such as Crystacal R can be used. On larger body-areas the alginate will need a supportive backing: if the alginate is applied directly to the tummy and chest and then bandaged in-situ as for the Body-Mould process above, the result is a mould which is sufficiently flexible that it can be separated from the body without distortion; plaster and layers of fabric are then applied on the inside to create the plaster replica, which is a shell rather than a solid mass. This is the method used by mums-to-be who want a naked-skin replica of themselves at the later stages of pregnancy, and is definitely a two or even three-person project, requiring 20 - 30 minutes of close co-operation to make the mould. The casting is often painted - metallic spray is very impressive. Mum-to-be life-cast kit
Painting & Decorating
Casting plasters will receive most types of paint, but large pieces may take several days to dry sufficiently to avoid the possibility of lifting or peeling of paintwork. A coat of PVA sealer
will improve adhesion and make application easier and more economical for most paints and sprays (particularly on less dense plasters). The sealer should be applied quickly and lightly to avoid brush-marks being left. In general, plaster objects will deteriorate if left outside or if exposed to moisture - sealing and painting only delays the process - however Cassini's casting plaster does not need any sealing or protection out-of-doors and can be sculpted or left 'as-cast'.
Poor quality moulds are usually the result of incorrect curing and premature separation from the prototype/master. Poor quality plaster casts are usually the result of using moulds which are not completely clean/dry, and premature demoulding - allow at least 2x the stated set-time for very detailed castings.
General mixing guide; unless similar pieces have been made previously, it is good practice to carry out a trial with a small amount of material to establish the ideal consistency for the particular type of work and setting time: this is particularly important with impression work; use the water-to- powder ratios stated in the table below. Except for non-critical work always weigh the plaster and use a calibrated jug, etc., for measuring the water.
1.
Weigh out the required amount of plaster into a clean dry vessel; break up any clumps in the powder at this stage.
2.
Measure out the correct amount of water; use tap water only. Use a clean container that will hold around 3x the volume of the loose plaster powder, to ensure plenty of space for mixing the paste.
3.
Gently sprinkle the plaster into the water and allow the material to sink; allow a few minutes for the powder to properly soak.
4.
Mix slowly and firmly using strokes of the stirring tool that limit any air entrainment, i.e. avoid any beating or dropping action; if using an electric drill with a stirring attachment, use a low speed setting.
5.
The fluidity will vary with plaster type, but the mix should have an even consistency, with no bubbles or swellings under the surface, and no free water on top or at the sides of the mix; make certain that there has been no clumping in the corner of the bucket, etc. Gentle tapping will help to bring any air bubbles to the surface.
6.
Allow the mixture to stand for a minute or so before using, and pour gently if making a solid piece to avoid splashing and air entrainment. Again, if feasible, gentle tapping of the mould/box will release air bubbles.
7.
The mix can be become quite warm as setting progresses, depending on the normal set time for the particular plaster (see table above), the amount used and ambient temperature, etc. It is usually safe to remove the cast at about 2x set time, when the initial warmth has subsided.
8.
Clean any non-disposable utensils and containers thoroughly in water immediately after use, but never down a drain or sink, etc. Alternatively, if using a flexible plastic bucket, etc, allow the excess plaster to completely set, and crack it off for disposal.
9.
Never attempt to dry any plasters in a microwave, and never pour molten materials into plaster moulds until the plaster is known to be completely dry, otherwise the plaster may explode!
All packs include detailed notes on plaster techniques, utensils and equipment, etc.
Technical information and water-to-powder ratios. Density is a good indicator of impression capability and surface absorption, but the values are approximate and are dependent on the correct water:powder ratio and consistent mixing. Strength characteristics are typical 7-day values.
‡Yield is the approximate volume of set plaster-of-Paris measured in litres for each kilogram of dry plaster powder used in the mix.
*Not suitable for metal-casting. †Cassini's has very high flexural strength, and is ideal where the inclusion of reinforcement or mesh is difficult. There is usually some latitude in the choice of plaster - both surface density and absorption can be adjusted with a small change to water content.
Delivery is normally within 1 - 2 working days of the order for most of the UK, but please allow an extra day for 'Highland and Island' addresses. Maragon - Craft & workshop materials.