FreeShip- Plasterworks ClayPlaster, Plastic Relief Sculpture Medium, Fast Set GP15- (Prompt rebate on orders with 3+ FreeShip items!)

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NOTE: Please go to the bottom of this description for mixing water ratios and other instructions. I'll include a copy of the most pertinent piece of info up here:
The suggested mixing ratio for this GP15 material is 32.9/100 Water/Powder by weight. That is not hard and fast, it can be adjusted if you want a softer mix or a stiffer mix. Note that if you don't have a gram scale and need to mix by volume here is a "rough" conversion factor: One level tablespoon of this powder weighs approximately 14.6 grams (that varies depending on how loose or packed the powder in the tablespoon is).

The best name for this is "Plastic Plaster", but it suggests plastic "fake" clay. This is made of actual clay and actual plaster. There are 3 kinds: fast set, slow set, and slower set. "Plastic" means clay that's malleable, easy to shape curved forms, with no cracking. Plasticity makes for handmade forms, sharp changes in curves when throwing pots.
We'd like to encourage sculptors to make architectural pieces for 3-D work, pre-sculpting on panels to set in or on walls or to sculpt right on the wall or ceiling. This is not meant to be grand, just shapes coming out of a wall for the person who lives there. Placement can be low or high or peeking from behind a door that surprises.
All three of the "ClayPlasters" are made of strong gypsum cement versus "ordinary" plaster, to retain strength and hardness in light of the clay plasticizers which are added to make the material as pleasing to work with as possible in the modeling process. Plaster alone does not possess good plasticity. Modeling in straight plaster can be frustrating unless you have spent a lot of time doing it and have expertise. We think this will be considered as worthy as pure clay to model with, and thus easier for those not experts in pure plaster modeling. Working directly with the "plastic plaster" is satisfying in several ways, one of which is that plaster does not shrink. Modeling in pure clay and then firing it makes for a very strong final piece, but one of the disadvantages of firing is the shrinkage. I for one am always a little disappointed when I sculpt something and it comes out a "size smaller" from the kiln when it's finished. Because I don't like glazing sculptures I don't get the compensation of that glazed pottery has which sort of counteracts the shrink "downer" with the element of color and sheen of the glaze, which often is a delightful (hopefully) surprise.

We would love to see "plasterworks" enjoy a resurgence and a change in scale from the huge and wealthy to panels or canvases made by an individual artist and having whatever visions that artist may have, certainly not just reproducing what has been made over and over through centuries of similar ornamentation. Plasterworks are, by definition, "relief" sculptures, either low relief (bas-relief) or high relief (alto-relievo). And sculptors have certainly been working in those relief modes continuously since olden times.

The combination of "plaster" and "works" makes a new word with a different meaning. "Plasterworks" is taken to mean ornate interior 3-D structures of decorations made of plaster. It refers to any decorative sculptural or ornamental 3D element that has a backing against a wall or ceiling and projects outward or inward in the space of the room. These old embellishments (one or more centuries ago) were done with lime plaster as opposed to gypsum plaster. What are the differences between lime plaster and gypsum plaster? Read on if you wish to know:
--Lime plaster (or lime mortar w/sand), also called non-hydraulic cement, sets by a carbonation process which is very slow. Lime starts out as limestone (calcium carbonate) which is heated to form "Quicklime" (calcium oxide), then water is added to form "Slaked Lime" (Calcium hydroxide). Slaked lime is allowed to dry and lumps automatically turn into powder when moved or spread out to dry into powder. When more water is added to the powdered slaked lime to form a paste (or a putty in an air tight container, non-setting) it slowly sets back into calcium carbonate by reacting with the carbon dioxide from air or from other sources. Depending on the thickness of the applied paste (to a surface, often wood lath), it can take about a month to fully carbonate (set).
--Gypsum plaster, also called hydraulic cement, sets by a crystallization chemical reaction between calcined gypsum and water. The reaction is fast, usually 10 to 15 minutes initial set, with steadily increasing strength for the first 45 minutes. That means castings should remain in molds for 60 minutes or more before removing them (unless you are working with the much stronger "gypsum cement" plaster. Exposed uncured gypsum plaster should be kept moist, unless you are using one of the new early-demold gypsum cement plasters like Drystone from USG. Full cure is within 24 to 48 hours.

Work that becomes part of a wall, almost always with the relief work projecting out from a wall is very enticing. You can show the panel mounted on top of a wall by a rounded edge, or better, by cutting out a square in the drywall, and inserting the backing panel on which the relief sculpture is done. The relief background being flush with the surrounding wall is very satisfying. The relief appears to be sculpted directly onto the main wall surface with the joints puttied and painted so no gap appears in the backing panel and the wall. It could be one panel or many, with a design that snakes across a wall's surface. It would require that the cut out drywall be placed wherever a wood support behind the wall is (in front of a vertical 2" x 4") ("stud"). That ensures that the inserted backing panel becomes flush with the rest of the wall and also provides a method of fastening the backing panel in place by nailing the panel to the exposed stud.

This description of a working method is a modest proposal that one person can do. No contractors needed for a major wall replacement. Drywall is a 4' x 8' flat panel premade of gypsum faced by a paper coating on both sides and almost always 1/2" thick. 32 backing panels (12" x 12") could be made from 1 sheet of drywall. This enterprise becomes easier if the backing panel of the relief sculpture be made of drywall itself, for several reasons, new wet plaster will stick to old dry plaster IF YOU WET THE OLD PLASTER* (*important point), plaster will not stick to wood, unless you use mechanical means and since you must wet any dry surface you apply plaster to, if you used a piece of plywood, it would warp because of the wetting. A building supply company (Home Depot?) will have smaller pieces of drywall (4' x 4' or 2' x 4'). Once you have the smaller piece transported home in your mini-car, you can cut it without saws. Drywall is cut by an inexpensive cutting tool which has a blade. Or you can just use a box knife, works fine (or it can be sawed with a small drywall hand saw). Cut a 12" x 12" piece by scoring it with the knife and then snap the scored piece off with the help of a table or counter edge (cut the remaining paper on the reverse side).

Before moving on, it should be mentioned that the panel size referred to above (12" x 12") is not the only size which is convenient because it divides a 4' x 8' sheet of drywall evenly. The unit size of sculptural relief applied panels will also come out evenly if you use dimensions of 16" x 16" panels.
Instead of 32 panels when 12" x 12" is used, you would get 18 panels when 16" x 16" is used from a sheet of 4' x 8' drywall.

Of course, there is nothing stopping you from sculpting your relief embellishments directly on the existing wall eliminating the backing panel which is later made to fit to a wall. If your relief is large you might want to use metal lath, a form of "expended" metal (having alternating diamond shaped open spaces between the metal that remains unexpanded) which is fastened to the wall where the main sculpture is to be sculpted (metal lath can be fastened to any surface, concrete wall, cement block, mortared brick, etc. No special fasteners are needed. For example, on wood galvanized roofing nails with washers that hold the lath to the substrate can be used as attachments on wood panels, or concrete nails when securing it to concrete and various types of stapes/nails when securing it to brickwork, cement block, or drywall itself.

When you are actually working on the relief sculpture (with our prepared "PlasterWorks Plastic Clay/Plaster", we hope!) you must absolutely remember to wet the backing panel THOROUGHLY for the relief sculpture if it's dry (as wallboard is), otherwise the dry gypsum/paper backing will suck the water out of your applied relief sculpture plaster and the plaster will be weak and crumbly. If you have a design drawing, transfer it to the paper on the drywall and make knife scores inside the bulk of the design so you'll have exposed some of the plaster the drywall is made of for better adhesion of the relief.

There still are ornate plaster mouldings and embellishments being made by companies, mostly in Britain and Europe, for modern versions of historical plasterwork, such as R.S. Plaster Mouldings in London which specialize in what's termed "fibrous plaster". That term comes up in modern plasterwork so it's worthwhile quoting that company's explanation of fibrous plastering:
"It is a form of precast plasterwork. The plaster casts are reinforced with open mesh hessian [burlap] scrim and strengthened with timber laths. This results in strong casts that are light in weight. Another advantage of fibrous plastering is the saving in cost when reproducing several similar types of moulded work which can be cast from the same mould. These casts can be prepared in a workshop, as the building progresses separately." Since such companies probably have hundreds of molds for virtually any design ever made (or can trade/rent molds from each other), there is little work that needs to be done by sculptors, thus saving a lot of expense for a sculptor's work on a design (if you, the individual artist is the creator of the new design, you don't need sculptural work done by others).
There is even a system of architectural molding called Forton MG which makes much stronger plaster castings with the use of gypsum cement, fiberglass, and 2 kinds of polymers mixed with the plaster/gypsum cement. The advantages are the extra-light-weight of the castings, which makes installation easier, and the superior strength of the castings. The cost of such castings is much more expensive because of the advanced technology of the materials. And specific contractors and workers familiar with the Forton system are needed to make use of the advanced materials.

This description, as you know (if you have read this far) applies to plaster when used decoratively, not when used as a flat wall surface, as in the majority of buildings in the modern western world using gypsum drywall. In older Western and Eastern Europe, and Southwestern Asia there are many buildings still standing that were constructed hundreds, even thousand of years ago. These are for the most part Palaces, Churches, Cathedrals, Towers, and great Lodges. They were meant to impress and project power, wealth, and belief (religious). Their exteriors (usually Cathedrals), may have had great structural and non-structural elements (like flying buttresses, bell towers, great arches, parapets, gargoyles, etc). Their interiors were also ornate with impressive domes in the great hall and the great chamber, and state rooms, drawing rooms, bed chambers, and so on. There was much interior ornamental "plasterwork" work done that covered walls and ceilings. In rooms, elements such as niches, half columns, inglenooks, and other parts, had mouldings, cornices, domes, and all manner of wall and ceiling treatments.

The rest of this description gives a brief historical account of the types of plaster used, how they were used and their individual advantages and disadvantages.
The use of plaster in history goes back millennium in association with building construction and building ornamentation (with some free standing sculptural use). There are two main types, "Lime Plaster" and "Gypsum Plaster". Gypsum plaster eventually became the material of choice, being the modern type used 90% of the time, while lime plaster was used 90% of the time in antiquity. They have their purpose, and the look of the finished material in common, but otherwise they are completely different physically and chemically. They also had some different working methods, due mainly to the fact that lime plaster has a curing (setting) time *way* longer than gypsum plaster, which sets in a few minutes and cures strongly enough in an hour to do anything around or on it (maximum strength won't be reached for several weeks or months). Gypsum plaster is a more recent material going back centuries (with it's use increasing over time). Lime plaster is significantly more ancient, going back many millennium (there are sites in Jordan and Turkey that used lime plaster dating back to 7,500 BC). There are records of gypsum plaster used for palaces and other buildings in the mid to early 1500's during Henry the VIII's time, and there are some sources which say gypsum plaster was used at least in some parts of the greatest pyramid in Egypt, Cheops. However, most sources say that only lime plaster was used in Cheops (some 500,000 tons of plaster!). Gypsum and lime plaster are the two main materials to which the term "plaster" is used, but actually there are several other materials which have been called plaster, two of which are: clay plaster and cement plaster.

Both types of plaster have disadvantages and advantages. Gypsum plaster has much higher early strength than lime plaster. Lime plaster can take a very long time, even months or years to fully cure depending on applied thickness and knowledge of the workmen. Lime plaster when placed and fully cured is surprisingly long lasting. In general, historically, when fully cured and dried (after weeks or months), lime plaster was stronger when compared with cured gypsum plaster. One reason for that is its flexibility compared with the rigid crystalline structure of cured gypsum plaster. It can flex with the building's settling. In the extreme case of Venice, Italy (which is sinking about 2 mm per year) it's a god-send. Another property of lime plaster when fully carbonated and set, is porosity. Most lime plasters are permeable to water vapor which allows them to breath in tune with whatever the humidity of the building might be. Venice's foundations are today mostly underwater depending on location in the city and whether they are located in areas of high flood-tides from the sea. So this unusual resistance to water by "becoming one with it" is especially valuable in a city like Venice. Gypsum plaster, although usually stronger when first applied, and later, when set, does not have the property of being resistant to water damage that lime plaster has, which is a pretty significant benefit in the long run. Lime plaster can weather the elements and be used for exterior surfaces also, gypsum plaster cannot.
It should be mentioned that somewhere along the line it was discovered that "pozzolanic" materials (volcanic ash for example) could be used as additives that would speed up the setting of lime plaster mortar. Most sources cite the Romans in 400 AD as the inventors of this new kind of "quick-setting" lime plaster. This transforms it into an artificially hydraulic (gypsum) plaster. Historically, pozzolans were not in continuous use in lime plaster for reasons unknown.

For painters of murals, lime plaster was essential to the fresco method. It had the benefit of creating a more permanent mural because the pigment, mixed with water, was painted directly onto the wet plaster. The pigment/water mix actually sank into the plaster and became a part of it. That eliminated the need for a pigment medium (powder-to-powder) binder and a gesso (pigment-to-substrate binder). Michelangelo's Sistine chapel is done over a lime plaster base. Lime plaster also creates a better bond with the underlying surface
It is still lime plaster, however, and one of the disadvantages of lime plaster is that it is physically weak and soft during carbonation, even with pozzolan additives. It needs an initially moist environment of around 1 month for medium to thick sections). When fully carbonated and set it is much stronger and harder (and more flexible than gypsum plaster which cures by forming rigid crystals). As mentioned, gypsum plaster is stronger than lime plaster before lime plaster is fully cured. For early applied lime plaster, protrusions like corners or edges in the decorative design will be easier to break with lime plaster than gypsum plaster. To counter-act this to some degree, reinforcement is added such as wheat or straw or pieces of wood (in todays world of fibrous-plaster, fiberglass, or modern polymers both fibrous and liquid are used like polyethylene or nylon and acrylic).
Another factor to mention is the highly alkaline nature of lime plaster. It can create skin burns if workers contact it. This becomes of less importance when the experience of tradesmen becomes high enough to not need special protection due to their expertise with wood or metal tools. Gypsum plaster has lower alkalinity and so was preferable in that regard. The disadvantage of lime plaster, being mainly the slower set-up time plus the advantage of gypsum plaster, being mostly the relatively higher early strength have made gypsum plaster become the plaster of choice over time. As mentioned above decorative 3-D relief work is most often made in molds in a shop offsite from the building being worked on. When needed they are transported to the building and fastened in place, with seams and gaps plastered over faster with gypsum plaster. Lime plaster is still being sold today when preferred for certain properties. For example, an extended setting time if needed, can be valuable for in place 3-D decoration. It can be found today even with pre-mixed water. It will not set if sealed in an airtight container for fairly long periods of time, with no carbon dioxide in new air to cause it to begin carbonation.

PRE-MIXING COMMENTS:

These three modeling plasters fall under the heading of "Gypsum Plaster", or the older term "Plaster-of-Paris", in relation to the above description. But they are modern versions which take advantage of the advanced chemistries and quality controls of "gypsum cement" in the twenty-first century.
The labels "Plaster" and "Gypsum Cement" are used by companies which make both materials. USG, the largest manufacturer of gypsum cement and plaster often refer to the two materials as different classes of materials by the marketing department, while the the technical department refers to gypsum cement as a subtype of plaster.
It all starts with the naturally occuring mineral Gypsum (Calcium Sulfate Dihydrate). When it is heated ("Burnt"= old historical name, "Calcined"= chemically correct name) it becomes Calcium Sulfate Hemihydrate (dried or dehydrated gypsum = Bassanite, the natural mineral name).
Anything relating to gypsum plaster has a majority of Calcium Sulfate Hemihydrate in it (bassanite is the naturally occurring mineral form). Usually 90 to 95% of the material is plaster and the rest are additives (Hydrostone, for example is about 95% calcium sulfate hemihydrate and about 5% white portland cement).
What is the difference between gypsum cement and plaster? Not as much as you might think, ingredient-wise. The main difference in the chemistry comes from tighter control over how the calcium sulfate hemihydrate crystallizes. Gypsum cements are refined so that the final crystal structure is more uniform in size and importantly, in shape. Plaster crystal structure has scattered crystals that are more or less different in size and shape. This makes the final crystallized calcium sulfate dihydrate be less uniform in structure and with wider spacing between crystals that gets taken up by free water, water that is not required to chemically transform the calcium sulfate hemihydrate into calcium sulfate dihydrate. This extra water does not contribute to the structure's strength. It makes it weaker. The more free water in a cured plaster, the softer and weaker it will be. Gypsum cement has ingredients that are engineered to produce calcium sulfate dihydrate crystals that fit together more tightly as a result of their more or less uniform shapes (and sizes). Gypsum cement's chemical pieces (crystals) fit together more like stacks of aligned playing cards. Plaster-of-Paris's crystals fit together like stacked groups of jigsaw puzzle pieces from several different puzzles, with pieces of all different shapes and thicknesses which have gaps and empty spaces that hold excess water in them.
Also, there are special additives, both known and trade secrets of gypsum cement manufacturers like USG: "there are additives that are used in gypsum, PC and CAC-based formulations to make water more efficient. By using these chemicals, also known as ‘consistency reducers’ less water is required to create a flowable slurry". These additives will act similarly to deflocculants added to liquid clay slip in ceramics slip casting, reducing the amount of water needed to get a pourable mixture.
All three of these modeling plasters contain gypsum cement rather than ordinary, plaster-of-paris plaster. They are complex mixtures mainly containing the aforementioned gypsum cements, with clay plasticizers, and very thin fiber reinforcement (so as not to interfere with the ability to achieve very fine detail). GP22 is of note for it's different gypsum cement, polymers, and extra strong and thin fibers, plus a unique plasticizer. It is also made from a denser gypsum cement (those factors make it the most expensive per volume of the three types of ClayPlasters).

MIXING NOTES:

The powder/water ratios below will give a consistent-pasty, easy-to-mix (by hand) material (small mixtures mix with a flat narrow spatula) which will yield a pretty quick higher viscosity mix after kneading. After an initial mix of about 2 to 10 minutes, it should be kneaded for about 2 to 10 minutes depending on the type (see below). Moisten your fingers a little before kneading since bare dry fingers will draw water out of the mixture. These three ClayPlasters will stick to each other with a little bit of help. ALWAYS ensure that the new wet ClayPlaster is not butted up or smoothed out over a already set ClayPlaster without wetting the set-up area. THOROUGLY wet the set-up ClayPlaster so it's saturated as deep down as possible before joining something new to a set-up area. Roughening up the set up area will also help give a strong bond (roughen up while it's still wet or when set-up).
The properties of these three ClayPlasters can be "adjusted" by small amounts by changing variables in their mixing. But it's true that if you change one thing, that will usually also change something else. The workability/plasticity can be changed by by varying the amount of water mixed with the powder. The water ratios given below are relative to each other, not absolute, because your water may or may not have minerals in it, your mixing method or time might be different (PLEASE mix a full 2 to 5 minutes). Longer mixing times give a faster set time, or your temperature might be way higher or lower. Our temp for reference was 76 F, higher temps of just 3 or 4 degrees can speed up the set time, lower temps slow the set time. Please refer to the section below "MIXING" for an itemized detailed list of possible variables in mixing and the anticipated effect making those changes will have.
When these three Clay/Plasters are totally dry they can be painted or coated with almost anything. Recommended oven dry at 120 F or less for 24 to 48 hours will give a much faster drying time. Here are a few more tips to get the best final product ahead of the list of variables below:
These three ClayPlasters are not suitable for exterior placement.
Add (sift) the powder to the water, not the reverse. A short soaking period prior to mixing and after sifting powder into water is recommended, but note that if you have experience mixing pure plaster, it's not possible that the entire amount of powder will become wetted by soaking as it does with pure plaster.

MIXING:

Fast Set (GP15) - Plastic ClayPlaster - 100/32.88 Powder/Water by weight. (Note: This mix is hard in about 25 minutes and has a working time of about 18 minutes.) Mix it for 2 or 3 minutes and knead it for just a couple of minutes. If in a cool environment (65 F to 70 F) those times can be lengthened a bit, a longer mix and kneading will give a somewhat better final product but will shorten the work time). Some people want that short set-up time, they can get a certain amount done that feels about right, and will go on to mix the next batch while the current one is hardening (in about 15 minutes), then continue where they left off, which has just hardened a few minutes earlier. Be SURE to rinse all dried plaster from your fingers and mixing spatula because just a little dry plaster from the last batch will bork your next batch by setting up the next new batch too fast, it acts as an accelerator and you won't have any spare time with this fast setting type.

Slow Set (GP22) - Plastic ClayPlaster - 100/27.40 Powder/Water by weight. (Note: This mix sets up much slower than GP15, intentionally, it's hard after about 1 hour, 25 minutes and has a work time of about 1 hour, 15 minutes.) Mix about 5 to 7 minutes and knead for about 5 to 7 minutes. This mix may be the ClayPlaster of choice among the 3 types since the time frame may be favorable, not too fast, not too slow. Note that of the three types this one is based on a different cement than the other two. It has a greater amount of a polymer fiber that is very strong yet very thin and so can stand up to existing in longer lengths while being mixed which gives greater reinforcement while not interfering with modeling plasticity.

Slower Set (GP19) -Plastic ClayPlaster- 100/31.51 Powder/Water by weight.
(Note: This mix sets up slower than GP22, it's hard after about 4 hours, and has a work time of about 3 hours, 40 minutes.) mix about 5 to 10 minutes and knead for about 5 to 10 minutes (depending on whether you want to alter the set; longer mix/knead times will shorten work time, as will higher temperatures). For those who want maximum working time to work with mixes for designs with high detail and don't want to be bothered with mixing multiple batches in the middle of their modeling, this will give over 3.5 hours of work time with a mix that slowly increases in thickness (viscosity).

VARIABLES AND TIPS

Please use weight for measuring, it's the only way you'll get consistent results from batch to batch, unless you have accurate volume measuring graduated cylinders. The only weight to volume conversion I did was the total weight of powder AND water, when mixed together, measured with a 10 ml graduated cylinder: 7.3 grams of powder (GP15) plus 2.4 grams of water (total weight = 9.7 grams): when mixed those weights yeilded ~6 ml of properly measured and mixed (by weight) wet material. 6 ml is 0.203 fluid (volume) ounces, 9.7 grams is 0.342 weight ounces.
Here are some variables in the mixing of these three ClayPlasters that will somewhat affect the properties of the mixture and final product. In most all of these variables they can be changed 5% to 10% without drastic damage to the mix, but that is not guaranteed.

1) Increase amount of water:
You can only do this at the beginning of mixing. If you do it after it's initiated the cure reaction, it will weaken the final mixture. Depending on how late you add more water it will not slow the hardening, it may even speed it up.

2) Decrease amount of water:
Obviously you can only do this before you start mixing. You can't reduce water you've already mixed in. If you increase the amount of ClayPlaster soon enough, before the reaction has initiated, it is the same thing as decreasing the amount of water. Using lower water amounts will densify the final product, speed up the hardening, and increase the exothermic heat.

3) Mix by hand:
This will give a "lower energy" mixture that will lengthen the set-up time. This might be recommended for the fast set (GP15) material if you want to get a longer work time.

4) Mix by powered mixer:
This will give a "high energy" mixture which will be not only a more thorough, consistent mix from batch to batch but will yield a faster set-up time (both due to higher energy and higher temperature due to the friction of powered mixing; higher temps also result in a faster set-up).

5) Mix for longer time:
This is similar to the effect of a high energy power mix. Longer mixing will also give a faster set-up time because it's more thorough and effectively higher energy.

6) Mix for shorter time:
This is similar to the effect of a low energy hand mixing. Shorter mixing times are effectively lower energy mixing.

7) Increase temperature:
Because a chemical reaction sets this material up, this is no different than other chemical reactions in that higher temperatures speed up chemical reactions.

8) Decrease temperature:
Because a chemical reaction sets this material up, this is no different than other chemical reactions in that lower temperatures slow the time of the reaction, and so with this material, slow the set-up time.

9) Add some set-up powder from previous batch:
In effect, the presence of already set plaster (or "dirty" water) will speed up the chemical reaction. The reason for this requires some knowledge of chemistry. Basically the already set-up plaster provides "seed crystals" which jump start the chemical reaction: "The placement of a seed crystal into solution allows the recrystallization process to expedite by eliminating the need for random molecular collision or interaction. ... Seeding is therefore said to decrease the necessary amount of time needed for nucleation to occur in a recrystallization process."

10)Change the amount you're mixing:
The amount that you're mixing (the mass) has an effect. Higher masses harden faster. Since higher temps speed up the reaction, it's a self-propagating process. The hardening is an exothermic reaction, it gives off heat. Greater heat makes it harden faster, the faster it hardens the greater the heat it gives off. Large masses have a harder time dissipating the exothermic heat. Therefore larger parts you're curing will heat up faster and harden set-up faster. It's the same principle as in thermoset resins like epoxy. This is a two part thermoset as well. Water is the curing agent (Part "B")