FreeShip- White Art Concrete #63-101, Complete Concrete Ready-Mix, (All-Agg) - (Prompt rebate on orders with 3 or more FreeShip items!)

DESCRIPTION-> Click "Learn more about this item" for article & instructions!
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This is one of 4 custom concrete ready-mixes made by us. There is a 5th called "Cement-All" that was added after the descriptions for the 4 custom mixes were written. Note that this #63-101 mix is formulated for quick setting of small castings 2 inches thick or less but with an adequate working life for placement of the concrete in the mold. There is a chance that thermal cracking can result in much larger masses than 2" due to curing exotherm. This is one of 2 White Art Concretes we carry. Although comprehensive testing of pigment coloration of a White Art Concrete was done with the sister concrete #82-102, it is probable that this White Art Concrete #63-101 can be colored with the same pigments and come out with cured concrete colors close to those shown in the #82-102 concrete listing.

PICTURE #1- Sample bag quantities of this listing #63-101 concrete.

--This #63-101 concrete mix is listed with 3 water ratio amounts by weight:
23.6 water/100 concrete powder (conversion factor = 0.190)
21.6 water/100 concrete powder (conversion factor = 0.178)
20.3 water/100 concrete powder (conversion factor = 0.169)
(The conversion factor = water/water+powder (23.6/123.6 = 0.190)
(See below "NOTES ON WATER RATIO, WORKING TIME, AND MIXING"
for detailed explanation). Mixing time should be about 2 minutes.

PICTURE #2- Tiles of our 4 concrete mixes with this listing on bottom.

Color Tile Samples Key (Percentages are of concrete powder by weight):
Note that pigments can be added to white concretes #63-101 or #80-102
but that #80-102 is most recommended.

PICTURE #3- Reds & Bordering Tiles:

7 Alizarin Crimson 0.4%
6 Alizarin Crimson 1.5%
24 Fluorescent Orange 0.6%
9 Chinese Red Vermillion 0.2%
10 High Purity Red Iron Oxide 1.5%
35 Fluorescent Red 1.2%
33 Fluorescent Magenta 1.2%
44 Ultramarine Rose 1.5%

PICTURE #4- Blues & Bordering Tiles:

52 Ultramarine Blue 0.6%
32 Fluorescent Blue 1.2%
19 Cobalt Blue 1.5%
14 Ultramarine Blue 0.4%
18 Cobalt Blue 0.9%
47 Ultramarine Blue 1%
46 Fluorescent Blue 2%
5 Phthalo Blue 1.5%

PICTURE #5- Yellows & Bordering Tiles:

25 Fluorescent Yellow 1%
28 Yellow Ochre 1.2%
15 Raw Sienna 1.5%
37 Yellow Ochre 0.4%
31 Fluorescent Yellow/Orange 1.2%
34 Fluorescent Yellow 2%
11 Hansa Yellow 0.4%

PICTURE #6- Greens & Bordering Tiles:

43 Kelly Green 2%
30 Fluorescent Green 1.2%
26 Fluorescent Green 0.4%
39 Chrome Oxide 0.4%
27 Phthalo Green 0.4%
54 Kelly Green 0.6%
4 Chrome Oxide 5%

PICTURE #7- Violet+B&W & Bordering Tiles:

56 Bone Black 4%
3 Ultramarine Violet 3%
29 Cobalt Tyrian Purple 2%
1 Ultramarine Violet 5%
36 Titanium Dioxide 2%
53 Ultramarine Rose 0.6%
2 Ultramarine Violet 1.5%
44 Ultramarine Rose 1.5%

PICTURE #8- Earthy & Bordering Tiles:

23 Van Dyke Brown 1.5%
40 Rutile 2%
48 Red Copper Oxide 4%
38 High Purity Red Iron Oxide 0.2%
13 Burnt Umber 0.6%
16 Burnt Umber 1.5%
51 Crocus Martis 0.4%
21 Cobalt Carbonate Rose 5%

PICTURE #9- Incompatible Pigment Tiles:

12 Phthalo Blue 0.2%
55 Toluidine Red 1.5%
45 Phthalo Blue 0.8%
8 Toluidine Red 0.4%
50 Copper Sulfate 5%

PICTURE #10- Tiles of #63-101 or #80-102 Aggregate Surface Treatments,
(right side of most coated with shellac):

294 "Silver Mica" 3.5%, integral mix, exposed agg by brushing, shellacked.
https://www.etsy.com/listing/500052386/mica-pure-medium-coarse-flake

296 "Coal Slag, Coarse" 178%, integral mix, exposed agg by brushing.
Available by custom listing, just let us know if you would like some

295 "Muscovite Mica, Very Coarse", non-integral mix, layered.
https://www.etsy.com/listing/1231706843/freeship-muscovite-mica

297 "White Art Concrete Over Dark Art Drops", non-integral mix, layered.
https://www.etsy.com/listing/1407954760/freeship-dark-art-concrete-252-

299 "White Art Concrete Over Silver Mica", non-integral mix, layered.
https://www.etsy.com/listing/500052386/mica-pure-medium-coarse-flake

341 "Concrete Foam", expanded 2x, integral mix, (a work in progress).
Foaming agent available by custom listing, let us know if you want some


Note that a binder was applied between layers of coated micro-flakes when they were post applied for making the above sample tiles. The binder I used was natural shellac because of its ease in handling, lack of toxicity, and alcohol solubility. For production, a strong binder like a transparent epoxy or urethane varnish should be used for its toughness and longevity. For the ultimate in binder/finishes go to an auto paint supplier. They have the highest quality finishes made (and most expensive). Finishes for automotive use are unsurpassed. Many of the samples had no post applied flake materials. If none are applied for production, a high quality finish should still be applied. It should be used only after evaluation determines it will uphold the beauty and protection of the product and will be compatible with your materials and methods.

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To jump down to the main article about this material, go to the next "****************", below.

NOTES ON COLORANTS:

--All in all, I was surprised at the number of our pigments that performed well, giving some rich colors that I didn't expect! Whether this was simply because they were tested at higher concentrations with a white concrete mix (compared to "normal" large projects like floors or driveways), or because our white concrete mix was less alkaline than most, I don't know.
--The two most stable, "safest" pigments to choose for coloring concrete are the iron oxides, both red and black (we mistakenly omitted testing black iron oxide, but have several types of it!). There are other "earth" pigments (yellow ochre, sienna, and umber) that are not strictly iron oxides but are derived from them and contain relatively high amounts of iron that are considered good concrete pigments.
--Oxides in general tend to be good choices.
--Pigments can be added to the White Art Concrete "All-Agg" #63-101 concrete if you wish, but the White Art Concrete "Add-Agg" #80-102 concrete is most appropriate and will likely give a stronger concrete if you chose pigments which have a broken tile sample. A broken tile means the pigment made the concrete somewhat weaker, although all are strong enough for concrete designs that do not have very thin walls. The test I performed for concrete strength was holding the tile in both hands and exerting a lot of force to try to bend it until it broke. It's true that some broken tiles may have been tested too early, before they reached full strength when fully cured.
--All carbonates that we carry just don't have the tinting power required for coloring concrete. Our quirky inclusion of them to pigments that can be used to make paint does not carry through when they are used to color concrete. We did not even include them in "Incompatible Pigment Tiles" because they all turn out nearly white.
-Phthalo pigments are problematic, tending to fade at low concentrations.
--Toluidine Red is simply not compatible with concrete. At any concentration it's splotchy.
--Colors which have 2% or less concentrations will be most economical. Check the prices of pigments you are considering against the concentrations. Expensive pigments with 5% concentrations will make the most most expensive colored concrete.
-Copper Sulfate is not compatible with concrete. It is a chemical used to color some inks and used in anti-fouling paint for its fungicide, algaecide properties but not as an oil painting pigment. It is water soluble and makes a solution rather than an suspension and thus requires more water to become less viscous which makes it a weak final concrete.

NOTES ON WATER RATIO, WORKING TIME, AND MIXING:

--This #63-101 concrete mix is listed with 3 water ratio amounts by weight:
23.6 water/100 concrete powder (conversion factor = 0.190)
21.6 water/100 concrete powder (conversion factor = 0.178)
20.3 water/100 concrete powder (conversion factor = 0.169)
Mixing time should be about 2 minutes.
Soft Set times at a given water ratio:
26 minutes @ 23.6/100, 20 minutes @ 21.6/100, 14 minutes @ 20.3/100, at a somewhat elevated ambient temperature of 76F to 78F.

Note that the given amounts above are what I used in my testing and will be the optimal ratios for this #63-101 concrete mix. But, you are free to use whatever proportions give you the best results for your application. Don't want to be bothered by carefully measuring units of weight? Then use measuring spoons for proportioning by volume. You will need to experiment using your spoons to see what will give workable mixes for your process. Just keep in mind that an optimal mixture will be the thickest that your process allows. Making soupy pourable mixes will result in weakened concrete and if you are adding pigments, it will lighten the colors. Also be aware that volume measuring is not accurate from batch to batch if you allow the amount of packing of powder in the spoons to change each time you measure a batch. What follows is for those who have accurate scales that will measure small amounts of weight (using grams is preferrable):
23.6/100 is the highest water content. More water in the concrete mix makes it more pourable, makes it weaker when cured, and can lead to more settling out of the dense ingredients. When adding pigments it will lighten the color slightly. But when adding extra aggregate it can allow more aggregate to be added and still have a workable mixture.
20.3/100 is the lowest water content. Less water will give a thicker mix, will make it stronger when cured, and will discourage settling out of the heaviest ingredients. Less water will give slightly more saturated colors when adding pigments (the difference in water content here is not a large amount).
Using the ratios to determine the proportions for a desired total amount of concrete mix can be done in two ways. The least specific is to just divide the numbers of the water ratio by the same amount (example: dividing each number of 23.6/100 by 10 gives a correct mix amount of 2.36/10 water/powder (by weight; I used grams). The easiest way to find the proportions for a desired total amount of mix is done by using the conversion factor: for example, if a total amount of 16 grams of concrete mix is wanted, multiply 16 by the conversion factor, then subtract that number from 16. So, for 23.6/100, conversion factor of 0.190 times 16 = 3.04, which is the water amount. Subtract 3.04 from 16 = 12.96, which is the concrete powder amount. That gives you a water ratio of 3.04/12.96 water/powder to use for a total mixture of 16 (grams or other unit weight).
Above are relative times of what I call "Soft Set", which is somewhat equivalent to "working time" (plus a degree more). It is the time when a very small spatula poked in slightly to the wet concrete surface lifts up a small amount of mix and the mix does not settle back into the concrete mass on its own. You will probably find that your Soft Set times do not coincide with my figures. Take the given times as a relative indication of which concrete mixes we carry set up faster or slower than the others and how the difference in water content affects the Soft Set time. Differences in temperature cause the greatest variance, but other factors like how effective your mixing technique is (and how long you mix), whether colorants or other additives are being used (they can act as accelerators or retarders), whether you are keeping freshly poured concrete covered with a plastic sheet or wet paper towel suspended above it (a good idea during the initial hardening phase of the concrete) and even the relative humidity since very dry conditions can rob some moisture from the concrete mix during stirring, placement, and settling (prior to covering).

NOTES ON WHAT THE PICTURES SHOW:

The 1st picture shows this listings concrete ready-mix powder in some of the sizes it's available in (the smallest sizes).

The 2nd picture shows all 4 of our concrete "ready-mixes" in sample tiles so you can compare how they look fully cured:
The tile that goes with this listing is at the bottom of the picture. Most of the tiles have a darker vertical section on the right side of the tile where we have brushed on a sealer/shellac to show how a "varnish" painted onto the cured concrete darkens the color.
Here's a list of the 4 concretes with the part # of the concrete :
-- Mix #80-102 = A White Art Concrete with some of the aggregate left out. We call it an "AddAgg" mix. It's the best mix for people who want to add some of their own agg (a special size, shape, or color), or want to add a pigment to make their own custom concrete blend.
-- Mix #63-101 = A White Art Concrete with all of the agg included. Best to use as a stand alone white cement concrete.
-- Mix #251 = A Tan Art Concrete with all of the agg included. It has light colored additives that make it especially strong as a "Pozzolan" type of concrete. The additives are colored enough to make it tan but not dark gray like common Portland cement concretes.
-- Mix #252 = A Dark Art Concrete with most of the agg included, but "cement-rich" enough for more agg if desired. It has additives that make it especially strong as a "Pozzolan" type of concrete. It is unique because it will remain a dark color when fully cured. Standard dark gray Portland cement concrete is a dark gray powder but cures to a light gray. This concrete contains some dark additives, and also has black pigments to force it to stay dark when cured. It works well when a dark background color is desired to match dark surface aggs or special powders like graphite, or to provide a contrast for light colored aggs.

The 3rd through 9th pictures show color tiles made with most of the pigments we carry added to this listings concrete #63-101:
The above list of the picture #'s on the colored tiles (1.75" x 1.75") show which pigments we sell will work with our two White Art Concretes to give a functional, visible color, not a bleached out low tint. The tiles are not as accurate as color charts of house paint, there are so many variables when trying to integrally color concrete (resin is much easier to color!).
The tile pictures show families of colors with tile #'s in the list that give the pigment name and the quantity added to the concrete mix (by percentage of dry concrete powder). Take what you see to be a relative guide as there are many factors that will lead to variations in color and none are in my control (measuring the pigment quantity accurately is the first and most common variable but there are others).
When I add one of our pigments to a white concrete mix, I'm checking to find out if, for example, does a green pigment give a green tile (is the tile at least a similar hue) and, is the amount of pigment small enough to not weaken the concrete? And that's it! The conditions which make me put a pigment in the "not compatible" category are splotchiness, very low tinting power, and fading within a short time (there's more info on colorfastness further down). If the tile hue is different from the pigment name I won't reject it as long as it is a pleasing color, because you will know ahead of time what pigment will yield that color.

The last picture shows examples of concrete additives other than colors:
It shows #63-101 or #80-102 with a "decorative" agg added in one of two ways: 1) "Exposed Aggregate"- variations are: mix the decorative agg with the wet concrete mix (integral addition), then when the concrete is semi-hard, brush away the surface of the concrete until the embedded agg is "exposed", or wait longer and chemically remove the concrete with a weak acid like vinegar, or wait even longer and remove the surface of the concrete by grinding with diamond abrasion until the agg is exposed (large surfaces use other techniques like applying a spray of retarder to the top surface, then when the body of the concrete is set enough, hosing off the top layer of the concrete with a spray of water), 2) "Non-integral Addition"- lay the decorative agg on a surface and pour the wet concrete mix on top of it, then after it's (partially or fully) cured, flip it over and the agg will be on the top (large surfaces use method 2 performed by spreading the decorative agg on top of an already placed layer of wet concrete that's thickening).

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MAIN DESCRIPTION:

This is a strong and hard white concrete mix which is specially formulated for small objects like jewelry, small sculptures, small vessels, and the like. It has small sized, scaled down aggregates so the mixture can fill any fine details which will be narrow cavities in your mold that would not fill if aggregates ("agg") are too large.
Instead of a standard "river" sand and gravel that construction type concrete contains this has a fine 80 to 120 mesh sand for the "fine" agg and a "medium" 30 to 60 mesh sand for the coarser gravel agg. Both aggs are free flowing sands.

We have 2 versions of this white concrete mix. Both are based on White Portland Cement, containing the same ingredients which include a total of 3 types of cements, plus additives such as superplasticizers. The only difference is in the aggs (the sand). Here is a description of the two versions:

The 1st, ("standard") version, #63-101, contains all aggs needed for a strong, attractively textured mixture. The coarser 30 to 60 mesh sand has particles large enough to be seen and they give an overall gently speckled bird's egg effect to the white concrete casting. We call this the "All-Agg" version (which stands for "[contains] All Aggregates)"

The 2nd ("special") version, #80-102, does not have the coarser medium sized 30 to 60 mesh sand. There is room left for those who would like to customize the mix in either of two ways:
A). Those who would like to create their own "exposed aggregate" effect, which sets their concrete apart from that of others by containing sand which might have unique colors, be sized or shaped differently, might have reflective surfaces, and so on. Up to 15% of new agg can be mixed to the existing amount which will bring the agg level back up to our "standard" concrete's amount of agg. More can be used, but over 25% will begin to result in a weaker concrete.
B). Those who have objects with the finest of details, which will have molds with the narrowest of cavities. They can't have aggs large enough to block the mix from flowing into all details of the mold. Since the larger 30 to 60 mesh particles are not present in this version, problem solved.

Our concrete mixes combine several ingredients to make a concrete "proportionately strong" for the small sized objects it is meant to cast. If you cast a 12mm (1/2") detailed jewelry pendant with the general purpose "High Strength" concrete mix found in 60 or 80 lb bags from masonry suppliers, you will probably fail, not just because the aggs are too big but because the concrete is not strong enough, mainly it's flexural and compressive strength is not great enough. Like it says on the bag of those mixes, for sizes 2" or thicker. It's strength is only high enough when its mass is large enough, in multiple inches.

Is our White Art Concrete mix considered a "pozzolan" mixture? Technically no, but that term is sometimes used to mean any concrete which has ingredients that make it significantly stronger (see our "Gray Art Concrete" or "Dark Art Concrete" which do have pozzolan ingredients). This does have some of those special ingredients, but not the ones that fulfill the definition of a pozzolan. Pozzolans are defined as:
"....a broad class of siliceous and aluminous materials which, in themselves, possess little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide (Ca(OH)2) at ordinary temperature to form compounds possessing cementitious properties. The quantification of the capacity of a pozzolan to react with calcium hydroxide and water is given by measuring its pozzolanic activity." That is from Wikipedia.

Details about our White Art concrete:

- Has multiple types of cement and additives which produce a denser and stronger concrete. An example of such an additive is a "water reducer" which allows a given amount of dry concrete mix to become fluid and workable using less mixing water. Excess water in concrete contributes to porosity. And porosity means lower density and lower strength. An object much smaller than sidewalks and walls, such as elements in jewelry or small sculptures need concrete which is dense for reproducing tiny details. And it needs high flexural strength to resist breaking when in thin sections.

- Is made with white portland cement, and light colored additives to produce a light colored concrete. A whitish concrete is much easier to color with pigments when mixed than the standard gray concrete. Also, "Exposed aggregate" effects are much more visible with white concrete than with standard gray concrete. In order to produce a white-as-possible concrete, all the extra ingredients (cements and additives) must also be nearly white colored. It's harder and more expensive to produce white ingredients, so the choices available when formulating a white concrete are more limited than with regular gray concrete. It's easier to make pozzolanic and/or very high strength gray concrete than white concrete.

- Needs only water to produce either a pasty or fluid mix. Concrete made with small amounts of water is very strong, but our concrete does allow for higher than normal amounts of water when needed to be quite fluid and still have surprising strength and hardness. One of our grades is "cement rich" (#80-102), meaning it has space for more agg to be added if the customer so desires (the amount of water may need to be slightly adjusted upwards to accommodate the added sand).

- Has high hardness. We formulate and test our concrete with small (1.75" x 1.75") thin tiles. After they're cured, the tiles allow us to do inexpensive testing by holding them at various heights and dropping them onto a slab of polished granite. We see how resistant to breaking they are and also how hard and dense they are by the sound they make when hitting the granite. The hardest samples have the highest pitched vitreous ringing sound when they hit the granite. We have another test of flexural strength which is simply attempting to break the tile with forceful bending by both hands.

- Can be heated to 120 F under a light or in an oven to speed it's cure and drying time. It's best to allow it to harden enough to demold at room temperatures. Depending on the concrete mix, the water used, the configuration of the mold, and the room temperature, objects can be demolded in 45 minutes to 4 hours. Surface treatments like exposed aggregate can be undertaken shortly after demolding. Coating/finishing/wetting with natural oils and finishes like linseed or shellac can be done after 2 to 6 hours depending on ambient temperature and humidity. Burnishing works best (hard concrete can be burnished with various metal tools) after full cure which may take 8 hours to 3 days (contrast that with construction concrete which must be covered to retain moisture and will not be fully cured for 1 to several weeks, depending on the type of concrete used).

- Has lower shrinkage than pure Portland cement concrete and is less alkaline which makes it safer to handle and easier to color. It is also less subject to efflorescence (crusty whitish mineral salts deposited on the surface by the movement of water through the concrete) than construction grade concrete.

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Rubber mold material considerations for concrete:

Rubber mold materials for casting concrete:
-- DIY custom silicone, platinum based, thick walled molds
-- Pre-made thin walled silicone molds
-- DIY custom urethane molds
-- DIY custom latex molds

Portland cement concrete mixes (either with or without other cements and high strength additives) can and should be cast into rubber molds for ease of demolding, especially with decorative or sculptural objects that are detailed. Large objects usually are cast into custom urethane molds. If shrinkage from the original object can be tolerated custom latex is an option if the proper release agents are used. Small objects like those that our concrete mixes are intended for more often use silicone rubber molds these days. Using the pre-made silicone molds with very thin walls that are available all over the internet are not a good choice for production molds but are great for a limited number of castings. More on that just below.
Urethane is less expensive, thus is more often used for larger molds. Latex is even less expensive than urethane. But besides cost, urethane has several things going for it that make it superior to silicone.
Urethane is much tougher (with greater tear strength, assuming you use a quality version) than silicone, but most urethane rubber must be used with adequate release agents for each casting made. The same can be said for latex molds. Silicone molds are most often not used with release agents and will more accurately reproduce fine detail as long as they hold up. But concrete is rough on rubber molds of any type. Concrete tends to stick to more substrates than plaster or gypsum cement and concrete is highly abrasive, unlike plaster and gypsum cement. It will dull shiny silicone molds if you are production casting scores of castings. For around twenty or fewer castings you should not have any trouble casting concrete into bare silicone molds and getting easy release with no significant mold deterioration, although mold shine will probably deteriorate before that.

The low-down on silicone molds:

The big advantage of silicone is that theoretically, you don't need any release agents. In fact, it's very difficult to get water based release agents to spread evenly on new silicone because of the extreme hydrophobic nature of silicone. And oil based releases are problematic because of silicone's tendency to absorb oils and swell, distorting the mold and also start a vicious circle of weakening the mold surface leading to pitting, roughness, and sticking of the casting. Urethane, most types of which need a release agent for each casting is very easy to release-coat.
The all-important outer surface of a silicone mold can start dulling (if shiny) and take on unwanted textures from wear in less than production casting 10 pulls, depending on the quality of the silicone and the presence of fillers. At that point, silicone molds will require release agents to get any further life from them.
Be wary of the pre-made thin-walled silicone molds that flood the craft market. Good quality pure platinum cured silicone rubber is expensive. Third party mold makers are free to add fillers to lower their costs. Some fillers such as fumed silica and carbon black can enhance certain forms of strength, but all fillers (with the possible exception of small amounts of pigment) will increase the permeability of silicone which is the root cause of silicone absorbing solvents from release agents and the casting material itself. Fillers will speed up the onset of the mold wear described above. A translucent, platinum cured, thick-walled silicone mold made yourself will greatly outlast a thin-walled mold (especially if it contains fillers). And, if you can find translucent premade silicone molds you should choose them instead of colored molds. They indicate lack of fillers.
Another peculiarity of silicone (and some other polymers) used to cast high quality concrete is a "whitish" appearance that castings can take on. Not many sources cite this phenomenon but it exists. Some people who notice this relate it to efflorescence (which is a well known problem), but it's presentation is not at all like traditional efflorescence, which most often appears on masonry walls. Urethane molds do not seem to share this odd property. You will find that castings in urethane tend to have more "color". I personally can't explain why this occurs. The only commonality with efflorescence is the whitish color. And, it's not a problem if you're wanting your castings to be white! If you're adding colorants to your concrete then it becomes a consideration and something to be tested for depending on your particular castings and processes. And, it's a problem you can do something about if you're making your own molds and have a choice of whether to use silicone or urethane.


Surface treatment of concrete castings:

Concrete has a wider variety of possible surface appearances than its cousins, plaster and gypsum cements, unless you chose the few gypsum cements that are made with the ability to accept aggs. Even if you're casting with the lower strength construction concretes that come in 60 or 80 lb bags, you can use exposed aggregate surface treatment to get a different appearance. But you can't effectively and inexpensively color gray Portland cement based concretes with anything but the red or black of the iron oxides that are the most saturated of the iron oxide pigments.
"Exposed aggregate" is a surface treatment that's been around since the early 1900's. "Aggregate" (or "Agg") refers to the sand and gravel of varying sizes that is necessary to make concrete. The strength of concrete is increased most effectively when the aggregate grain sizes are a mixture varying from fine to coarse. The other ingredient of concrete is the "cement" which binds the agg grains together. Portland cement is the type most often used as the binder, but there are others with different properties.
Exposed aggregate involves removing the outermost layer of the concrete binder and its smaller aggs to a depth that reveals the integral larger aggs, effectively "exposing" those aggs, making them appear to have emerged from the concrete body. The "larger" exposed pieces of agg can be medium or coarse. Most often they are coarse enough to visibly distinguish individual agg particles. The resulting surface will have a "bumpiness" dependant on the size of the largest agg grain. Agg particles will be partly submerged into the mass of concrete and partly protruding upward away from the mass. The protrusions will result in a slightly bumpy surface which can be smoothly rough if the agg is made of rounded particles or sharply rough if the agg is angular.
The exposed agg can be over the entire surface of the concrete or only over areas of a pattern that is walled off by strips of dividing borders, curved or straight, which define the pattern. Parts of the pattern can consist of agg of different colors, sizes, or particle shapes.
The tricky part of exposed aggregate is in removing whatever depth the binder and smaller aggs need to be removed accurately. There are several methods employed to remove the concrete surface: by chemical means, by brushing before full cure of the concrete, or by abrasion.
A chemical that reacts with the alkalinity of the binder ( a mild acid) is applied evenly over the surface which dissolves the binder to the desired depth immediately followed by a pure water rinse which carries away the dissolved binder and smallest agg grains, leaving the now lower outer surface of the concrete intact. Timing is crucial to avoid weakening the concrete too deeply.
For small objects vinegar is an acid that will work for removal of depths 1 mm or less. Either brush the vinegar or immerse the object into a container of vinegar for 1 minute or less, and then use a soft brass brush to get rid of the softened concrete. Follow this with a thorough brushing with a non-metallic brush while the object is soaking in a container of pure rinse water or by brushing under a stream of running warm water.
An alternate method that avoids the use of a chemical reaction is to demold the object as soon as possible, while the concrete is hard but not cured. Us a thin bristle wire brush to abrade the concrete surface and small agg grains away to a shallow depth. This method depends on demolding the object soon enough and it won't work on objects with fine details, it will ruin the detail. Also on detailed objects you won't want to demold early because you need the concrete to be hard enough to withstand the demolding process without breaking off the detail.
Removal of the surface layer of concrete by abrasion can be done in several ways. One is by blasting with hard grinding material such as aluminum oxide, silicon carbide or other loose abrasive media in a sand blasting cabinet. Using this method the blasting nozzle "gun" which is held by hand is easy to control and areas to be removed by varying depths can be accurately accomplished. Areas to be left shiny (if the concrete is polished before going into the blasting cabinet) can be protected by adhering rubber sheeting onto the object where the concrete is to be left polished. Patterns can be created consisting of brightly polished areas against a varying depth matte surface finish
Another way to remove surface concrete by abrasion that is not strictly an exposed aggregate method involves grinding away the surface concrete with diamond pads or burrs (for curved surfaces) after the concrete is fully cured. Often this method goes further, to actually polish the concrete. It differs from exposed aggregate in that the resulting surface is smooth and the agg grains themselves will have been ground, revealing the interior color of the agg pieces. This method works to full effect when the agg consists of larger pieces.
Another less often used method of concrete surface treatment is burnishing. A cured concrete surface, either "as is" from the mold, or with an outer surface that's been ground smooth, is hard enough to be burnished with metal tools rubbing and compressing the surface to a bright, very polished-appearing state, leaving a mark of metal ground on the concrete surface that the burnisher stylus is made of. If softer metal styli are used more metal will be deposited and line drawings can be made on the concrete surface. A brass pencil-like stylus, for example, would leave brass lines that are drawn upon the surface. Wider tipped hard metal tools can be made to compress without transferring any of the metal. A professional mechanical burnisher usually works using a tip that is a ball or roller that rotates against the surface,

Coloring Concrete:

There are two ways, integral and staining/coating.
Integral means that colorants are added to the mixing water or the concrete powder before they are mixed together, which colors the entire mass of the casting. This requires more colorant (usually pigments) which makes it more expensive.
When coloring integrally, sources will recommend adding the coloring pigment(s) to the water portion of the premeasured powder/water ingredients. It is stirred into the water until an evenly dispersed color is achieved. But, differing pigments will mix with water with varying degrees of ease and the high amounts of pigments sometimes required will be difficult to completely disperse (some thick pigment will remain at the bottom of the mixing water). Some will require a wetting agent (the dishwashing additive product called "Finish" is an easy to find example) to get the pigment to mix at all with water. And some will resist mixing even with a wetting agent. For those difficult pigments more drastic action will be needed.
For the great number of mixtures needed to be done for my testing tiles, I used a homemade titanium stirring spatula with a curved cross-section which matched the curve of the small container (a disposable plastic 1 oz Solo portion cup) holding the concrete powder. I added the pigment powder to the concrete powder and stirred it in, pushing it against the side of the container cup. Streaks of pigment powder show up in the concrete powder when it is not yet mixed completely using this method. This is effectively a form of mortar and pestle. Because I was testing for repeatable colors, I needed an accurate but efficient method to disperse *all* of the pigment into the concrete mix.
Since you will likely lack a special stirring spatula, best practices would be an actual mortar and pestle for the most difficult of pigments if you find that adding the pigment powder to the water is not dispersing it fully. You can purchase an inexpensive one online. You don't need to disperse the pigment into the entire portion of concrete powder, just enough to be able to see the pigment streaks as they are lessened with mortaring. That mixed portion will then be easy to combine with the remaining amount of concrete powder. When added to the mixing water the use of a wetting agent may still be needed. Trial and error will tell.
Staining involves mixing colorants with a binder and applying that liquid colorant to the surface of the dry concrete casting. The concrete must be completely cured and dried, since the process involves the stain being absorbed by the concrete's outer surface, and the deeper it's absorbed the more permanent the color remains.
Colorants will not work well with the "standard" gray portland cement concrete since the colorant needs to overcome the dark opacity of the concrete and its alkalinity. Concretes made with white ingredients such as this White Art Concrete of ours provide a lighter base material that's easier to color, requiring less colorant than the gray concrete mixtures and tending to look more like the colorant itself (a more accurate presentation of the pigment used), but even then guaranteed results are not assured.
Coloring a very complex chemical mass of opaque mineral oxides, silicates, and alumina that concrete is made of is not easy. It is alkaline in nature and that alkalinity can vary from concrete mix to concrete mix depending on what kind of cement binders are used. For example, cements with high early strength made by the addition of sodium hydroxide will increase alkalinity (sodium hydroxide, aka lye is extremely alkaline, with a pH of 13). Pigments are chemical compounds themselves and some will deteriorate or break down completely by strongly alkaline environments. The effects can vary from simply shifting or changing the color of the pigment (which can be acceptable if you know ahead of time what the resultant changed color will be), to the unacceptable result of the disappearance of any usable color displayed (such as a weak gray) by the broken down remnants of the chemical pigment. Other factors that can affect the expected appearance of a pigment known to give a particular hue is the amount of water added to the concrete. Higher water content will lighten the pigment color. This can happen easily and unexpectedly with the case being that a certain amount of concrete pigment will give a certain hue with a certain saturation on one day, but the next day more water is added to the concrete mix to extend the pourable duration of the mix. The result is a version of the concrete color that is lighter and does not match the color of a previously poured batch. Other factors that can result in color variability from batch to batch are the addition of calcium chloride to the concrete mix, often done to accelerate the cure. Another can be the ambient temperature the concrete is mixed and placed in. If it changes from batch to batch that can change the water content available (high temperatures can rob available water by evaporation) and water content will in turn change the color.
For more details on this topic read the article on color in concrete:
https://www.buildsite.com/pdf/daviscolors/Davis-Colors-Color-in-Concrete-Beauty-and-Durability-Technical-Notes-62199.PDF
and:
https://www.wrmeadows.com/blog/blotchy-concrete/#:~:text=Concrete%20discoloration%20is%20not%20a%20rare%20event&text=These%20factors%20include%3A,The%20use%20of%20calcium%20chloride

Exposure to Sunlight:

All materials containing colorants will be affected by sunlight. It is only a question of when, not if. Our White Art concrete when mixed with water and cured has not yet been tested by the ravages of time in the sun, it has not been around for a year so far. We recommend interior use only. In any case it is inevitable that a concrete containing cements other than regular Portland Gray will not hold up as well as construction type concrete when used outdoors. Our White Art concrete will be more affected than our Tan Art and Dark Art concrete.
When colored by pigments, White Art Concrete should be kept from direct sunlight as much as possible. Pigments are the first to be affected in any material to be colored, including paint mediums, plastics (such as epoxy "resin"), glass, and cementitious materials like plaster or concrete. The lightfastness of colorants varies depending on the chemistry of the pigment, its opacity or transparency (pigment versus dye), the concentration in a medium, the chemistry of the medium (linseed oil versus epoxy versus white concrete), the direction of the sunlight (a sun high in the sky will transmit more UV radiation than a sun low on the horizon), and other factors.
But it can be said that pigments used with organic mediums such as natural or synthetic polymers (linseed oil, epoxy, etc) will fade faster than pigments used with inorganic materials such as concrete. And of course, organic pigments in themselves will fade faster than inorganic pigments. Let's finish on a positive note: although pigments will fade when exposed to sunlight, a given pigment that is added to linseed oil and put on a painting's canvas will be more subject to fading than the same pigment added integrally to a compatible white concrete (following best practices in the "NOTES ON COLORANTS" section above) such as White Art Concrete.