Bo's Easy Mixes For Small Projects
Mixes for hand-built projects and for non-critical uses are described. Generally, it can be preferable to use pure Portland cement powder and add locally found sands or aggregates. Some suppliers include all ingredients pre-packaged, (just add water), but these prevent tailoring mixes for your specific requirements. Common Portland cement is generally safe to handle by healthy people without extreme sensitivities. It is advisable not to breath dust of any kind. For more information, search the web. Setting up a fan to control dust might in some cases help. I tend to position myself up wind from dust sources, when possible. In slow moving air, cement dust settles fairly close to the source and rarely rises upwards unless air currents stir up clouds. Dusk masks may help but are not perfect. I believe cement wash-up water is good for many plants (living plants that are not acid loving). I tend to let this accumulate on work area ground surfaces since mine are all dirt surfaces anyway. I primarily use pail mixers to better recycle wash water in the subsequent batch.
I use approximate mix proportions and rarely attempt precise measurement by weight, (for small projects. Engineering specifies precise mixing by weight and not by volume). I use assorted containers or shovels to proportion mixes by volume, but with an awareness about the limitations. Exact proportions are not highly significant in small projects. The first mix is for thin sections of work like non-critical ferrocement or coatings. I prefer pail mixing and avoid use of large mixers because larger mixers require more clean up effort and more clean up waste. Following are rich mixes i often use. For many years i also used cheaper mixes with much less cement for less critical work like garden ornaments. The rich mixes have been called "grout" by concrete people and are not always advisable for large contiguous surface areas. Stone masons have traditionally used mortar which is typically based on fine sand and Portland plus lime mixes. While rich mixes can be very strong at first glance, they will eventually shrink more than sandier mixes. (Shrinkage can manifest as cracks). Rich mixes are good for small projects and do-it-yourself repair work.
A Simple Mix For Ferrocement, innovative masonry , or modified, thin Coating applications.
1 Part Portland Type I Cement *
2 Parts Sand
Generally, just enough water to obtain a sticky, plastic consistency. Some special applications like sand molds may benefit from wet slurry consistencies. Add fibers like PVA or AR Glass for slight strength and plasticity improvements*.
I prefer to add water first and also prefer to use this same water to wash down the previous batch inside the bucket. This can be accomplished with a hose and fine spray. Mixing tools should be kept in the shade and wind free. If work must proceed under full sun light or dry winds, then further compensating measures should be considered. Approximated proportions may be checked by feel: With too little cement powder added, the result will lack a feeling of cohesion and stickiness. To test a fresh cement batch: Simply be sure a "snow ball" can be formed and lightly juggled between two hands without falling apart. If too wet, simply add a little more dry ingredients. If too dry add a misting of water.
The following links feature some of my cement and concrete uses.
Sand cast methods to build almost anything.
An introduction to building easily-built, low cost, low wastew, free standing frameworks.
My page with many links concerning cement and concrete structures.
More will be added to this list eventually but here are features and ingredients which improve sculptural or free standing work.
Increased Plasticity -- plaˈstisitē - noun - the quality of being easily shaped or molded.
Note- Most concrete users want fluidity, not plasticity! Sculptural users often want plasticity. Some projects include both qualities.
The following increase plasticity.
Masonry Light Cement can be used instead of Type I or Type I II. Or Portland cement mixed with (hydrated) lime will work (traditional mortar cements).
Portland Type II cement is generally used for sulphate resistance but it has seemed slightly more plastic in sculpting.
Various kinds of air-entraining agents are available which can also improve plasticity. (Shaving cream or soap also might help, but try these sparingly).
Sand can be reduced to 1.5 or 1.0 for each part of cement for somewhat improved plasticity and stickiness in small hand molded work, (easier & surer).
Additional fiber can be added during wet mixing, however, finer diameter fibers are advisable for very thin coating work, (fiber also disperses shrinkage).
Clay or local soil can sometimes be added in small amounts (less than 10% of cement paste) which improves plasticity but these risk strength and shrinkage.
Pebbles or gravel can increase stiffness or bulk plasticity. Selective sizes can be tried separately to better address a users specific need.
Many kinds of organic waste may be found helpful. Saw dust, rice hulls, and almost any clean, none soluble material may work.
Light weight aggregate, vermiculite, perlite, certain volcanic soils, etc., can improve plasticity when sized smaller than one third of the final thickness.
Absorbent materials can allow wet or muddy quality to begin work and then absorbent ingredients will slowly reduce the excess watery effect, while finishing.
Additionally, styrofoam shipping peanuts (ground up or whole) will greatly reduce the weight of wet cement. As the mix lightens in weight, gravity will have a smaller influence in slumping the mix. This provides a new and unique plasticity. However lightweight cement or concrete is generally weaker to some degree. One strategy is to use lightweight mix as a sculpted core. After partial hardening (and perhaps some pre-hardened carving) this core can be coated with an appropriate coating mix of cement.
Don't use corn starch packaging, except when weak results are acceptable. Simply test by wetting with saliva on a finger! Starch type immediately dissolves.
Silica additives in various forms will improve mold ability and plasticity, but caution should be exercised to avoid breathing silica dust. It is far more dangerous to breath than is ordinary dust or cement dust. Also if one uses it in a confined room- All dust in the room can become more suspect in terms of safety, (in the log run). Silica additives are best known for adding strength to plain mixes and were a key cement ingredient in ancient Rome, (volcanic pozzolanic ash).
A very notable gum substance in powder form, called methocel in small doses can improve the plasticity and stickiness. It is very difficult to find. I eventually found one large bag costing $500!. I bought Dow Brand, J75MSN (viscosity 75,000 cPs @ 2%) Small doses produce a large effect.
Additives can add a great deal of cost to a project. For most work i have generally used the plain recipe without additives.
Another useful commercial admix is commonly called "acrylic" or "latex". Formulae vary but the effects are very similar. These are generally sold as liquid additives and are sold in varied concentrations. Frankly, a product with 100% concentration would be preferable to reduce shipping and handling costs, but it is difficult to find on the market. Many building suppliers sell diluted acrylic or latex in pails or bottles. Furthermore, some manufactures also offer refined powder ready-mixes which are finely sifted and pre-mixed dry. These are OK but can require much longer shipping distances of sand and cement. I prefer use of local materials when possible, to reduce wasteful shipping habits. I have preferred use of these acrylic or latex additives in thin work for some combined effects: 1) Cure acceleration along with reduced evaporation from surfaces. Acrylic or latex mixes will better seal in the needed water to complete bulk curing. There are instances where it is highly desirable to achieve a full strength cure, quickly. 2) A modest plasticity-improvement and water reduction is achieved. Achieving low water cement mixes helps to reduce shrinkage. Plasticity and stickiness is slightly increased. 3) An overnight cure or an accelerated cure is made possible with acrylic/ latex additives. (Do check labels for more specifics and variations). One can also gain these benefits to a degree and at lower cost: Visit your local surplus dealer or super sales:. Some of the price-cut latex or acrylic paints will work satisfactorily in cement mixes. Try before buying too much. The coloring may or may not be right, but the resulting cement mix may attain some of these mentioned qualities.
Yet another method to cheat a little and achieve very significant plasticity is to use up some of those lumps of cement you might otherwise have thrown away: However do not count these lumps as part of your cement portion in the mix (because lumps can reduce ultimate strength).. Instead simply make sure that the largest of these lumps is smaller than one third the thickness of your work piece. Add these lumps at the very last minute before pouring or sculpting the cement. Compact the fresh pour quickly. Note how the lumps absorb excess water and therefore consolidate the fresh cement making it very stiff, quickly. With practice and familiarity, this method can be used as an instant plasticity technique, but do not use it in structurally critical applications, as some strength can be forfeited).
Water reducers: In case one is filling commonly-used form work, (not absorbent forms like sand molds), then additives called "water reducers would help a great deal. Water reducers can save labor in large pours where work speed is important. This additive almost always makes the cement more runny, which resembles excess water without the ill effects of excess water. This feature helps in most concrete applications which are thick or physically large. Where complex reinforcement arrays must be fully penetrated. Where the laborer needs to physically move wet concrete a notable distance. The small user will often confront very different work issues in small work pieces. Sometimes the runny effect is desired, but more often the opposite effect is sought. Very often the small user is keenly interested in plasticity which should be understood as "staying put". once placed and shaped, the small user will very often desire that the shape not slump down at all. High range water reducers can cause cement to slump and in some cases almost automatically "self level". This "self leveling" quality is very useful and with a vibrator tool can sometimes self-smooth a flat surface very satisfactorily. (So smooth in fact that it almost can sometimes appear polished).
There are many other kinds of commercial additives but these listed above have been most useful for small projects and sculptural work.
There are many publications concerning differing applications of cement products. In times passed these tended more often to address engineering interests and not small scale artistic uses of cement or concrete. More recently the internet allows artistic users to share experiences in the real world and in every day contexts. I have encountered countless questions about cements, concrete and composites. For lack of better information, easily obtained, i turned to direct experience of trial and error. I learned that weak mixes can sometimes performed satisfactorily, even under severe conditions like freeze-thaw cycles of a cold climate. The freeze-thaw stresses are most evident where deicing chemicals are used. Freeze-thaw stress is little noticed in small sized, well cured works. Shrinkage rarely effects small pieces but it can drastically affect large work pieces.
A Simple Concrete Mix For Small projects.
1 Part Portland Type I Cement *
1 to 2 Parts Sand
1 to 2 parts stone (crushed or smooth pebbles).
Generally, just enough water to obtain a sticky, plastic consistency. Some special applications like sand molds may benefit from prior coating like wet slurries (grout, also called Neat's Cement or more rarely- "slip"). Add fibers like PVA or AR Glass for slight strength and plasticity improvements** (as well as a shrinkage-control measure). Other, softer fibers may serve equally well to disperse shrinkage effects (avoid cracking). However softer fibers will not improve strength qualities, because they stretch elastically.
I prefer buying Portland Type I* cement without added sand or stone because it reduces unnecessary shipping handling, and drying costs. Equally important, in my mind, is control of the proportions. Commercial pre-mixes are based on specific bulk uses, but not on focused innovative uses. Furthermore, as one having used up a palette full of the premixed bags of concrete mix, i can testify that the proportions have in fact varied, (even though these should have remained constant). This proves that some of the bagged material failed to meet engineered standards. Also, in case one intends to store dry mix, much more bag protection will be required by premixed cement since it involves more bulk (due to sand and/or stone).
I have tended to use very simple mixes at the lowest possible cost and focus my attention on design research more than on material chemistries. During the 1980's i appreciated receiving many material samples obtained from manufacturers but these additives appeared to provide little benefit in terms of cost, (when used in my low budget projects). The primary reasons for this included the questionable aggregates. I was able to find reasonable aggregates in local "bank run" pits since the worlds best aggregates are not readily available at low prices. Even the local ready mix plants sold aggregate which was not always significantly better than material available from near by pits. (One may discover that local pits supply the ready mix people).
One caveat is that, the cement supply available in bags is marketed in a way which readily spoils the cement. One might indeed buy full palette loads of factory fresh Portland cement. However, as soon as one receives a delivery, these bags would already be absorbing humidity from the air. The reason for this is to be found in the numerous small holes punched in the bags deliberately by the cement manufacturer. A user should invest in bulk containers and bulk handling, but pricing in this approach is beyond small incomes. The easy alternative for the small user is to use plastic containers like large garbage containers or else plastic hampers. Or use any tightly sealing container. However this can require extra steps and is troublesome if a person wished to buy a full palette.
*However the Portland Type I Cement manufacturers seem to be officially substituting the Type I formula with the Type I II (pronounced one-two). For thinner coating or improved penetration, the sand amount can be reduced of finer sifted sand can be used. Do not confuse Type I II with Type III. (Type III (three) has been defined simply as Type I ground twice as fine and it is said to cure 4 times faster as a result).
**I think the main advantage of adding fibres is that normal shrinkage is partly controlled. My own reasoning is that that elasticity of most fibers distributes shrinkage and associated stresses. Instead of shrinkage focusing on restricted parts of the work, it will widely distribute shrinkage to each fiber location. Where a manufacturer claims that their product bonds well to cement, i would recommend that a user test this claim by flicking off exposed fibers from a cured surface. I find that all fibers are relatively easy to flick off the cured cement surface, by use one's ones finger nail.
Test Your Mix Batches For Strength -Easily
My favorite method for testing customized mixes is what i call "The Wafer Test". It is simply a small sample from a given mix which is formed into a simple, very thin wafer. I make these wafers with a very small portion of a cement batch. Random shaping is fine but it must be thin and well compacted.
Above photo shows one example of a wafer which has been well cured before it was split.
I will place this wafer close by to where the batch was used. Thus i will remember which part of a project mix can be tested. Furthermore, it is kept moist since i tend to damp cure my work. Damp curing can be achieved with a sheet of plastic or rubber. Under severely dry or windy conditions, an additional water absorbent material, beneath the sheet is very helpful to insure that the curing cement will not dry before it has cured. Occasional water spray is also advantageous. Keep the work damp, or loose some of the ultimate strength. Keep the work damp and assure a higher ultimate strength. The length of the cure varies with temperature, The first few days are the most critical, for keeping the cure damp or wet. Often a week will secure most of the available strength. A full 30 day cure is one of the official recommendations for Type I. After a reasonable cure period the said wafer can be tested. My test is simply to break the very thin wafer by hand. Ordinary mixes are fairly easy to break.
Next Above is the exposed fracture. Note the blue circles in which a piece of stone aggregate (pebble) has been itself split. This signifies that the cured cement is stronger than that piece of aggregate. There were some small slit pebbles which were likely quartz is generally fairly strong among stones, a good sign we should appreciate.
Look closely at the surfaces exposed by breaking the wafer. Within this surface observe whether or not the sand particles remain whole or whether the sand particles have indeed split along the break. Splitting the sand particle tells us that the wafer has reached or exceeded the strength of those particular sand particles. Splitting sand particles tells us the result is as strong or stronger than the aggregate, which is what we want to achieve. If we see none of the larger sand particles breaking... If we know the mix had larger sand particles.... If the larger sand particles stick out, unbroken, along the wafer split... We will then know that either the cure is retarded or that the mix was to some extent faulty. Yet if we unknowingly had used extremely strong aggregate, (like expensive corundum), these particles are stronger than the cement paste itself, (and therefore might not break for this reason). So there are more issues than quickly listed here, but a beginner has plenty to learn by wafer testing. Quarts sand particles are fairly common and generally strong. Yet a wafer test could split the larger, common quartz sand particles.
Note: These pages are placed in the public domain and are furnished "as is". The author assumes no responsibility for the use or misuse of the concepts in this series. All authorities should be satisfied first, as might be required, by relevant laws, before any building proceeds.
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