Concrete and Hypertufa

Concrete Consistency

Concrete is composed of cement, sand and/or gravel, and water. Cement is the key ingredient to any concrete, being the “binder” or glue that holds all the other components together. Pre-mixed concretes can vary significantly in the relative proportions of cement, sand and gravel. Mixes high in crushed rock or gravel are common in commercial concrete, but for pouring stepping stones, excessive amounts of gravel can mar the detailed finish on a stone. High cement content mixes create a smooth, consistent surface finish, but are slightly more expensive. A mix using more fine-grained sand can be used to produce a stone with a surface resembling sandstone. For a very high-detail, smooth finish, mortar mix is ideal. It contains no rock or gravel, just sand and cement.

Mixes also harden at different rates, depending upon temperature and the percentages of cement in the mix. The more cement, the faster the cure. The warmer the ambient air temperature, and/or the warmer the water added to the dry concrete, the quicker the set time. For producing strong, durable stepping stones, however, aim for a slow, cool and damp cure. Concrete curing is a chemical process, not a drying process.

The percentage of water added to a concrete mix is the main factor affecting the strength and quality of your finished stepping stone. Less water produces stronger concrete. But when creating stepping stones with high-definition detail, an overly-stiff mixture doesn’t easily settle into the nooks and crannies of a mold. Try striking a balance between a thick and thin mix- muffin batter or brownie batter consistency is good. Start with a little less water, blend well with the concrete or mortar mix, then add more water a little at a time until you reach the desired consistency.

Concrete Mixes

Either pre-mixed concretes or mortar mix are the fastest and easiest ways to create stepping stones and other garden ornaments. But if you wish to experiment, blending your own mixes requires very little extra effort, and the reward is a much wider range of colors and textures in the finished stone. Keep in mind that concrete should roughly contain (by weight, not volume) a minimum 15% cement, 60-75% aggregate (this can be all sand, or a mix of sand and crushed rock or pumice) and a minimum of 15-20% water.

To make your own blends you’ll need:

Cement

The base material of concrete is cement. Portland cement is sold in any hardware store or home improvement center. “Portland” refers to the method used to create the cement, and not to a specific brand. Portland cement is most commonly grey in color, but white Portland cement can be purchased as well. It’s more expensive and a little more difficult to find than the grey, but most masons’ supply houses will carry it.

Grey Portland cement alters the hue of any added pigments. By increasing the quantity of pigment, the color can be intensified, but the color will still remain somewhat muddied – particularly lighter tones such as ochre. This isn’t necessarily a bad thing – it just depends on the desired look.

White Portland cement blended with white sand is ideal for creating more saturated, true-to-value colors. When white cement is blended with white sand, the resulting rock resembles plaster. So-called “pool sand” (actually white marble dust) makes an especially bright white mix; think of it as a versatile canvas for fine-tuned color blends. This might not be important for the production of stepping stones, but if you wish to use the molds for creating decorative wall plaques, white Portland cement may be more suitable.

Sand

Bags of sand can be purchased in any hardware, building or home improvement store. This sand is invariably grey river sand, so if you wish to make lighter-colored stones using white Portland cement, you’ll need to source white sand. Mason’s supply stores are your best bet. NOTE: beach sand should never be used in cement mixes due to its high salt content.

Aggregate (optional)

Beautiful, strong and fine-textured stepping stones can be made without aggregate; aggregate is usually added to lower the cost. Crushed rock is the most commonly used aggregate, but pumice can be used as well. Certain percentages of pumice in a concrete mix create a rough, aged look to the stones.

Concrete Recipes

Many interesting, creative possibilities exist for concrete blends. Don’t think of these recipes below as your only options; think of them as a starting point. After you’ve made a few batches and are comfortable with the process, try concocting your own concrete mixes. Each recipe is enough for approximately one stepping stone, but keep in mind that there will be some variance due to differing mold sizes. All measurements are by volume, not weight.

TIP: A one-quart yogurt container is ideal for scooping and measuring.

Recipe #1 – Basic Concrete without Aggregate

2 1/2 quarts Portland cement, white or grey
5 quarts sand, white or grey
1 3/4 – 2 quarts water

Mix the dry ingredients well. Slowly add water until the concrete is workable. Don’t add all of the water at once- you may not need the full amount. Continue to add water until the mixture resembles a thick pancake batter.

Recipe #2 – Basic Concrete with Aggregate

2 quarts Portland cement, white or grey
4 quarts sand, white or grey
3 quarts aggregate- rock, pumice, etc.
1 1/2- 1 3/4 quarts water

Mix the dry ingredients well. Slowly add water until the concrete is workable. Don’t add all of the water at once- you may not need the full amount. Continue to add water until the mixture resembles a thick pancake batter.

Recipe #3 – Concrete with Perlite
Perlite is an ultra-light, glassy volcanic rock. Added to a concrete mix in higher percentages, it creates an interesting pock-marked, antiqued look in the finished stone.

2 quarts Portland cement, white or grey
3 quarts sand, white or grey
3 quarts perlite
1 quart water

Mix the dry ingredients well. Slowly add water. This mixture doesn’t contain as much water as a standard concrete recipe because the finished stone should have a more open, porous texture. Therefore add water until the mix resembles a crumbly cookie dough. Press the mix firmly into the mold.

Hypertufu Recipes