Mixing Concrete and Mortar Without a Hardware Store

Understanding the Ingredients

Portland cement: The grey powder that binds everything. A bag weighs 94 lbs in the US (50 kg in most other countries). It reacts chemically with water — this reaction (hydration) is what makes concrete hard, not drying out. Concrete underground or underwater can cure perfectly.

Sand: Clean, coarse sand (sharp, not rounded beach sand) fills the spaces between aggregate particles and bonds with cement. Sand must be clean — organic material and clay both weaken concrete. The field test: squeeze a handful of sand over a white surface and shake. Minimal dust indicates clean sand.

Aggregate (gravel): Crushed stone or natural gravel in 3/4-inch size for general work, 3/8-inch for thinner pours. Aggregate provides compressive strength and reduces the amount of cement needed.

Water: The catalyst. Must be clean enough to drink — salts and organics interfere with the hydration reaction. Sea water produces corrosion in reinforcing steel and is unsuitable for reinforced concrete.

Standard Mix Ratios

Different applications require different proportions.

| Application | Cement | Sand | Gravel | Notes | |---|---|---|---|---| | Structural footings/slabs | 1 | 2.5 | 2.5 | Standard mix | | Light construction, paths | 1 | 3 | 3 | Less cement, lower strength | | Masonry mortar (block/brick joints) | 1 | 3 | — | No aggregate; add hydrated lime for workability | | Stucco/plaster coat | 1 | 3-4 | — | Fine sand only | | Repair grout | 1 | 2 | — | High cement for flowability | | Rich structural mix (columns) | 1 | 2 | 2 | More cement, higher cost |

These ratios are by volume for field use. Measure by consistent scoops, shovels, or buckets — the ratios matter more than the precise measurement tool.

Mixing by Hand

Equipment:

• Mixing board (a sheet of plywood on a flat surface) or a metal wheelbarrow
• Hoe (masonry hoe preferred — has holes to reduce drag, but any heavy hoe works)
• Measuring container (a 5-gallon bucket gives consistent scoops)
• Water in a separate bucket (so you can add incrementally)

Adjusting for Temperature

Hot weather (above 85°F): Concrete sets faster in heat. Use cold water or ice water for mixing. Wet the forms and substrate before placing. Place and finish quickly. Begin wet curing immediately after finishing.

Cold weather (below 40°F): Hydration stops below freezing. Use warm water (not hot — it accelerates set time, making the mix difficult to control). Cover placed concrete with insulating blankets. Do not allow concrete to freeze in the first 24-48 hours before it has gained sufficient strength.

Ideal range: 50-75°F produces the strongest, most workable concrete.

Making Mortar for Masonry

Mortar has no large aggregate — it is just cement, sand, and water (and often a small amount of hydrated lime for workability).

Standard mortar mix: 1 part portland cement : 3 parts sand : (optionally) 0.25 parts hydrated lime

Hydrated lime (Type S) is not the same as agricultural lime. It improves workability, reduces cracking, and extends working time. In field conditions without lime, a slightly wetter sand-cement mix with careful application works.

Masonry mortar consistency: Mortar should hold firmly on a trowel when turned upside down but drop cleanly when shaken. Too wet and it sags out of joints. Too dry and it tears when the trowel lifts away from freshly laid block.

Joint thickness: Standard masonry joints are 3/8 inch. Thicker joints are weaker because mortar is weaker than properly made brick or block.

Sourcing Ingredients Without Hardware Stores

Cement: Portland cement has a limited shelf life once opened (6-12 months in a dry bag) but unused sealed bags store indefinitely in dry conditions. Stock it now. In a post-supply scenario, lime-based mortars can substitute for non-structural applications.

Sand: River sand (screened for organic material), crushed stone screenings, and decomposed granite all work. Avoid beach sand (salts corrode steel). Test any unfamiliar sand by making a small test batch and curing — if it is weak or crumbly at 7 days, the sand has contaminants.

Gravel: Crushed stone, river gravel, or broken rock all work as aggregate. Maximum particle size should be no more than 1/3 the thickness of the concrete section being poured.

Water: Clean water is the only requirement. Well water, collected rainwater, and stream water (in non-industrial areas) are typically suitable. Avoid water with high organic content (swamp water) or visible color.

Lime Mortar: When Portland Cement is Gone

Lime mortar (calcium hydroxide + sand + water) was used in all masonry construction before the development of portland cement in the 1820s. Many historical stone buildings built with lime mortar have outlasted concrete-era construction.

Making lime: Burn limestone (calcium carbonate) in a hot fire (kiln) at 1650°F+. The result is quicklime (calcium oxide). Slake the quicklime by adding water carefully in small amounts — this is an extremely exothermic reaction. The result is hydrated lime (calcium hydroxide). Aged lime putty (hydrated lime stored wet for months or years) produces the best mortar.

Lime mortar mix: 1 part lime putty : 3 parts sand. This is much weaker than portland cement mortar (roughly 300 PSI versus 2,500+ PSI) and cures slowly, but it is workable, flexible (accommodates settlement), and self-healing. It is appropriate for mortared stone walls, chimneys, and plaster.

The critical difference: Lime mortar carbonates as it cures — it slowly re-absorbs CO2 from the air to return toward calcium carbonate. This process requires air contact. Lime mortar cannot cure in solid interior masonry the way portland cement can.