Concrete vs Mortar
Both contain cement, but they are not interchangeable. One is structural fill; the other is masonry glue. Using the wrong one can mean a failed project.
| Factor | Concrete | Mortar |
|---|---|---|
| Ingredients | Cement + sand + gravel (coarse aggregate) + water | Cement + sand (fine aggregate) + lime + water |
| Compressive Strength | 3,000-5,000+ PSI | 750-2,500 PSI (depending on type) |
| Application Thickness | 2 inches minimum, typically 4-6 inches | 3/8" to 1/2" joints |
| Cost | $5-7 per 80-lb bag ($120-150/cubic yard) | $7-12 per 60-80 lb bag |
| Cure Time | 24-48 hrs initial set, 28 days full strength | 24-48 hrs initial set, 28 days full cure |
| Best for | Slabs, footings, post holes, foundations | Brick/block joints, stone veneer, tuckpointing |
Watch the material breakdown
Understanding Concrete, Cement, and Mortar
A helpful visual explainer once readers have the chart, because it reinforces why the mixes differ in structure and use.
Loads the YouTube player only after you click play.
Watch on YouTubeThe Critical Ingredient: Gravel
The single most important difference between concrete and mortar is coarse aggregate — gravel. Concrete contains gravel (typically 3/4-inch crushed stone), which gives it the mass and compressive strength to serve as a structural material. Mortar omits the gravel entirely, using only sand as its aggregate, which keeps it workable enough to spread in thin layers between masonry units.
This is why concrete is strong but cannot be spread thin, and mortar is spreadable but cannot bear structural loads on its own. Concrete with its gravel skeleton resists compression forces that would crush mortar. Mortar with its fine-sand consistency flows into the irregularities of brick and block faces, creating the bond that holds masonry walls together.
When to Use Concrete
Concrete is a structural material. Use it for anything that needs to bear weight or resist force independently:
- Slabs: Patios, sidewalks, garage floors, shed pads. Standard residential slab thickness is 4 inches with a compressive strength of 3,000-4,000 PSI.
- Footings: The underground base that supports posts, walls, and columns. Footings are typically 12-24 inches wide and 8-12 inches deep depending on frost line and load.
- Post holes: Fence posts and deck posts are set in concrete to resist lateral force from wind and use. A standard fence post hole is 10 inches in diameter and 30 inches deep.
- Foundation walls: Poured concrete foundations carry the weight of the entire structure.
For DIY projects, bagged concrete mix (just add water) is practical for jobs under about 1 cubic yard. Beyond that, order ready-mix concrete delivered by truck. Use our Concrete Calculator to determine whether bags or ready-mix makes sense for your project size.
When to Use Mortar
Mortar is a bonding material. It is the "glue" between masonry units — bricks, concrete blocks, and natural stone:
- Brick and block walls: Mortar fills the joints between units, bonding them into a wall system that acts as a single structure.
- Stone veneer: Mortar adheres stone facing to a wall substrate, filling the irregular gaps between natural stone pieces.
- Tuckpointing: Repairing deteriorated mortar joints in existing masonry walls. Match the mortar type to the original — using stronger mortar than the brick can cause the brick to crack.
- Retaining wall caps: Adhesive mortar or construction adhesive bonds the cap row to the top course of a block retaining wall.
Mortar includes lime (in addition to cement and sand), which makes it more workable, slightly flexible, and slower-curing than pure cement-sand mixes. This flexibility is important — it allows masonry walls to accommodate minor movement without cracking.
The Strength Hierarchy
Standard concrete mix achieves 3,000-4,000 PSI compressive strength — strong enough for residential slabs, footings, and posts. High-strength concrete reaches 5,000+ PSI for structural applications.
Mortar is deliberately weaker than the masonry units it bonds. Type N mortar (750 PSI) is the standard for above-grade residential work. Type S mortar (1,800 PSI) handles below-grade and structural applications. Type M mortar (2,500 PSI) is for heavy-duty foundation work. The mortar must always be the weakest link in the wall assembly so that if movement occurs, the mortar cracks rather than the brick or block — mortar joints are repairable, while cracked masonry units must be replaced.
Common Mistakes
Using mortar as a structural fill: Mortar cannot replace concrete for post holes, footings, or slabs. It lacks the strength and mass, and it will crack when applied thickly because there is no gravel aggregate to control shrinkage.
Using concrete for masonry joints: The gravel in concrete makes it impossible to spread in the thin layers that masonry requires. It would also be too strong relative to the brick or block, causing the units to crack under stress rather than the joint.
Confusing cement with concrete or mortar: Cement (Portland cement) is just one ingredient — the powder that reacts with water to harden. By itself, it is too weak and too expensive to use as either concrete or mortar. It must be mixed with aggregate (sand, gravel) to become useful.