Summary:
If you’ve been searching for cinder block retaining wall options and hitting dead ends, you’re not alone — and you’re not doing anything wrong. The problem is that “cinder block” is a term most people still use, but the product it describes has largely disappeared from masonry yards. What’s replaced it is better. Stronger, denser, and built to handle the kind of winters Nassau County throws at everything you build outdoors.
This page explains what’s actually available, what the differences mean for your project, and how to make a material decision you won’t regret come March.
What's the Difference Between a Cinder Block and a Concrete Block?
The short answer: one is a relic, the other is what gets used today. True cinder blocks were made using coal cinder — the ash left over from burning coal — as the primary filler aggregate. That made them lighter and easier to handle, but also more porous and significantly weaker under load. As coal use declined, so did cinder block production. Most suppliers stopped stocking them decades ago.
What you’ll find now at any serious masonry yard is a concrete masonry unit, or CMU. CMUs use Portland cement, sand, and crushed stone or gravel as the aggregate. The result is a denser, stronger block that’s built to handle structural load, soil pressure, and the repeated freeze-thaw cycles that are part of life in the Northeast. When someone today says “cinder block retaining wall,” they almost always mean a CMU wall — they just don’t know the terminology has shifted.
Why the Naming Confusion Actually Matters When You're Buying Materials
This isn’t just a terminology trivia point. If you walk into a yard asking for cinder blocks without understanding the distinction, you might not ask the right follow-up questions — and the block you end up with may not be right for your application.
Standard CMUs come in several sizes. The most common for retaining walls is the 8″ × 8″ × 16″ block, which weighs between 28 and 36 pounds and is manufactured to meet ASTM C 90, the governing standard for load-bearing concrete masonry. For walls retaining heavier soil loads or taller grade changes, a 12″ × 8″ × 16″ block is more appropriate. These aren’t interchangeable decisions — the block size affects how much lateral pressure the wall can resist, how deep your footing needs to be, and whether you’ll need rebar reinforcement through the cores.
Compressive strength matters too. Standard CMUs are typically manufactured at around 2,000 psi. Premium blocks can exceed 5,000 psi and offer meaningfully better resistance to moisture absorption and freeze-thaw spalling. In Nassau County, where you’re looking at roughly 30 to 50 freeze-thaw cycles per year and a frost depth of around 36 inches, that performance gap between a budget block and a quality CMU is not theoretical — it shows up as cracking, spalling, and leaning walls within a few seasons.
True cinder blocks are more porous and absorb more moisture. In a climate like Long Island’s, that’s a structural liability. Water gets in, freezes, expands, and works its way through the block face over time. It’s one reason so many of the original cinder block walls built on Nassau County properties in the 1950s and 1960s are now failing — and why homeowners are replacing them with modern CMUs rather than trying to source the original material.
If you’re not sure which block size or density is right for your project, that’s exactly the kind of question worth asking before you order. The right answer depends on wall height, soil type, proximity to structures, and whether the wall will be mortared or dry-stacked.
What Makes a Cinder Block Retaining Wall Fail — and How to Avoid It
The block itself is rarely the only factor in a wall failure. Most retaining walls fail because of what’s behind them, not what they’re made of. Poor drainage is the leading cause — when water builds up in the soil behind a retaining wall and has nowhere to go, the hydrostatic pressure it creates can push even a well-built wall off its footing over time.
A properly built CMU retaining wall needs gravel backfill directly behind the block to allow water to drain freely. It also needs weep holes or a perforated drain pipe at the base so that water exits the wall system rather than pooling. These aren’t optional details — they’re the difference between a wall that lasts 50 years and one that starts leaning after the third winter.
Footing depth is the other critical factor in Nassau County specifically. The footing — the concrete base the wall sits on — must be placed below the frost line. On Long Island, that means going down approximately 36 inches. A footing that sits above the frost line will heave as the ground freezes and thaws, gradually pushing the wall out of plumb. A lean of more than an inch per four feet of height is considered structurally serious and typically means the wall needs professional intervention, not just monitoring.
For walls under about three feet on flat ground with good drainage and sandy soil, a capable DIYer can manage the project. But Nassau County’s North Shore communities — Great Neck, Roslyn, Port Washington, Oyster Bay — have more topographic relief and heavier clay-loam soils than the flat South Shore. Clay expands when it’s wet and when it freezes, which puts significantly more lateral pressure on a retaining wall than sandy soil does. If your property is in one of those areas, or if your wall is over four feet, you’re in professional territory. Most Nassau County municipalities also require a permit for walls over four feet, and some require engineering review at that threshold.
Retaining Wall Sleepers: Concrete vs. Block Construction
When researching retaining wall options, you’ll sometimes come across the term “concrete sleepers.” It sounds similar to a concrete block wall, but it’s a different system entirely — and worth understanding if you’re weighing your options.
Concrete sleepers are precast horizontal concrete panels that slot into vertical steel posts driven into the ground. The structure works like a post-and-panel fence, with the panels stacked between the posts to hold back the soil. It’s a cleaner, more uniform look than stacked CMU block, and it can be installed without mortar or footing work in many applications.
Concrete Sleepers vs. CMU Block Walls: Which Is Right for Your Project?
Both systems have real advantages, and the right choice depends on your project specifics rather than one being universally better than the other.
CMU block walls — what most people mean when they say “cinder block retaining wall” — are well-suited for taller walls with significant soil pressure, situations where the wall will be mortared and reinforced with rebar, and projects where the wall needs to integrate with other masonry elements like steps, pillars, or a patio. They’re a proven structural system with decades of performance data behind them, and they’re available in a range of surface finishes including smooth face and split face, which gives you some design flexibility.
Concrete sleepers work well for lower walls, garden borders, and applications where a faster installation timeline matters. Because they don’t require a continuous poured footing in the same way a mortared CMU wall does, they can be a more accessible option for smaller projects. The precast panels are manufactured to consistent dimensions and strengths, and the post-and-panel system handles some of the drainage challenge inherently, since water can move between panels and posts rather than building up behind a solid face.
The tradeoff is that concrete sleeper systems are generally less suited to taller walls under heavy soil load, and the aesthetic — while clean — is distinctly different from the look of a traditional masonry block wall. If you’re trying to match existing stonework or brick on a Nassau County property, CMU block with a split face finish or a natural stone veneer is usually the better fit. If you’re building a garden terrace or a low border wall and want something that goes up quickly without a lot of site prep, concrete sleepers are worth a look.
Either way, the materials need to be right for the application. That’s not something you want to figure out after the blocks are on site.
Frequently Asked Questions About Cinder Block and Concrete Block Retaining Walls
**Are cinder blocks still available to buy?** True cinder blocks — made with coal ash aggregate — are largely obsolete and very difficult to find. Most suppliers stopped carrying them as coal use declined. What you’ll find at a masonry yard today are concrete masonry units (CMUs), which are stronger and more durable. The terms are used interchangeably in everyday conversation, but the products are different. For a retaining wall, CMUs are the better material regardless.
**How long does a concrete block retaining wall last?** A properly built CMU retaining wall — with a footing below the frost line, gravel drainage backfill, and appropriate rebar reinforcement for taller walls — can last 50 to 100 years. The keyword there is “properly built.” Walls that skip the drainage step or sit on shallow footings tend to fail within a few seasons in Nassau County’s climate, regardless of block quality. We’ve seen walls that should have lasted decades fail in three winters because the footing wasn’t placed below the 36-inch frost line.
**Do I need a permit for a retaining wall in Nassau County?** In most Nassau County municipalities, walls over four feet in height require a building permit, and some require engineering review at that threshold. If your wall is close to a property line, a structure, or a utility easement, the rules can be more stringent. It’s worth checking with your local building department before you finalize your design — not after you’ve already ordered materials. The permitting process in Nassau County can add a few weeks to your timeline, so plan accordingly.
**What type of mortar should I use for a cinder block retaining wall?** Type S mortar is the standard recommendation for exterior retaining walls. It’s formulated for below-grade applications and provides better bond strength and water resistance than Type N, which is more commonly used for interior or above-grade work. If you’re dry-stacking blocks rather than mortaring them, mortar selection isn’t a factor — but drainage design becomes even more important.
**What does a retaining wall cost in Nassau County?** Material and installation costs in Nassau County, NY typically run between $20 and $62 per square foot depending on the material chosen — CMU block, natural stone, interlocking segmental block, and other options all fall at different points in that range. Material costs alone will be a fraction of that figure. If you’re sourcing blocks directly and hiring a mason separately, or doing the work yourself, getting accurate material quantities before you order is the most important step in keeping costs predictable.
**Can I use cinder blocks for a retaining wall myself?** For walls under about three feet on flat ground with sandy soil and good drainage, a capable DIYer can manage a CMU retaining wall project. Once you’re dealing with walls over four feet, clay soil, significant slope, or proximity to structures — which describes a lot of Nassau County’s North Shore properties — the project moves into professional territory. The consequences of a wall failure aren’t just cosmetic. A leaning or collapsing retaining wall can damage structures, create liability issues, and cost significantly more to fix than it would have cost to build correctly the first time.
Where to Buy Concrete Block Retaining Wall Materials on Long Island
If you’ve made it this far, you have a clearer picture of what you’re actually looking for — and it’s almost certainly a quality CMU, not a true cinder block. The good news is that CMUs are widely available, competitively priced, and better suited to Long Island’s climate in every measurable way.
What matters from here is buying from a supplier who stocks the right sizes, can answer your questions honestly, and can get materials to your site when your project needs them. That means skipping the big-box store aisle and working with a yard that carries a real inventory, has knowledgeable staff on hand, and runs its own delivery fleet.
We’ve been supplying masonry and landscape materials to Long Island homeowners and contractors since 1972. If you’re planning a retaining wall project in Nassau County and want to get the material selection right before anything goes in the ground, reach out to us — we’d rather spend 30 minutes helping you choose correctly than have you deal with a problem wall two winters from now.
