Retaining Wall Block Systems Compared: Allan Block, Versa-Lok, Keystone, Belgard and Fortus
The major segmental wall systems differ in how blocks lock together, how much each block weighs and covers, and how tall the maker lets you build without geogrid. Here's how they compare on published specs, and how to pick one for your wall.
Retaining wall block systems differ mainly in how the blocks connect (a molded lip, pins, lugs or a rear lip), how much each block weighs and covers, and how tall the maker says you can build before the wall needs geogrid and an engineer. There’s no single best retaining wall block: the right one is a system sold near you, rated for your wall’s height, soil and load, with corner and cap pieces that suit your layout.
Quick answer
Most makers’ guidance lands in the same place: unreinforced walls of roughly 3 to 4 feet in average soil with level ground above (less with a slope or driveway on top), and engineering or geogrid past about 4 feet. Codes based on the IRC draw the same line: an engineered design past 4 feet of retained soil, or past 2 feet with a load on top. Allan Block uses a front lip, Versa-Lok and Keystone use pins, Fortus uses lugs, and some Belgard units use a rear lip. Pick by local supply, height rating, corners and how much weight you’ll lift, then follow that maker’s installation guide.
Best retaining wall block by wall type
The best interlocking retaining wall block is the one rated for your wall’s height, soil and load, made close enough to haul, with the corners and caps your layout needs. Here’s where we’d start, using each maker’s published limits.
| Your wall | Where we’d start | Why |
|---|---|---|
| Garden wall, planter or bed edge under 2 ft | A 4 in. garden wall unit (Keystone Garden Wall, LibertyStone Garden Wall) or Allan Block’s 18 lb AB Junior Lite | Light to lift, and Keystone keeps its 4 in. units to 2 ft |
| Retaining wall up to about 3 ft, level ground above | A structural unit made near you: AB Classic, Versa-Lok Standard, Keystone Compac or Fortus Square Foot | Allan Block’s gravity chart allows 3 ft 2 in. with its 6° blocks, even in clay |
| Wall near or over 4 ft | A structural unit with geogrid and an engineered design | IRC R404.4 requires an engineered design past 48 in. of retained soil |
| Driveway, parking or patio above the wall | A structural unit, with an engineered design once the wall passes 2 ft | Allan Block’s chart drops to 1 ft 4 in. in clay with a driveway above, and the IRC line is 24 in. with a load on top |
| Tall or commercial wall with little room for geogrid | Large precast block, such as Redi-Rock | Redi-Rock says its gravity blocks allow walls up to 21 ft without reinforcement, depending on site conditions. The blocks run about 1,160 to 3,290 lb, so they’re set by machine. |
What interlocking means: how the blocks connect
All of these are segmental walls: dry-stacked concrete units, no mortar, sitting on a compacted aggregate base, with each course stepped back into the hill. If that’s new, our guide to the segmental retaining wall explains how they hold soil.
What separates the brands is the connection between courses, and that connection is what “interlocking” means. The Concrete Masonry & Hardscapes Association’s guide calls this shear capacity, the way each course passes sideways force to the next, and lists how units get it: keys or lips molded into the units, or clips, pins or compacted gravel in open cores. The same feature usually sets the batter, the lean of the wall into the hill. It also decides how corners get built and what you handle on site: pins, core stone or both.
- Front lip (Allan Block): a raised lip on the top front of each block catches the block above and sets the lean. No pins or clips. The hollow cores get filled with wall rock.
- Pins (Versa-Lok, Keystone): fiberglass or nylon pins tie each block to the course below. The hole you use sets either a setback or a near-vertical face.
- Lugs into cores (Fortus Square Foot): molded lugs drop into the gravel-filled cores of the blocks below. Keep the rear lugs for setback, or remove them for near-vertical.
- Rear lip (some Belgard units, LibertyStone Garden Wall): a lip under the back of the block hooks behind the block below. Belgard’s guide has you knock it off the base course so the first course sits flat on the pad.
Other systems use the same idea in a different shape. Redi-Rock’s big blocks have knobs on top that fit grooves cast into the bottom of the block above, Unilock’s Pisa uses a tongue-and-groove connection, and Belgard’s Diamond Pro Air uses a front lug that sets a 9/16 in. setback per unit. In hollow-core units the stone does part of the work too: CMHA notes that gravel in open cores adds weight and shear capacity.
The main systems at a glance
These are representative structural units, with the numbers from each maker’s own site or, for Versa-Lok, from literature published by block producers that make or sell it. Keystone and Belgard sell many units with different specs, so check the sheet for the exact block.
| System | Example unit | Connection | Weight | Face per block | Lean options | Published height guidance |
|---|---|---|---|---|---|---|
| Allan Block | AB Classic, 8 x 18 x 12 in. | Front lip | about 75 lb | about 1 sq ft | 6° (AB Stones 12°, AB Vertical 3°) | Gravity chart: 3 ft 2 in. (clay) to 4 ft 7 in. (silty sand), level ground, 6° blocks |
| Versa-Lok | Standard, 6 x 16 x 12 in. | Two pins | 82 lb | 0.667 sq ft | 3/4 in. per course or vertical | Producer bulletin: generally engineer walls over 4 ft |
| Keystone | Compac and Standard (structural) | Fiberglass pins | see unit sheet | see unit sheet | Near vertical or 1 in. | 4 in. units 2 ft, 6 in. units about 3 ft; structural units engineered for 6 ft to 50 ft+ |
| Fortus Square Foot (CornerStone, sold by LibertyStone) | 8 x 18 x 10 in. | Lugs into cores | 58 lb | 1 sq ft | Setback or near-vertical | Geogrid guide flags walls over 4 ft |
| Belgard | Several wall lines | Rear lip or pins, by product | by product | by product | by product | Follow the product guide |
For a closer look at three of these, see our Allan Block vs Versa-Lok comparison and our LibertyStone Fortus guide.
Other retaining wall block manufacturers
Allan Block, Versa-Lok, Keystone, Belgard and Fortus aren’t the only names you’ll be quoted. These makers also sell wall systems. Check each maker’s dealer locator before you plan around a line.
- Unilock: calls itself a manufacturer of interlocking pavers and segmental wall products. Its Pisa unit has a built-in setback and a tongue-and-groove connection, and Unilock rates it for gravity walls up to 39 in. and geogrid walls up to 20 ft, with a 5 ft tightest radius.
- Rosetta Hardscapes: wet-cast concrete products modeled on natural stone, with wall lines including Outcropping, Grand Ledge, Kodah and Belvedere. Outcropping is a large-format block: one retaining pallet weighs about 4,000 lb and covers 18 sq ft, and Rosetta pairs it with a specially designed lifting device.
- Redi-Rock: large precast blocks (its common gravity blocks run roughly 1,160 to 3,290 lb), made from Redi-Rock’s forms by more than 130 local producers around the world and used for gravity and reinforced walls.
- Pavestone: owned by The QUIKRETE Companies, with retaining wall block alongside its pavers and edging.
- Anchor Wall Systems: Oldcastle Architectural acquired Anchor Block Co. and Anchor Wall Systems in 2015, putting those brands alongside Belgard under Oldcastle Building Products. Belgard itself is part of Oldcastle APG, a CRH company.
How to choose a retaining wall block system
1. Start with height, soil and what sits above the wall
Height rating beats brand. Allan Block’s gravity chart shows how much the answer moves: a 6° block in clay with level ground above tops out at 3 ft 2 in., but only 1 ft 4 in. with a driveway or patio above it. Keystone’s FAQ keeps its 4 in. landscape units to 2 ft and its 6 in. units to about 3 ft without geogrid. A Versa-Lok producer’s bulletin says walls over 4 ft should generally be engineered, and LibertyStone’s geogrid guide singles out walls over 4 ft as the ones that need grid to resist soil pressure.
Codes say much the same. IRC section R404.4, which many states and towns adopt, requires an engineered design for a retaining wall holding back more than 48 in. of soil, or more than 24 in. when it also carries a load such as a driveway. So if your wall is near 4 feet, or holds up a driveway, patio or slope, plan on an engineered design from the start. Our guide to the retaining wall over 4 feet covers what changes.
2. Check what’s made near you
Block is heavy, and all of these systems are made by regional or licensed producers. Keystone and Allan Block both say color options vary by region, and Versa-Lok producers each publish their own color lists. A system you can buy within a reasonable haul, with corners and caps in stock, usually beats one you have to ship in.
3. Match the system to your layout
- Curves: Allan Block says most curves need no cutting and recommends curves over corners. Keystone says its pins let you build tight corners and radii in running bond without cutting units.
- 90-degree corners: Allan Block uses dedicated AB Corner blocks on every course and calls outside corners more time and skill. Fortus has a 90-degree corner piece. Versa-Lok corners are split from Standard units.
- A vertical face: Versa-Lok and Keystone can pin near-vertical, and Fortus can go near-vertical without its rear lugs. Allan Block’s 3° AB Vertical is a custom-order commercial block.
4. Think about who’s lifting
Weight per square foot of wall face is a better measure than weight per block. Belgard’s Diamond Pro Air is about 54 lb for a 1 sq ft block, Fortus Square Foot about 58 lb per square foot, AB Classic about 75 lb, and Versa-Lok Standard about 123 lb (82 lb / 0.667 sq ft). The hollow blocks get lighter to set but add core stone to shovel. For low walls, most systems sell small units: Allan Block’s AB Junior Lite is about 18 lb, and Keystone and LibertyStone both sell 4 in. garden wall units. Face area also sets the count: our guide to how many retaining wall blocks you need works it out row by row.
5. Read the base and drainage details, because they differ
Every system goes on a compacted aggregate pad with the first course buried, but the details aren’t the same:
| System | Base and burial in the maker’s guide |
|---|---|
| Allan Block | Trench 24 in. wide and 6 in. deep, plus 1 in. of buried block per foot of wall height (18 in. wide and 4 in. deep for walls under 4 ft); at least 6 in. of wall rock, compacted |
| Belgard | Leveling pad of 3/4 in. minus with fines, at least 6 in. deep and 6 in. past the block front and back; bury the base course at least 6 in. |
| Keystone | Most walls on 4 to 6 in. of compacted granular base; bury 1.5 in. per foot of wall height, no more than three courses |
| Versa-Lok | Bury at least 6 in. with level ground in front, or 1/7 of the wall height on a slope |
| Fortus (LibertyStone) | Leveling trench 6 in. below the first course; embed 6 to 12 in. or one block |
Our guide to retaining wall base depth explains why the buried course and the pad matter, and our retaining wall drainage guide covers the stone, pipe and outlets behind the block. On our own jobs, block walls go on a leveling pad of clean crushed stone (2B in Pennsylvania), and we call 811 before we dig.
6. Get the warranty in writing
Warranties differ and some have steps you have to take. LibertyStone’s, for example, covers structural defects for the original purchaser in residential use only if you register online within 60 days, and it replaces block but not labor. Ask your dealer for the written warranty on whatever block you’re pricing.
Builder’s note: Buy the caps, corners and any half units at the same time as the wall block, from the same producer. Caps and corners from a different run or brand rarely match the color, and the cap is the part of the wall everyone looks at.
Garden walls vs structural walls
Small 4 in. garden wall units, like Keystone Garden Wall and LibertyStone Garden Wall, are made for low walls, planters and bed edges, and Keystone keeps its 4 in. units to 2 ft. Structural units like the AB Classic, Versa-Lok Standard, Keystone Compac and Fortus Square Foot are the ones their makers back with gravity charts, geogrid guidance or connection testing for engineered walls. If a wall holds back a slope you walk or drive on, it should be built with a structural unit and a design that fits the site.
If you’d rather have the wall laid out before you pick a block, our online landscape and retaining wall plans draw it to scale with its layout, sizes and materials, from $349.
When to call a pro
- The wall is over 4 feet, or has a driveway, patio, parking or slope above it
- The soil is wet clay or old fill, or the wall is near the house or a property line
- The design needs geogrid, terraces, steps or tight corners
Whichever system you pick, the wall will need upkeep once it’s built. Our checklist for keeping a retaining wall in good shape goes season by season, from drain outlets to signs of settling.
Building a wall in central PA? Our own crews build block retaining walls from Lock Haven to Montoursville. See how we build a retaining wall in Lock Haven or a retaining wall in Williamsport (the same crew covers South Williamsport, Loyalsock and Montoursville), plus State College.
Farther out, we build walls in Centre and Union counties too: retaining walls in State College, hardscaping in State College, hardscaping in Williamsport, and patios and walls in Bellefonte and Lewisburg.
Frequently Asked Questions
What is the best retaining wall block?
No single block is best for every wall. As a starting point: a 4 in. garden wall unit for beds and planters under 2 ft; a structural unit made near you, such as AB Classic, Versa-Lok Standard, Keystone Compac or Fortus Square Foot, for walls up to about 3 ft; and a structural unit with geogrid and an engineered design past 4 ft, or past 2 ft with a driveway above. For very tall or commercial walls, large precast block such as Redi-Rock is another option. Allan Block, Versa-Lok, Keystone, Belgard and Fortus all build sound walls when the base, drainage and design are right.
Which retaining wall block is easiest for a DIY wall?
For a low garden wall, the lightest units are the easiest to handle, such as 4 in. garden wall blocks or Allan Block’s 18 lb AB Junior Lite. For a structural wall, compare weight per square foot of face: Belgard’s Diamond Pro Air is about 54 lb for a 1 sq ft block and Fortus Square Foot 58 lb, while Versa-Lok Standard runs about 123 lb per square foot.
Are pinned retaining wall blocks stronger than lip blocks?
Not as a rule. Keystone says its pins add shear strength at the face and a positive connection to geogrid, and Allan Block’s lip-and-notch walls have published gravity heights by soil. On tall walls, the engineered geogrid does most of the structural work in either type.
How tall can a block retaining wall be without geogrid?
It depends on the block, soil and load. Allan Block’s chart for its AB Collection blocks runs from 1 ft 4 in. (6° block, clay, driveway above) to 5 ft 4 in. (12° AB Stones, silty sand, level ground), and Keystone keeps 6 in. units to about 3 ft. Codes based on the IRC still require an engineered design past 4 ft of retained soil, or past 2 ft with a load on top, whatever the chart says.
Can I mix block brands in one wall?
Not within the same courses. Blocks from different systems have different heights, depths and connections. Pick one system for each wall and buy its caps and corners to match.
Do retaining wall blocks come in the same colors everywhere?
No. Allan Block and Keystone both say color options vary by region, and Versa-Lok producers each publish their own color lists. Ask a nearby dealer for physical samples.
What does interlocking mean for retaining wall blocks?
It means each block locks to the course below without mortar, so the courses pass soil pressure from one to the next. CMHA lists the usual ways: keys or lips molded into the block, or clips, pins or compacted gravel in open cores. The same feature usually sets how far each course steps back into the hill.
Who makes retaining wall blocks?
Besides the five systems compared here (Allan Block, Versa-Lok, Keystone, Belgard and Fortus), makers include Unilock, Rosetta Hardscapes, Pavestone, Anchor Wall Systems and, for large precast block, Redi-Rock. Oldcastle, Belgard’s parent, acquired Anchor in 2015. Not every line is sold everywhere, so start with what a nearby dealer stocks.
What makes a retaining wall block commercial grade?
Check the spec, not the label. Segmental retaining wall units are covered by ASTM C1372. Allan Block’s commercial specification, for example, calls for a minimum 28-day compressive strength of 3,000 psi under that standard, recommends 4,000 to 5,800 psi for freeze-thaw durability, and calls for a passing ASTM C1262 test report in northern or cold-weather climates. Each maker can also supply design data for its block, which an engineer uses to design the wall.
Sources: Allan Block, AB Collection retaining wall blocks (product specifications); Allan Block Residential Installation Manual, Designing a Retaining Wall (maximum gravity wall heights); Allan Block Residential Installation Manual, Basic Installation; Allan Block Residential Installation Manual, Building Corners in a Retaining Wall; General Shale Engineering Services, Versa-Lok SRW Walls Rule of Thumb Guidelines (technical bulletin); Rochester Concrete Products, Versa-Lok Standard retaining wall cut sheet; Keystone Retaining Wall Systems, FAQs; Belgard Technical Resource Guide, Basic Installation Construction Guide: Retaining Wall (p. 32); LibertyStone, Fortus Square Foot (product page and specifications); LibertyStone, Geogrid Reinforced Walls: What Are They and How Do You Build One?; LibertyStone, Warranty Info; 2021 International Residential Code, Section R404.4 Retaining walls; Concrete Masonry & Hardscapes Association, Guide to Segmental Retaining Walls (SRW-TEC-005-09); Allan Block, Commercial Installation, Product Specifications; Redi-Rock, Common Gravity Blocks (specifications); Redi-Rock, company overview; Unilock, company overview; Unilock, PISA Walls and Verticals (product page); Rosetta Hardscapes, product lines; Rosetta Hardscapes, Outcropping (product page); Belgard, Belgard Introduces Diamond Pro Air, Its Newest Block System (Business Wire, Jan. 2025); Landscape Management, Oldcastle acquires Anchor Block and Anchor Wall Systems (July 2015); Pavestone, product lines; D Magazine, FrontBurner, on the sale of Pavestone to the Quikrete companies
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Written and reviewed by Thayne Muthler, owner of Muthler Landscaping & Construction. How we check facts: editorial policy.