Do retaining walls need to be waterproofed

I have lost count of how many times we show up in Calgary and the problem is not the block face at all, it is what is happening behind it. Soil gets saturated, freeze-thaw does its thing, and suddenly you are staring at a bulge, a lean, or a crack that was not there last season. People ask if a moisture barrier is “extra”, but once you have watched water pressure push a structure out of line, it stops feeling optional. Well, usually anyway.

If you are still at the stage of figuring out the basics, this quick explainer on what is a retaining wall helps, because the whole question changes depending on height, soil type, and what is sitting uphill. A short garden edge holding back a bit of topsoil is one thing. A tall grade change near a driveway or patio is a different animal, and that is where water management starts to decide whether it lasts.

From what I have seen on our builds at Sungreen Landscaping Inc, drainage and moisture protection are tied together. You can have great compaction and still get trouble if water has nowhere to go. We have been building outdoor spaces since 1990, and the fixes are almost always the same: clean gravel backfill, a drain tile to daylight or a sump point, and a membrane where it makes sense, especially when the structure is close to a foundation or finished space.

And yes, materials matter too. The block itself, the cap, the adhesive, the drain rock, all of it. If you are sourcing locally, here is a handy guide on where to buy retaining wall blocks in calgary ab. I am not saying you cannot mix and match, but I have seen mismatched systems cause little gaps that turn into big wet spots over time.

If you want us to look at your yard, we do free consultations and a 2D design sample, and we talk through where the water goes before we talk about the pretty stuff. For tall grade-support structures over 4 feet, we pull the City of Calgary permits and work with an engineer, because that is the only way I sleep at night on those jobs. We also back our work with a signed warranty and a dedicated warranty rep, so if you are wondering what level of moisture protection makes sense on your property, call (403) 256-7500 and we can sort it out on site.

Do Retaining Walls Need to Be Waterproofed?

If you are building a soil-holding barrier in Calgary, the question is not really about some magic paint that stops moisture forever. It is about controlling where the water goes so it does not sit behind the structure and push. I have seen gorgeous blockwork look fine from the front, then start to bow because the back side was basically a mud sponge all spring.

Most of the time, what you actually want is a combo: a drainage layer, a pipe at the bottom, and a barrier membrane on the back face if the conditions call for it. Clay soils, tight backfill, poor grading, downspouts dumping right into the area, those are the jobs where I get more serious about a membrane. If the grade is open and the gravel and pipe are done right, moisture pressure drops way down, and that is the real battle.

Homeowners sometimes focus on the visible materials and forget the hidden parts, which is backwards. The face blocks are the easy part, the stuff behind them is what decides whether it stays straight. If you are still in the planning stage, skim through landscaping and retaining walls and then ask whoever is building it what their drainage spec is, because “we will throw some gravel back there” is not a spec.

There are also cases where you do want a proper damp-proof layer, like when the structure is close to a house, near a basement walkout, or you have finished surfaces above that you do not want stained by seepage. Freeze-thaw makes all of this touchier here. Water gets in, freezes, expands, and little issues turn into cracks that look “minor” until they are not.

If you already have one that is leaking, staining, or leaning, the fix is rarely just smearing on a coating from the front. You usually have to relieve the pressure from behind, and sometimes that means excavation, redoing the backfill, and adding drainage where it should have been. This guide on how to fix a retaining wall lines up with what we end up doing on real sites pretty often.

When we build these at Sungreen (we have been at it since 1990), we think about water first, then structure, then finishes. For anything over 4 feet we pull the City of Calgary permits and work with an engineer, because guessing is expensive later. Every project leaves with a signed warranty and a warranty rep you can actually reach, which matters when spring melt shows you what got missed.

If you want a straight answer for your yard, it depends on soil, height, slope, and where the runoff is headed, and I cannot pretend otherwise. Call us at (403) 256-7500 and we can do a free consult and a simple 2D concept, then you will know if a membrane makes sense or if good gravel and pipe work will do the job. Well, usually anyway.

How to Tell If Your Garden Grade-Change Structure Should Get a Moisture Barrier

Soil tells you a lot before the block or stone does. If you’ve got heavy clay in Calgary (and a lot of us do), it holds water and stays wet, so the pressure behind a grade-change structure builds fast after rain or spring melt. That’s when a moisture barrier makes sense, because you’re not just dealing with dampness, you’re dealing with trapped water pushing. Sandy or gravelly soil drains quicker, so you might get away with less, but only if the base and backfill were done right and the outlet stays open. If you’re unsure, look at the site after a storm: puddling along the back edge, soggy turf that never dries, or water staining on the face are all signs the ground is feeding moisture straight into the structure. Drainage is still the first question I ask on a site visit, same as it’s been since 1990, and this page lays out the basics well: do retaining walls need drainage.

Material matters too, and I’ve seen homeowners assume “concrete block equals sealed” and then wonder why the face gets white salts and the joints start opening. Segmental concrete units and mortarless stone both let moisture move through them, and freeze-thaw does the rest. Timber is its own story: it can look fine for a while, then you probe a post and it’s soft where it sits against wet soil. Poured concrete can perform great, but hairline cracks happen and water loves a tiny path. If you’re still deciding what to build with, it helps to think about how that material handles water and frost in our climate, not just how it looks on day one. We talk through that stuff during our free consults and 2D design samples, and this is a decent read for homeowners weighing options: what is the best material for a retaining wall.

Site conditions are the tie-breaker. Downspouts dumping near the backfill, a neighbour’s grade sloping toward you, a low corner where snow piles up all winter, those spots almost always show trouble first: dark damp patches, algae film, efflorescence, or a face that looks dirty no matter how much you scrub it (yes, cleaning helps, but it also tells you where water keeps coming back). If you’re already seeing bulging, a lean, or gaps that open after spring melt, a barrier alone won’t save it and you’re into repair territory. If you want a quick guide for cleaning without wrecking the surface, here’s one we share a lot: how to clean retaining wall blocks. And if you’re staring at a section that’s past the point of patching, this walkthrough is the realistic version of what replacement looks like: how to replace a retaining wall. If you want us to look at yours in person, call (403) 256-7500 and we’ll tell you straight what’s going on, and what it’ll take to fix it under a signed warranty.

Q&A:

Do all retaining walls need waterproofing, or only certain types?

Not every retaining wall needs a full waterproofing system, but many benefit from some form of moisture protection. Walls that hold back soil (especially with irrigation, clay soils, or high rainfall) are exposed to constant wetness and hydrostatic pressure. In those cases, a waterproof coating or membrane on the soil side plus drainage is often recommended. Small gravity walls, freestanding garden walls that don’t retain much soil, or walls in very dry conditions may do fine with drainage stone and a perforated drain pipe alone. The deciding factor is how often the backfill stays wet and whether water can escape quickly.

If I install a drain pipe, can I skip waterproofing?

A drain pipe helps, but it doesn’t automatically replace waterproofing. Drains can clog with silt, roots, or construction debris, and then water pressure rises fast behind the wall. Waterproofing reduces water absorption into concrete or masonry, helps prevent damp spots on the exposed face, and lowers the risk of freeze–thaw damage in cold climates. Many builders treat it as a “belt and suspenders” approach: drainage to relieve pressure, and a coating/membrane to keep moisture out of the wall material. If you must choose one due to budget, drainage and proper backfill are usually the first priority—but skipping waterproofing raises long-term risk.

Which side of the retaining wall gets waterproofed, and how far up should it go?

Waterproofing is applied on the soil side (the back of the wall), because that’s where moisture comes from. In many cases it’s run from the footing up to near the top of the retained soil. If the grade steps or the wall has multiple levels of backfill, the coating should cover the sections that contact soil. For walls next to buildings, the waterproof layer is often tied into the building’s foundation waterproofing so water can’t sneak in at the joint. Protect the coating during backfill with a drainage board or protection mat so rocks don’t puncture it.

Is “damp-proofing” paint the same thing as waterproofing for a retaining wall?

No. Thin “damp-proofing” coatings (often asphalt emulsion) can slow moisture, but they may not hold up well against constant wet soil and pressure. True waterproofing is typically a thicker elastomeric coating, a sheet membrane, or a liquid-applied membrane rated for below-grade use. The right choice depends on the wall material (CMU block, poured concrete, stone), soil conditions, and whether freezing is a concern. For many residential retaining walls, a below-grade membrane paired with a drain pipe, clean gravel backfill, and filter fabric is a reliable setup.