You have just purchased dimpled drainage sheeting to solve drainage problems behind a garden wall, in a planter, on a green roof, or as a protective layer on a flat roof. It is the simplest and most economical solution when the water flow to be evacuated is low or moderate. In this guide, we show you how to correctly orient, fix, and finish it so that the air gap created by the dimples performs its function.
Product Specifications
Dimpled drainage sheeting is a thermoformed high-density polyethylene sheet with embossed dimples (egg carton type). When placed against a wall, the dimples create a continuous air gap that directs water to the drainage system at the base. It also separates the wall from the damp soil and protects the waterproofing against puncturing during backfilling.
| Specification | Dimpled Drainage Sheeting |
|---|---|
| SKU | 875876 |
| Material | High-density polyethylene (HDPE) |
| Grammage | 700 g/m² (20.6 oz/yd²) |
| Structure | Thermoformed with embossed dimples |
| Roll width | 2 m (6.6 ft) |
| Roll length | 20 m (66 ft) |
| Coverage per roll | 40 m² (430 ft²) |
Step-by-step installation guide
Dimpled sheeting works by creating an air gap between the dimples. If you place it the wrong way, the gap is against the ground and water won't flow. The only critical aspects are orientation and the top edge finish; the rest is common sense.
Waterproof the wall face
Apply asphalt paint or a waterproof membrane to the wall and let it dry. Dimpled sheeting protects and complements the waterproofing, it does not replace it. Without prior waterproofing, the dimples create an air gap but water will still penetrate the wall.
Cut the sheeting to size
Measure the height of the wall and cut the sheeting with a retractable knife or tin snips. Leave an extra 10 cm (4 in) at the top of the wall for the top finish. The sheeting should extend 5 cm (2 in) below the base of the wall, resting on the gravel of the drainage pipe.
Place with dimples facing the wall
This is the critical rule: the dimples (embossed side) go AGAINST the wall. The smooth side faces the backfill soil. This way, the air gap formed between the dimples and the wall is where water flows down to the base. If you reverse the orientation, the sheeting will not drain.
Fix to the wall with impact nails
Use impact nails with a wide washer every 50 cm (20 in) at the top and every 1 m (3.3 ft) on the body. The fastening is only to hold the sheeting in place until the backfill presses against it. Do not over-nail: each nail is a perforation of the underlying waterproofing.
Overlap adjacent rolls
Overlap 10 cm (4 in) between adjacent vertical rolls. Most sheeting has an integrated smooth overlap strip on one edge; use it to overlap the dimples of the next roll. This creates a continuous joint and prevents water from entering.
Seal the top edge
Fold the extra 10 cm (4 in) at the top towards the wall side and seal with waterproof sealant or a metal finishing profile. This prevents water or soil from entering above the sheeting, which would clog the air gap with dirt.
Backfill gradually
Backfill in 30 cm (12 in) layers and lightly compact each layer. The backfill load presses the sheeting against the wall. Compact gently: polyethylene can withstand distributed pressure but not localized impacts from heavy machinery.
For green roofs and planters, the dimples serve an additional function: they retain water within each inverted cup and gradually release it to the substrate. This reduces irrigation frequency and mitigates water stress for plants during the dry Caribbean season. In these cases, the dimples face UPWARDS, towards the substrate, not towards the roof.
Do not install the sheeting with the dimples facing the backfill soil. This is the most frequent mistake: visually, the dimpled side is striking, leading people to think it faces outwards. But the air gap that channels water forms BETWEEN the dimples and the wall: that's why the dimples are against the wall. Reversing it turns the sheeting into a simple plastic layer that drains nothing.
Dimpled sheeting or geocomposite?
If you're hesitating between dimpled sheeting and drainage geocomposite for your application, or don't know how to orient it for a green roof vs. a retaining wall, ask the virtual assistant. It will guide you according to the type of work, height, expected flow, and backfill soil.
Complementary products
Dimpled sheeting is a self-contained product, but depending on the project scope, it may be advisable to reinforce the solution with one of the following complementary products.
The drainage geocomposite is the alternative for taller walls (over 2 m) or soils with a lot of fines where the dimpled membrane falls short: more drainage capacity and included filter geotextile. The metal rod with anchor cap is used to fix the top edge when you don't want to nail into the waterproofed wall, anchoring against the backfill soil before refilling.
Maintenance and care
The dimpled membrane is a buried system with a lifespan of several decades. The guidelines focus on protecting the water outlet and preventing subsequent mechanical damage:
- Annual inspection of the wall base: check the drainage pipe outlet at the base. If it is obstructed by sediment or vegetation, clean it before the rainy season.
- Attention to dampness on the wall: if permanent dampness appears on the inner face after the first season, it usually indicates an obstructed pipe or improperly oriented membrane during installation.
- No subsequent nearby excavations: mark the area on plans so that future works respect the membrane's location.
- Storage of leftover rolls: in a covered place, on a pallet, vertically to prevent permanent deformation of the dimples.
- Scraps: HDPE is recyclable. Scraps and leftover rolls are recycled as plastic through authorized waste managers.
Frequently asked questions
What is the difference between dimpled sheeting and drainage geocomposite?
Dimpled sheeting is a thermoformed HDPE sheet with dimples that creates an air chamber: simple, economical, and sufficient for low walls and moderate flows. The drainage geocomposite incorporates geotextiles on both sides of a drainage core that filter fine soil particles and handle larger flows. For planters, garden walls, and green roofs, use dimpled sheeting. For buried walls over 2 m or with high water tables, use geocomposite.
Which side do the dimples go on for each application?
For walls: dimples against the wall, smooth side towards the soil. For green roofs and rooftops: dimples UP against the substrate, smooth side against the roof. For horizontal planters (bottom): dimples up so they fulfill the water retention function. The simple rule: dimples always go against the side where the water comes from.
Can I use the sheeting as waterproofing?
No. Dimpled sheeting is not waterproof: it is for drainage. It has intentional perforations for water to enter and flow through the air chamber. Waterproofing must be done beforehand (asphalt paint, membrane, water-repellent mortar). If you use it without prior waterproofing, water will pass through the wall despite the sheeting.