Should You Put Plastic Under the Paving?
It's a question that comes up often: should we put plastic sheeting under the paving to prevent weeds? It seems logical — block the light and stop things growing. The reality is more complicated, and in most cases, plastic sheeting under paving causes more problems than it solves.
Why People Consider It
Weeds and grass growing up between paving bricks are a genuine nuisance. They lift bricks, trap moisture, and look untidy. The instinct to prevent this with a barrier makes sense in theory. The problem is how brick paving actually works.
How Brick Paving Is Designed to Drain
Properly installed brick paving has a sand bed beneath it. This sand bed serves multiple purposes: it allows the bricks to be levelled, it provides a flexible base that accommodates minor ground movement, and critically, it allows water to drain down through the paving and into the sub-base below.
If you install an impermeable plastic sheet under the sand bed, this drainage cannot happen. Water that falls on the paving and percolates through the joints has nowhere to go. It pools under the paving, saturates the sand bed, and begins to undermine the base. In wet conditions, this can cause the paving to heave, sink unevenly, or become unstable surprisingly quickly.
What About Weed Membrane?
Permeable weed membrane (geotextile fabric) is sometimes suggested as a compromise — it lets water through but blocks weed growth. In theory this is better than solid plastic. In practice, we still don't typically recommend it under brick paving for several reasons:
- Weed seeds blown onto the surface can germinate in the sand that sits above the membrane
- The membrane can interfere with the consolidation of the sand bed over time
- Roots from established plants can penetrate membranes given enough time
- If paving needs to be relaid at any point, the membrane complicates the job
What Actually Prevents Weeds in Paving
The best defence against weeds growing through paving is:
- Good ground preparation: Remove existing vegetation thoroughly before laying. A healthy sub-base with good compaction gives weed roots less opportunity to establish.
- Tight jointing: Bricks laid with tight joints and well-settled jointing sand give less opportunity for seeds to establish.
- Polymeric sand: Jointing sand mixed with a binding agent that, once set, is harder for roots to penetrate. Worth considering for low-maintenance areas.
- Regular maintenance: Dealing with weeds when they're small prevents them from establishing. A weed killer applied to joints once or twice a year keeps things manageable.
When a Barrier Makes Sense
There are situations where a geotextile layer is appropriate — in sub-base construction to separate different layers of material and prevent migration, for example. But this is different from placing it directly under the sand bed beneath the bricks.
If weed control is a specific concern for your project, discuss it with us when we quote. We'll advise on the best approach for your specific situation rather than a one-size solution.