Gravel Backfill Vs. Filter Fabric
Gravel backfill and filter fabric are materials typically used when laying underground pipes or installing a retaining wall, or in any outdoor project where drainage and support are needed. Both materials are simple to work with, and play key roles in allowing moisture to travel away without silt and other debris blocking its path. When comparing the benefits of gravel and filter fabric, consider the existing drainage conditions to determine if both are necessary.
Gravel Backfill Applications
Gravel backfill serves several purposes. Behind a retaining wall, the gaps between crushed stones are large enough for underground moisture to seep down through weep holes in the bottom of a wall. This reduces water pressure on the wall, while preventing the soil being retained from washing away. In a drainage system, gravel is laid under and over drainpipes to keep large debris from clogging the system and to protect the pipes from underground roots. It also prevents the soil walls on both sides of the pipe from caving in.
Filter Fabric Applications
Constructed from synthetic materials, filter fabric is typically unwoven and not biodegradable. It’s designed to allow water to drain through while blocking weeds and fine silt from passing through it. Standard drainage for a retaining wall entails lining the back of the wall with filter fabric and then backfilling it with gravel. The fabric prevents dirt from working its way into joints and weakening the wall. When installing underground pipes, you can lay fabric over the bottom of the trench and over the top layer of gravel to protect the gravel from debris.
Gravel Backfill Substitutes
Gravel is an affordable, versatile material with few substitutes. Depending on the project, sand, soil, crushed concrete or filter fabric alone can take its place, but will not be as effective. If you backfill a low retaining wall with sand, line any drain holes drilled through the front to the back of the wall with pipe and filter fabric to keep the sand from flowing out. Crushed concrete is more porous and has the benefit of absorbing water while reinforcing the wall. Underground drainpipes can be laid directly over filter fabric, but without gravel on top of the pipes, soil can get waterlogged faster than moisture can penetrate down into the pipes.
Filter Fabric Substitutes
One primary advantage of filter fabric is that it’s made to last. Repairing retaining walls and drainage systems is labor-intensive and messy. Without the added barrier, fine silt will eventually seep between the gravel and clog the passages of drain water. If you skip the fabric or use a sheet of plastic instead, the possibility of a clog or other problem developing increases, as the plastic will tear over time.