This is a common question we get from local DIY’ers and homeowners. Everyone wants to save money, so the unassuming roll of black fabric being dropped off on site is an easy target. What does it even do, anyway?
Whether you are a new DIY homeowner looking to upgrade your driveway, patio, paving stones path, or any other do-it-yourself project that includes a gravel base – this article should be helpful for you.
To answer the question, I should quickly cover what the purpose of geotextile is.
What Does Geotextile Do?
The purpose of geotextile (a.k.a. filter fabric) is to act as a barrier between the fine-grained, native soils on your site, and the coarse gravel being used as the base material for your driveway, patio, paving stones, etc.
In addition to keeping the two materials separate, it also allows water to pass through it, so water doesn’t collect within the gravel base.
Why Do The Materials Need To Be Kept Separate?
It may not seem like a big deal, but keeping your gravel base separate from the native site materials is actually an important step that shouldn’t be ignored.
Why is it important?
Since gravel typically has a lot more void spaces than fine soils like clay or silt, when gravel and silt/clay sit on top of each other for a long time, the small clay and silt particles will slowly migrate into the gravel. The gravel, which is supposed to allow water to move relatively freely through it, becomes plugged with fine grained silts and clays, stopping water from moving freely in the gravel.
Once the gravel’s voids have been plugged by silts and clays, it will no longer allow water to move through it. Water will now pool on and collect inside the gravel base, softening and weakening it. Should these conditions persist into winter, the water now trapped within your gravel base will freeze and expand, causing cracks in your driveway.
In addition to preventing your free-draining gravel base from filling up with clay/silt and fines, geotextile also helps to prevent settlement. Without separation between gravel and clay/silt, the same process of merging between the gravel and silt/clay also results in an overall reduction of thickness of the gravel base. This means that your driveway will settle. Lumps, cracks, and potholes are all to be expected.
Depending on your native soils and how many fines are within the gravel you’re using, you might be okay without using geotextile, but for the low cost of geotextile, it’s not really worth the risk.
In our opinion, it is recommended in almost all cases, unless you’ve consulted with a geotechnical engineer who says otherwise. The cost isn’t high, and the benefits are great.
Where Can I Get Geotextile?
Typically you can find geotextile from a local construction materials supplier. Just google your city name + “geotextile” and something should come up. If you require more assistance, usually they’re happy to help you out with any questions you have related to geotextiles. If you’re in Alberta, we’re happy to help.
In the vast majority of cases, a light-duty non-woven geotextile filter fabric will get the job done. This is not to be confused with landscape fabric, which is NOT the same thing – although they look very similar.
Conclusion
If you’re worried about your driveway project, I recommend speaking to a local geotechnical engineer so they can assess your site conditions (if you live in Calgary, feel free to contact us).
