Geotextile Interlayer FAQ

Does the edge of the geotextile really require daylighting or drainage?
Yes, good drainage is important. Nonwoven geotextiles exhibit transmissivity which allows the material to transfer water across a horizontal plane. If there is nowhere for this water to go at the end of the horizontal plane, it becomes trapped. It is common knowledge that water trapped under the surface layer can and will lead to durability issues. The amount of potential damage that may be the result of water trapped in a nonwoven geotextile depends on a number of other design factors including loads, joint design, slope, and amount of water able to penetrate through the surface.
Do the nails have to be flush against the discs, or can they stick up?
It is best to have the nails flush against the discs when securing the geotextile to the subbase. If the nails are not able to completely penetrate the subbase, try to obtain a stronger drill. If that is not possible or still does not solve the problem, try slightly shorter nails. Be aware, however, that the shorter nails must still be able to keep the geotextile in place securely. Shorter nails may require discs be spaced closer together in order to be effective. That will have to be a job-specific decision.
What if the geotextile tears?
If the geotextile tears, repair it. Overlap the tear with a single piece of material as if it were a patch and secure it with fasteners. Do not leave the tear because this will create the potential for keying of the surface to the subbase.
What if wrinkles or folds occur during placement?
It is best to keep the material as tight as possible (without tearing it) and fasten it right away in order to minimize wrinkles and folds. If you are getting wrinkles, pull the material a little tighter BEFORE you fasten it. If you get a fold, it is better to cut the fold and simply overlap the material. Secure the overlap with a fastener. What you don’t want is a fold that is thicker than the material overlapped twice. This may cause durability issues in the future.
Does mix design have an effect?
When water-to-cementitious material ratios are increased, the geotextile may experience more paste intrusion.
How does it hold up to traffic?
The geotextile can sustain some construction traffic, but maneuvers cannot be hasty. Sharp turns and sudden breaking or acceleration can cause the geotextile to tear. It should never be opened to general traffic.
How wet should the material be before placing the concrete?
There is debate over this question. The material should not be soaked. Instead, lightly moist to almost dry is best.
What is the most efficient way to place it?
Placement efficiency really depends on available equipment and crew experience. The geotextile can be rolled out by hand, placed with a forklift, or even laid out using a tractor. Knowing how to keep the material from flying up in windy conditions, how to keep it tight, and how to prevent wrinkles and folds is the key.
Does the paste soak through the material and result in a bond?
The paste will soak into the top of the geotextile resulting in an intentional bond between the geotextile and surface layer of concrete.
What size fasteners (washers) should be used and why?
It is recommended that 50- to 70-millimeter (mm) (2- to 2.75-inch (in)) galvanized washers or discs be nailed in every 2 m (6 ft) or less. There has been some experience with smaller sized discs. Smaller discs tend to not be as effective in keeping the geotextile held tightly in place during construction particularly in windy conditions. If smaller than recommended discs are being considered, spacing should be much closer.
How many laborers does it take to place?
This will depend on the method used for placement. Generally, a minimum of 3 to 4 crew members are needed. In windy conditions, additional workers may be beneficial for keeping the textile properly in place before it is fastened.