FAQ’s – Geomembrane

Most Commonly Asked Questions on Geomembranes

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Is it Fish Safe?

• PVC is not fish safe exposed or by itself, but if it is used properly and buried with 12” of dirt/sand/silt then it is fish safe. A 4” layer of shotcrete/concrete will make the liner fish safe also.
• Reinforced Polypropylene (RPP), HDPE, LLDPE, EPDM, Hypalon, PE, MDPE, Woven Coated PE, Duraksrim(NWL SRP), Unreinforced Polypropylene are all fish safe and can be left exposed.
• GCL’s, Coolguard HR, L, XR-5, Urethane’s, L, NESU , and all polyurethanes are not fish safe.

What is the buried depth? 

• 12” high is standard depth to backfill a geomembrane liner. For access roads 18” depth should be used. You cannot spread two 6” depths to make your backfill if you have to drive on the material, because you cannot drive equipment on 6” of material. If you can place it by excavator or conveyor belt then it is possible.

What is the UV (ultraviolet) Resistance?

• It’s a measure of how long the geomembrane lining will last in exposed conditions to the sun. HDPE, RPP, and Hypalon all have excellent UV resistance and will last 20 plus years exposed 40 mil and above.  PVC, Thin Polyethylene, Non Black Polyethylene Products and urethanes do not have good UV resistance.

How long will it last?

• 40 mil HDPE exposed             12-20 years
• 60 mil HDPE exposed             25-45 years
• 80 mil HDPE exposed             30-50 years
• 36 mil RPP and Hypalon 20-35 years
• 20 mil PVC buried with 12” 20-40 years
• 30 mil PVC buried with 12” 25-50 years
• 40 mil PVC buried with 12” 25-50 years
• GCL buried with 12-18”             15-25 years
• 45 mil EPDM 15-30 years
• L, Coolguard, XR-5             10-15 years
• Urethanes & tri-polymers             10-15 years
• Woven Coated PE 2-8 years (depending on thickness)
• 30 mil and 40 mil MDPE or PE             10-20 years
• Duraskrim(6 mil to 20 mil) 2-7 years (depending on thickness)

Do I need a Geotextile cushion underneath the geomembrane?

• You need a geotextile cushion under the lining if you have any sharp angular rocks or round rocks bigger than ¾”. Commonly you will use PermeaTex (8ounce nonwoven product) as a cushion geotextile up to 1” minus rock.  A 4 -6” lift of sand or select soil can also be used for a proper sub grade cushion as well. On small decorative pond you could use carpet remnants as a cushion.

How do I seam and install my chosen geomembrane?

• Installation is the most important part of the geomembrane selection process. No matter what geomembrane you choose, if it is not installed properly then it will not work as it was intended.  Geomembranes can either be solvent welded or heat welded depending upon resin make-up of the product.  Some products have contact adhesive and tapes that only last several months to several years, these are not ideal products.

1. Solvent & heat welded products—PVC and Hypalon only
2. Heat welded products—HDPE,LLDPE, PE, RPP, tri-polymers, and urethanes
3. Taped, sewn, or contact adhesives—EPDM, Duraskrim(SRP), woven coated(not suggested long term products when you need welds or penetrations to the liner done)

What is the difference in the geomembrane product types and what is best for my application?

• The best long term and cost effective products, no matter what the application, are 20 & 30 mil PVC with 12” dirt cover, 40 & 60 mil HDPE/LLDPE, 36&45 mil RPP and Hypalon. For fuel containment, Coolguard and XR-5 and some polyurethanes. The chemical resistance required for containment, and sun exposure life, are the primary factors in choosing one of the products listed above.

What are boots?

• Otherwise known as pipe penetrations or pipe boots (through a liner). We can provide pre-fabricated boots for PVC, RPP, and HDPE. Just make sure you get exact dimensions of the outside diameter of the pipe and the exact slope angle (typical measurements are 90 degrees, 3 to 1, and 2 to 1). Also, make sure that the customer is familiar with installation and knows how to install boots. Most pipe boots are field fabricated. This requires a technician with several years of experience.

Banding Kits – How do I figure out what I need?

• The purpose of the banding kits is to secure the pipe boot nose to the pipe itself. Typically with a boot we will add enough banding strip & clamps along with neoprene rubber for the application. For example, on a 12” OD pipe boot, we will give the customer 4’ of rubber and SS banding to make the seal. The customer will have to provide their own caulking. It’s always good to fax or send the pipe boot detail to the customer.

I need a patch kit for my liner. How do I use it? 

• Patch kits should really only be sent for PVC liners.  All other liner types are too technical to perform repairs.  We can sell them contact adhesive, tape, or some type of mastic strip to try and seal the liner, but there are no guarantees.  Most people don’t understand that the liners really don’t have repair kits that are permanent.  Most problems occur due to wrinkles, dust, moisture, old liner, dirt, and lack of knowledge in the seaming process.  Also, most liners are heat welded and it takes specialty equipment to perform this process (anything from a leister for RPP at $550 to an extruder for HDPE at $ 6,500).

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