You can connect two tarps together using overlapping edges, grommets with cord or zip ties, adhesive bonding, or seam sealing, depending on whether you need a temporary setup or a permanent waterproof join. The right method depends on your tarp material, how much weather exposure you expect, and whether you want to separate the tarps later.
Overlapping: The Simplest Approach
The most common way to join two tarps is a reverse overlap, where each tarp’s edge folds over the other. You align the tarps side by side, then connect the overlap flap of Tarp A to the bottom edge of Tarp B, and the overlap flap of Tarp B to the top edge of Tarp A. This interlocking design sheds water in both directions, since neither seam faces upward as a single exposed gap. Most tarps built for this purpose come with about 1 foot of overlap fabric along their edges.
For wind and rain protection, the overlap matters more than you might think. Industry standards recommend 3 to 4 feet of overlap between two tarps (roughly 36 to 48 inches) to prevent wind and water intrusion. That’s a lot more than most people assume. If you’re covering a campsite canopy or a woodpile in your backyard, a smaller overlap works fine. But for flatbed loads, construction sites, or anything exposed to sustained wind, that wider overlap prevents the tarps from separating and flapping.
Grommets, Zip Ties, and Cord
If your tarps already have grommets along the edges, lacing them together with paracord, bungee cord, or zip ties is fast and effective. Lay the tarps with their grommet edges overlapping by at least 6 to 12 inches, then thread cord back and forth through alternating grommets in a zigzag pattern. Zip ties work for a quicker connection, especially on flatbed or construction tarps where you just need things held in place.
If your tarps don’t have grommets where you need them, you can add your own with an inexpensive grommet kit, which includes a punch tool, setter tool, and the metal eyelets themselves. Space new grommets 12 to 18 inches apart along the edge, or closer together if you expect high winds. To install one, punch a hole through the tarp fabric, place the grommet halves on either side, then strike the setter tool firmly with a hammer to crimp it into place. A measuring tape and pliers round out the toolkit. The whole process takes a few minutes per grommet.
Tarp clips offer another option if you don’t want to punch holes at all. These clamp onto the tarp fabric and provide a loop or hook point, letting you clip two tarps together or run cord between clips. They’re not as secure as metal grommets, but for lighter duty or temporary setups they save time.
Gluing Vinyl Tarps Together
For vinyl-coated tarps, a solvent-based adhesive creates a permanent, waterproof chemical bond. HH-66 Vinyl Cement is the standard product for this job. It’s a fast-drying, waterproof adhesive designed specifically for bonding vinyl-coated and vinyl-laminated fabrics to themselves. It resists the chemicals found in vinyl products, so the bond doesn’t break down over time the way general-purpose glues would.
To use it, clean both surfaces thoroughly, apply a thin coat to each side of the joint, let it get tacky (usually a minute or two), then press the surfaces firmly together. The bond reaches full strength within 24 hours. If you need to thin the adhesive for a smoother application, a compatible thinner is available from the same manufacturer. One important note: HH-66 is made for vinyl-to-vinyl bonds. If you’re working with polyethylene tarps (the blue or silver hardware store variety), this adhesive won’t hold reliably.
Heat Welding for Poly and PVC Tarps
Heat welding creates the strongest possible joint between two tarps of the same plastic material. Using a hot air gun, you melt the overlapping edges together so they fuse into a single layer. This is the technique used in commercial tarp manufacturing and billboard fabrication.
The temperature depends on your tarp material. High-density polyethylene (the most common tarp plastic) welds at 300 to 320°C (about 570 to 610°F). PVC tarps need slightly more heat, typically 330 to 370°C depending on the specific type. You’ll also need consistent airflow from the heat gun, around 40 to 50 liters per minute. The goal is to partially melt the material so it flattens and fuses without burning through. If the material barely changes shape, you’re too cold. If it smears completely flat or bubbles, you’re too hot.
This method requires practice and the right equipment, so it’s best suited for people who work with tarps regularly or have a specific project worth the investment. For a one-time job, grommets or adhesive are more practical.
Waterproofing the Seam
However you connect your tarps, the seam is the weak point for water. Even a tight overlap can wick moisture through capillary action, and any holes from grommets or stitching create direct paths for leaks. You have two main options for sealing: seam tape and liquid seam sealant.
Seam tape is a polyurethane film applied under or over the seam to block water from passing through needle holes and gaps. It works well on heavier tarp fabrics (roughly 68 denier and above), where it adheres tightly for long-term protection. On thinner, lighter materials, tape degrades faster with exposure to moisture, heat, and humidity. It can start to flake off, and once it does, scraping away the residue to reapply becomes a hassle.
Liquid seam sealant is essentially a waterproof glue you brush or squeeze across the seam. Products like Seam Grip +WP create a flexible, waterproof barrier that conforms to uneven surfaces and holds up for years. Some users report a single application lasting a decade or more. For tarp joints that will see real weather, liquid sealant is generally the more durable choice, especially if you’ve stitched or laced the tarps together and need to seal cord holes.
For the best results, apply your sealant on a dry day, let it cure fully before exposing the seam to rain, and inspect it once a season if the tarps stay outdoors year-round.
Choosing the Right Method
- Temporary or adjustable setup (camping, covering firewood, seasonal storage): Use grommet lacing with cord or zip ties. Easy to set up, easy to take apart, and the tarps stay reusable for other purposes.
- Semi-permanent weather protection (carport extension, garden cover, long-term storage): Overlap generously, secure with grommets every 12 inches, and seal the seam with liquid sealant.
- Permanent waterproof bond on vinyl tarps (boat covers, industrial enclosures, custom fabrication): Use HH-66 vinyl cement for a chemical bond that won’t separate.
- Heavy-duty or commercial applications (flatbed trucking, construction enclosures): Use reverse overlap with at least 3 to 4 feet of coverage between tarps, secured with zip ties or industrial fasteners at tight intervals.
The overlap width is the single most overlooked factor. Most people use 6 inches and wonder why their tarps leak or separate in wind. For anything exposed to weather, more overlap always outperforms a tighter, more “finished” looking joint.