Guide to Seam Sealing Ultralight Tents and Tarps
The Complete Guide
to Seam Sealing
Everything you need to know about seam sealing your Six Moon Designs shelter — which sealer to use, how to apply it, and when to let us handle it for you.
Why Seam Sealing Matters
Every sewn seam creates tiny needle holes where thread passes through fabric. In traditional tents, manufacturers seal these holes with adhesive seam tape applied at the factory. But Six Moon Designs shelters are different by design.
To minimize weight, our shelters combine elements of the inner tent and outer canopy into a single structure. This creates compound seams where three or more fabric panels meet — and seam tape simply can't conform to these multi-layer intersections. Instead, our seams require liquid seam sealant that can penetrate between the layers and seal every needle hole from the outside.
Fabric Determines Sealer
Silicone-coated fabrics can only be sealed with silicone-based sealant. Polyurethane-coated fabrics need a urethane-based sealer. Using the wrong type won't bond — and won't protect you.
Seal from the Outside
Our compound seams are designed as butt seams with the thread on the interior. Sealing from the outside allows sealant to penetrate down into the seam and coat the exposed thread.
Not Tape-Friendly
Factory seam tape works on simple two-panel seams. Our weight-saving single-wall construction creates complex intersections that tape can't seal effectively.
A Lifetime Bond
Silicone sealant bonds permanently with silicone-coated fabric. Unlike polyurethane coatings that can degrade and peel over time, a properly sealed silnylon seam lasts the life of the shelter.
Which Sealer for Your Shelter
The fabric coating on your shelter determines which seam sealer to use. Most SMD shelters use silicone-coated nylon or polyester, which requires a silicone-based sealer. A few models use polyurethane-coated polyester, which needs a different product.
The majority of our shelters use silicone nylon (silnylon) or silicone polyester (silpoly) for the canopy. Because silicone only bonds to silicone, these shelters must be sealed with Gear Aid Seam Grip + SIL — a silicone-based sealant that forms a permanent, flexible, waterproof bond with the fabric.
A small number of our shelters use polyurethane-coated polyester. These require Gear Aid Seam Grip + FC, a water-based urethane sealer that cures in about two hours and is easy to clean up. Some seams on these shelters may already be factory-taped — check the underside and skip any seams that already have tape applied.
How to Seam Seal Your Shelter
Seam sealing your own shelter is a straightforward process that takes about an hour of active work. We always encourage it — the process helps you understand how your tent is constructed and lets you personally inspect every seam. There's nothing like weathering a storm knowing you sealed those seams yourself.
Set Up & Inspect
Pitch your shelter fully tensioned outdoors or in a well-ventilated space (a garage with the door open works great). Get inside and make sure everything looks right — check that all seams are properly sewn and the shelter fits your needs. This is the time to identify any issues before you commit sealant to fabric.
Prepare Your Materials
You'll need your seam sealer (Seam Grip + SIL for silicone shelters, Seam Grip + FC for PU-coated), a small disposable cup or dish, and a small foam brush (¾" works well). If using Seam Grip + SIL, keep the cap on when not actively pouring — it thickens quickly once exposed to air.
Seal All Exterior Seams
Pour a small amount of sealer into your cup and work one seam at a time. Apply a thin, even coat of sealant to every seam on the outside of the canopy. For butt seams, gently hold the seam open to allow sealant to soak down into the stitching and coat the threads beneath. Work methodically so you don't miss any seams — a consistent approach from top to bottom helps.
Stripe the Floor (Optional)
For shelters with a built-in floor, applying thin stripes of sealant across the floor surface serves double duty: it seals any floor seams and adds grip to the silicone-coated fabric, reducing the tendency of your sleeping pad to slide around.
Cure & Test
Leave your shelter pitched and allow the sealant to cure for 8 to 12 hours. Once dry, the sealer cures to a clear, flexible, nearly invisible matte finish. Seams may feel slightly tacky at first — this dissipates with use. If you prefer, a light dusting of unscented talcum powder eliminates any residual tackiness immediately.
Make Your Own Seam Sealer
For silicone shelters, you can easily make your own sealer from hardware store materials. The DIY version dries clearer and thinner than commercial products, penetrates seams better, and costs a fraction of the price — especially handy if you have multiple items to seal.
DIY Silicone Seam Sealer
For silicone nylon & silicone polyester shelters only
In a glass jar, combine equal parts silicone caulk and mineral spirits. One ounce of each is enough for a one-person shelter. Stir thoroughly until the mixture is smooth and milky with an even, flowing consistency — similar to thick cream. If it's lumpy or too viscous, add a bit more mineral spirits until it flows easily off the brush.
Mixing by hand with a paint stick works, but silicone caulk is stiff — using a paint-stirrer bit in a drill produces a noticeably smoother result that dries clearer and applies more evenly. If the mixture thickens while you're working, add a small amount of mineral spirits to thin it back out.
Let Us Handle It
Over the years, Six Moon Designs has seam sealed thousands of shelters — we know a thing or two about the process. If you lack the time or space, you can add our professional seam sealing service when purchasing a silicone-coated shelter.
Seal It Yourself
- Full control over sealant application
- Inspect every seam as you go
- Get to know your shelter's construction
- Save $25–$35 on the service fee
- Make your own sealer for even more savings
- No risk of cosmetic transfer from drying rack contact
We'll Seal It for You
- Professionally sealed by our experienced team
- Consistent, thorough coverage on every seam
- Just add the service option at checkout ($25 or $35)
- Shelter ships sealed and ready to use
- Satisfaction guarantee on appearance
How We Seal Your Shelter
Laid Out on Table
Each shelter is laid out flat on a large work table. Sealant is injected directly into the seams using a bottle with an applicator tip — we've found this method penetrates compound seams more effectively than brush application.
Cured on Drying Rack
After all seams are coated, the shelter is hung on our drying rack. We generally allow two days for curing before shipping. Timing varies with conditions — warm summer days can cure in under 24 hours, while cold, humid winter weather may take longer.
Inspected & Shipped
Once fully cured, your shelter is inspected and packed for shipment. You may find that fabric pieces in the seams are stuck together from drying — this is normal. Simply pull them apart gently; the seams are perfectly sealed underneath.
During rack drying, shelters can occasionally contact adjacent shelters, which may leave small traces of sealant on exposed fabric surfaces. This is purely cosmetic and does not compromise the integrity of the sealed seams in any way. If you want to ensure a pristine cosmetic finish with zero chance of transfer marks, we recommend sealing your shelter yourself.
Some shelters combine different materials — particularly at vents. Since vent fabric isn't always silnylon, you may notice sealant flaking on vent material. This isn't a problem; the structural interior seam is fully sealed. The silicone simply doesn't adhere as well to non-silicone fabrics.
If you purchase a shelter with our seam sealing service and are dissatisfied with the appearance of the sealing, you may return the unused shelter for a full refund — or exchange it for a new non-sealed shelter and we'll refund the difference between the sealing fee and the cost of shipping the replacement.