Seam Sealing the Borah Gear 7’x9’ Ultralight Tarp

I was supposed to display this new piece of gear at the Danish Outdoor Festival in the last weekend April 2019, but I never got a chance to attach the guy lines and line locks to the tarp so it never came up. However, in mid May 2019 I found some time and fixed the attachments and my first pitch was initiated. Shown below in “storm mode” with the wind side pitched flush to the ground. I’m looking at a hike later in 2019 where I need to stealth camp so this will most probably be my choice of shelter together with the Borah Gear Utralight Cuben Bivy Sack. I polished up on my knot tying skills that I learnt as a boy in the scouts; bowlines and a couple of clove hitches. Great handmade custom kit from Borah Gear!

Shown above in “storm mode” with the wind side pitched flush to the ground

Seam Sealing

I purchased a tube of McNett silcone based SilNet which is designed to seal and waterproof the seams of tents and tarps constructed from Sil-Nylon fabrics (silicone based fabrics). First I emptied the contents of the McNett SilNet silicon seam sealer tube into a glass jar. Then mixed a small amount of turpentine spirit to thin the silicone a little and mixed well. It’s best to use odourless turpentine if you can find it. You can also use some standard clear silicone (not coloured) instead of SilNet. The mixture should be just right so that you can paint it on; not too thick and not runny. It’s also a good idea to pre-test the mixture on a small hidden area first before wider use.

The tarp should be pitched so that the ridge line is taut. Try pulling the tarp tight enough so that the threads are stretched enabling the silicone mixture to penetrate the holes where the threads are sewn through thus waterproofing the seam.

Then I applied the mixture to the tarp with a paint brush. I cut my brush to size so that it was just the right width. Don’t apply straight from the tube; it is too thick. I did this when I seam sealed my Tarptent Notch. It turned out too thick & the result is not so pretty. Also the weight addition is higher than if you thin the mixture first.

After 24 hours the seam sealing job was complete and the silicone mixture had cured. I let the tarp stand a further half day just to be on the safe side. Note that fully cured SilNet may cling to itself when folded. I lightly dusted the fully cured areas with some talcum powder before storage.

Additional info

The tarps are not seam sealed as standard from Borah Gear. You don’t have to seam seal if you don’t think it necessary, but water can seep through the ridge line seam. If you have a water resistant bivy bag that you will use together with the tarp then maybe you don’t think it’s needed. I did it and the seam sealing only added an additional 9 grams.

Someone who commented on my YouTube channel reached out to Borah Gear and John’s response was:

“…it comes down to personal preference. It seems like most people do seal them (any silicone based sealer works) but others including myself haven’t bothered. If you want to make 100% sure no droplets ever find their way through the ridge in a heavy downpour, I’d do it.

I’ve noted that on the Borah Gear website they have announced that the 5.5’x9′ tarps from April 2019 are being made from Sil-poly instead of Sil-Nylon. I’m not an expert on Sil-poly and so I can’t give any advice on it and I’m not sure if it should be or needs seam sealing.

My Borah Gear 7’x9′ Ultralight Tarp including stuff sack not including guy lines or line locks weighed 282 grams before seam sealing and 291 grams after seam sealing. The seam sealing exercise added an additional 9 grams. The guy lines and line locks weigh 38 grams.

Total weight for the tarp after seam sealing including stuff sack, guy lines & line locks is 329 grams.

Below is the YouTube video that I published relating to this blog post. I’ll post an additional article on the Borah Gear Utralight Cuben Bivy Sack after I have used it.

I can’t wait to use both the tarp and bivy sack this year!

Product(s) discussed in this video were purchased by myself from a retailer or manufacturer. I do not accept compensation or donated product in exchange for guaranteed media placement or product review coverage without clearly denoting such coverage as an “ADVERTISEMENT” or “SPONSORED CONTENT.”

2 Replies to “Seam Sealing the Borah Gear 7’x9’ Ultralight Tarp”

    1. If you click on image one it will take you to my Flickr site. Just enlarge the image and you will see that I tie a Cloth Hitch knot. It will not slide or come undone.


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