Seam Sealing: A Thread for Tips and Questions

[WilliamC]

There is quite a lot of information about seam sealing on TL but it's scatted around a number of threads. As I have a question and searching around to see if it had already been answered took a lot of time, I thought it would be useful to have a thread specifically for advice on the topic.

 

[WilliamC]

To kick us off, I have always seam sealed flysheets on the outside as I figured it would stop moisture getting into the seam, where it might be very slow to try out. I recently picked up a tube of Silnet (actually Seam Grip + Sil) and notice that the instructions say to seam the inside of lap felled seams.
Other than aesthetics and perhaps prevention of UV damage, can anybody think why it might be better to seam the inside rather than the outside?

 

[Fossil Bluff]

Good idea - who’s the seam sealing guru?

Some fundamentals would be good.

Dilution
Application
Tools
Drying
Where



I personally like Bob’s explanation/

https://www.backpackinglight.co.uk/seam-sealing.html

 

[WilliamC]

One thing that is often is misunderstood about silicone sealers is about how they "dry". In fact, silicone cures on reacting with moisture, so you want a humid day, rather than a dry one. Warmth helps, too. Take your tent to a sauna with you

 

[WilliamC]

I personally like Bob’s explanation/

https://www.backpackinglight.co.uk/seam-sealing.html

I notice he seals the outside.

 

[SteG]

I personally went with @Mole suggestion on a previous thread and weighted the apex with a heavy kettle bell, stretched it and applied straight out of the tube and used my finger to rub it in. Ive done this on two shelters now and worked a treat both times. No drips and looks ok.
Ps just did the outside and got in the grooves as well. If covered properly not sure why you would need to do the inside too. A bit of a tedious job to have to do inside also.

 

[Teepee]

Silicone sealant is often more UV resistant than the fabric and protects the stitches too. Also easier to apply. It's got an easier job though on the inside as the seam stops a lot of water ingress.

It also helps stick the threads and makes the seam stronger.

Do both sides I say.

Flowable windshield silicone sealant does the best job on sil tents and stuff sacks etc. It flows into threads and gaps, sets smoother and has a much higher modulus when cured than a lot of sealants.

For the strongest bond and longest lasting seam sealing on PU coated and non siliconized substrates, PU sealant like McNett seamgrip is the best.

To thin Silicone, you can use white spirit/white gas/lighter fluid effectively.
To thin PU, Xylene paint thinners is very good.

 

[WilliamC]

Ps just did the outside and got in the grooves as well. If covered properly not sure why you would need to do the inside too. A bit of a tedious job to have to do inside also.

To be clear, the Silnet instructions are to do ONLY the inside.

 

[SteG]

To be clear, the Silnet instructions are to do ONLY the inside.

Oh, I'm not sure what I used now. It's what ever MLD send with their shelters William

 

[Rmr]

One thing that is often is misunderstood about silicone sealers is about how they "dry". In fact, silicone cures on reacting with moisture, so you want a humid day, rather than a dry one. Warmth helps, too. Take your tent to a sauna with you

It will dry sauna or later.

 

[OwenM]

Ffs, I'm going camping in the wilds not going to an art show. Splat it on with a finger and get on with your life.

 

[SteG]

Just familiarising myself with MLD sealing instructions and it says in bold text to only do the outside when using sil net??

 

[Stuart]

Perfect timing @WilliamC !!

I need to seal the ridge of our car camping tent, a Quechua 4 person job. It's in the style of a Nallo GT. The seams of the flysheet are taped but over the years these have come away slightly in places. To be clear the tape as a whole is intact, there are just a few spots where it's come away. I'm not sure if I'm best removing the whole tape and sealing it all or just trying to fill the few places where water is getting in.

 

[WilliamC]

I need to seal the ridge of our car camping tent, a Quechua 4 person job. It's in the style of a Nallo GT. The seams of the flysheet are taped but over the years these have come away slightly in places. To be clear the tape as a whole is intact, there are just a few spots where it's come away. I'm not sure if I'm best removing the whole tape and sealing it all or just trying to fill the few places where water is getting in.

My only experience is with a couple of sil/PU nylon waterproofs, which had been taped on the inside/PU side. I left the tape in place and sealed the outside with silnet. The tape continued to peel.
I suspect that if you only seal the gaps, the tape will continue to peel in places and you'll get new leaks.

 

[Fossil Bluff]

I notice he seals the outside.

Yes, there's a reason for that , on that shelter... bu99ered if I can remember why, it depends on the type of seam. Thats how I did my Hex - works a treat and looks neat and tidy - but there was a good reason to do the outside. I'll have to search again.

 

[WilliamC]

Yes, there's a reason for that , on that shelter... bu99ered if I can remember why, it depends on the type of seam. Thats how I did my Hex - works a treat and looks neat and tidy - but there was a good reason to do the outside. I'll have to search again.

The instructions say inside for lap felled seams, outside for butted seams.

In the video, it looks as if it has both types of seam, though I thought butted seams weren't recommended for flysheets as all the stress is on one row of stitches.
I'm going to go with the outside, anyway. If it's good enough for Ron Bell...

 

[Fossil Bluff]

Here we go, this was from Bob's website where the Youtube is lifted from.

Seal the Seams - Most of seams on these shelters are designed using butt seams (See below). These seams keep the the threads on the inside where they are less exposed to dirt and grim. Butt seams must be sealed from the outside of the canopy. Applying sealer to the underside of the seam will not seal them.

 

[Myles21]

I haven't heard of sealing a sil shelter on the inside. I also like Bob's (BPL UK) seam sealing video - the Hex Peak that he's sealing is only sil coated on the outside (PU on inner) so he applies it to the exterior. Both he and Franco (on YouTube) advise using a 'splodge' of sealant and mixing the white spirit in gradually to get a 'thick olive oil' consistency, no need to measure proportions. I've found that I need to add a splash more white spirit a couple of times during the sealing process, as the mix thickens due to evaporation. I also found that the sealant can thicken in the brush so it helps to have a little pot of white spirit on hand to keep the bristles unclogged.

 

[Myles21]

Perfect timing @WilliamC !!

I need to seal the ridge of our car camping tent, a Quechua 4 person job. It's in the style of a Nallo GT. The seams of the flysheet are taped but over the years these have come away slightly in places. To be clear the tape as a whole is intact, there are just a few spots where it's come away. I'm not sure if I'm best removing the whole tape and sealing it all or just trying to fill the few places where water is getting in.

Is this any help?
https://www.msrgear.com/blog/tents-101-seam-taping-vs-seam-sealing/

 

[Fossil Bluff]

I haven't heard of sealing a sil shelter on the inside. I also like Bob's (BPL UK) seam sealing video - the Hex Peak that he's sealing is only sil coated on the outside (PU on inner) so he applies it to the exterior. Both he and Franco (on YouTube) advise using a 'splodge' of sealant and mixing the white spirit in gradually to get a 'thick olive oil' consistency, no need to measure proportions. I've found that I need to add a splash more white spirit a couple of times during the sealing process, as the mix thickens due to evaporation. I also found that the sealant can thicken in the brush so it helps to have a little pot of white spirit on hand to keep the bristles unclogged.

I followed his instructions WRT thick olive oil. I found the process quite satisfying, I thought it would be a nightmare

 

[Myles21]

I followed his instructions WRT thick olive oil. In found the process quite satisfying, I thought it would be a nightmare

I know, quite absorbing and meditative.

 

[WilliamC]

Well, I seam sealed the Aricxi Mid today and I think I know the answer to my question.
If you seam on the exterior (the upper side in the diagram below), its hard to get the the silicone under the roll (at x) without making a mess. If water gets in at x, it can easily get through the stitching at y. However, if you seal on the interior the stitching at y is protected and it's relatively difficult for water to get through to z. So, it seems to me that seling the interior would be more likely to be watertight.

I also found, seam sealing with temperatures in the upper 30s, that sweat beads up nicely on the tents nylon - hopefully a good sign for its waterproofness

 

[WilliamC]

Seek Outside has a new seam-sealing video. They also seam the outside but have some slightly different techniques.

 

[Enzo]

I've got a lap felled folder coming for my twin needle sewing machine.
No idea why.

 

[simplerandomwalk]

Question: can I seam seal my shelter indoors? Like set it up in the evening (possibly sleep under it as I'm not sure my apartment is big enough) and let it dry overnight?

I don't have my own garden and yes I could go on an overnighter to do this (in the spring) but then I have to bring all the equipment and it would save a little bit of hassle if I could just do it at home..

Also, is Wilko the only place where I can buy white spirit?