Is seam sealing all tents necessary?

Generally, if the tent comes from a larger factory brand (ie. REI, Mountain Hardware, Sierra Designs, Marmot, NEMO, etc.) then the seams are usually taped and don't need sealing. However, make sure first!

If the tent/tarptent comes from a cottage manufacturer (ie. Tarptent, Six Moon Designs, MLD, etc.) then it usually needs to be sealed. Some of the manufacturers offer a seam sealing service for a fee.

Again, this is a general rule, and if in doubt, check with the manufacturer.

As above, it depends.

Most all tents on the market are made with either nylon or polyester fabrics — and all but the cheapest should come with seams that are factory taped. These do not require any manual seam sealing.

Important exceptions are tents, tarptents and tarps made with ultralight fabrics such as silnylon and cuben. These materials cannot be machine taped — but must be seam sealed manually. I believe both Henry Shires and Six Moon Designs provide optional manual seam sealing for an additional charge.

As Benjamin notes, shelter fabric is the key. For example, Black Diamond (a large factory brand) shelters made with silnylon require seam sealing.

Time and space requirements make manual seam sealing a poor business…

Big Agnes does not require it.

Does Big Agnes make a silnylon tent?

It all depends on how much leakage you'll tolerate. For example, Nemo single-walled tents (the Tenshi, Moki) are seam-taped, but the instructions say to apply Seam Grip to the outside of the seams anyway. If you don't, rain will seep in through all the points where the inner attachments have been sewn to the canopy after the canopy has been seam-taped.

With two-layer tents having separate flies and canopies, you won't get the horrendous flow of water inside as you would by not applying Seam Grip, but the attachment points on the underside of the fly on SD, TNF, and MH tents are all sewn on after the seam taping has been done, and will leak if not prepped–I do it on the inside of the fly.

Another potential leak point is on tents that have a seam around the perimeter of the floor. This seam is very hard to tape (although the TNF used to do so on its expedition tents), and water dripping off the fly onto that seam will result in leaks if the seam hasn't been treated with Seam Grip.

Bibler four season tents (the one's with ToddTex) are very well seam-taped, but I know from experience that there will be leakage if Seam Grip isn't applied to the outer surface of the seams.

In addition, a less apparent benefit is that seam sealing reinforces the seams, so they are less likely to tear and/or wear.

I'm assuming that something like this $5.00 seam sealer is all I need to use or should I be using a special tape?

Moss, GoLite, Quest and perhaps others used hydrophilic thread they claimed would swell and prevent seam leaks, eliminating the need for seam sealing or taping. How well that translated to preventing leakage in the field seemed to vary quite a bit.

Seams in super-light fabrics like thin sil-nylon and spinnaker cloth benefit from the strenghtening provided by sealing in addition to waterproofing, so this step should not be skipped on any very lightweight shelter.

Cheers,

Rick

Yes, you can use Silnet straight out of the bottle — which is what I did. However, it is kind of thick — and can be a bit unsightly.

Others have used thinners to thin out Silnet for smoother application.

I can verify that my both my Moss Stargazer and Tentwing have no seam sealer, and, to my perception, have never leaked.

For some reason there is this close association in the forums between "Tarptent " and "seam sealing". In reality many brands have or are selling tents that need to be sealed by the consumer.
Here is a partial list :Bibler,Black Diamond ,Macpac, Integral Design,Eureka,Golite, Terra Nova, Lightwave, Nemo, MSR (they send you a tube with some tarps if you have problems..) and of course all of the cottage manufacturers that use silnylon , cuben or spinnaker .
Reading many threads it is clear that some tents that are taped also need at least a touch up in certain areas. All you need to do is Google seam sealing and a brand and chances are that someone will post about having had do do theirs, usually as a "repair" on a leaky tent.
Adding a PU coating on the underside allows silnylon to be taped but that has problems as well as Stephenson's Warmlite point out :
"Seam sealing (which we let you do, or offer as a service) is done with silicone adhesive we supply, (use for repairs if ever needed). The finish is extremely slippery, thus stays clean and wears far better than urethane coatings usually used on tents, and doesn’t turn sticky from damp storage as urethane coatings do"
Of course they have a biased view, nevertheless what they state can and does happen.
On the other hand at least Tarptent (and me soon) and SMD offer that service for a relatively modest fee.
This is obviously not possible for ,say, the like of Eureka with 500-1000 tents made in one single production run.
Franco,
franco@tarptent.com

"On the other hand at least Tarptent (and me soon) and SMD offer that service for a relatively modest fee."

I feel sorry for you already.

Ben
Yes I can see why. I make pizza from scratch for my self but would not want to do it for others…
I have sealed several tents, some for friends, however as usual doing something as a hobby when you feel like it and doing it when it has to be done it isn't same thing.
Anyway , still not there yet.
Franco