Since last year I’ve received several further questions about the re-coating of my tarp. I had made a rather brief post about it, without explaining my method in much detail. Now as I’ve re-coated my tarp again a few weeks ago, I now can show you a more comprehensive explanation about my method. This post will probably bring no news to many of you, but for those who don’t have experience with coating a shelter and like to hear my method, I hope it will further clarify the process.
Why and when re-coating a shelter?
During my recent trip to the Verdon, I noticed the fabric of my tarp was starting to suck up moisture on a few spots again and rain droplets didn’t bead up nicely anymore everywhere on the fabric. As soon as you notice the fabric of your shelter doesn’t repel water anymore it is wisely to re-coat your shelter, especially if you have plans to make a longer trip with it soon. If you don’t and let the coating further degrade, the fabric of your shelter will start to suck up moisture each time in the rain or on a condense loaded morning and will become more heavy then necessary. Furthermore the fabric will become very slow to dry once saturated. The ultralight silnylon fabric, which is used in lightweight tarps and shelters today, will even start to mist in heavier rain and you eventually risk to get wet under your shelter. Spinntex/spinnaker fabric (though not used anymore in new shelters these days it seems) will even start to leak quite badly. This misting or leaking does not happen with all tent fabrics however. I’ve never noticed any leaking through kerlon fabric of Hilleberg tents, even when the coating was totally eroded, though once the coating is degraded Hilleberg tents will suck up a lot of moisture also as all other tents will do. A new shelter doesn’t need a new coating soon and the water repellency should remain working for many years at best, though after those years of use you’ll notice the coating on the fabric will eventually degrade. The fabric will start to suck water and you should think about re-coating your shelter for the first time. As soon as you’ve applied a first coating yourself after the first degradation, you’ll have to re-coat the fabric again every one to four years depending on your frequency of usage as your own new applied coating will degrade too over time.
Can I re-coat every shelter?
Shelters made out of cuben fabric never need re-coating. All other fabrics do have a coating which will degrade over their lifespan, mainly due to rubbing, the degrading effect of UV light from the sun and storing it wet. Shelter fabrics usually have either one of those two coatings: a silicone coating or a PU-coating (polyurethane). Tent floors usually have a PU-coating while tent flysheets usually have a silicone coating. However, a PU-coating is still used by some manufacturers on their tent flysheets. It is important to know which kind of coating has been applied to your shelter as each of these two kind of coatings need another product and solvent for re-coating. Some tents like for example those of MSR even have a different coating on each side of the fabric of the tent fly, a silicone coating on the outside and a PU-coating along the inside. If you’re not sure about the type of coating, try to contact the manufacturer.
Coatings based on silicone are the easiest to renew. In case of a PU-coating it is more difficult to find the right product and solvent. Most outdoor stores also sell a specific product that can be used to re-coat or revive the water repellency of your shelter, like for example Nikwax Tent and Gear SolarProof. You can use these, but I find them very expensive if you want to coat a whole tent compared to what you can do yourself with products from the hardware store and I’ve found Nikwax’s solution less effective and durable then my own re-coating method.
Ok, what do I need?
These are the necessary items for a silicone coating:
- White spirit
- A tube of silicone: transparent and odorless (without additives)
- A silicone syringe
- A clean pot or jar
- An accurate weighing scale (one gram accuracy recommended)
- A paint brush
- A pair of protective gloves (you’ll notice I didn’t wear gloves but you should know better)
For a PU-coating you’ll need an urethane based product and an appropriate solvent. I’ve no experience yet with adding a PU-coating so I cannot give advice about what exact products to search for. Anyone with experience with applying a PU-coating, please feel free to share your experiences. You can also try the expensive option like Tent Sure Tent floor sealant from Mcnett or the Nikwax variant. Otherwise the method for a PU-coating will be rather similar as I’m going to explain for a silicone coating.
This is the method I use:
- I pitch the tarp or tent in a way so that it is easy to reach the fabric. Best is to choose a well ventilated place. Just outside in the garden is the place I recommend. It is not a good idea to try re-coating inside the house as your house will smell for days and become dangerously unhealthy to live in! I’ve once re-coated a tent in the garage with the garage door wide open. Even in these circumstances I had to pause regularly to search for a fresh breath of air because I started to get dizzy from the dangerous odor of the white spirit. Outside in the garden I’ve never had that problem so I really recommend to do it outside. Choose a day with the correct weather forecast, this is not too windy and no rain if you don’t have a roof available. However during the spring season there might be a lot of anther dust and/or fluff hovering in the air during fair weather days. This will creep into the coating while drying so I try to avoid this type of days, even though it is not a disaster if some anther dust gets embedded in the coating. Sticking fluff is another matter however.
To coat the Hilleberg Akto I used two battens nailed together at the centre and pitched the tent onto it with the aid of nails beaten on the slats at the right places. This way you can put the tent upright against a wall and easily reach the fabric everywhere. I use this method also to simply wash my tents after a trip. You can follow a similar approach with many other tents.
- Then I clean the tent or tarp from any dirt and oils that have accumulated on the fabric during its usage. I do this by washing the fabric with a non aggressive soap (like Nikwax Techwash or plain simple dish soap), rinse well with water afterwards and rub dry with a towel. Be sure the fabric is completely dry before you start with painting.
- Then I prepare the silicone mixture. This is done by pouring white spirit and silicone into a clean pot or jar in a weight ratio of about 15:1 respectively. This means I have 15 times the weight of white spirit in the pot compared to silicone. How many silicone should you take? I count for about 1,5 grams of silicone per one square meter of fabric for one layer on one side. So for the Trailstar for example which has a fabric area of about 10,5m² or 21,0m² for both sides and if I would choose to apply one layer to the inside and two layers on the outside, I should then take a total of 47 grams (3 layers x 1,5 grams x 10,5m²) of silicone and 705 grams of white spirit. Then I stir well with the brush in the pot until all the silicone is dissolved into the white spirit. This might take a while. If the silicone is very difficult to dissolve you can try to warm up the mixture a bit (don’t exaggerate!). At warmer temperatures I’ve noticed that silicone dissolves easier into the solvent.
- Then I paint the fabric with the silicone mixture as evenly as possible and keep attention to avoid running droplets on the fabric. After adding one layer, I let it dry and once dried I paint another layer on top of the first one if necessary. Normally one layer should be sufficient for silnylon. Spinntex however needs a thinker coating and thus two or three layers for a longer lasting water repellency. Or in case the initial coating on silnylon or tent fabrics has already been very degraded, two layers on the outside might be more advantageous over a single layer only. Once dried, I rub over the new coating with my fingers. This way I can judge if the coating is thick enough to my liking or if yet another (possibly thinner) layer might be desirable. To control the thickness of the new coating you can off course play with the mixing ratio between silicone and white spirit (choose between 20:1 and 10:1) and the amount of layers painted, judge for yourself.
- As soon as the whole tent/tarp is coated, I let everything dry sufficiently for several hours till the coating is clearly dried out and doesn’t stick anymore. Sunlight and a breeze speeds the drying process remarkably. Sprinkling talc powder or anything similar on the fabric afterwards is absolutely not necessary (as is sometimes done with seam sealing). Afterwards you will notice the tarp/tent will show a slightly difference in shade over the fabric because it will be impossible to paint an exactly even coating. While some might find this not appealing, I personally don’t worry about it as the shading difference will gradually fade away with use during the first few trips as the coating degrades again.
Now your tarp or tent has a new coating and will be ready for many more trips. Hope my explanation has been helpful to you.