Weathering your Glawning
Canvas is a wonderful material to make tents from for many reasons, primarily its breathability. However, it behaves in different ways to more common nylon awnings so it requires special care.
One of the unique features of canvas is the need to weather it in order to make it fully waterproof. Here we will try and explain how it works so you can avoid any nasty surprises when it might appear like your tent is leaking on first use.
Canvas tents usually come pre-treated with chemicals to make them resistant to water. This has the effect of making water bead on the surface of the canvas and run off, thereby keeping it from getting through. So when you first pitch and put a hose on a new canvas tent, you will notice water beads off very easily - this inspires confidence that the tents is fully waterproof.
However, there is only so much water this coating can deal with before it starts to soak into the canvas. So, if rain is very persistent, or very fine, or if strong winds are pushing the water into the canvas, water will start to penetrate and be absorbed by the canvas fabric. This will be exacerbated if all three of these conditions are present.
This isn’t the end of the story, however. Water penetrating the waterproof coating and being absorbed by the canvas is actually a good thing in a new canvas tent, because it kicks off what’s known as the “weathering” process. This is required to make the tent fully waterproof.
Basically, what happens is that the fibres of the canvas absorb water and expand. Equally important, however, is the subsequent drying out. As the canvas drys, it shrinks very slightly to knit the weave together and close up any tiny holes in the fabric, together with any needle holes where the canvas has been stitched (these are usually wider holes which is why tents often take longer to weather on the seams).
Sometimes the tent will take a few wetting and drying cycles before the water ingress stops completely, but the waterproof properties will improve with every cycle until eventually the tent is completely waterproof.
So if your tents appears to be leaking on your first outing, the key is not to panic. Lighting the fire and putting a few towels on the floor will usually help to manage the problem, which will disappear over time. On a new tent, water ingress might manifest itself as dripping along the seams where the tent has been stitched, or a fine mist coming through the main panels of the canvas. The problem can be exacerbated if conditions are particularly bad, with a combination of fine, persistent rain and strong winds. Because the floor of the tent is PVC and impermeable, water may collect in pools on top of the groundsheet, but under your matting, giving the appearance that it’s coming through from below when its not.
The good news is that the weathering process can be accelerated at home by pitching the tent in fine sunny weather and sticking a hose on it. However, please be aware that you might need to keep the hose on for a good while in order to penetrate the canvas. Using a fine mist setting on the hose will help, so that the water sits on the canvas rather than running off. Once the canvas starts getting wet on the inside, you know that it is properly soaking in. When you’re satisfied that it has fully soaked in, let the tent dry naturally in the sun (with the guy ropes slightly slack so as not to put strain on the stitching etc). You can repeat this process 2 or 3 times to ensure that the job is done.