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If you already know what a footprint is and why you might want one you can skip this section. A footprint is an extra groundsheet that provides extra protection on rough ground, especially for lightweight tents with delicate groundsheets. They’re also useful if your existing groundsheet is getting a bit leaky. For some tents that pitch inner first they can also give the option of pitching outer first (very handy in the rain!) or without the inner at all.
The footprint is sacrificial – it’s being used where you expect some damage. Cheap tarpaulins are waterproof, tear resistant and as light as ordinary groundsheet material. I’ve not found anything that offers better value. ‘Proper’ groundsheet fabric is 80g/sqm or more, and around £7/m. My cheap tarp is about the same weight, and cost that for 3.7m x 2.4m.
You can fold over and weld the edge of the footprint to reduce the risk of the layers separating and the edge getting frayed. If you think it’s worth the effort then allow 10mm to 25mm extra on each side, and mark it out when you are measuring up and cutting.
This really depends on your tent, and how you are going to use the footprint. You probably want one attachment point for every place the groundsheet would be pegged, or where a flexipole would attach. You could use plastic or aluminium rings, eyelets, webbing, rope or elastic loops.
My tent normally pitches inner first, with the ends of the flexipoles in an aluminium tab on each corner of the rectangular groundsheet of the inner, and pegging loops outside. The aluminium tabs are attached to the inner by ~50mm of 10mm wide webbing. I want to be able to pitch with the footprint and outer first, then add the inner from the shelter of the tent. To do this the footprint needs to be able to locate the ends of the flexipoles at the same separation as the inner would, with pegging loops outside. With the inner on top of the footprint I will then have to pass the webbing and tab round or through the footprint attachment to get it onto the end of the flexipole. I chose 20mm plastic D-rings to go in each corner of the footprint, big enough for the tab and webbing to go through.
Your footprint should be slightly smaller than the groundsheet you’re trying to protect. This is so that the edges of the footprint are covered by the groundsheet, stopping rain landing on the footprint and running between it and the groundsheet. If you’re planning on folding over the edges of the footprint to make it a little more robust then remember to add this to the size.
Now you can pick your tarp. I picked this one so I had enough for two footprints. If you find something that’s the right size, and you intend to just peg it down or put it under your groundsheet, you can stop here. Be careful to check the eyelets though – on something this cheap they aren’t always made well, and may have sharp edges.
Now mark out the footprint on the tarpaulin and cut with the scissors. Don’t rely on the tarpaulin having straight edges or right angles.
We’re going to be using an iron which will be hot enough to burn us. We’re aiming to get plastic hot enough to be sticky, but if we get it wrong the plastic could melt and/or stick to things we didn’t want it to, so be careful or don’t do it. Most of that also applies to doing the ironing…
If you look at the tarpaulin you’ll see it’s got a middle woven layer between two thin skins. The inner layer has a higher melting point than the skins, so if you get the temperature of the iron right you can weld bits of tarpaulin together by ironing them. This is going to need some experimentation and practice with offcuts of tarpaulin material.
Prepare your ironing area, whether it’s the ironing board, or just a flat surface with some flat cotton padding of some sort. We want cotton rather than synthetic because it’s more heat resistant. Get a but of baking paper ready too. The size depends on how big the join you’re making will be. It’s going to stop the hot tarpaulin material from sticking to either your ironing board or your iron, so it needs to be big enough that when doubled over it will cover the whole of the bit you’re welding. If you’re doubling over the edges then you’ll have to do a bit at a time.
Set your iron to a low to middle heat and plug in. It’s better to start too low than too high. While it’s heating up you can prepare some offcuts to try welding. I used a strip about 50mm wide and 500mm long, doubling the end over to practice welding, then cutting it off and repeating until I was happy with the process. Double over a bit of material, put it between the layers of doubled over baking paper, then press with the iron for 10 to 15 seconds to weld. Remember not to iron past the edge of the baking paper Ideally press with something else while it cools, although I didn’t have anything to do that. When it’s cooled you can check how well stuck it is, and how much the ironed area has shrunk. If it’s not stuck well enough then turn the heat up a little, or press for a bit longer. If it’s a melty mess then turn the heat down or don’t press as long. Repeat until you’re happy with the process. Multiple layers need a bit more heat or time, and you may need to iron both sides if you have a lot of layers.
To attach my 20mm D-rings I cut a strip of material 40mm wide, then folded the edges in to meet in the middle and ironed to get a double thickness 20mm strip with strengthened edges. The D-rings were to be positioned where the webbing attached at the corners of the inner, about 50mm past the corner of the footprint. Folding the strip in half with the D-ring in the middle and the ends welded to the footprint should be secure. I guessed about 70mm of welded length on the footprint should be enough, making about 240mm for the length of the strip. Welding the ends to opposite faces of the footprint and spreading them to make a V should distribute the load better, and a rectangle of reinforcement over each side even more so. The rectangle would also cover the ends of the strip, reducing the chance of them peeling from the corners. This may have been overkill.
I folded the strip in half, threaded the D-ring, spread the ends about 30 degrees to form the V, then ironed just the bit next to the D-ring to tack the V in place. Next I positioned it at the corner of the footprint and ironed on both sides to weld the strip to the footprint. Finally I cut the reinforcement patch for each face and ironed them on each side. Now repeat for the remaining attachment points.
The plan is to make some aluminium or plastic tabs similar to the ones on the outer, and attach them to the D-rings with some 10mm grosgrain ribbon. On the outer end there will be some pegging loops.