Tarps are a handy resource in just about any camp (or around home too). They can be used for extra shade, extra rain protection, to cover equipment, and as ground cloths under or inside your tent or even to make a tent. Tarps come in many different strengths. The lightest and least expensive tarps (not counting plastic drop cloths) are polytarps and they come in different colors. The blue tarps are usually the lightest and least expensive. They will normally be sufficient for most camping temporary tasks. For a stronger tarp (good for under your tent or longer term use), choose a green "farm tarp" or one of the heavier silver tarps. For really heavy duty applications, go for a heavy canvas tarp. There are different grades or weights of canvas tarps, depending on what you need to cover and for how long. Another consideration is whether the tarp will be stationery or on a vehicle or otherwise subjected to high winds and extreme weather. How heavy a tarp you need depends on how you're going to use it and how far you have to carry it! Heavy canvas tarps will be the most durable and provide the most protection, but they are very heavy to carry around if you're hiking or have any distance to tote your equipment from your vehicle to your camp site. They also tend to be stiff and somewhat harder to work with, especially when its cold. Light weight "poly" tarps are usually sufficient without the added weight and they take up far less room. And they are inexpensive and are usually waterproof. u But there are even heavier alternatives out there. My parents have roll up tarp "walls" on their carport in Oregon. They are made of the heaviest canvas I've ever seen, at least 3/16" thick and the weave is as coarse as a wood rasp (I have had the skinned knuckles to prove it)! They've been in use for over 50 years of Oregon rain and are still going strong. They are permanently mounted to the carport but can be rolled up when necessary. Of course, they are WAY too heavy to consider for camping. Plastic painter's sheets are just the opposite -- very light, very thin plastic film. It is inexpensive, waterproof, and easy to carry. But it isn't very sturdy and is easily punctured or torn. You might use one or more temporarily to keep the rain off, but they won't provide much shade and probably won't stand up to wind and weather very well. Using one as a ground cloth is pretty much an exercise in futility. They are so fragile that small twigs and pebbles will easily make holes in them and render them useless.
Tarps come in a variety of sizes so you can usually find one close to the size you need. Harbor Freight has a wide selection of tarps in various strengths and sizes. Watch for their ads and flyers and you can often find them on sale to save even more money.
Actual measurements of tarps are usually slightly smaller than the advertised size. For example, an 8x10 tarp will probably actually measure 7'6" by 9'6". Be sure to take that into consideration when you buy a tarp. The actual finished size is usually marked somewhere on the package. If you want a ground cloth for an 8x10 tent, you may have to buy the next size bigger tarp and fold the excess under. On the other hand, using a standard "8x10" tarp fits nicely inside an 8x10 tent and even might be just right for use under an 8x10 tent. It would likely be about 2-3" smaller than the tent on each side so it wouldn't stick out and collect run-off. But -- it could also leave 3" of tent floor exposed to the damp ground and/or debris. Since you usually won't be walking that close to the walls, the 3" probably won't be a problem. The trimmed size is usually very good for an inside layer to protect the floor.
For best results as a ground cloth, use a heavy duty tarp underneath your tent to protect the floor against debris and ground moisture. Use a second tarp inside your tent for added waterproofing to your sleeping bags don't absorb moisture. The inside ground cloth doesn't need to be as heavy as the one underneath the tent but it should be waterproof, like a plastic tarp. Using closed cell foam sleeping pads beneath your sleeping bags will give you even better protection and comfort. Even if you are using sleeping pads to protect your sleeping bags, having an inside ground cloth covering the entire tent floor will help keep the floor clean and be more comfortable when you are moving around in stocking feet and will help protect the floor from damage. For exceptional comfort, add foam tile to cover your tent floor inside. It will be like having a wall-to-wall sleeping pad. The foam tiles are light weight, easy to assemble, and easy to clean. With both foam tiles and a sleeping pad, you'll be sleeping on cloud 9!
With use tarps will eventually loose some of the their water repellent capability. Repeated folding, crushing, or whipping in the wind breaks down the structure and wears away the coating. When your tarp begins to get soft and fuzzy and the color begins to fade it is probably time to replace it. Not only will it have lost some of its ability to keep you dry, it will have been weakened and may rip in the next strong breeze. Most polytarps will be kind of shiny when they are new and begin to dull as they age. Sometimes you can extend a tarps waterproof lifetime by spraying it with a waterproofing like Camp Dry.
Tarps can be hung between trees or vehicles or on poles to form a makeshift canopy to provide shade or protection against light rain. Tarps can be added as an extra "rain fly" over tents for extra protection against rain and sun. Tarps can be used to cover your firewood and your camping equipment and OHVs to protect them from weather. I've even seen multiple tarps used to cover an entire camp site. The center was very high, both for rain run off and to allow building a campfire. It rained almost that entire weekend, but the large, extended family stayed dry and enjoyed their outing. Some of the teens had fun dumping the water out of the low spots periodically to help prevent the tarps from coming down.
You can make your own tent using tarps. A simple shelter can be made by hanging a single tarp over a rope or other cordage or a rafter stretched between two uprights For more weather protection, use multiple tarps to also enclose the open ends. . Or you can use one to make a simple lean-to ito keep the rain off.
Tarps are often used to cover equipment in the bed of a truck or utility trailer during transport. They need to be securely anchored to withstand the wind forces that occur at highway speeds. For the best protection against rain, drape the tarp over the sides of the bed and secure it underneath. If you leave it inside the bed water can run down and soak your cargo. In camp they can protect equipment from sun and from rain and snow. They provide some level of security too -- sometimes just keeping your stuff out of sight avoids it being "acquired" by opportunistic thieves. "Security by obscurity" is a valid and valuable way of protecting your stuff.
We have found several uses for tarps on our sailboat. Because wind driven rain can sometimes blow under the companionway slide we usually drape a small polytarp over the cabin to protect the companionway from the rain when anchored. We hang a larger tarp over the boom and tie it off to the lifelines to make a "boom tent" for extra shade in the cockpit when at anchor. Tarps can be used as temporary sail covers if you don't want to take the time to flake the sails and put them away when you stop for a while. Large tarps can be used to cover your boat to protect it from the elements during the off season.
Small holes or tears can usually be repaired using duct tape or vinyl tape. Make sure the surface is clean and dry before applying the tape. For added security, put tape over the damaged area on both sides of the tarp. Because of the oily waterproofing used on canvas tarps, regular tape may not always stick well. If any tarp is exposed to wind and weather, the tape may come off. For best results stitch a waterproof patch in place and seal it with tent seam sealer -- or just replace the tarp. If there are too many holes and repairs, it becomes something like a description I once heard of how to make a net: take a bunch of holes and sew them together. You'll want to replace your tarp long before it reaches that stage.
Tarps usually come with metal grommets evenly spaced around all 4 sides. These are useful for tying or staking down the tarp. If you have a tarp without grommets or need more grommets you can buy grommet kits at most camping stores. They usually include two-piece grommets, a tool for punching the right size hole in the tarp, and a tool for "setting"the grommet. That tool consists of a shaped bottom plate that holds the flat piece of the grommet and a driver tool that is used to rivet the second piece to the first using a hammer. You can also buy tarp clamps that will add "eyes" for attaching ropes without punching holes in the tarp. Another trick for securing a tarp is to out small rock or short twig near the edge and wrap the tarp around it and secure it with a piece of rope or twine and tie a guy rope to it. There are also tarp clamps you can use in place of grommets Here is an example of commercially available tarp clamps:
You can buy them at places like Walmart, Harbor Freight, Home Depot, and Amazon.
Tarps and tent fabrics degree of water proofing are measured by something called hydrostatic pressure. It represents the pressure necessary to force water through the fabric. Heavy rain and wind-driven rain will create a higher hydrostatic pressure than light rain so you need a stronger fabric to keep out extreme weather. A rating of 1000 mm hydrostatic pressure is regarded as shower resistant. 1500 mm rating is sufficient for a summer tent. 2000 mm is the minimum for an all season tent. Higher ratings of around 3000 mm are used for expedition tents and 5000 mm for really good quality ground cloths. You probably won't find the ratings for a particular item without doing some extra research.
We use a small polytarp to cover the cabin on our sailboat to prevent wind-driven rain from blowing under the companionway slide when the boat is not in use. We pull a larger tarp over the boom and tie it off to the lifelines to make a "boom tent" for added shade in the cockpit when at anchor. Commercial boom tents can cost hundreds of dollars. They may look nicer, but don't really function any better than an inexpensive tarp.
Small tarps can be used as emergency ponchos. The only downside is that you need to cut a hole in the middle to put your head through, perhaps limiting its value for other uses. For short term use you may be able to just drape it over your head and shoulders like a cape. Conversely, ponchos can sometimes be used as small tarps. The built in hood helps compensate for the hole in the middle.
In an emergency you might cut open a large plastic trash bag and use it as a small tarp, but for best results keep a variety of tarps on hand to accommodate different needs. Small tarps are surprisingly inexpensive. I often see them at dollar stores. Large plastic garbage bags make pretty good ponchos too, and they're a lot cheaper than tarps.
Tarp it!