The Mabnol

Finding bird droppings on outdoor canvas furniture is a fairly common occurrence. If not cleaned off, the stains are unsightly and can leave marks.

[Edit]Steps

Try brushing before adding anything else. If this works, then you're set; if not, move onto another method. Use an old toothbrush or a clean household brush.^[1]
Do this regularly. Keep an eye on canvas furniture, awnings and sails around the house. As soon as you spot bird droppings, remove them. The faster this is done, the easier the stain will be to remove.^[2]

Brush off the droppings to remove anything that will come off easily. Use a household small dustpan brush to do this.^[3]
Rub the stain using mild, plain household soap. Dampen the bar of soap and rub it over the stain to cover. Leave the soap that has been rubbed on for half an hour.
Rinse off well with clean water.
Repeat the rub and rinse process until the bird droppings are removed.

Brush off the droppings to remove anything that will come off easily. Use a household small dustpan brush to do this.
Pressure wash the bird droppings stain off the canvas furniture. Check the strength of the canvas before doing this though. Strong canvas in good shape will be okay, such as that used for overhead sail cloths but finer and older canvas may be weaker and pressure washing could break the fibers. A hose wash without the pressure attachment but putting a finger over the end of the hose to produce a stronger spray may be better for more delicate canvas.^[4]
Apply a mild liquid laundry soap suitable for delicates or baby clothes on the stain. Mix 2 liters/1/2 gallon of warm water to 1/4 cup of liquid soap. Gently rub it over the stain to lift.
- If the canvas is removable, such as seat cushion covers, remove and wash in the washing machine using the mild liquid laundry soap.
- For really bad stains, using liquid soap may not suffice. See the section on using commercial preparations.^[5]
Wash off with the pressure washer or hose again.

Choose a nice sunny day for this method, as you'll be harnessing the power of the sun to help clean.

Brush off the droppings to remove anything that will come off easily. Use a household small dustpan brush to do this.^[6]
Hose or pressure wash the stain with clean water. (See the previous method for tips about pressure washing with care.)
Make a paste of salt and lemon juice. One lemon should be sufficient for a standard stain but you'll need to judge by how large the extent of the bird droppings. Add enough salt to the juice to form a paste.
Rub the paste over the bird dropping stain that remains.
Let sit in full sunshine. When you find it hard to see the stain, it's time to remove the paste.
Wash off. Hopefully the stain will go with it.

Check the manufacturer's instructions. They may have recommended a product suitable for cleaning the canvas furniture. A lot of canvas furniture has special waterproofing features which must be considered when using a commercial cleaning product.
Ask for a recommendation at a store that sells canvas furniture. When selecting a product, check that it doesn't affect any waterproofing placed on the canvas.
- Some suggested options from a sweep of various online forums include: Barkeeper's Friend, LAs Totally Awesome and Spot Shot Upholstery Stain Remover. However, such products tend to be very strong and may cause new stains. If you do use them, always test a small patch first, to see if the product stains or removes waterproofing properties.

If possible, save yourself the effort of cleaning by investing in furniture covers and using these regularly to ensure that stains do not fall onto the furniture. Furniture left outdoors is subject to bird droppings, pollen stains, dirt stains, general grime build-up, etc. and covers can reduce the impact of outdoor use.
Clean canvas stains quickly; this will make it more likely that you'll remove the stains completely.
A paste made from baking soda might shift more stubborn stains.
Put shiny objects, such as CDs, around your outdoor area to scare away the birds.

Tent and boat canvas may require different processes; this article is for outdoor furniture canvas.
If the bird droppings include berries, treat as if it were a berry stain.
Detergents and bleach products will likely remove waterproofing surfaces.