Sponge painting walls (on or off) is not the most difficult faux paint technique. Still, there are certain things you should know that can make or break your decorative painting project...
The only appropriate type of sponge for sponging on and sponging off is a natural sea sponge. You can buy one in any paint store, home improvement center or craft store.
The size of the sponge you buy should be determined by the area that you wish to tackle, although anything bigger than the size of your fist can become unmanageable. It's a good idea to have a small selection on hand.
Always moisten a sponge in clean water and wring it out before using it for applying or removing paint or glaze (never use it dry). If the sponge is new, work it under water several times until it becomes loose and pliable. During your work, wash the sponge as soon as it starts getting stiff.
If you need to take a break from sponge painting walls (even for a couple of minutes), make it a habit to drop your sponge(s) into a bucket of water first. That way they won't dry out and become useless.
A build-up of glaze in the sponge will cause smudging, so don't overcharge it when sponging on, and regularly clean it in water when sponging off.
Always test the effect of your technique on a poster board before applying it to the surface in question.
Latex paints are very drying to the skin, so always wear rubber gloves when applying/removing paints with a sponge, or when washing the tools.
The positive and negative methods of sponging are appropriate for any flat surface (walls, ceilings, floors, furniture) that is free of intricate carving or elaborate details.
Don't allow any water to get on the freshly sponged on or sponged off surface - water will leave white spots/marks and ruin your finish.
The most challenging part of sponging on is maintaining the same sponge pressure throughout the entire process, and re-loading the sponge at just the right time (to prevent an uneven, blotchy finish with faded and overly saturated sponge impressions).
Natural sea sponges come in round and flat shapes - but flat ones work best for sponging on purposes. And if you can't find a flat one, you can always cut a round sea sponge in half and use the flat side to apply glaze or paint to the surface.
The size, shape and number of the pores in a sponge will determine the imprint it will leave - keep this in mind when choosing a sponge for your project.
Be careful not to rotate, drag or slide the sponge on the surface, or the glaze will smear.
Don't jump around when sponge painting walls, or the effect will be uneven. Instead, complete one 2'x2' section at a time, then move on.
You can fill in the corners as you go, or you can do them all at once at the end.
When you use a sponge correctly, you shouldn't see the individual strokes of paint or glaze on the surface.
If you make a mistake, correct it immediately - use a wet rag wrapped around your finger to clean up any drips or smudges. If the mistake has dried already, use the base coat paint color to make touch ups with a blunt artist's brush.
To soften or tone down a sponged surface, let the glaze dry completely. Then, using a sponge, cover the surface with a layer of very diluted colored glaze and immediately wife it off with a clean sponge.
The most challenging part of sponging off is moving quickly in order to maintain the wet edge (dried edges will mean you'll have to start over).
Water-based glazes dry too fast, leaving very little open time to remove the glaze (for this reason, this method works best on small areas such as the wall under the chairrail). To slow down the drying time, turn off the A/C or heater in the working area (if the weather permits, of course), and have an air humidifyer running in the room.
If you rinse the sponge after every few pounces, much more of the base coat will show through. However, to do this successfully, you'll have to work much faster.
Every time you rinse the sponge, resume pouncing in an unobtrusive area - because the clean sponge will remove more glaze.
When removing the glaze, you can occasionally drag the sponge over the glaze to blend the colors together. Also try rolling the sponge on the surface - that will create a different finished effect.
It's better to remove too much glaze than too little when sponge painting walls, because you can always go over the surface with more glaze, if needed.