There are two basic types of paint sprayers. Conventional sprayers use air to create the fine spray and with a gun and hose can be run off a standard air compressor. Conventional sprayers are not commonly used any more. Airless sprayers are the sprayers of choice for most applications. The paint is forced through the hose and gun by an electric or gas powered motor that runs a diaphragm or piston pump. They are more versatile and create less overspray than conventional sprayers.
Airless sprayers run the gamut from small cup guns, sold in many home improvement stores, to large machines capable of running multiple hoses and guns and spraying more than a gallon of paint per minute. Most sprayers have pressure control settings and can be used with multiple spray tips for different materials, such as paints, stains and lacquers. By controlling the pressure and choosing the right tip, the paint can be applied at fan widths from 2 to 24 inches.
Hand-held cup guns, like Wagner Power Painters, typically hold a quart of paint at a time, while large sprayers have a siphon hose that pulls the paint directly from a 5-gallon bucket, allowing for almost continuous spraying.
Smaller sprayers can make short work of projects like wrought iron fences, shutters, decks and acoustic ceilings. However they may not be up to the task of spraying a large house and because of the constant refilling of the paint reservoir, won't be very fast. Larger airless sprayers can be very expensive to buy but economical to rent, so it might make more sense to rent a big rig for a larger job.
For a very smooth, mirror-finish work on furniture, trim or cabinets, consider an HVLP (High Volume Low Pressure) sprayer. These produce a fine, even coat of paint at low pressure, making them excellent for interior work and smaller projects. A conventional air-compressor powered sprayer also works well for trim work, although they tend to produce a lot of overspray.
Many small and mid-sized sprayers can't be used for spraying thick masonry block fillers and elastomeric paints. If you have an entire basement to waterproof, it would be worth your while to rent a larger sprayer for the job. When you consider that you can apply these coatings at a rate of a half gallon per minute, the rental cost may be well worth it.