Decorative concrete artisans use sprayers for a variety of tasks on almost every job — applying form release, spraying stains and dyes and applying sealers. Knowing how sprayers work will help you equip your customers with everything they’ll need for spraying different materials.
How a sprayer works
Most spraying on the concrete jobsite is done with hand-held or backpack pump-up sprayers. They are used to apply form releases, curing compounds, dyes, stains and sealants.
A few pump strokes will build up air pressure above the liquid that forces it through a small hole in a nozzle, breaking up the stream of liquid into droplets. The nozzle can be designed to produce a spray shaped like a fan or a cone. The sprayer’s tip and internal pressure determine the size of the droplets. They’ll get larger when the pressure runs low.
“The adjustable cone is what comes on a lot of acid stain sprayers to give it a fine mist,” says LeighAnne Steen, who works in purchasing and sales at Decorative Concrete Supply in Carrollton, Texas.
To deliver higher volumes of sealer, a fan tip is used. Fan tips are not adjustable, but they come in different sizes, Steen says, and are marked with how many gallons per minute they can deliver. “If you’ve got a sealer with a nonslip additive, you need a larger tip so the additive can go through.”
For higher-solids sealers, “The fan tip is usually what is used, but higher-solids polyurethanes are usually rolled on,” she says. “Some people get into airless sprayers for those products as well.” Airless sprayers, commonly used for painting, draw material out of a bucket and pump it through a piston pump through the spray nozzle.
Plastic pump sprayers operate at about 30 psi, says Dan Lucianek, marketing services manager at H.D. Hudson, a sprayer manufacturer. Metal sprayers that can hold a higher pressure are best to spray thick curing compounds. For the construction industry, H.D. Hudson makes a Constructo line of sprayers that include galvanized steel sprayers with the company’s Spray Thick technology, designed to spray compounds with up to 35 percent solids.
Another type of sprayer useful in decorative concrete work is the high-volume low-pressure (HVLP) sprayer, or cup sprayer. This is a spray gun attached to an air compressor tank, resembling a large airbrush. A reservoir on the gun holds a pint or so of liquid to be sprayed. It may be an open cup that feeds the liquid by gravity, or a closed container with a siphon tube.
Bob Harris of the Decorative Concrete Institute recommends HVLP sprayers for use indoors because their low pressure (10 psi or so) reduces overspray and airborne dust. They give good control of acrylic sealers that must be applied in 1-mil coats, and can handle high-solids compounds. These sprayers can be used with solvent-based dyes and water- or solvent-based sealers, but their metal construction makes them unsuitable for acid stains.
Because the investment is high, small decorative concrete contractors might appreciate being able to rent HVLP equipment and a compressor from you.
Match sprayers to applications
A sprayer’s component materials must be compatible with the contents. Acetone-based dyes need a sprayer with EPDM seals (seals made of ethylene propylene diene monomer rubber). Acid stains require a sprayer with an acid-resistant seal (sometime called a COPT seal). Viton seals are suitable for curing compounds and sealers that contain neither acid nor acetone. If a product is likely to attack sprayer components, its labeling will specify what kind of materials will resist it.
When spraying form releases, droplets should be small and the application layer thin so the compound doesn’t bead up and create “bugholes” in the concrete. Cresset Chemical Co., a manufacturer of form release compounds, recommends a fan spray tip for producing the thinnest possible layer of form release. A hollow cone spray tip makes droplets 40 percent larger than a fan tip does, and a full cone tip produces droplets 300 percent larger. Fan tips designed to make extra-fine droplets exist, but care should be taken to avoid drift on windy days.
A solid cone spray pattern is best for applying stains evenly, notes Harris in his instructional materials. Cone tips can be adjusted to produce anything from a stream to a mist. For work with stains and dyes, a sprayer with dripless shutoff reduces the likelihood of dripping color where it’s not wanted.
Smaller sprayers, one in each hand, can be used to simultaneously apply two colors of stain or dye. Search YouTube for “concrete stain sprayer method” to see Jimmy Ezell’s video of an artisan wearing two 2-gallon sprayers on his belt and rapidly creating a mottled finish on a pool deck with two hoses.
Engrave-A-Crete, a manufacturer of concrete engraving tools, recommends in its instructional videos a 2-quart sprayer for projects up to 400 square feet and a 3-gallon sprayer for larger jobs. Since a 3-gallon sprayer will weigh more than 25 pounds, larger quantities are best handled in a backpack sprayer to reduce worker fatigue.
For work on large projects, rechargeable battery-powered backpack sprayers are available. A 4-gallon model from Chapin has a lithium-ion battery and is designed to allow 1.75 hours of continuous spraying between charges, while the NeverPump Bak-Pak sprayer from H.D. Hudson has a rechargeable lead-acid battery said to allow 10 hours of spraying.
Two- and 3-gallon sprayers range in price from about $50 for a poly sprayer to $150 or $200 for an epoxy-coated steel sprayer.