Spraying smooth plaster on drywall (gyproc board) is a new opportunity for painters. The national shortage of plasterers has lead to many properties, even quite expensive ones, being left with naked drywall that has not received a skim of plaster. This can make painting of it a problem, as often the sanding of the filled joints raises the nap of the board surface, which then shows through the paint. Wallpapering directly onto unskimmed drywall can cause problems later if the wallpaper is stripped off. To be able to offer to skim a drywall before painting, is a new profit opportunity for painters; it can also be used to mask Artex.
Many commercial properties, such as hotels and offices, are being built with precast concrete walls and ceilings which need to be skimmed with plaster to cover the fine holes and panel joins, prior to painting. Spraying plaster is the efficient way and compatible with the speed of this type of construction.
Laying it off
Laying it off
While traditional plastering with a float is a skilled job and hard work, a thin layer of sprayed plaster on the flat drywall surface is easy to lay off with a wide spatula, usually 24" wide. The plaster most suited to skimming drywall, is more like a heavy paint, as it contains organic binders that give it flexibility, which resists cracking as the stud wall timbers or ceiling joists dry and move. This type of material dries fast and can be painted after as little as 24 hours, depending on the ambient temperature and humidity, which compares very well with traditional plaster that may require several weeks before it can be painted.
Spraying plaster is best applied with a machine having a worm drive pump. This type is widely used on the Continent where plaster spraying is commonplace. It is a low pressure system feeding a gun having a large spray tip (nozzle) and compressed air injection; it will apply plaster fast but requires a compressor.
Spraying plaster is often available ready mixed with water, in a plastic bag, which avoids the hard work of hauling water, mixing tubs and plaster dust. Surplus plaster during the laying-off is collected with a short spatula and returned for reuse; unlike traditional plaster, providing that it is kept moist, it will not harden for many days. Many plasterers keep the plaster in the machine for a whole season. Traditional plasters can also be used, providing that the solids do not separate under pressure; but they need to be premixed in a separate tub.
A suitable worm-drive plaster sprayer is a HAMA MC3V which is available in 110v for site work with its matching powerful (2.2 kW) H460 compressor; it comes with a bag roller. This unit can also spray textured materials (renders) having an average particle size of up to 3 mm. It is not suitable for solvent based materials, as the solvent would attack the rubber stator
HAMA MC3V worm drive pump
The NEW T-Max 506 and 657 plaster/render sprayers
The new Graco T-Max plaster and render sprayers are exciting pieces of equipment with much more powerful motors than the old T-Max 405, to give you the extra pressure and volume that plasterers need. The big advantage of the T-Max machines is that you can spray plaster without needing a compressor, unlike the worm-drive units. This means a big cost saving on the equipment. With up to 940 psi, the T-Max 657 can spray the coarse blue grade ready-mix plaster without compressed air and you can connect it to 30m of 1" hose. The smaller T-Max 506 can support a 15m hose with up to 730 psi.
With a compressor, the T-Max guns can be set up to spray plaster with a textured effect, or they can spray renders having a particle size up to 3.0 mm (average of 1.5 mm). All the materials need to be solvent free. Useful accessories include a bag-roller kit, a stirrer mounting kit, a 1 m gun extension and a 1.2 m gun extension for texture spraying with air.
When it comes to cleanup time, the T-Max are very easy to disassemble, but it is better to use pre-mix plaster as this can be left in the machine between jobs if covered with a plastic sheet and a dash of water.
If you need to spray textured materials that are solvent based, the President 10:1 Evenflo will handle these materials with ease; it is a time tried and tested unit, which can also spray premixed plaster. It requires a compressor that can delivery up to 40 cfm (1,133 lpm) of clean air, which usually means a trailer mounted single tool compressor.
Graco President 10:1 airless pump
If you are a painter who wants to spray mainly paint and only plaster occasionally, then you can do this with some large airless sprayers, having a long stroke piston and able to support at least a 33 thou' (0.033") spray tip, but you will need to strip the pump at the end of the job, to ensure that all the plaster has been removed. Also a hopper is required to prevent the pump suction drawing-in air.
A suitable machine is the Graco MkV fitted with a hopper and bag roller if you are going to use the bagged material; this unit will also spray paint, including intumescent coatings for fire protection and many roof coatings