Jan 2000 Volume 22 Number 2

Technical Exchange

HVLP Spray System

The Williamstown Art Conservation Center sought a portable spray system for on-site treatments of architectural elements and sculpture. The purpose of the new system was twofold, for spraying clear coatings (e.g. 10% Acryloid B-72, Incralac, etc.) both outdoors and indoors, and for spraying viscous pigmented coatings (e.g. two-part polyurethane) for large outdoor sculpture. A year ago we settled on a high volume, low pressure (HVLP) system made by Graco Inc. (1-800-367-4023), supplied by Sherwin Williams Inc., a distributor.

In-lab spraying for paintings continues to be done with a conventional high-pressure system and small Devilbiss guns (1-pint pots) within a spray booth, where these touch-up guns are kept cocked, so to speak, with solvent always in the pot (no cleaning). A new spray booth will be built in four years and at that time regulations may require an HVLP system.

The first part of our new HVLP system is a 4-stage turbine (model 4900) with a 1-quart non-bleed spray gun (GTS 980S) and air hose (cost: $1,250.00). Part two (which has not yet been used) is intended for pigmented and viscous coatings in larger applications, and consists of a compressor cart with remote 2-gallon pressure vessel (GTS Pro-cart, series A), pressure feed gun (GTS-980), and material and air hoses (cost: $850.00). The 2-gallon remote pressure pot will enable more spraying between refills, and the pressure feed gun can be angled to spray the underside of surfaces since there is no cup attached to the gun.

We have successfully used the turbine with the 1-quart gun for outdoor and indoor applications of low viscosity solutions (10%) of clear protective coatings. Surfaces have included historic interior woodwork in Shaker and plantation houses, together with bronze and iron sculpture for indoor and outdoor exhibition. Painting conservators here have not yet used the HVLP system!

The principal advantage of the HVLP system is greater material transfer, since less is lost through overspray, and this translates to less solvent use (and resin), which interests the operator. The HVLP set up has a softer spray pattern and causes less air disturbance (about 5 lbs. pressure is used), and this results in a better finish from the gun. Compared to our high-pressure system with small guns, the new HVLP system is the Cadillac of sprayers.

The gun is fitted with the standard controls for pattern of spray (air cap), pattern size (air cap, which is not a feature on our small high-pressure guns), fluid flow (back of gun), and in-line air control valve. Five different fluid sets are available for the different viscosity of materials, and we commonly use #3.

The gun has a wide (1in. OD) hose that connects to the turbine and this is more cumbersome than the high-pressure hose used in the spray booth (5/8in. OD). An imagined improvement would be a swiveling bent hose connection at the base of the gun. We chose a large 4-stage turbine to handle viscous applications, and the unit is noisy. This has not been an issue during on-site spraying where the reduction in solvent use is preferred anyway. A quieter 2-stage turbine would probably be adequate for spray applications to paintings, for example. The in-line air control valve is crude (relative to its influence) and difficult to reset accurately. We have also experienced some dripping and clogging at the air cap/needle after extended periods of use, but we hope to overcome this with adjustments.

The turbine should not be located in the spray area due to the risk of fire. For safety we situate the turbine inside the door of our spray booth where air exchange is more rapid. Preparations for on-site spraying remain the same, with masking of surfaces, ventilation with fans through windows and doors (where applicable), together with full enclosure personal protection. Under these circumstances any spray method that reduces solvent use will gain acceptance.

Hugh Glover

Omega Brushes

I recently visited New York Central Supply, where I found the Omega Series 40 varnish brush for well under list price. You can order these from their catalogue.

Monica Jaworski