FAQs - Installation

Answers to your most common questions about installing acoustical ceilings.

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Use our FAQ database to look up answers to frequently asked questions. The questions are grouped with topics of a similar nature to shorten your process.

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What is the minimum clearance needed to suspend a 2' x 2' or 2' x 4' ceiling?
3" from the hard surface of the plenum to the face of the grid, is the minimum for a 2' x 2' and 2' x 4' panels. It is not only a matter of getting the boards in, but the installers need room to twist the hanger wires, etc. Fiberglass is, of course, easiest to work with in the minimum clearance situation.  Where necessary, 2' cross tees can be left out to accommodate panel installation and then put in.  More clearance should be given whenever possible to make the installation easier.

Will ceilings alone provide me with a 1-hour rating?
No, Fire resistance ratings apply to a floor/ceiling or roof/ceiling assembly in its entirety. Individual components, such as ceiling panels or suspended grid systems, are not assigned fire resistance ratings. If your architect has not yet determined which UL design should be followed for your specific project, you may have to select a UL Design for code official approval. If so, here is how to select the correct UL fire-rated assembly:

  • Establish the hourly rating needed to meet code requirements.
  • Determine the existing or planned building elements, including structural, mechanical,electrical and finish materials, in the fire-rated assembly.
  • Refer to the Fire Resistive Rating Summary in the back of the Armstrong ceilings catalog to determine which UL design numbers resemble your building. The summary is divided into categories based on construction type and components.
  • Submit the chosen UL design to the code official for approval.

Can ceiling panels be installed using glue?
Yes, but we only recommend glue applying 12"x12" tiles. An example of acoustical adhesive is Henry #237 Acousti-Gum.

Armstrong 12" x 12" concealed ceiling tiles can be applied to a variety of substrates with an Acoustical Ceiling Tile adhesive. Please refer to the Armstrong Ceiling Systems Catalog for the 12" x 12" tiles that have been selected for use with a glue-up application.

Which Armstrong ceiling products can be glue-applied?
741 FINE FISSURED™ (12" x 12" x 1/2")
746 FINE FISSURED™ (12" x 12" x 5/8")

Installation tips:

  1. If you prefer to use adhesive, follow directions on the adhesive packaging.
  2. As the tile is pressed to the ceiling, the adhesive will spread and cover an area of approximately 3" across and 1/8" to 3/16" thick. Acoustical tile adhesive is recommended. An example of such an adhesive is Henry #237 Acousti-Gum.
  3. Do not "butter" too many tiles in advance, as a skin will form on the adhesive dabs and weaken the bond.
  4. Level tile by inserting a 1/16" thick fiber spline approximately 3" long at each corner (works out to one spline for every tile.)
  5. Use a 48" to 72" straight edge and press to the face of the installed tile to help level the ceiling.
  6. If a trim is needed at the perimeter, use one of the Armstrong Slip-on Wall Moldings. These moldings are 10’ long, have a 15/16" flange and are available in thicknesses of ½" (#7841), 5/8" (#7842), and ¾" (#7843).

Special Note: Do not bend tile during installation. The "spring load" will cause the adhesive to release. Avoid working with warped tile, as the same problem will occur. On surfaces that were previously tiled, do not place new adhesive on top of old adhesive.

For additional information on glue-up applications for acoustical ceiling tile, we recommend referencing the CISCA Ceiling System Handbook; this has a complete chapter on this procedure.

How do I cut and treat tegular edges for mineral fiber and fiberglass panels?
Field Tegularization. Let's look at the knife angle recommendation. Keep the blade sharp and on a sharp downward angle. This way, more of the blade edge is doing the cutting which results in a smoother edge. Tegular cut can be made on a flat surface:

  • Lay tile and knife on table
  • Slide knife along edge to cut

Another way of making tegular cuts is to use your finger as guide.

Fitting Board
For accuracy and simplicity, we recommend the following:

  • Cut the tegular board the same size as a regular board and lay it in position.
  • With a pencil, mark the face of the tegular board along the molding edge, or scribe the wall molding with a knife.
  • Remove the board, and with a sharp knife, cut along the pencil line halfway through the panel. Then run the knife blade down the edge of the panel in order to achieve the tegular detail.

Coloring Cut Edges Where Necessary
Naturally, it is not necessary to paint the edges of boards along the perimeter walls, as it is impossible for the eye to get close enough to see the raw cut. However, there are those situations where the cut edges will be visible and should have a factory-type finish. For these situations, refer to the section on painting recommendations for mineral fiber products.

We also have Armstrong Touch-up Paint #5761 (ordered separately).  One 32 oz. bottle of touch-up paint will coat 200-250 lineal feet of tegular edge on Ultima (mineral fiber board).

Field Tegularization of Fiberglass Products
Field fabrication of reveal edges on a PAINTED NUBBY or OPTIMA® High-NRC fiberglass ceiling panel is accomplished in the same manner as a reveal edge would be cut on a mineral fiber panel. When the field cut will be exposed after installation, the edge can be treated using Armstrong Touch-up Paint #5761 (ordered separately).  One 32 oz. bottle of touch up paint will coat 75-115 lineal feet of tegular edge on Optima® (fiberglass board).

Repair of Vinyl Facing
A tear in the vinyl facing can be covered and resealed utilizing a white, latex base, tub and tile caulk (such as Dap or Red Devil). Place a bead of caulk in the opening caused by the tear, tool with a wood stick and allow to dry prior to installing in the ceiling.

What is the minimum clearance for installing an exposed T-bar grid system?
If you are tying hanger wires, we recommend a minimum distance of 3" from solid substrate above the ceiling to the bulb of the grid (this space is required to bend the wire) or 4 1/2" to face of T-bar grid.

Are there general instructions for installing a suspended ceiling?
Installing Suspended Ceilings North America Version (pdf)

We reference the installation standard ASTM C 636. To obtain a copy call ASTM (610) 832-9500 or www.astm.org.

What defines the load classification of a suspension system?
ASTM C 635 states the duty classification of a grid system is determined by the load-carrying capacity of the main beam.  Section 4.2 of this document states, "Cross runners shall be capable of carrying the load specified by the manufacturer without exceeding the maximum allowable deflection equal to 1/360 of its span."


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