Spectis polyurethane cornice installation method can be easily applied by most skilled craftsmen.  A quick, clean and very  secure installation is achieved using PL Premium adhesive and low root style wood screws.

Spectis polyurethane cornice can be installed over most any clean interior or exterior surface. It should not be installed over  wallpaper as the paper may separate or the adhesive may stain the wallpaper.

Moulding which has been stored in “hot” areas must be allowed to “acclimatize” to the location of installation for at least  48 hours prior to installation. (Just as wood requires)  Do not install product that has been sitting in a hot trailer or the sun  without allowing for this acclimation.  Doing so, may result in excessive shrinkage could manifest itself as joint cracks.  Moulding stored in cool areas can be installed without product acclimation.

To begin, screw a support border on the wall for the moulding to sit on. (An experienced installer can use a chalk line as a  reference) Apply copious amounts of adhesive (PL Premium) to all bedding edges of the moulding.  Once the moulding is  installed, remove the support border and fi ll the holes.

Place the moulding on top of the support border and fasten the moulding to the wall and ceiling using #8 low root style wood  screws, plated for exterior use, and long enough to penetrate well into the substrate. Continue installing lengths of crown  using the same method, leave a gap (gap size varies based on size of Closed Cell Backer Rod being used, it should be  75% (3/4) of the width of the Closed Cell Backer Rod to allow for proper joint movement, the gap size should be no less then  3/16 ”, dimension A) at the joint of two crown lengths, ensuring the moulding profi les are in alignment. Once the mouldings  are installed, clean the joints and insert the backer rod a suggested maximum depth of 3/8” (B Dimension) from the highest  point of the backer rod to the moulding face.

*Follow MFG of joint compound recommendations.

Figure 1 image

On smaller crowns, screw spacing can be as little as 2’, but on crowns over 12” X 12”, screw spacing should be approximately  12” on both the ceiling and wall interfaces.  Make sure the screws are sunk in the surface of the moulding, as it is necessary  to fi ll in the screw holes with exterior grade, non-shrinking, sandable, and paintable fi lling products such as automotive grade  “bondo”.


1. Before any adhesive is applied, cut and fi t each piece of moulding.  Use standard woodworking tools when working with Spectis High Density Polyurethane product.  Although most of our smaller mouldings can be miter cut on a compound miter saw, it is recommended (on larger crowns, it will be necessary) to construct a miter box and use a hand saw to make the cuts. (see Figure 2)  This will ensure that the cuts are made with the correct angles and remove any guesswork trying to fi gure out table and blade angles on a miter saw. (see www.spectis.com for plans to construct miter box)

Figure 2 image

2. It is possible to install moulding by two separate methods, but remember to leave a gap of no less then 3/16” at the joints to insert the backer rod into.  It is recommended to use a jig for equal spacing at every joint.  

  • The first is to begin installing moulding in the most inconspicuous corner, and work around the room in sequence until all the moulding is installed. (Keep in mind that it may not be possible to have the pattern match at the last joint or corner) 
  •  The second method is to install short, prefabricated corner elements and run straight moulding between them, which can reduce the difficulty in making good miter joints on long moulding sections.  However, the later procedure does not work well with mouldings which have repeating profiles.

3. It may be necessary to install extra blocking behind the moulding for additional support, especially on large crowns, where it is not possible to screw directly to the wall.

4. Although every attempt is made at the factory to ensure all moulding match end to end, it is necessary to check all moulding for thickness variations.  It may be necessary to remove material on some edges or add wedges on other sections for good face alignment.  Tighten screws in a sequence, which allows for good alignment.

5. Excess adhesive should be removed immediately.  Once cured, it will be necessary to use a knife to remove the adhesive.  Wedges can be trimmed or removed once the adhesive has stiffened.  

6. Screw holes, wedge gaps and joints can be filled only after the adhesive is cured, approximately 24-48 hours. 

7. To fill joint gaps between two mouldings, you will need some closed cell backer rod that is approximately 25% larger than the joint gap (width).  Proper size selection is important, as it controls the depth of the sealant bead.  It must be oversized to fit tightly into the joint, and prevent bottom-side adhesion of the sealant.  Just prior to inserting the backer rod, clean all the joints as per the sealant manufacturers recommendations. 

8.  Once the backer rod has been inserted into the joint gap (according to Figure 1), it is recommended to fill the joint with Silicone Building Sealant “DOW CORNING 795” or similar product, making sure that the sealant bead is at a minimum 2:1 ratio (width vs depth). *see Figure 1 

9. Do not apply more sealant than is necessary.  More than one coat may be needed to get satisfactory results.

10. The product comes from the factory with two coats of paint.  The final coat is a UV stable primer, which is ready to receive a site applied finish.  (see finishing section)  Spot prime areas where necessary and paint the prepared product using high quality products, which are compatible with each other.  Be sure to select the proper grade for the installation, exterior or interior.  High gloss and dark colored products are not recommended since any imperfection in the installation or product will be easily visible.

Please note that the DOW CORNING 795 silicone building sealant can be tinted to match any color.