When we googled the internet under the term of “fritting” we registered 221,000 hits. Having scanned some of the sites, we see from the extensive range of products and projects how technical the painting of Architectural Glass can be, whether it is enamel fritting, screen printing or spandrel panels.
One of the biggest challenges, we find in detailing Architectural Glass solutions is how to visually create an acceptable aesthetic finish to the edge of an Insulated Glass Unit, a unit referring to the assembly of two or more panes of glass with an internal cavity consisting of a spacer bar, sealant and adhesion tape.
Very often, and particularly on Commercial Architectural projects, there is a tendency not to frit frame-less face glass. Visually this is poor, as shown in the example below.
Fritting of this Frame-less Glass solution would have successfully concealed the materials within the joint and extended many years to its Design, Service and Warranty life.
Instead, border lines are uneven, critical sealant components and adhesion tapes are exposed to ultra violet light and, when viewed against a silver spacer bar, aesthetically it is very unappealing across this semi frame-less Architectural wall for both clear and solar control options.
Technical complexity is added to these issues when soft coated control glass is introduced. The photograph here demonstrates the same characteristics above but with a diffused blue coating around the perimeter of this frame-less glass.
Both of these examples are without fritting and show the sealant within the cavity when viewed externally.
This Architectural creation in glass would have been a lot more attractive with coloured paint and this is what we would like to promote within the content of this blog.
Enamel colouring and printing of glass opens up new dimensions in creativity to the Architect and whereas little can be done when a project is completed, creative opportunities exist at the design and detailing stage of a project and this is where we can help.
Painting glass can be used for various architectural purposes:
- Decorative coating, patterns including lines and dots applied to the glass by silk screen printing.
- Spandrels and parapet glazing
- Edge enamelling, ie fritting.
This blog will focus on edge enamelling commonly referred to as fritting and the application difficulties with coated glasses, it will make some practical recommendations, hopefully it will be of use to those detailing Frame-less and semi Frame-less Architectural glass solutions.
What is “Fritting” all about?
It is the application of a ceramic enamel paint to the inside face of the glass which creates an acceptable architectural finish to the face glass and protecting the edge of a unit against ultra- violet protection thereby enhancing the service life of the unit.
Enamels have been carefully developed for printing and firing on normal soda-lime based float glass. During the tempering process of the glass, these enamels melt and fuse permanently to the glass surface to form a coloured ceramic layer.
Glass enamels may react during firing with coatings causing some hazy appearance or even complete destruction of the coating. Therefore, it is necessary to test the compatibility of enamels with coated glass under production firing conditions in order to get optimum results. We recommend running preliminary tests with the selected colour glass combination using the intended production furnace, glass geometry and ceramic covered area. Unfavourable temper conditions could be the reason for poor results.
Compatibility and suitability tests are essential for each project, you can see from the project below the difference a sample makes to the outcome of this particular project.Quality control is important, samples act as bench mark on which to judge the f inished product.
Let’s look at a project:
Image A, is a sample of a tempered stepped solar control unit, Fritting face 2 of the glass was considered due the technical difficulties in edge deleting of the soft solar control coating on face 2 of the glass,so as an alternative to improve the visual aspect of this stepped corner, we specified a black dow corning 791 silicon smear to face two of the glass.
The result as you can see is aesthetically poor, the outside perimeter of the unit is highly reflective with an uneven sight line both on the outside of the unit and at the interface between the vision glass and silicon smear.The silicon smear is manually applied to the tempered solar control glass and with the soft coating results in a reflective bronze mirror finish.The black 15mm line around the perimeter is the Dow corning seal of the unit which adds to the overall untidiness of the proposed frameless glass solution.
What did we do?
As the façade was north facing, we re-looked at the design of the stepped corner detail, there was no benefit to using a solar control glass which enabled us to alter the glazing configuration, we were able to use tempered clear glass externally with a low-E glass internally.
Image B shows the result, clean crisp line, aesthetically pleasing whist protecting the edge of the unit against the weather.
Our recommendations for successful fritting are as follows:
- Solar control, consult with the glass supplier, coated glasses come as hard or soft coated, edge deletion of soft coated glass are more difficult to work with, removal of the coating leaves a residue which creates an uneven surface on which to frit, in such situations look at alternative products, examine the possibility of hard coated glasses which are easier to work with.
- Aesthetics, always request a working sample; a sample will show the selected frit colours with the glass type. Lighter colour can sometimes be more difficult to work with; this is because they fail to conceal what’s behind within the cavity of the unit. Black and dark greys are always less risky as image b shows.
- Always make sure that you specify the minimum thickness of the wet coating when painting the face glass, this should take into consideration corrected adjusted processing viscosity; we generally recommend 90 um for fritting but your glass producer will provide further information.
- Always asks the glass producer to confirm the final coating thickness after firing, we recommend that it is not less than 30 um but each glass producer looks at it differently.
- In order to ensure a dense and uniform covering with a minimised porosity, the glass producer should ensure that the ceramic frit melts without bubbling under normal temper conditions. Melting behaviour and surface roughness can be measured with a gloss meter.
- Ask the glass producer to carry out a halogen lamp test, this will detect the number of pin holes in transmission of the enamel coating.
- We recommend when carrying out the test that the observer is no greater than 50 cm from the glass. In respect of the worst area, we recommend there should be no more than 30 pinholes/dm2 with single holes no greater than 2mm in diameter.
- Design the glazing configuration to suit the performance criteria, alternative glass types may be more appropriate in managing solar gain, light transmission, reflectance, etc. Some options include laminating panes of glass together , heat strengthening or using hard coated glass , these are always worth exploring.
- Cost, if you want an acceptable finish always request for the cost of fritting and any technical difficulties that may be encountered in achieving same as extra over. Very often we have lost jobs to find afterwards that the related costs have been omitted.
If you are considering the detail design of your glass facade give us a call to discuss the best solution for your project. Contact us directly at +353 (1) 464 2970 / +353 86 270 7415
Or email us at email@example.com
Frederick Trenaman MSc Façade Engineering, Dip Arch