Repair of Dalle de Verre – find out how from the experts!

Written by John in abstract stained glass,dalle de verre,General Glass Info,glass color,glass repair,Repairs,Stained Glass,stained glass colors

Dalle de verre

Dalle de Verre, from the French “slab of glass” has been a popular way to make stained glass windows since the mid-1950s. Although it appears to be stronger than traditional leaded glass, it can be broken by determined vandals. So, how is Dalle de Verre repaired? Find out from the glass experts in this post.

Dalle de Verre panels are heavy so minor repairs are best made in-situ. Seriously damaged panels must be removed, broken apart, & remade with new epoxy resin.

Dalle de Verre looks strong but …

Although Dalle de Verre appears to be strong because it is made with thick (up to 1 inch) slabs of glass in robust epoxy – it can nevertheless require maintenance and repair.

In the 1950s, problems occurred because the slabs were embedded in various types of reinforced concrete. Unfortunately, concrete has different thermal properties than glass and expands at different rates. This differential expansion and contraction resulted in the slabs (dalles) of glass coming loose and falling out.

Learn all you need to know about Dalle de Verre in this post.

More recently, special two-part epoxy resins have been used to overcome this problem but extreme heat, rain, frost, snow, and vandalism can still take their toll. So, even though Dalles de Verre panels appear strong, custodians should nevertheless assess the risks and consider installing protective glazing. For detailed information on protecting stained glass and Dalle de Verre windows watch this video:

What to do if your Dalle de Verre gets broken

 In the event of damage or vandalism follow these steps:

  • Carefully secure the panel with strong, sticky tape to prevent further damage.
  • Board up the window if necessary.
  • Collect and save any detached fragments of glass and store them in plastic bags. Samples will be useful for the glass repairers to match for replacements (Take care to use protective gloves – glass is very sharp).
  • Take digital images of the damage. It is important to get both close-ups and general views to show the overall context and the nature of the framing (how the panels are installed).
  • Call your local stained glass company, send them the images, and request their advice.
  • Southern Arizona customers should contact Artistry in Glass to schedule a site visit and prepare restoration estimates for insurance purposes.

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Repair of Dalle de Verre panels – how to find a studio

Dalle de Verre panels are very heavy (jump to this section to calculate weights) so it is highly beneficial to use a local glass repair studio. Costs will escalate dramatically if you have to ship panels out of state!

Choose an established company

Check the company’s references and study their Google testimonials. (These are not infallible but, taken as a whole, they are almost always genuine). Evaluate their range of experience and expertise.

Make sure that the company has a physical location with employees and legitimate liability insurance (many workers these days operate from their garage or back yard).

Understand the repair process

It is a good idea for the responsible owner of Dalle de Verre panels to understand the repair options in order to make informed decisions.

The first step for your chosen glass studio will be to locate and purchase replacement dalles. Two sources have traditionally been available to the US customer – the famous Blenko Glass Co in Milton, WV., and the Kokomo company in Indiana. Unfortunately, Blenko stopped manufacturing dalles in 2020 although some inventory may still be available from secondary sources.

So the only reliable source of supply is Kokomo which makes dalles in standard 8” x 12” x 1″ slabs. Follow this link to see the Kokomo Dalle de Verre Color Palette.

Using the broken fragments and color images, the glass repair studio will attempt to match the colors as closely as possible from Kokomo and order the dalles ready for repair.

Once the replacement dalles are available, two main approaches are possible:

  1. On-site restoration
  2. Off-site restoration

On-site restoration

Dalle de Verre panels are very heavy and many of them are cemented permanently into the masonry of their host building. For these reasons the panels are often very difficult to remove and restoration must be done on-site

The problem with on-site repair is that we cannot easily use the recommended epoxy resin (we use a proprietary resin made by the Key Resin Company in Batavia, Ohio) because it has a runny consistency. It needs to be poured or squeezed from above as shown in the image below:

Pouring resin on to dalles
Epoxy resin is squeezed between the dalles using a funnel like those used for cake icing

So, for a successful repair of a vertical (in-situ) panel, a stiffer matrix material is necessary and Artistry in Glass has tested and successfully used the “Apoxie Sculpt” brand, available on Amazon:

We recommend Apoxie Sculpt, a 2-part epoxy modeling compound available from Amazon in 4 lb jars (we like the “natural” grayish color.)

We have tested Apoxie Sculpt attached to slabs of glass (dalles) and subjected to freezing and heating (300 deg F). The epoxy remained attached to the test dalles through repeated heating and cooling cycles.

It also has the benefit that it can easily be tinted to match the existing damaged epoxy:

Natural, earth-tone pigments can be mixed with Apoxie Sculpt to match the existing epoxy exactly. To complete the repair, sand can be added to the surface if necessary.

Steel sculpting set – recommended for manipulating the stiff epoxy around the glass dalles

Apoxie Sculpt sets up gradually and gives the repairer about 30 minutes of working time. We used this epoxy to complete repairs on badly vandalized panels at St. Francis de Sales Catholic Church in Tucson.

Vandalized dalles at St Francis de Sales
Vandalized dalle de verre (cavity protected by black plastic sheeting)
St Francis de Sales windows
Before (left) and after images showing the successful repair of Dalle de Verre windows from behind the altar at St, Francis de Sales Church.

Dalle de Verre panel from St Francis de Sales Catholic Church in Tucson – this damage was repaired on-site by Artistry in Glass.

Off-site restoration

When the damage is very great, many dalles are broken or missing, and the panel can be removed, then the best option is off-site repair. The panel is taken to the glass studio for repair while the window is boarded up for security.

Depending on the degree of damage, several approaches are possible. The most extreme and expensive (complete rebuilding) is recommended when multiple dalles are broken or missing and when the epoxy resin is weakened by pervasive cracking. Where the damage is less severe, resin stabilization may be an option.

Complete rebuilding

In this case, a careful tracing of the remaining dalles is made to create a new, annotated pattern. Then the resin is removed from the dalles with pliers (as shown below) or by careful hammering.

Breaking epoxy from the dalles
Breaking off epoxy resin using pliers

This stage is time-consuming and labor-intensive. Once the dalles are released and cleaned, new, replacement dalles are cut and faceted.

Sawing dalles on a diamond saw
New dalles are cut with a diamond saw
Faceting dalles with a chisel
Faceting the dalle with a carbide chisel

Arrange the restored dalles and pour the epoxy

To hold the epoxy we make a wooden mold by screwing 1 x 2’s onto a piece of 1/2″ thick plywood. Various methods are used to make sure the epoxy releases from the plywood – fine sand, waxed paper, latex paint, and caulking are all effective.

Using the traced pattern (cartoon) as a guide, the new dalles are arranged and the epoxy is poured in to fill the gaps.

Pouring resin on to dalles
Pouring epoxy over the dalles

The epoxy needs to cure for at least 48 hours (some prefer to wait a week). Then the completed panel is carefully released and cleaned ready for re-installation.

Resin stabilization

If the damage is limited to cracks in the resin it may be possible to stabilize the panel without taking the whole thing apart. The feasibility of this method is a judgment call and should not be attempted if the resin is pervasively cracked and loose.

Grinding epoxy with a dremel
Excavating a crack with a cutoff wheel

The technique is to open up the cracks by grinding crevices with a cut-off tool or angle grinder. The groove is then cleaned out and epoxy adhesive is inserted to bond the crack together.

As a final strengthening method, an additional layer of matching resin can be poured into the ground-away areas.

An inexpensive angle-grinding tool (available on Amazon) easily removes resin for stabilizing process. Use ultra-thin wheels for the best results.

Price calculators for Dalle de Verre

When evaluating the pros and cons of restoring a badly damaged Dalle de Verre panel, it is prudent to take into account the replacement cost. The cost of a Dalle de Verre panel depends crucially on the complexity of the design. That means that simple designs with few slabs per square foot are much less expensive to make than complex designs with multiple pieces:

Simple, average & complex designs
Simple, average, and complex designs

Beware of the weight – Dalle de Verre is very heavy!

In the price calculators below, take careful note of the weight of the panel. For ease of transport and installation, most Dalle de Verre experts make their panels 36″ square or less to keep the weight down to a manageable 100 lbs or less.

The prices indicated above are rough guides to the cost of manufacturing a Dalles de Verre panel. But, remember that the total cost of a project will include artwork, design, and installation charges.

Insider tips from a glass professional

We recommend you enlist the help of a qualified art glass studio to appraise your panels for insurance purposes. This should be updated periodically to take into account the effects of price inflation.

Conclusion

Dalle de Verre panels are stunningly beautiful with their vibrant colors and bold designs. They are well worth repairing but it is important to choose a fully qualified glass studio. Call Artistry in Glass for detailed advice on the protection and restoration of Dalle de Verre windows in Southern Arizona.

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John

I was an exploration geologist and University Professor working in Botswana, Zambia, Brazil, Saudi Arabia, the Netherlands, Portugal, and other countries before opening Artistry in Glass in 1986. In my more than 35 years of experience, I have brought my technical abilities as a scientist to the trade of glasswork. During this time I have become an industry expert in glass and glass-related skills. Watch out for special insider tips developed from my detailed knowledge of the glass business.

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