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Re: Sash Glazing & Painting (with Video)

Posted: Mon Sep 16, 2019 8:00 pm
by lohmann
Question on glazing a sash with very shallow rabbets. I'm restoring a bunch of 12-light casement windows that have very narrow/shallow rabbets - when I do final tooling of the putty to leave 1/16" remaining (room for paint), my putty knife has a tendency to catch on the glazing points which messes up the putty. I end up having to sacrifice all of the "extra" space in order to not catch on the points - net result is you can see the paint lines through the inside of the window. I hate it! I'm using the tiny triangle points and a Fletcher #5 point driver with the tips ground all the way off. What to do?

No Back Bedding

Posted: Tue Jun 23, 2020 6:40 pm
by johnleeke
A little historical perspective might sometimes explain the lack of back bedding.
Since at least 1820 the trades manuals and workers journals say that it was best practice to bed the glass for long term durability and considered a cost cutting shortcut to not bed glass. Sealing the interior joint between the glass in the wood against interior condensation is sometimes cited as the reason for back bedding.
The 3 houses where I have found no bedding were all built during the Great Depression, or earlier economic recessions. From the construction details of these houses it was clear they were built on extremely limited budgets, including the windows which had no bedding. So often we extol the virtues of glass that is extremely wavy with rheams and seeds. However, during every era, there has been "best glass" valued for its optical clarity and "cheap glass" with defects and optical distortions. In the window glass industry of past centuries it was common practice to sort out glass with a lot of these defects as seconds and thirds and sell it at lower prices for the barn, factory and greenhouse market. It is not surprising that some of this cheap glass made it into low cost housing during hard times. Perhaps not bedding was another cost saving practice during hard times.
It was a known building practice throughout the 19th and 20th century to put low cost glass into a building with the initial plan to remove it and upgrade the glass later. This was common in churches and other institutional buildings. I saw this in one elaborate high-end mansion built in the 1890s. Would you bother to back bed if you knew the glazing was temporary? Sometimes the upgrade was never done.
If you are finding sash with no bedding, it would be fascinating to learn what the economic conditions were when that house was built.

Priming Putty, Wrinkling

Posted: Thu Dec 17, 2020 3:15 pm
by johnleeke
Putty, to prime or not to prime--that is the question. (with a long response)

Some window specialists are reporting wrinkling of the surface of the putty after glazing and painting.

The Forest Products Laboratory (FPL) has done conclusive wood window tests and demonstrations since the 1950s that prove a four coat paint system excels. The four coats are pre-treatment, oil-base primer and two topcoats. I adapted the FPL's results into my own window work and testing.
My own research with side-by-side comparative field testing on wooden sash goes back to the late 1970s. In the late 80s I placed a series of three tests that demonstrated to me that it was worth priming the putty because it adds 8 to 15 years to the service life of the glazing system. This has pushed the service life of my sash work from 18-20 years out to 27-30+ years.

I attribute that 30+ years to three key factors:
==> Pre-treatment on the wood
==> Continuous 3-coat paint system across the face of the sash over the putty and onto the glass
==> Lap onto the glass is painted "to the line," and not scraped off with a razor, which provides a longer-lasting seal than if it is scraped back

Through the 80s, 90s and aughts I tested and developed those three factors adapting them into my own practical methods and materials that routinely produce a 25 to 30 year service life. For the details on these methods and materials see:
"Window Preservation Standard," Glaze and Paint Sash traditional, pages 59-63
"Save America's Windows," Plazing & Painting Sash, pages 63-82

Wrinkling Paint on Putty
I have never had the wrinkling paint problem, but I have investigated the details of four cases in different parts of the US where the putty was primed.
The most common cause was a slow-dry penetrating oil-base primer. These primers use a few solvents that have different evaporation rates that control and slow the drying and curing time. Some of the solvents penetrate the skin of the putty expanding it in volume, producing the wrinkles. Fast-dry primers have a different solvent system that usually does not cause this particular problem. Two of the investigations included conversations with Ed Sarsfield about their recommendation for no primer on Sarco putty. Ed said the recommendation was set because they got a lot of problem calls with primer on the putty, but they had not kept track of what kind of primer and had not done any testing. My research showed that there were two kinds of oil-base primer, slow-dry and fast-dry, and the slow-dry is far more likely to cause wrinkling.
Earlier this year, in May, I placed yet another putty & paint field test. This test compared priming the sash and putty with fast-dry alkyd oil-base primer, and a slow-dry oil-based linseed oil "long oil" primer. The only difference in the two test areas was the primer, all other materials and conditions were the same My intent was to push all the known factors that cause wrinkling to produce some wrinkling. I began the paint process the day after glazing with priming. The pre-treatment, glazing, priming and painting were done during a five-day period that was warm, damp and humid. But I got no wrinkling. So, I did another section of the test allowed the putty to skin over for three weeks, and was primed and painted during another damp spell. Initial results: after 8 months I got some wrinkling with with the slow-dry primer on skinned putty, no wrinkling on any other sections. I'll keep you posted on further results.

(The message I want you to take away is that there are many substiles to this glazing and painting, and you should do your own testing to determine what works for you and work consistently so when something goes wrong you can figure it out . The message is not to tell you whether or not to prime your putty.)

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Types of Whiting

Posted: Tue Aug 10, 2021 6:28 pm
by johnleeke
Whiting is a fine white powder that is brushed onto the glass immediately after glazing to clean the oil residue off the glass pane. Here are some notes on the different types of whiting and other powders used for this purpose.

Calcium Carbonate Types:
--Precipitated, chemically precipitated, very small particle size, usually what is available at ceramic and pottery suppliers, the small particle size makes it less suitable for glass cleaning as the small particle size does not linger on the glass rising and hanging in the air long enough that a respirator should be worn
--Whiting, physically ground up and sifted limestone, chalkstone, dolomite or marble, medium particle size, made for paint and putty manufacturers, most suitable for glass cleaning because it is entirely compatible with putty and glazing compounds, this mineral form of calcium carbonate is softer than glass and not likely to scratch it, respirator usually not necessary
--Ag Lime, ground limestone, made for garden and agricultural uses, not well sifted, wide range of particle size often including some larger and harder particles of other minerals that could scratch glass, could be used for glass cleaning when you can't get anything else, I've run it through a sifter before using it for glazing and found larger particles
--Pumice, is not calcium carbonate, it is silica a form of volcanic glass, the particles can have sharp glassy edges, which you might not want to breath into your lungs and may contribute to the risk of silicosis, the particles can be as hard as glass and so might be able to scratch glass
--Joint Compound, Plaster of Paris, etc, these contain gypsum, which gets embedded in the surface of the putty, if it gets wet it can grow sharp crystals that penetrate the paint film

Refurbishing Sash for Others

Posted: Sun Mar 13, 2022 2:13 pm
by johnleeke
When I refurbish sash for homeowners or contractors and they want to do the painting, I always take the sash through pre-treatment (includes faces and glazing rabbets), glazing and priming (includes priming the faces, over the putty and onto the glass) to assure the pre-treatment and primer are compatible with my putty, and to avoid incompatibilities with their paint and paint methods.