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The old cement/putty recipe question
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 Posted: Fri Jul 14th, 2017 10:28 pm
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Tod
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I've been "chatting" online with someone who makes his own cement. When I told him my basic recipe (boiled & raw linseed oil, whiting and color to suit, occasionally a splash of turps to help mixing as it seems to evaporate quickly) and said that I felt cement is best when it remains elastic rather than becomes rock hard.

He likes a similar mix but insists on adding plaster of Paris because it makes the cement "stronger". He also maintains that the lack of plaster will result in whiting drying out & becoming white powder. While I've seen this sort of powder in some old leads, I never thought it might be dried out, oil-less whiting.

He also contends that if plaster attracts humidity from the air then his open bag of plaster should be hard as a rock!

I thought the oil & whiting created some sort of chemical reaction which bonded the whiting and the curing oil. I also thought plaster needed water to set up and assumed oil wouldn't make it hard.

I feel fine about folks having their favorite recipes but I'm not chemically knowledgeable enough to be sure others who read our "chat" will get the best information or even the best foundation for forming an opinion. Can anyone here clear up at least the chemistry for me? I doubt that this person will change his mind but I'm very uneasy about leaving the science in doubt.
Thanks, Tod



 Posted: Sat Jul 15th, 2017 03:56 am
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Vic
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Your friend would need a VERY humid place to make plaster in the bag as you need about a quart of water for 2 1/2 pounds of dry plaster.
The issue is that dried plaster in the putty will absorb moisture and will leach (bloom) out onto the surface of the glass, allowing the possibility of mold and microorganisms to form that can damage the glass. Much like mildew forming on interior plaster walls.

https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/plastering-technical-guide-environmental-factors-plaster-application-en-PM10.pdf



 Posted: Sun Jul 16th, 2017 05:43 pm
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BloodGlass
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The old school recipe that I was taught consists of Portland cement, painters black for color, and gasoline... it makes a cement that really works into the came nice with a brush, cleans up ok with whiting and hardens to a rock pretty fast.
With that said I NEVER use this recipe... at my studio we use premade glazing putty, we use Wonder Putty, we use it straight for installs requiring glazing as intended. But we also use it for all cementing of windows, I have an old paint shaker so I mix putty with some paint thinner and a little japan dryer, shake it till it's mixed together and very soft and use a brush to putty and clean up with wood flour rather than whitening.
This gives an elastic putty, not a rock hard one. After working on hundreds of restorations with all sorts of different puttys I have some opinions based on my experiences. I will always advocate for elasticy, softer putty. It makes for more forgiving install with less break risk, it allows windows to move and flex with the structure it's installed in throughout the year. Also not least important it makes for a MUCH better situation down the road if the window needs to be repaired or even for the next guy 80years from now restoring it. If you've ever needed to dismantle or repair a window that's been actually been "cemented" without breaking anything then you know how I come to these opinions.



 Posted: Sun Jul 16th, 2017 05:52 pm
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BloodGlass
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Also I was taught that the white dust that you find within and old came is mostly broken down lead resulting in lead dust, this is one of the most dangerous things that we working in this field can encounter... it is not safe to assume that white dust is just old putty.



 Posted: Sun Jul 16th, 2017 08:29 pm
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Vic
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A couple of points
1- When the manufactures speak of "elasticity" of their glazing compounds they are referring to putty glazing of glass to sash. The putty is applied in larger (thicker) amounts then what we push under the lead came. It is also painted on the surface. Thus preventing air from "hardening" the putty. So I am not convinced that Wonder Putty is much, if any, better then linseed oil putty in stained glass work.
2- By adding Japan drier and paint thinner you are speeding up the set up time of the putty, thus reducing long term elasticity.
3- Old putty, prior to 1978 often times contained either red or white lead. This helped create a better bond to the glass. Also making the putty dust toxic when dried out.

Last edited on Sun Jul 16th, 2017 08:48 pm by Vic



 Posted: Tue Jul 18th, 2017 09:04 pm
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Tod
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Thanks, Vic & BloodGlass for your comments, information & suggestions. I've been out of touch for the past week expect to take up my life again tomorrow. - Tod



 Posted: Fri Aug 11th, 2017 01:08 am
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MattKolenda
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We use plaster in our mix. 2 parts whiting, 1 part plaster mixed with boiled linseed oil and a dash of black powdered mortar pigment. This is very similar to the recipe you'll find in the SGAA's "Standards and Guidelines for the Preservation of Stained Glass. I very much understand the argument against this practice and used to feel the same way.
I started adding plaster about ten years ago when I read a very compelling article, "Maintaining Stained Glass Windows" in Stained Glass Quarterly by Geoffrey Wallace. He explained how when the plaster is mixed with oil it will repel water rather than absorb it and thus never cure into the hardened form of plaster we might associate with the name. It does render a stiffer panel but is still quite flexible and serviceable.

He also wrote about the procedure of cementing windows in situ and, through capillary action, the cement is able to regenerate itself when new oil or a thin mix of cement is introduced. Since we rarely completely relead a window and only partially relead most of the old windows we encounter, we've had plenty of opportunity to see this first hand both on the bench and in situ. I'm still amazed at the transformation you'll see when you feed thirsty old windows a good helping of oil or thinly mixed cement. The lead and painted glass also seem to appreciate the treatment and shine like new afterward. You don't want to use any whiting during this process and will want to keep the in situ work limited to the exterior. The idea is to leave the cement looking wet with oil. Excess is simply wiped and buffed with rags.

I don't think there will be a day we can ALL agree on a standard mix. We do what works for us. Just don't use Portland or Inland which will render a panel practically disposable.

-Matt

Last edited on Fri Aug 11th, 2017 01:10 am by MattKolenda



 Posted: Fri Aug 11th, 2017 02:26 pm
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Vic
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"repel water rather than absorb it"
"He also wrote about the procedure of cementing windows in situ and, through capillary action, the cement is able to regenerate itself when new oil or a thin mix of cement is introduced."

Aren't these contritictory statements? How can the plaster repel water and absorb oil? How does the plaster know what liquid is trying to get absorbed?
Geoff's concept on insitu rejuvenation of putty is predicted on adding the putty/slurry mix when the old putty starts to dry out before absorbed moisture can cause damage. And this is based on routine inspection and maintenance. In my experience, there is very little if any routine inspection and maintenance in this country. Maybe OZ is different.

Last edited on Fri Aug 11th, 2017 02:27 pm by Vic



 Posted: Sat Aug 12th, 2017 01:02 pm
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MattKolenda
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You're right on that Vic. The cement would be capable of siphoning water as well as oil without maintenance. Routine maintenance is critical in the longevity of any window regardless of the cement used, and this would certainly be no exception. Like you, we have rarely seen diligent maintenance performed on stained glass windows. I've even had a church tell me their windows (behind two layers of unventilated PG) will last 100 years without service and since they are only 95 years old, they've got five more years before they have to deal with them. We have also worked on a large collection of F.X. Zettler windows ca. 1910 that had been recemented in situ once before many years ago, and we cemented them once again. The condition of most of these windows was remarkable in that there was no deflection and not one broken joint or failed came. Had this maintenance contributed to the healthy life of these windows that were still weather tight? If so, would there not be benefits to a cement that readily accepts oil if it means they can remain in their original installation well over a century if maintained?

We speculate the use of plaster in cement was commonplace 100 years ago. Many windows in our area have some form of PG and we have not seen first hand any permanent harmful effects of plaster in cement. Any church we have worked on with windows exposed to the elements has welcomed the idea of cementing their windows every 30 years or so, which is a very simple and delicate procedure. Many of them are also undertaking large roofing, tuck pointing, plaster and painting projects and it seems a lesson is being learned that it's better to stay diligent with their building maintenance rather than let it go until the point it's a significant problem. Now, not all churches have the funding or awareness to stay on top of every little issue their building may encounter, but we work closely with other trades and do our best to promote this philosophy. If such building maintenance can be picked away at in small pieces it spreads out the cost over the years and hopefully diminishes the necessity for massive costly projects which will not only benefit the parishioners but also anyone in the restoration trades.

Maybe it's wishful thinking, I guess I'm a dreamer.



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