To Back Glaze or Not
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dhoggard



Joined: 23 Jul 2008
Posts: 13
Location: Greensboro, NC

PostPosted: Sun Feb 07, 2010 2:54 pm    Post subject: To Back Glaze or Not Reply with quote

What, in your esteemed opinions, is the benefit to back glazing?

We have removed original glass from, and re-glazed, thousands of panes over the years and have NEVER found evidence that they were originally, routinely, "back glazed". The glass is usually installed directly to the rabbet and it seems to have done just fine for 100+ years.

I have a theory that the process was added to the directions on the can by glaze putty manufacturers some years ago to sell more product than they would with face glazing only.

Kind of like what you read on the shampoo bottle: "Wash, rinse... repeat".

I believe it to be a waste of time and material with no benefit. But I can be convinced otherwise. Convince me.

David Hoggard
Double Hung, LLC
Greensboro, NC


Last edited by dhoggard on Mon Feb 08, 2010 6:11 am; edited 1 time in total
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sswiat



Joined: 01 Sep 2004
Posts: 231
Location: Cambria, New York

PostPosted: Sun Feb 07, 2010 4:24 pm    Post subject: Reply with quote

If I am understanding your question correctly, what I would have concern about is with old antique glass which is far from flat as a newer float or even older plate glass. Without the bedding, the glass would never sit flat in the glazing rebate. Any down pressure would likely crack the glass. Also, most very old sash are handmade and the rebates are never perfect so even if the glass is perfect you will have voids.

Next, when the exterior putty dries after some time, the sash glass will likely rattle more excessively than it does normally when the bedding dries out. This is often evidenced when a large heavy truck passes by.

The last issue I could think of and not sure if it always exist )especially down south) is any condensation on the interior of the glass would have a sure path down into the unprotected glazing rebate once the paint barrier is breached.
Back glazing or bedding has always been the standard as far as I know.
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jade



Joined: 11 Feb 2005
Posts: 786
Location: Hawley MA

PostPosted: Sun Feb 07, 2010 5:16 pm    Post subject: Reply with quote

i concur with steve....

back bedding acts as a gasket for laying glass whether the substrate or glass is flat...when the substrate or glass is not flat, it is essential to lay a bed before placing the glass so that the glass does not rattle in the rabbet--hence the very popular phrase 'riveting rabbet rattle'...ha, actually i just made that up...

the only time i have seen a sash without back bedding is when the finished putty has thumb prints in it...a sure sign that a handy homeowenr replaced the glass at some point...

it could be a southern thing but, as steve suggested, i would think condensation from humidity may present problems...

i shampoo....rinse...condition....rinse...
...jade
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johnleeke
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Joined: 20 Aug 2004
Posts: 2972
Location: Portland, Maine, USA

PostPosted: Sun Feb 07, 2010 5:49 pm    Post subject: Reply with quote

Water from condensation may seep into the joint between the glass and the glazing rabbet on the inside of the sash if the joint is not well-sealed. Typical forms of deterioration are lower sash joints rotting out, bowed meeting rail of the upper sash, and a line of decay within the glazing rabbet.

If you never see these forms of deterioration when there is no bedding putty then it could be your local local weather conditions and tradespeople and sash makers found it was not needed or it was accounted for in other ways. For example, interior condensation may not be a common phenomenon, or decay resistant wood was always selected for sashes.

Many of the old trades manuals from the 19th and early 20th century say that bedding putty is best practice, and the lack of it is "short-cut" work of lesser quality. It was done going back to the earliest days of glass in sliding or swinging sashes, 1400s to 1600s.

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by hammer and hand great works do stand
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dhoggard



Joined: 23 Jul 2008
Posts: 13
Location: Greensboro, NC

PostPosted: Sun Feb 07, 2010 5:50 pm    Post subject: Reply with quote

Generally, we put back the same historic glass that came out and, generally, in the same location in the sash. We've been restoring sash for many years, so I am very familiar with the characteristics of historic materials.

This is not to say that we don't "spot" back glaze if there is a noticeable void on the interior between the glass and the muntin following face glazing. This is, as you say, due to the unevenness of the glass and/or rabbet - but this condition rare.

Regarding glass rattling "when the bedding dries out". There is no dried-out bedding so excessive rattling is not all that much of a problem.

I certainly understand about how condensation could gather in any interior glass/rebate void, but we don't generally note any excessive moisture damage problems and no back glazing was originally installed.

It could very well be a 'down south' thing, but there is no evidence that sash were routinely and completely back glazed (set in a contiguous bed of putty) originally when we remove the glass.

Are you saying that when you remove glass that was originally set in place 100 years ago, that you have to scrape and remove an old, dried out, bed of putty from the rebate?

We don't - because it doesn't (usually) exist.
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johnleeke
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Joined: 20 Aug 2004
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Location: Portland, Maine, USA

PostPosted: Sun Feb 07, 2010 5:52 pm    Post subject: Reply with quote

Yes, always having to clean out the bedding putty after glass is removed. In these locations I have seen bedding putty and think it is common:

New England
Nebraska
South Dakota
Atlanta
Jacksonville, FL
New Jersey
Banff, Alberta

Is it possible they did something else between the glass and wood in your area, like lay the pane in a heavy application of thick lead-oil paint? That is occasionally mentioned in the old manuals.

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by hammer and hand great works do stand
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dhoggard



Joined: 23 Jul 2008
Posts: 13
Location: Greensboro, NC

PostPosted: Sun Feb 07, 2010 6:05 pm    Post subject: Reply with quote

Re: thick bed of paint. No, not usually John - but occasionally. When we remove the glass, the rebate is *gasp* un-primed. The sash around here were usually installed without any paint on them at all - interior or exterior. They were usually finished "on the hoof".

98% of the sash we work on are original growth, Southern yellow (heart) pine (Long leaf). To the point about damaged rails and horizontal muntins due to moisture. That is a problem perhaps 2% of the time - even with no back bead.

Likely a Southern thing. Any other Southern restorers out there?

Re: "the lack of it is "short-cut" work of lesser quality...." Ouch... that hurt.

We do when it is specified - or when needed due to ill-seated glass - but not as a standard course. We are simply restoring it back the to the way it was. I am struggling with changing our spec to do it always and that is why I brought it up.
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johnleeke
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Joined: 20 Aug 2004
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Location: Portland, Maine, USA

PostPosted: Sun Feb 07, 2010 7:34 pm    Post subject: Reply with quote

Quote:
Re: "the lack of it is "short-cut" work of lesser quality...." Ouch... that hurt.


Just reporting what the old books say, not making any personal judgments. (don't believe everything you read in a book)

Do you see the same detail on very high-end buildings (mansion on top of hill, high-style federal government building) as well as obviously low-end buildings (shed out back of the barn)?

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by pen and thought best words are wrought
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dhoggard



Joined: 23 Jul 2008
Posts: 13
Location: Greensboro, NC

PostPosted: Sun Feb 07, 2010 8:01 pm    Post subject: Reply with quote

Again... it is the vast preponderance of the windows we undertake that are not back glazed... not all. I've noted no difference in high end vs. low end, but will start paying better attention to that.

As for our location pedigree... The Carolinas and Southern Virginia is our stomping ground
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sswiat



Joined: 01 Sep 2004
Posts: 231
Location: Cambria, New York

PostPosted: Mon Feb 08, 2010 2:21 am    Post subject: Reply with quote

Reporting in from across the pond. As far as I know back bedding is done in the European+Scandinavian countries.

I imagine it may be a southern practice as cold temps on the outside and warm on the inside would not be as frequent or severe down south.

I hope that this disagreement will not be the basis for a reason to startup " the war" again....lol
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rncx



Joined: 21 Jun 2008
Posts: 660
Location: Little Rock, AR

PostPosted: Mon Feb 08, 2010 2:37 am    Post subject: Reply with quote

i'm also in the south (little rock) and do quite a bit with old longleaf pine myself, although i prefer cypress for window construction, it cuts easier, requires less heavy weights since it's lighter, and can be had alot cheaper around here. don't restore old ones, but i built new ones to match my neglected rotten old ones in my own house.

that said, i do use a clear caulk bedding for the glass in the ones i build, simply because it's 'accepted' practice.

like you dhoggard, i have seen both with and without. on my originals in my ~1908 house, they didn't put any. i've seen others in the same neighborhood with. may have been personal preference on the part of the glazier.
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cabinfeverarts



Joined: 05 Aug 2008
Posts: 114

PostPosted: Mon Feb 08, 2010 7:11 am    Post subject: Reply with quote

Speaking from experience here...

In 2007, I didn't know any better and didn't back glaze. I've learned now, but I still have the old windows that I did before to compare. Moisture is definitely seeping in. They are going to have to be redone.

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dhoggard



Joined: 23 Jul 2008
Posts: 13
Location: Greensboro, NC

PostPosted: Mon Feb 08, 2010 7:31 pm    Post subject: Reply with quote

Thanks for all of this input. I'm confident that windows in the northern climes are much more prone to interior condensation than we Rebels. Nothing else I can think of would account for the difference in technique.

As I type this I am looking at my very own 1908 windows that I restored 14 years ago. They had no back glaze originally and I didn't do it either. They are as perfect as the day I completed them back in my early days.

That said, I can find no reason NOT to do it from here on out but i want to make it as 'labor neutral' as possible.

I'm considering just laying down a thin bead of high quality latex caulk and setting the glass in that. Then face glaze as normal with proper putty.

Any objections?

David Hoggard
Double Hung, LLC
Greensboro, NC
www.double-hung.com
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johnleeke
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Joined: 20 Aug 2004
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Location: Portland, Maine, USA

PostPosted: Mon Feb 08, 2010 9:14 pm    Post subject: Reply with quote

Quote:
I'm considering just laying down a thin bead of high quality latex caulk and setting the glass in that. Then face glaze as normal with proper putty.
Any objections?


Think about how long the sashes you are working on have lasted with ordinary putty.

Think about how glazing putty fails gracefully, without damaging the wood or the glass.

Think about how easy it is for you to clean up an old glazing rabbet that has be glazed with putty.

Think about the adhesive properties of latex caulk that is designed to never let go.

Think about Ed and Denise Sarsfield making that good old fashioned Sarco putty at their shop in Chicago.

Think about the petrochemical industry that makes latex caulk and how much Exxon executives got in unearned bonuses last year.

Think about the next person sometime in the future who will be maintaining the sash you are working on today.

Let us know what you think.

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John

by hammer and hand great works do stand
by pen and thought best words are wrought
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dhoggard



Joined: 23 Jul 2008
Posts: 13
Location: Greensboro, NC

PostPosted: Tue Feb 09, 2010 7:51 am    Post subject: Reply with quote

Ok, Ok...

Glaze putty back glaze it is (You had me at "PetroChemical")
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