Pre Treatment of the Sash Glazing rabbit

sschoberg
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Joined: June 9th, 2011, 9:43 pm

Pre Treatment of the Sash Glazing rabbit

Postby sschoberg » June 24th, 2011, 8:14 am

We are fairly cautious when addressing any pre treatment of this glazing rabbit. It the sash is dry (and I think this is an obvious and easy observation) we will treat with BLO. If the rabbit looks and feels good then we leave it alone and go on with the glazing procedure.

Many restorers are using an oil primer to pre treat and although I really can't argue with success I wonder if this isn't just over kill or maybe even harming the ultimate longevity of the putty. We are still seeing many 100 year old sashes with putty in excellent condition with no obviouse signs of any pre treatment, let alone any primer showing once putty is removed.

johnleeke
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Re: Pre Treatment of the Sash Glazing rabbit

Postby johnleeke » June 24th, 2011, 12:08 pm

If the sash is dry (and I think this is an obvious and easy observation)...


Steve, could you describe the 'dry' look in more detail, so others who don't know the look could recognize it?

We are still seeing many 100 year old sashes with putty in excellent condition with no obvious signs of any pre-treatment, let alone any primer showing once putty is removed.


I wonder about the difference between the putty they used back then, and the putty we have to use now. A hundred years ago the linseed oil used in the putty was probably very different stuff than the linseed oil, safflower oil, petroleum oils and plasticizers found in today's putties and glazing compounds. Many of the sash mills made their own putty, and if they did not pre-treat the glazing rabbet they might have been mixing up a putty that had more oil in it, so there was enough oil to soak into the wood without depleting the putty of oil right next to the wood surface of the rabbet that would cause adhesion problems. (I don't know, just wondering....)

I have done some side-by-side testing on this, and found that most putties and glazing compounds adhered better to pre-treated wood. (This was just a "stuff test" and not a real field comparison test.) Here's a photo:

Image
More info here:
http://historichomeworks.com/forum/view ... ?p=608#608

Another more recent test included shellac as a pre-treatment and more putty products and gave very similar results after one year and three years. Some of you who have been to my window training sessions have seen this test.
John
Standards Co-Founder
Standards Editor

http://www.HistoricHomeWorks.com

sschoberg
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Joined: June 9th, 2011, 9:43 pm

Re: Pre Treatment of the Sash Glazing rabbit

Postby sschoberg » June 24th, 2011, 6:57 pm

You can see and feel when a sash is "dried out" . It is lighter weight when compared to one in excellent shape. It has sharper edges, with no noticeable cracking. A dry sash just doesn't look new.

Which brings me to another question that I have asked myself on occasion. At what point do we say that a sash is "too far gone" to be restored. Very light, twisted or bowed and rounded edges which shows no retentitive oils left in the wood. At what point is a sash a good candidate for duplication instead of restoration?

oculus
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Re: Pre Treatment of the Sash Glazing rabbit

Postby oculus » July 5th, 2011, 5:56 pm

I have to look at the historic nature of the structure I am working on when determining whether a sash needs to be replicated or if it can be saved. If the sash is from the third oldest house in the state and is one of only four original sash in the house then I will restore it to the best of my abilities but if the sash is from a 1927 bungalow in Portland (we have 1000s of bungalows here) then I might be more inclined to say "lets talk about replication".
Also, I often have the SHPO watching over my shoulder. So I better have a good reason not to keep an original sash.
Amy Harrington McAuley
Oculus Fine Carpentry, Inc.
http://oculuswindow.blogspot.com/
oculuswindow@gmail.com

"Opportunity is missed by most people because it is dressed in overalls and looks like work"-T.Edison

sschoberg
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Re: Pre Treatment of the Sash Glazing rabbit

Postby sschoberg » July 7th, 2011, 7:55 pm

Of course, the possibility for the need to replicate would need to be addressed when an assessment of each window is done. But there comes a point (and condition) where it would be not feasable to restore a plain worn out, rotted and twisted, dry rotted junk of wood that only has a resemblance to a working sash. These are the ones I'm talking about where consideration for replication is a must.

Or if a sash is crumbling to powder when touched maybe an indication that restoration is not gonna work, regardless of whom is looking over your shoulder.

But still there will be some that will glob on and form up as much epoxy as needed to come up with a something that looks "as good as new" but will only last as long as what its comprised of. haha

Jason Whipple
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Re: Pre Treatment of the Sash Glazing rabbit

Postby Jason Whipple » July 30th, 2011, 10:02 am

I'm one of those who has normally primed the glazing rabbit before glazing. I must say that I've reconsidered this step with a recent project that we were doing in extreme heat. It may have caused a problem with our paint adhering to the glazing. Another window restoration specialist suggested that once the glazing rabbit has been primed, the oils have no where to escape to when drying quickly in the heat.

I tried the next few windows without primer in the rabbit and had much better results.
Jason E Whipple
Historic House Restoration
Cincinnati, Ohio
(513) 633-4332

https://www.facebook.com/RestoreOhio

johnleeke
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Re: Pre Treatment of the Sash Glazing rabbit

Postby johnleeke » December 16th, 2011, 8:45 pm

Steve, judging the character and condition of wood may be one of those things that is so subtle that it must be left up to the knowledge and skill of the worker. It may be a matter of training and experience rather than something that can be detailed in a standard or specification.

Some of the standards here will be on glazing and painting. I know that some of them will include a step of oiling or priming or shellacking the glazing rabbet. None are posted yet, but when they are I'd like you to comment on them with this in mind.
John
Standards Co-Founder
Standards Editor

http://www.HistoricHomeWorks.com


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