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Spot Putty Maintenance (final)

Posted: March 20th, 2013, 4:58 pm
by johnleeke
WPSC Window Standard Work Method

Status: [ ] submitted work method, [] proposed treatment standard, [x ] final treatment standard
Update: 3/20/13
Author: John Leeke
References: Historic HomeWorks website, discussion forum, (Accessed on 3/20/2013.)

Title of Treatment: Spot Putty Maintenance
Class of Treatment: [x] Maintain, [ ] Stabilize, [ ] Repair, [ ] Upgrade, [ ] Exception
Type of Treatment: [x] Traditional, [x] Contemporary, [x] Conservation

Condition to be Treated: Putty failure in tightly localized spots.

Description: Remove sections of loose putty, seal cracks in putty and paint. This treatment is suitable for sections of missing and cracked putty when the remaining putty is tightly adhered or is in good condition. If more than 25% of the putty on a sash is damaged, consider completely reglazing the entire sash. Save all putty in good condition if doing a conservation type of treatment. Movement of the sash and shrinkage of the putty over the long-term causes the putty to crack and fall out. Spot putty maintenance helps seal the glass to the wood helping to prevent movement of the wood due to moisture; it can extend the life of the putty for several or many years. Many spots on more that one window can be treated at the same time, achieving an efficiency of scale. Linseed oil materials may dry and cure slowly. For a faster production rate a penetrating drying oil can be used instead of boiled linseed oil. This may shorten the life of the repair somewhat, so use boiled linseed oil for best durability and longer life of the repair.

Typical Procedure:

1. Remove loose putty. Use a 1/2" wide steel brush and pull-type scraper to to clean up glass and wood surfaces in the glazing rabbet. The surfaces must be perfectly clean: bare bright wood, and sparkling glass. A razor blade may be needed on the glass.

2. Mask off the neighboring glass and wood surfaces with 2" wide blue masking tape to the glass along the edge of the putty before starting. Also apply tape to the face of the stiles and rails if you will not be repainting them.

3. Brush a pre-treatment on any exposed bare wood in the glazing rabbet and let it dry. Pre-treatment can be the traditional boiled linseed oil mixed with turpentine or alcohol, or a penetrating oil-base primer.

4. If the putty has cracks but is still well attached, brush some boiled linseed oil onto the line of putty and brush it back and forth so it soaks into the cracks.

5. If the putty bevel surface is rough and needs to be smoothed, sand it right in the wet oil. The oil will help control any lead-containing dust. But, DON'T SCRATCH THE GLASS WITH THE SANDPAPER. Use a thin metal slat from an old Venetian blind or strip of sheet metal to protect the glass. The oil will seep into the cracks, then brush again, more will seep in, come back in 10 minutes to apply a little more and brush, repeat three times.

6. Mix a little boiled linseed oil into a bit of glazing putty so it forms a loose runny paste. Work the paste into the cracks with a tooth brush. Fill any cracks that remain open with straight putty, working it in with a putty knife. Finally, wipe off all remaining oil and putty with a rag, refill any cracks that are still open.

7. Clean up the repair area by removing the tape and cleaning off the surrounding wood and glass surfaces with a rag and a little mineral spirits. Safety: Do not leave oily rags laying around, they can spontaneously combust causing a building fire. Store oily rags under water in a metal container.

8. Pack and tool putty or glazing compound into the sections of missing putty. Let the putty cure and skin over

9. Prime and paint the putty with two coats, lapping 1/16" onto glass and wood. Allow to dry between coats. Sand lightly between coats if surface feels rough.

· Blue masking tape, 2" wide
· Sandpaper, 100 grit
· Putty or glazing compound, oil-based
· Boiled linseed oil or oil-based pre-treatment
· Rags
· Primer, oil-based
· Paint, top coat, oil-based or waterborne acrylic

Quality of Results:

Best Work: Cracks are filled with linseed oil and putty. Putty is tooled smooth and neat. Paint coating presents a smooth surface and even luster. Paint and primer lap onto glass and wood. A slightly noticeable unevenness in the surface bevel of the putty is acceptable.

Inadequate Work: Remaining loose old putty or unfilled cracks. Paint does not lap onto to glass and wood. Repaired putty surfaces feel jagged or abrasive.

Re: Spot Putty Maintenance (draft)

Posted: March 22nd, 2013, 7:53 pm
by tfrancis
Your discussion is certainly well detailed. I have nothing to add to your excellent treatment of glazing repair. I do have a question about the quantity of failed glazing which would trigger a re-glaze or possibly a more aggressive approach . I have found that when 25% or so of the glaze has failed, there has been enough water ingress into the mortise and tenon connections that the pins have begun to rust or the pegs have begun to fail. As rust and rot are tenacious, I typically will disassemble such sashes, treat the wood with consolident, repair the wood as needed and than replace the pins before re-glazing. Jim Turner and I at a recent event in Northern Kentucky, discussed the value of sash disassembly. For the small of time it takes to separate a sash, we seemed to agree that it certainly was beneficial to the longevity of the repair in many situations. Your opinion sir? (This is probably not the right spot to ask this question. I apologize for any breach of forum etiquette. Please feel free to edit as necessary.
Thanks! Tom

Re: Spot Putty Maintenance (draft)

Posted: March 23rd, 2013, 12:40 am
by johnleeke
Questions and comments are always welcome. Any place a question comes to mind is the correct place to ask it.

You are correct, a sash may also need other repairs. There are standards here to cover some of the repairs you mention, such as:

Re-building a sash joint:

Re-pinning a sash joint:

It can be a complex issue to decide when spot repairs and maintenance are enough, or if complete refurbishing and disassemble are needed. The decision might involve the money or time available, the philosophy of the project, the skill and knowledge of the workers available, etc.

Thanks for your thoughtful comments.