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Glazing

Nothing is more crucial to the success of a sash repair than glazing compound. I use a professional-grade product called Perm-E-Lastic Glazing (Atlas Putty Products, 800/373-2727, www.putty.com) that spreads easier and remains more elastic than over-the-counter versions. I tool the compound with a curved putty knife — technically called a 35-degree bench glazier — which I find easier to control than a straight-bladed knife, especially when working in corners. I bought mine online from a supplier of glazing products, but it took a bit of searching (Ro-Don, 800/829-0687, www.ro-don.com).

To keep glazing putty from sticking to my fingers, I dust them with a light coating of plaster of Paris. Starting at a corner and holding a ball of putty in one hand, I tear off thumb-sized chunks and press them roughly in place with my fingers. When one side of the sash is fully loaded, I place the clean knife blade in a corner and hold it at an angle steep enough to ensure that the edge of the putty won't be visible from the other side. Then, using pressure from my forefinger to hold the knife blade tight to the edge of the rebate, I draw the blade smoothly from one side to the other.

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Holding a ball of glazing putty in one hand, a worker tears off manageable chunks and presses them in place with her fingers.

Credit: Maurice Duke

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When one side of the sash is fully loaded, she tools the compound smooth with a glazier's curved putty knife.

Credit: Maurice Duke

To ensure that the putty stays smooth and doesn't pull out, the knife should be absolutely clean and free of pits. I've found that a light spritz of WD40 also helps.

After trimming away the excess putty, I roll it back into the ball and move on to another section. When all the sash have been reglazed, I set them aside to cure for a few days. The glazing compound I use skins over enough to accept primer in as little as 24 hours, but the longer drying time means fewer brush marks in the still-soft putty.

I put a second coat of primer on the exterior faces and follow that with a coat of paint.

Saving Energy

The easy way to make antique windows more energy-efficient is to add storm windows. Lots of low-profile storms are available these days that can be installed from the inside or the outside. I've also had good luck retrofitting sash with weather stripping. Instead of the spring bronze systems that are a nightmare to install, I use an assortment of silicone beads and nylon pyle (brush-type) weather seals; they snap into narrow grooves that I rout into the surfaces of the sash with a specially designed slot-cutting bit.

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The author prepares a sash to receive weather stripping by routing a 3mm groove into the mating surfaces of the sashes. After the sash is fully primed, horizontal surfaces — such as the meeting rail shown above — are fitted with silicone bead.

Credit: Maurice Duke

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On the exterior of each sash, vertical surfaces are fitted with brush-type weather seals, which seal tightly to the stops but don't interfere with opening and closing.

Credit: Maurice Duke

All these products are sold by Resource Conservation Technology (800/477-7724, www.conservationtechnology.com).

Restringing the Sashes

Unless a client specifically asks me to fix the top sash in place, I prefer to make both sash operable. This feature is particularly welcome on cool summer nights, when opening both halves allows the air to circulate freely.

Whether I'm restringing both sash or just the bottom, the procedure is the same. I open the covers that allow access to the weight boxes and cut the old cord from the sash weights. If the weights are missing, I weigh the sash with a hand-held fishing scale, then divide by 2 to determine the correct replacement size (old window weights are usually coded at the top with Roman numerals, so a 6-pound weight would be marked "VI").

I fish the new cord through the pulley by attaching it to a 5-foot length of string with a lead fishing weight on the end. Sash cord is available in a variety of sizes and strengths; for residential windows, the stuff I use is rated for a working load of 94 pounds.

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A weighted string helps the author fish new sash cord over the pulley and down to the bottom of the weight box.

Credit: Maurice Duke

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He secures the cord to the sash weight with two half-hitches, then captures the excess cord with a hog ring to prevent it from ever getting snagged in the cavity.

Credit: Maurice Duke

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To allow plenty of slack for attaching cord to sash, he pulls the weight to the top of the cavity and clamps the cord.

Credit: Maurice Duke

I loop the cord through the hole in the weight and tie it with two half-hitches, leaving a few inches of slack pointing upward. To prevent any future snags, I crimp the loose end back onto the cord using a hog ring. Next I pull the cords as high as they'll go and secure them with a spring clamp. Placing each sash in turn at the bottom of the jamb, I cut the cord about an inch below the knot mortise in the edge of the sash and tie it in a simple overhand loop. When both sides are done, I remove the clamps and operate the sash to make sure it enjoys full range of motion. If the weights bottom out or catch on the pulleys, I retie the cords and try again.

Once I'm satisfied with the length of the cords, I secure each to the sash with two copper roofing nails — one through the knot, the other about two inches above the first.

Before fastening the cords to the lower sash, I temporarily remove the sash so that I can replace the box covers and the parting bead. I secure the parting bead with 1 1/2-inch hardwood trim nails (Maze Nails, 800/435-5949, www.mazenails.com) spaced approximately 24 inches apart. If there's a noticeable gap between the bead and the frame, I cover it with a light bead of caulk.

Next, I replace the stops. First I make sure that any paint on their inner edges has been scraped off. Then I hold each one snugly against the bottom sash and tack it with the same nails I used for the parting bead. I don't drive the nails home until I'm satisfied that the window operates as smoothly as any modern unit.

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A restored double-hung's authentic divided lights and period glass are visible even behind a storm window. With occasional maintenance, this unit should serve faithfully for another century.

Credit: Maurice Duke

After all the stops are in place, I rub a block of paraffin wax along the channels of the window frame to provide lubrication.

Dixon Kerr is a restoration contractor in Richmond, Va., and the co-founder of the Alliance to Conserve Old Richmond Neighborhoods.