We would like to discuss the operation of hung windows, specifically the function of weights in a weight and pulley balance system. The system was very popular with traditional windows and is still relevant in restoration and contemporary projects.
Sash weights working with pulleys provide the counter balance to keep sash either partially or fully open or closed. The two weights equal the weight of a given sash, making single or double hung windows easy to operate. Traditionally these weights were round, one piece cast iron, with an eyelet for the chain or rope cast into one end. Often times the poundage was indicated in the side or the end of the weight. This mark can be in the form of Roman numerals or standard Arabic numerals. Sometimes you will see a number followed by a smaller digit 2, such as 52 indicating a 5 and a half pound weight. In residential work, 1-3/8” diameter weights are most common.
Frequently, even if sash have been replaced or the weight and pulley system has been disabled, the weights have been left in the weight pocket and can be retrieved and used again without modification. Care must be taken that the refurbished sash weighs the same as the original sash, so that the weights will provide proper balance and operation.
Many people assume that weight and pulley systems are merely a quaint throwback and that by now, surely, some more sophisticated method must be the state of the art. However, the weight and pulley system is the most durable and effective way of balancing hung sash. In addition, there are compelling reasons why they are the very best solution for some contemporary applications. For example, in the pursuit of high energy ratings, many architects and builders of large homes are utilizing double and even triple glazed, hung sash. The sheer weight and scale of these applications precludes the use of common systems such as block and tackle balances.
The biggest contributor to differing sash weight is increased glass thickness. Glass is quite heavy and changing from single strength to say double strength or laminated glass will greatly increase the weight of the sash and may render the existing weights inadequate. If the weight increase is not great, perhaps a pound or two of add-on weights can set the balance.
Many new windows include the use of insulated glass units which are very heavy and pains must be taken to use every bit of available space in the weight pocket. This is accomplished by using weights with a greater cross section (but never greater than the thickness of the sash), square section weights, and in extreme cases using lead weights instead of cast iron. These applications can require ball bearing pulleys and metal sash chain for strength.
The absolute necessity of using weights for large or heavy sash caused the development of stackable sash weights. These modern cast iron weights can be found in 1, 3 and 5lb sizes and also 10lb cast lead weights. This system allows for any sized weight to be efficiently configured while only requiring a few different sizes of weights to be stocked. The technical drawing below shows how the weights can be stacked and fitted together.
SRS Hardware manufactures and stocks four sizes of weights. Both cast iron and cast lead weights are 1-3/4” square with a stackable pyramidal top and socket bottom so that the two types can be used in concert. This allows for the most flexibility and economy. The preferred method is to use cast iron as much as possible, reserving the use of the denser (yet more expensive) 10 lb. lead weights in situations where weight pocket space is at a premium. In these cases the smaller cast iron weights can be added to the top of the lead weights for fine-tuning to achieve “finger-tip” balance and operation of any sash.
One of the first questions many customers have is “which putty is best for glazing my wooden windows?” The easy answer is “Sarco.”
Sarco is a small, family owned company that developed a number of industrial putties including several for sash. The new glazing compounds are easy to handle and have elasticity that the old calcium carbonate putties lacked.
The more difficult answer is which type of Sarco is best for your application. For wooden sash, there are two options: Sarco Dual Glaze and Sarco Multi-Glaze Type M.
Before reading on, it’s good to know that the compounds are very similar and rely on soybean and linseed oils to work. Neither contain hazardous materials or emote noxious fumes. Both compounds require painting after skinning and Sarco does not recommend priming the putty. They find that paint adheres better directly to the putty itself and when primer is used the putty has a greater likelihood of wrinkling.
Both putties meet Federal Specification TT-P-781A, Type I.-TT-G-00410E.(Click to learn what this specification means)
Review the Material Safety Data Sheet here.
It will be easier to select the correct putty if you understand how the two are meant to be applied:
Dual glaze is formulated for wood and metal sash and meets the requirements of most glaziers, painters and intrepid DIY homeowners.
Dual Glaze may need up to 2 weeks to skin over for painting. The amount of time to skin over is greatly effected by environmental conditions. However, one of the greatest advantage of Dual Glaze is that it can withstand exposure to the weather before it is painted, allowing sash to be glazed in place and painted later as the schedule permits. This means users can glaze a sash while it remains in the window frame or sits outdoors during a restoration project.
This user friendly putty is available in convenient, ready to use quart and one and two gallon buckets.
Sarco Multi-Glaze type “M”
Type-M is a quick skinning product, usually forming a strong enough surface skin to be painted in 5 to 7 days, again skinning is dependent upon environmental conditions. Type M skins and sets more quickly and is a good option for production shops who need to build, glaze and paint sash before delivery.
This is the best production putty available and our parent company, Smith Restoration Sash used Type M for its own wooden windows for over 20 years without a single failure.
Keep in mind that Type “M” must be applied and finish painted before the sash are exposed to the weather, so the work must be completed while under cover.
The (almost) last question is “how much putty will my project require”?
This is a good and fortunately easier question to answer. We have developed a quick “putty calculator” to let you know precisely how much putty you need to order, just visit our website: http://srshardware.com/shop/sarco-multi-glaze-type-m-putty/ Scroll down and click on the putty calculator.
For wood window restoration companies and sash shops, SRS Hardware offers both putties in 5 Gallon buckets by special order.