Master Window Cleaners of America


Construction Window Cleaning

Fabrication Debris and Scraper Information

"Construction Window Cleaning" Seminar with Dan Fields Now on DVD

    Contributed by Dan Fields
    Fields Construction Services
    Technical Consultant to MWCoA

  1. Scratched glass is a major issue for Window Cleaners and builder's alike and fabricating debris is the number one cause.

  2. What is fabricating debris? What causes it and how it CAN be prevented by ANY fabricator who cares to produce QUALITY Tempered Glass?

  3. The fabricating debris issue needs to be exposed to all Window Cleaners and builders.

  4. Window Cleaners Tempered Glass WAIVER and why it's important.

  5. Education on scrapers, how they should be used and a clear understanding that they DO NOT scratch glass, ever.

  6. Construction Window Cleaning Basics.

  7. Dan Fields Seminar on DVD

The path to stopping scratched glass starts with the choices and decisions every general contractor makes when selecting material suppliers and subcontractors for their projects. Selecting only quality window suppliers and competent subcontractors will have a direct effect on the resulting quality of any house or building. Most scratched glass is related to, or is a direct result of fabricating debris.

The best solution for any problem is prevention. The general contractor and all subcontractors have a responsibility to insure all windows are protected during the entire construction process. This will help prevent harmful construction debris, such as paint, texture, plaster, and concrete from coming into contact with the glass surface. The more construction debris that is present on the glass, the higher the possibility of scratching when that glass is cleaned. Protecting windows during all phases of construction must be implemented and enforced if scratched glass is to be significantly reduced or eliminated.

The fabrication of tempered glass can be broken up into 4 major steps: sizing, edging, washing, and tempering. The details of each step are listed below.

Sizing the glass

The first step in the process of manufacturing tempered glass is to cut a piece of annealed glass to the desired size. The sizing of the glass must take place before the tempering process because attempted cutting of tempered glass with result in breakage.

Edging the glass

Once the sample is cut to the desired size, it is necessary to seam the edges of the glass. This is normally done with a diamond wheel grinder or sander, and results in a piece of glass with squared off and smooth edges.

Washing the glass

The sizing and edging work done in the previous steps generates fabricating debris which is deposited over the entire surface of the glass. For this reason, all glass should be washed prior to entering the tempering furnace. If this debris is not completely washed off prior to the glass entering the tempering furnace, the remaining debris will be fused to the glass, resulting in a surface defect. This is by far the major cause of scratching on defective tempered glass.

Tempering the glass

With the piece of glass sized, ground, and washed clean, it is ready for the actual tempering procedure. In this step, the glass is heated in a tempering furnace to approximately 1200F. The glass is then removed from the furnace and immediately quenched with cold air, reducing the temperature of the glass to 400-600F. This quenching produces the temper.

Most common types of tempering furnaces

There are three basic types of tempering furnaces most commonly used in the fabrication of tempered glass. The first and oldest of the three types positions the glass vertically (held by metal tongs) as it moves through the furnace. The second and most common furnace style in use today has the glass positioned horizontally on ceramic rollers. The third style is a gas hearth style, which transports the glass in a horizontal position on a bed of gas (at a 5 slope) and moves through the furnace with edge rollers.

Why does some tempered glass scratch?

The majority of the scratches found on tempered glass result from poor glass quality. The surface quality of tempered glass will have a direct effect on the possibility of scratching the glass during cleaning. Low-quality tempered glass has fabricating debris fused to its surface, which at the time of cleaning has a very high likelihood of being dislodged and dragged across the glass surface, resulting in scratching.

The source of fabricating debris

The third step in the process was to wash the glass after it had been sized and ground, but not all glass manufacturers do an adequate job at this step. Most problems in this area are related to the lack of maintenance to the washer and tempering furnace. If the glass washer and tempering furnace are not properly maintained, fabricating debris will build, making them less effective in cleaning and tempering the glass. Due to this, the glass will exit the washer with much of the fabricating debris still present as the glass is sent into the tempering furnace. Once the glass is inside the furnace, the debris will begin to liquefy and fuse itself to the roller side surface of the glass and to the furnace rollers. It is this fabricating debris that causes the poor quality surface and the scratching on defective tempered glass. When a window cleaner removes construction debris from the glass surface, they also remove these defects, which scratch the glass as they're moved across the glass surface.

Over time, the tempering furnace will also become contaminated with fabricating debris and must be serviced to clean the furnace rollers. To date, washing glass prior to tempering is not required or enforced by any regulation or standard.

All builders should know the difference between high and low quality tempered glass so they can make an educated decision about what is used in the windows installed on their projects. It is frequently encountered in the field, and has been repeatedly confirmed by experts, that some tempered glass will scratch during normal construction window cleaning. This scratching is a direct result of fabricating debris which was not properly removed from the glass surface prior to the tempering process. As a result, these particles are detached during normal construction window cleaning and cause major scratching, usually over the entire glass surface. During the past several years, defective tempered glass has been the leading cause in most cases of excessively scratched glass. The general contractor has a responsibility to select quality window manufacturers that will stand behind their products, if and when scratched glass problems arise.

Waiver Sample
Heat-Treated Glass Waiver To Builder:

Releasing Window Cleaner From Any Liability For Scratches on Heat-Treated Glass

(This includes both Fully Tempered and Heat-Strengthened glass)

Due to the widespread problems related to poor quality Heat-Treated glass, (Your Company Name) will not be held liable for any scratches on any heat-treated glass during construction window cleaning.  

It is accepted and understood by ALL parties that properly used razor blades and scrapers are standard tools and techniques for construction window cleaning and can safely remove limited amounts of construction debris (plaster, paint, texture, tape, stickers, etc.) from quality glass, without scratching the glass surface.  

Furthermore, it is accepted and understood that razor blades and scrapers will be employed on all construction window cleaning and no other cleaning method will be offered by (Your Company Name) to remove any construction debris from any glass surface.  

If Builder does not choose to have window cleaner use razor blades or scrapers, Builder must cover all glass during entire construction process, which would protect glass from any construction debris and could eliminate the need for (Your Company Name) to use razor blades and scrapers to clean glass.    

This clause must be included on all contracts. If this clause is not acceptable, there is no contract between (Your Company Name) and Builder.    

Please sign and date acceptance of this clause.

____________________________     __________________________     ____________________
            Building Contractor                                            Representative                          Date

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From Builder to Glass/Window Supplier:


Heat-Treated Glass Waiver for Builders

To All Window Suppliers

(This includes both Fully Tempered and Heat-Strengthened glass)

Due to widespread problems with poor quality Heat-Treated glass scratching during stan-dard window cleaning procedures, Builder requires Glass/Window Supplier to provide ONLY blemish-free glass surfaces on ALL windows requiring Heat-Treated glass.

This will enable cleaning contractor to employ standard construction window cleaning tools and techniques to remove any and all construction debris from windows without scratching the glass surface. It is also accepted and understood by ALL parties that properly used razor blades and scrapers are standard tools and techniques for safely removing limited amounts of construction debris (plaster, paint, texture, tape, stickers, etc.) from quality glass, without scratching the glass surface.

Any Heat-Treated glass with a blemished surface that results in scratching during clean-ing will be rejected by Builder. Such glass will be replaced at the sole cost of Glass/Window Supplier. This clause must be included in all contracts between Glass/Window Supplier and Builder.   No Exceptions!

Please sign and date acceptance of this clause.

____________________________     __________________________     ____________________
 Glass/Window Supplier/Distributor                        Representative                          Date 

____________________________     __________________________     ____________________
            Building Contractor                                            Representative                          Date

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Common Myths

There are many commonly held ideas about what is, and what is not, safe to use to clean windows. Unfortunately, many of these ideas are not valid. Below is a list of the most commonly spread falsehoods about glass scratches.

Window cleaning scrapers scratch glass. If used properly, a scraper will not scratch glass. This includes any size or style of metal scraper.

A nick in a scraper will scratch glass. This is also incorrect. Aside from leaving sections of the glass inadequately cleaned, and nick in the scraper with not adversely affect the glass.

Steel wool (#0000) will scratch glass. This is also false. Experimentation has shown repeatedly that #0000 steel wool with not scratch the glass surface.

The Facts

With some of the myths exposed, what are some facts about construction window cleaning? Construction window cleaning carries a very high risk of glass damage if excess construction debris is present or if the window cleaner is not properly trained.

Here is a list of what can cause scratches.
  1. Construction debris.
  2. Construction debris behind a scraper, or rust on a scraper.
  3. Construction debris or rust in steel wool.
  4. Construction debris in a strip washer.
  5. Fabricating debris fused to the surface of low-quality tempered glass during the tempering process.

Listed below are some basics of construction window cleaning that, when followed, can greatly reduce scratches.

  • Always keep the glass wet when scraping construction debris from the glass.
  • Use only new razor blades or sharpened scrapers.
  • Never move the scraper backwards on the glass. Construction debris caught behind the scraper can scratch the glass.
  • Notify the project manager at the first sign of excessive construction debris on the glass. The offending party should be held responsible for any extra cost or liability for removing the construction debris.
  • Get scratched glass waiver signed for all tempered glass prior to starting any window cleaning. For example, "(Your company name) will not be liable for any scratches on any tempered glass".

When glass scratches are noticed, it is helpful to observe the direction of the scratches. Many assume that if the scratches are in the same direction as the path taken by the window cleaner's scraper that he is to blame. Often times these types of scratches result from excessive construction debris or defective tempered glass, and are not the result of the window cleaner's scraper. Upon closer examination, it is often seen that the scratches do not extend from the beginning of the scraper's path to the end of the scraper's path. On defective tempered glass, as the scraper passes over each glass defect, it dislodges the defect and creates a scratch as it is dragged across the glass surface.

Plastic Scrapers

Metal scrapers have always been highly suspect for causing scratches. As a result, it has been occasionally suggested that the use of plastic scrapers would be a safer alternative. In an attempt to test this theory extensive testing on new clean tempered and annealed glass samples was done. These tests showed most tempered glass with excessive fabricating debris was scratched by the plastic scraper as well. The experiments also showed that as a result of their use on the defective glass, the plastic scrapers were contaminated with embedded fabricating debris. If this scraper was then used on quality glass, it would result in scratching every window it touched. These tests conclusively showed that the use of plastic scrapers is a destructive alternative to safe metal scrapers.

Construction Window Cleaning Basics:

Construction window cleaning includes the removal of several types of construction debris from glass surfaces, including plaster, stucco, concrete, paint, texture, taping mud, mortar, silicone, stickers, and tape. Removing this debris without scratching the glass is the real challenge of construction window cleaning. This article covers techniques and recommendations in meeting this challenge (it does not cover ladder use, which may be required).

Prior to Starting any Construction Window Cleaning

Before signing a contract or starting any construction window cleaning, it is highly suggested that you examine the entire project. A pre-contract inspection should give you a good idea of what to expect. You must always ask yourself, "Can the windows be cleaned without scratching the glass?" If not, this should be discussed with the builder before signing a contract.

It is also important to know your capabilities and the capabilities of your crew before attempting to take on a construction window cleaning project. Never consider accepting a window cleaning challenge a builder is proposing if you are not 100% confident you can remove all construction debris without scratching the glass. If windows are covered with excessive construction debris, you should consider the possibility that the glass is already scratched.

Most builders require their subcontractors to protect the home from the effects of their trade and to clean after themselves. Check other subcontractors' contracts to understand their responsibility for window protection during the entire construction process. Always keep in mind you will likely be the first person the builder comes to for the replacement cost of any scratched glass.

Lastly, it is vital to get any liability agreements or waivers in writing, prior to starting any construction window cleaning. Especially important is an agreement covering liability for existing scratches, scratches caused by others, and scratches caused as a direct result of defective tempered glass.

Note: Defective tempered glass is covered in more detail in the Glass Quality section of this site.

Required Tools

Before we can cover the proper procedures, it is important to make sure that you have the necessary tools. They are as follows.
  1. Soaps, acids and chemicals
  2. Bucket
  3. Squeegees (2 sizes, 14" & 8")
  4. Holsters and belt for tools
  5. Scraper (Razor or broadknife)
  6. Razor blades
  7. Small angled putty knife
  8. Green nylon pad
  9. Sponges
  10. Rags
  11. Window brush or stripwasher
  12. 12" flat fine mill file (for sharpening broadknife)
Strip Washer or Window Brush?

Due to the high amount of construction debris found in most construction window cleaning situations, we do not recommend using a strip washer. This debris can easily get caught in the strip washer, and result in scratching the glass. This is not as likely in a window brush as the bristles do not cling to the debris the same way the shag of the strip washer does. It is also much easier to clean this debris from a window brush. These issues, along with the fact that it can hold far more water, make the window brush the clear choice for construction window cleaning purposes.

Razor Scraper or Broadknife?

Razor scrapers are by far the most popular tool for safely removing construction debris from glass, without scratching. However, there are a number of drawbacks to razor scrapers.
  1. A razor scraper comes with a risk of serious injury to its user.

  2. Razor scrapers have limited use on heavy plaster and concrete, and frequent blade replacement is required as a result.

  3. Overnight storage of razor scrapers must be examined for iron oxide (rust) prior to reuse. Because rust on the blade of a razor scraper will scratch glass, razor blade replacement is required if any rust is present.

  4. Aside from the inconvenience and time loss related to frequent blade replacement, there is also the issue of high replacement costs for the physical blade itself.
Prior to the development of razor scrapers, broadknives were the scraper of choice for removing construction debris from glass. This method has been employed for over 40 years, and brings with it some of the following benefits.
  1. Broadknives have a far reduced risk of injury to its user compared to a razor scraper.

  2. Broadknives are very durable and work well to remove heavy plaster and concrete from glass, without as much damage to the scraper.

  3. Replacement cost for a broadknife is $6-8 and is only required about once per year.

  4. If a broadknife is damaged or gets dull, it can be easily resharpened with a fine mill file.
The choice between a razor scraper and a broadknife is one that depends on the situation and your personal preference. However, the durability and safety associated with a broadknive, combined with the inherent risk and cost of replacement of a razor scraper, makes the broadknive our tool of choice.


Soaps, Chemicals, and Acids

The use of soaps and chemicals can greatly assist in the window cleaning process. However, it is important that you know which product to use in which situation. Listed below is some information to assist in this selection.


The selection and use of soaps in window cleaning applications is often misunderstood and overcomplicated. For most window cleaning projects, soap is not a key issue. Only use soaps that you know will help in the process. Sometimes, no soap is better than too much soap or the wrong soap. Rarely is more soap better. It's important to first select which type of soap to use, and then determine the amount to use. At Fields CSI we use Fields WPR, a soap that is manufactured for us. However, many window cleaners use dishwashing soap, which is usually sufficient for normal paint removal.

Chemicals and Acids

When encountered with more than just paint and dust on the window, many times it is necessary to use chemicals to aid in cleaning the glass. We use Fields Scale Remover, a product that is manufactured for us. It is used to loosen plaster, stucco and concrete from the glass surface, prior to scraping. This product will also remove the film (effervescence from cement) that runs down the glass during and after plastering exterior walls. Fields Scale Remover contains phosphoric acid, a key ingredient in the removal of concrete, plaster and mortar from glass. Products containing phosphoric acid help dissolve the cement in construction debris and make it much easier to remove. Any chemicals or acids you decide to use should be tested to be safe for human use, the building exterior, and the IG (Insulated Glass) seals.

The Construction Window Cleaning Process

Start off by filling your bucket 2/3 full with water. The more water you have in your bucket, the cleaner the water will stay. If you have sponges that have soap in then from a prior use, now is the best time to remove it. The best way to accomplish this is by squeezing the sponge a dry a possible. Then, while still squeezing the sponge, submerge it in the bucket of fresh water and release. Once the sponge has filled with water, remove it from the bucket and squeeze it out, making sure that the water does not go back into the bucket. Repeat these steps as needed. If your application requires the use of soap, add the soap after the bucket is filled to prevent suds.

If you have chosen to use a broadknife rather than a razor knife, now is a good time to sharpen the knife. When sharpening a broadknife, the goal is to create a smooth, squared-off end. The knife should not be sharp to the touch, but the faces of the knife should come straight down and meet the edge at a 90 angle. Using a towel under the file can help smooth out the sharpening. Next, sharpen the small angled putty knife for cleaning window frames. Always clean scrapers prior to sharpening to prevent rust and debris from contaminating the file. Keeping the file clean can greatly increase the life of the file.

Note: Razor scrapers can be used in place of a broadknife.

Cleaning Inside Windows

Whenever possible, the inside windows should be cleaned before the outside windows. This is advised because the cleaning of the inside window will require opening and closing the window, which could result in leaving streaks on the glass. It is also advised that the window tracks be vacuumed prior to cleaning the window. With this in mind, here are the steps to cleaning the inside windows.
  1. Wet entire window, frame and track with window brush.

  2. Remove any stickers with a small razor blade, while glass and frames are soaking.

  3. Clean window frames and tracks with the little angled knife in one hand and the green nylon pad in the other. The green pad should be kept wet at all times. It is important that the green pad never touch the glass, as it will scratch. Also, avoid contact between the green pad and textured window jams so as not to remove any of the texture.

  4. Remove all excess texture and taping mud (if any) from glass with scraper. Use single upward motions and throw into empty bucket.

  5. After excess texture is removed, rewet glass with window brush.

  6. Start scraping the glass with the window brush in one hand and the scraper in the other. Scrape the glass nearest to you first to prevent splash back. When scraping, have a pattern or system to cover every inch of the glass. The method we use starts with a stroke across the top, and then down the right side. We then go back to the top of the window, where we work down in rows, from right to left.

  7. After glass is entirely scraped, rewet glass with window brush.

  8. Sponge down window frame and tracks. Touch up the frames with green pad and angled knife, if needed.

  9. Sponge down perimeter of glass, prior to squeegeeing.

  10. Squeegee the window nearest to you first. If you start with the window farthest from you, it is likely you will splash water onto the finished pane while squeegeeing the window nearest to you. On hot days, you may need to rewet the window. In construction window cleaning we choose not to fan squeegee our windows because the windows are usually too small. Also, sand and other debris could be a problem with this method.

  11. Sponge out window track, if there is one.

  12. Touch up glass and frames with rag as needed.
Cleaning Outside Windows

If the outside of the building is stuccoed, we recommend using Fields Scale Remover (or any suitable product with phosphoric acid) to assist in removing stucco and concrete from glass and frames. The process for cleaning exterior windows is similar to that for cleaning interior windows. The process is listed below.
  1. If stucco is present on the glass, run a stream of Fields Scale Remover (or other phosphoric acid) across the top of each window before wetting the glass. As it runs down the glass, spread over entire surface with a slightly wet window brush. DO NOT let acid run down stucco.

  2. Wet your window brush again and wet the entire glass, and frames if needed.

  3. Remove any stickers with razor blade, while glass and frames are soaking.

  4. Clean window frames and tracks with the little angled knife in one hand and the green nylon pad in the other. As discussed above, make sure that the green pad does not touch the glass.

  5. Rewet the glass and start scraping the glass with the window brush in one hand and the scraper in the other. Again, scrape the glass nearest to you first to prevent splash back.

  6. Rewet glass with window brush.

  7. Sponge down window frame and tracks. Touch up the frames with green pad and angled knife, if needed.

  8. Sponge down perimeter of glass, prior to squeegeeing.

  9. Again, squeegee window nearest to you first to prevent splash back. On hot days, you may need to rewet the window. In construction window cleaning we choose not to fan squeegee our windows because the windows are usually too small. Also, sand and other debris could be a problem with this method.

  10. Sponge out window track, if there is one.

  11. Touch up glass and frames with rag as needed.

The information on this site represents the views and opinions of its contributors and is intended for educational purposes only. Any information taken from this site, and any results thereof, are the sole risk of the user.
Fields Construction Services Inc. and MWCoA accept no responsibility for the interpretation or use of any information on this site.
Material on this page by Dan Fields,  MWCoA Technical Consultant   -   Copyright Laws apply.