Surface Preparation for Roof Coating
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Surface Preparation for Roof Coating

Once you as commercial roof contractor have correctly identified the composition of the substrate, which we covered in our previous blog titled “Commercial Roof Substrates Overview”, and have determined it to be sound and dry, the next step is repairing flaws and preparing the surface for coating.

Above all, the application surface must be smooth, free of grease, wax, dirt, contaminants, moisture and other matter, which would interfere with adhesion. It must also be free of loose roofing material or other debris.

When preparing your substrate, you will need certain tools and equipment, depending upon the substrate in question. A complete listing of equipment used in roof preparation can be found at the following link: Roofing Tools and Equipment List. Consult this list for a guide of needed rental tools before you begin surface preparation.

Proper Aging of the Roof

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Before repairing or coating a built-up asphalt roof, one must consider its age. Before applying the coating over recently-applied asphalt roofs, it is necessary to allow the asphalt to dry and cure properly. Asphalt must be free of oil or solvent surface residues in order to permit proper bonding of the coating. Consult the proper curing times chart for curing times. Under poor weather conditions, longer periods may be required.

Proper Curing Times

New hot mop roofs                                         30 days
New cold process roofs                                  60 days
Old roof recoated with cut-back asphalt        30 days

Preparation of Built-Up Roofs

Built-up roofs are prone to alligatoring, splitting, blistering, delamination, gravel turnover, exposed felts, and other signs of age. Exposure to ultraviolet light over time gradually causes loss of flexibility, encouraging brittleness and the inability to tolerate the normal expansion and contraction that occurs on a roof. Severe deterioration (more than 30%) requires tear-off and replacement with an approved substrate. Read the following brief descriptions and illustrations of many of the common problems and the treatments required prior to normal cleaning procedures.

Alligatoring

An alligatored roof is one in which the surface is severely weathered, usually with cracks that are criss-crossing and running in various directions. This is the sign of an old, brittle roof, with limited years of service left. Applying a new system over an alligatored roof will merely mask the problem and will not hinder the deterioration underneath. Alligatored roofs should be removed completely and replaced with new materials before a Conklin roofing system is applied. If the owner does not agree to this expense, you may want to reconsider taking the job, as the performance of your new system over this deteriorated substrate is questionable.

Splitting

Splits in a roof can result from a number of conditions. It could be that substantial movement has occurred in the roof deck, causing stress to the roof and resulting in cracks. This possibility bears careful investigation. If the whole building is subject to continued structural movement, your coating will almost certainly crack and fail prematurely.

If structural movement is not apparent and the deck appears sound, the roof itself could be nearing the end of its life expectancy. In this case, splitting is a result of the roof becoming dry, brittle and intolerant of the normal expansion and contraction of the roof deck. A complete tear-off may be necessary.

If the splitting is evident only in isolated areas, the cracked areas need to be cut out from the roof deck and replaced with new, stable materials. With the material removed, you should conduct a moisture check to determine if water has seeped in through the cracks down to the insulation. If so, the wet insulation must also be replaced.

Blistering

Blistering is a sign of trapped moisture. All blistered areas must be removed with the underlying insulation checked for dampness and replaced if necessary. An approved roofing material such as polyurethane foam or boardstock must then be used to fill in the void before coating with a Conklin system.

Gravel Turnover

On thick built-up asphalt roofs, the aggregate frequently sinks below the surface, bringing the asphalt to the top. This is indicative of excessive thickness and weight, either in isolated areas or over the entire roof surface. All such areas must be replaced with approved materials before coating.

Felt Exposure

This condition indicates that the asphalt has eroded away completely from certain areas, leaving a dry, brittle and unstable surface. Any portion of the roof where felt is visible must be removed. Replacement with approved roofing materials is required prior to coating.

Delamination

Delamination can refer to the separation of the various layers of a built-up roof or can refer to the actual pulling apart of the lamination of a plywood panel. In either case, an unacceptable substrate condition exists. The affected areas must be removed and replaced with approved materials.

Removal/Replacement Guidelines

Some rules to keep in mind whenever replacing faulty or deteriorated roof sections are:

  • Always use approved roofing materials in your replacements.
  • Ensure that the new surface is uniform; this will simplify the applications of your coating product.
  • Avoid the use of caulking compounds to fill in large gaps or voids; caulk may extend drying times.
  • After removing any portion of a roof, the same rules apply for the cleaning and preparation of the surface. Any dust or debris resulting from the repair procedure must be removed. The whole surface must be cleaned and dried before coating can take place.

Preparation of Alligatored, Built-Up Roofs

Alligatored roofs are nearing the end of their life span. Exposure to ultraviolet light and temperature extremes have made them a brittle and unstable substrate, which cannot be directly coated with any Conklin roofing product. Alternate methods include:

  • A complete tear-off of the built-up roof down to the original deck.
  • Installation of a divorcing membrane such as Conklin-approved isocyanurate insulation board to provide a stable substrate for the coating, prepared according to requirements for boardstock.
  • Installation of approved plywood by the American Plywood Association (APA); AC, BC, or CC plugged exterior sheathing (15/32” thick), mechanically fastened to the deck, then prepared according to requirements for plywood.
  • Sprayed-in-place polyurethane foam over the built-up roof.

Graveled Built-Up Roofs

Direct application of Conklin systems over a graveled built-up roof are difficult applications due to the poor adhesion and excessive amount of material needed to develop a continuous membrane on this irregular surface. Even calculating the true surface area and the amount of product to use is a challenge since gravel can increase the actual surface area by up to 75%. In addition, the likelihood of pinholes occurring in such an application is high due to the roughness of the surface.

As with the smooth built-up roof, it is important to recognize the possibility of splitting in the substrate, leading to splits in the coating system itself.

New Substrates Over a Graveled Built-Up Roof

A preferred alternative to attempting to repair and prepare a graveled built-up roof is to remove gravel and install a new, sound substrate over the existing roof.

The installation of a new, properly fastened substrate will “divorce” the new system and protect it from splits, which may occur in the graveled built-up roof underneath. With the addition of insulation board or foam you can expect increased energy savings, plus better drainage through added slope.

Preparing Boardstock or Plywood

The installation of boardstock or plywood is a common solution to the problem of unsuitable or unstable substrates such as wood decks, graveled built-up roofs and certain concretes.

Preparation of these two materials for direct application of a Conklin roofing system is as follows:

All joints and seams must be caulked and taped with Conklin SpunFlex fabric. For installation of polyurethane foam or the Hy-Crown single-ply membrane over boardstock, the caulking and taping procedure is not necessary.

The taped boardstock or plywood installation should be checked for surface dust or debris and swept if necessary before any coatings begin. Check for moisture content if there has been rain or heavy dewfall. These materials must be completely dry before coating.

Preparing a Metal Roof

When preparing a metal roof for the application of the MR System, the following procedures must be followed:

  • Inspect the roof for signs of surface rust and remove by wire brush, sand blasting, manual scraping or acid etching.
  • Acid-etch surface of galvanized metal with a 1:20 solution of Rust Off rust and oxide remover and water to clean all conditions, which will affect bond of roof membrane. Follow with a thorough water rinse. Power wash and scrub all other surfaces.
  • Clean until free of loos, flaky rust, and prime whole roof with Conklin’s Metal Ready Universal rust-inhibiting primer.
  • On new exterior metal surfaces, remove oil contaminants by wiping the metal with a coarse cloth and mineral spirits. Conklin coatings require all galvanized surfaces to be “etched” (roughened) first. Most surfaces should be allowed to “weather-etch” by leaving exposed and uncoated for three to six months. As an alternative to weather etching, clean the metal with an acid such as Conklin’s Rust Off cleaner.
  • Retighten all fasteners and secure substrates firmly. Replace fasteners or washers where missing. When prior movement has enlarged the fastener hole, install a new oversized fastener to effectively tighten and secure the deck substrate. Kwik Kaulk all exposed fastener heads and seams wider than 1/8”
  • Just prior to application, remove all dirt, dust and other contaminants by brushing, vacuuming or power blowing.

Preparing a Concrete Roof

Concrete systems may take many forms. Most frequently used as a decking material, concrete can also serve as the substrate for your roofing system. However, there are special requirements for its successful preparation.

First, check the surface for “efflorescing,” indicated by the presence of a white, powdery material (salt deposits), which has leached to the surface. If this condition exists, the surface must be etched with a ten to fifteen percent solution of muriatic acid and water, then rinsed with water to remove all traces of mineral deposits. The roof should then be allowed to dry thoroughly, verified by some method of moisture detection, before application of a Conklin product.

Another phenomenon frequently encountered is “spalling,” the chipping, cracking or peeling of the top layer of concrete. In this case, all loose or chipped material must be removed and any depressions filled with an appropriate cement patching material, which must then be allowed to dry.

Small cracks in concrete surfaces are a common occurrence, due to the seasonal expansion and contraction of roofing materials. Large cracks may indicate more serious structural damage to the building and this possibility must be thoroughly investigated before proceeding. Minor cracks of ¼” or less should be filled with Kwik Kaulk acrylic or 360-S caulking compound. Larger cracks must be carefully re-grouted and struck smooth. All patching treatments must be allowed to dry thoroughly before any Conklin coating is applied.

Cleaning the Roof

Assuming that all necessary repairs have been made to an existing substrate, you may proceed to the next step in surface preparation, cleaning the roof.

Many types of equipment are available to provide the best possible cleaning for each roof.

In general, a dry method of preparation is initially recommended. Professional sweepers, power brooms, scratchers, power blowers, spudders and similar roofing equipment should be used to remove any loose material from the roof.

Removal of gravel from a roof is most easily accomplished when the asphalt is cool, such as in the early morning hours. Vigorous manual sweeping assists in this procedure. On a built-up or graveled roof, a high-pressure washer is extremely effective in removing embedded dirt. However, it is essential when using a wet method to first seal all cracks or holes in the existing roof prior to washing, so that no water seeps into the roof or insulation beneath.

It is crucial that cleaning be thorough and complete. The longevity and performance of your roofing system depends on it!

Preparing a Weathered Conklin Roof

You can prepare a weathered Coklin acrylic roof for recoating by using Conklin’s Weathered Acrylic Roof Cleaner (WAC). WAC II is a highly-concentrated cleaner designed specifically for cleaning weathered Conklin acrylic roofing systems prior to recoating. The product is applied through a power washer or airless sprayer to thoroughly clean all dirt from roof surfaces in one step, followed by a water rinse. Extremely dirty areas may require scrubbing with a stiff bristle broom to remove all dirt. WAC II increases surface adhesion, enabling you to apply a new top coat over an older Conklin acrylic system without needing to apply a new base coat.

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