Service Bulletin 10-3-97 

Diagnosing Electrolysis

Coating Sheet Rubber

Coating Plywood

Recoating Liquid Roof

Service Bulletin 104

Alpha Rubber

Diagnosing Electrolysis:

The term electrolysis generally describes a condition where an aluminum or galvanized metal roof skin corrodes from underneath. The metal acts as a catalyst causing the adhesive bonding it to the plywood to decompose. Some of the decomposition products then react with the metal causing pitting and loss of adhesion. This condition will continue at an unpredictable rate until the catalytic effect of the metal is lost or the adhesive completely degrades. 

Advanced stages of electrolysis can be recognized visually. Make a 2” T cut and bend the skin back. If there is poor or no adhesion to the plywood and the underside of the skin appears mottled or rough then the electrolysis process has already begun. The beginning stages will be more difficult to recognize but will start with loss of adhesion and then progress to eroding the metal. 

DO NOT apply Liquid Roof® to a roof diagnosed or suspected of having active electrolysis. The coating will eventually fail as the skin deteriorates from underneath. Removal of the metal skin is the only way to stop the electrolysis. When pitting or corrosion is only on the topside of the metal, it may be top-coated with Liquid Roof®.

Liquid Roof® over Sheet Rubber:

Liquid Roof® is recommended for application over sheet rubber because it is the same chemistry and has identical flexibility and weathering characteristics. Liquid Roof® does not chalk and can be used to eliminate the chalking of sheet rubber. When a solvent containing product like Liquid Roof® comes in contact with sheet rubber, the applicator should be prepared for a phenomenon which will make it appear as if something has gone radically wrong. Some of the solvent in Liquid Roof® will be absorbed by the sheet rubber and cause it to swell. If the sheet is not glued tightly to the plywood the swelling causes wrinkles or bubbles to form. Depending on the temperature, this condition will persist for days or sometimes weeks. However, as the Liquid Roof® begins its cure process and solvent slowly evaporates, the sheet will shrink and return to its original shape.  Do not apply Liquid Roof® in a heavy film as this will aggravate the swelling reaction in the sheet.

Coating Plywood:

Liquid Roof® has been used directly over plywood to make a finished roof in situations where expediency and minimal cost were the primary considerations. Although this procedure results in a weaker roof structure, water-tightness can be achieved if the application is performed carefully. 

The joint between sheets should be positioned directly over a roof truss and securely fastened to prevent warping. Next, to seal the pores, coat plywood with oil based exterior primer paint. Allow an overnight cure. Seal the joint by bridging it with 3” wide pieces of Butyl Tape and Polyester Fabric.  Complete job by applying a liberal coat of Liquid Roof® over entire roof surface, being especially careful to completely cover the fabric over the joint without skips or pinholes. 

Using an oil base primer on the wood considerably improves the appearance of a one-coat application of Liquid Roof®.

Recoating Liquid Roof®:

Since Liquid Roof® cures by chemical reaction, a single heavy application will be preferable to multiple thin coats. A second coat will bond to a previous film but that bond will not be as strong as the internal bond within each layer. 

If a second coat is applied before the first has thoroughly cured, some wrinkling may result as the first coat absorbs solvent and swells. This will, however, recover as the solvent evaporates

It is generally recommended that only a single coat be applied over non-porous surfaces, the thickness of which can be varied as desired. Thicker films will take longer to cure through. 

Liquid Roof® and Alfa Rubber

Pro Guard Coatings, the manufacturer of Liquid Roof®, has received a number of reports from dealers and private users of Liquid Roof® that have described a condition similar to the following: 

.....”We applied Liquid Roof® over an existing rubber roof one or two years ago and now it is tacky, leaves are sticking to it, and it has turned gray”…..

After some considerable probing we are able to establish that the rubber that has been coated over was of the ALFA brand that has a distinctive cream color. The common denominator for the Liquid Roof® starting out appearing normal but then becomes “tacky” after one or two years seems to be the ALPHA brand of rubber. 

The technical explanation for the process that is softening the coating and making it tacky is “reverse polymerization”. This is a process of decomposition that slowly reduces the rubber to its starting point composition. The suspect cause for this is the antioxidant used in the ALPHA rubber. 

CONCLUSION:

Do not apply Liquid Roof® over cream color ALPHA rubber.

RECOMMENDATIONS:

Use Liquid ProPoly® or RV Roof Aid™ coating in place of Liquid Roof®. Liquid ProPoly® or RV Roof Aid™ is a flexible, one coat, liquid urethane rubber roof membrane.  Liquid ProPoly® or RV Roof Aid™ has similar properties as Liquid Roof® but is stronger.   Liquid ProPoly® or RV Roof Aid™ coating will not cause a swelling reaction in sheet rubber due to solvent absorption. 

The information presented herein is furnished free of charge and is based on technical data that Pro Guard believes to be reliable. It is intended for use by persons having technical skill and is at their own discretion and risk. Since conditions of use are outside our control we make no warranties, express or implied, and assume no liability in connection with any use of this information. Nothing herein is to be taken as a license to operate or a recommendation to infringe any patents.
 

EPDM Liquid Rubber®

Liquid ProPoly®

RV Roof Aid™

Glass

Plastic

Paper

Proflex® Crack Filler for Asphalt Paving

Proflex Primer®

Butt Putty® Crack Filler Gel for Masonry

ProFill®

Propoxy® 2228

Propoxy® 2468

Propoxy® 3009

Masonry

Tile

Wood