Wednesday, July 29, 2009

GACO Silicone Roof Coating - flat roof repair

Quick Conclusion: GACO Silicone Roof Coating is a superior solution for flat roof water proofing. Easy to prepare and apply. Highly recommended, even at the high price.

A few years before I was born, my parents built our home, circa 1954, with sweat equity. My father's idea, to facilitate self-maintenance, was to build it with a flat roof.

Unfortunately, the flat roof had less than 5% slope. So over the decades it has been prone to more leaks than has been necessary.

After my father's death in 1988, I was left with the maintenance chore.

The primary surface had been layers of heavy paper roll roofing coated below and on top with spread asphalt (spread tar).

In 1991 I found a new roll roofing of polyester cloth, which had superior expansion and contraction tolerance than the heavy paper roll roofing - the paper would readily crack in the course of one year, requiring repeated patching.

So I surfaced the main roof and carport with spread asphalt, polyester cloth roll roofing topped with another layer of spread asphalt. Once the asphalt dried, I topped with a single coat of aluminum paint to reduce sun and weather deterioration to the tar asphalt. This solution lasted well for about 10 years with no significant leak repair required - the polyester cloth would not crack from the expansion and contraction.

From 2002 to 2006 I had to do some minor leak repairs, but far less often than with the paper roll roofing and spread tar.

By 2006 there was one persistent leak area.

For a few years I had seen a new roof coating of silicone rubber, GacoRoof Silicone Roof Coating, which was among the most expensive elastic roof coats. By this time I could no longer locate any of the polyester cloth roll roofing - I had a half roll remaining from the 1990's.

So I chose to try the silicone coating for the recurring leak area, at worst needing 2 or 3, 5 gallon buckets, $350 to $400, for the test.

I used the same patching layer strategy of wet coating first, with a cutting of polyester cloth over the worst cracking, topped by a wet coating of the silicone spread. Letting the silicone coating cure for at least one week I applied the second silicone coating per the Gaco instructions.

Since the rest of the roof was still in good shape, I let the test area idle through the winter of 2006 - '07. Not one drop came through the new application, and by late spring 2007 there was no sign of cracking.

Pleased with the result I chose to complete the rest of the main roof and carport with 2 coats of Gaco Silicone Roof Coating. I used only a small amount of polyester cloth to reinforce suspect spots of cracking. The summer of 2007 I coated the main roof. I completed the carport in the summer of 2008.

As of this writing (July 2009) there have been no leaks through any of the areas coated with Gaco Silicone Roof Coating. I see no signs of cracking.

Why Gaco Silicone Roof Coating?

You will discover that the Gaco Silicone Roof Coating is the most expensive of the elastic roof coatings - there are at least 2 other elastic roof coating brands, but without silicone. The deciding factor for me was that all the other elastic roof coatings required a primer treatment to apply another layer of their coating product. Gaco Silicone requires no primer treatment for the second coat to adhere. I was willing to pay more to eliminate a whole application treatment.

When I waited for local hardware store sales, I was able to buy the Gaco Silicone coating at $165 to $180 per 5 gallon bucket, down from the normal $200 to $220 price. I used a total of 15 - 5 gallon buckets to apply 2 coats on the main roof and carport, so a total cost of approx. $2,700 for the whole project. I was probably applying the silicone coating thicker than recommended. The 1991 full roof surfacing (polyester cloth roll + tar coating) was probably just less than $2,000. I was the sole labor for both projects.


The photo below (Sept 2007) shows the general condition of the main and carport roof beginning in 2006. The light areas are the aluminum paint from 1991 wearing off from weathering. Unless there was cracking of the underlying polyester roll cloth + tar coating, this surface was still leak proof. [click pic for full size - all pics]

The only surface preparation I did was sweeping away surface dust and dirt, I did not power spray with water. In one limited area on the main roof, I used a pocket knife to scrape away some small moss build up. I did not treat the moss area with any herbicide.

Below are the tools I used to complete the project - broom to clean surface, flat head screw driver to open bucket tabs; roller-spreader with low cost roll-brush; heavy plastic stick to stir-mix silicone coating. I used no mineral spirits for clean up - I let the used roller cure, then removed and discarded, replacing with a new roll-brush. It would take about 15 minutes to mix the silicone coating with the plastic stick. You can use a power mixing method, but I found manual mixing satisfactory.

Application / Result

The following pictures are the main roof, with silicone coating. The dirty (dusty) areas are the initial patching test from 2006. The dust accumulation does not appear to affect the waterproofing of the silicone coating. The fresh coated areas are the bright white. The bright white of a new coating will dull and dust up after one winter. The main roof was completed in 2007. Small black rectangle along the roof edge (left) is one of the 2 drains, at the low end of the roof.

Following pic is to the right of the image above, 2nd drain in right far corner ...

Another angle of the 2nd drain (now at left corner of pic, just "below" the car) ...

Corner of roof above 2nd drain, high side of roof at the upper right of pic ...

Roof above 1st drain shown (high end of roof) ...

The results on the carport roof are the same as for the main roof, so I show no pics of completed carport roof.

General Notes / Comments
  • For leaking cracks, I did the following - cut your patch cloth; spread wet silicone coating around crack; adhere patch cloth to wet silicone coat (roller down into wet coating); top cloth with wet silicone coating. Allow the 3 layers to cure (I did one week), apply 2nd coat of silicone spread. I have not seen any layer separation with this patching sequence.
  • Using this silicone coating, with minimal crack patching with cloth where needed, was far easier than the 1991 surfacing. Very easy application.
  • I did no surface tear up of old, previous layers from 1991 and earlier.
  • The dulling and dusting of the silicone surface does not appear to impact waterproofing - the surface is not degrading. Retaining the bright white may be nearly impossible.
  • Do not use footwear which will puncture or scar the silicone surface - I use a generic rubber soled boot.
  • I allowed 3 days to one week for the first coating of silicone to cure, before applying the 2nd coat.
  • I strongly recommend following the instructions of applying 2 silicone coatings; one coat will be too thin.
  • Caution/Danger - once you get your silicone surface completed, you must be EXTREMELY careful walking on the surface when wet with water, or with ice and snow.Traction is nearly non-existent with water or ice/snow on the surface of the silicone.
  • I was only able to find the Gaco Silicone Roof Coating at a regional hardware vendor (6 stores around Seattle), McLendon's Hardware - the big box hardware stores did not sell this product!!!
  • Do not let the high price of this silicone coating deter you from using it - it appears to be worth every penny, for the quality of waterproofing and ease of application (remember, no primer prep for 2nd silicone coat!!!).
  • My expectation is that this coating will easily last 10 years, and I hope far longer - I expect a longer durability than my 1991 surfacing.
  • I am not a roofing professional, and have no business connection with Gaco company - I am your generic home consumer. I have not been paid for this review and opinion.
Price Tracking

This section will note Gaco Silicone Roof Coating prices, as I see them advertised (locally). McLendon's Hardware has an annual founder's weekend sale around mid-August, with 20% off, probably the best price break of the year.
  • Aug. 1, 2009 sale flyer - McLendon's - 5 gallon, $219.99 sale, $239.99 regular; 1 gallon, $49.99 sale, $54.99 regular
--- West Seattle, Washington State



  1. I would like to appreciate you the way you have presented your opinion. Images you have shared with us were really exclusive one.

  2. Excellent report. The GACO site says you only need to let the first coat cure enough that you can walk on it before applying the second coat.

    About three summers ago, I found the GACO gallons were cheaper at Dunn Lumber (Renton).
    Using it on a deteriorated plywood shed roof, I applied three or four heavy coats and it saved me from replacing the plywood.

    I'll likely buy the five gallon containers and coat the torch-down roof on my addition. In addition to adding years of life, I hope for cooler temperatures inside during the summer.

  3. On Febr.3, 2011 I purchased 10 five gallon drums of Gaco Roof Coating from a local supplier for my 2500 sft flat roof. I had not used the product before and I am not a professional roofer. When we opened the first container it had a very thick (1 to 1 1/2") layer of hard material. I called the Gaco Customer Service office for advice and they suggested to skim the layer off and use the rest of the material.
    We found that the application of the material was very cumbersome and back straining as well as very time consuming. We continued the same way with the remaining containers until we come to a container with a different lot #.
    This material went on like a charm, more like paint than the glue like substance we found in the other containers. Due to the poor material we received in the first containers we spend an extra day of applying the coating resulting in additional labor cost for the project.
    We have not been able to finish the project because of the "defective" material that we received and because the gluelike substance of the material made us use more material than you usually need.
    I am currently in discussions with my supplier and Gaco to see how this issue can be resolved.
    The moral of the story: If you start a project, open all the containers to check if they have any significant layer of hard material on the surface. If
    any of them do, return the product immediately otherwise you will be using more material than necessary because of the thickness of the material below the surface layer plus you will be breaking your back to apply it. If you use paid labor, you will be spending more money than necessary to apply the product.
    anonymous in Miami

  4. Thanks for posting, i am really glad to check out this information, this is really what we all need to know and i am sure we all can get lots of benefits through this post, keep posting.

  5. Thanks for the informative write-up, very helpful.

    For your readers that aren't able to find the product stocked locally, World of Stains can deliver the GacoRoof directly to them at a reasonable price.

    Find GacoRoof at this link:

  6. I work for a professional water proofing company in San Francisco, we have been using Gaco for a few years now and here is what we learned. Gaco works great over metal surfaces, gutters etc, If you are going to apply it over a tar roof do not use the primer. The primer tends to crack over this type of surface. The Gaco will stick just fine without the primer and is more flexible without the primer. Make sure you apply enough material near trouble spots and up corners into parapet walls.

  7. Some really good advice here, I just wanted to update this with news that Gaco Western has brought out the GacoRoof in a factory tinted Gray color. This eliminates the need to mix in any colorant.

    If you want a white roof, the Gray is still handy to use as the first coat, as it can help you to monitor your coverage and make sure that you have hit every surface evenly.

    You can find it here at this link:

  8. GacoRoof is now launching various colors matching many of the metal roof colors. Green is already out and matte black and colonial red are next. Tahoe Blue, Bronze, Tan, Red and a brown are also on the list too. They will custom make any color if it is 180 gals+ order.
    Saw the new colors at the National Hardware Show in Vegas this week. Love this stuff. If you have a flat or foam roof this is the only way to go. They are going after low pitched metal roofs here. They also have a new Liquid Roof Tape-Dry Patch coming out. Silicone with micro fibers for crack ,seems, fasteners and high traffic areas.