Can Elastomeric Waterproof Coating Go on a Tar & Gravel Roof?

Gravel Roofs

• Tar and gravel roofs are made out of layers of heavy roofing felt and hot tar covered by gravel. These roofs are either flat or have a rise of no more than three inches for every 12 inches the roof runs. Because of this flatness, these roofs can have a tendency to develop standing pools of water that can damage the roof beneath them. These pools are not always easy to spot, as they can be hidden by the gravel. Additionally, service people walking on the roof to fix leaks, install satellite dishes and do other maintenance actually can grind the gravel into the layers beneath it, poking holes in the roof. Tar and gravel roofs are prone to leaking problems and consequently have limitations and are not intended for localities with large amounts of rain or heavy snowfalls.

Elastomeric Waterproofing Application

• Elastomeric waterproof coating can be applied with a trowel or a brush. It can also be applied with a sprayer. All of these devices apply it to the upper surface of the roof. These methods of application make this waterproof coating inappropriate for use on tar and gravel roofs.

The Problems

• Because the coating can only be applied to the top of the gravel, it may not be able to make the flawless coat that is needed for a waterproof seal. It is nearly impossible to coat all the surfaces of all the pieces of gravel from every angle, and gaps will form. Even if it could be applied so thoroughly that no gaps would form, a gravel surface is bumpy and irregular. It would take much more coating to make a seal on a flat roof and would be much more expensive.

The Solution

• The only practical method of using the elastomeric waterproofing on a tar and gravel roof it to first remove all of the gravel. The roof can then be covered with a different type of roofing. It might not be wise to simply put down new gravel, as it could poke through the membrane formed by the waterproofing.