Appying Dow Contractors Weatherproofing Sealant

Joint Design

While most urethanes suggest a depth of 1/2" to 5/8" in wide joints, the excellent weathering of this silicone adhesive allows a 3/8" depth in wide joints. Dow Contractors Weatherproofing Sealant can be used in the following joint configuration:

  1. Minimum width of joint should be four times the anticipated movement, but not less than 1/4" in width
  2. Joint depth to be 1/4" for joints 1/4" to 1/2" in width.
  3. Maximum joint depth is not to exceed 3/8"
  4. Maximum joint size approximately 1-1/4" wide x 3/8" in depth in a single application.
  5. Consult your local Dow representative for specific design requirements.

Surface Preparation

The joint interface must be clean, dry and free from any oils, loose mortar, laitance, form release agents, waterproofings, damp-proofings, and other type of contaminants. A thorough wire brushing, grinding, sandblasting, or solvent cleaning may be required to expose a clean, sound, pure surface.


Dow Contractors Weatherproofing Sealant is primerless on most common nonporous building substrates. Consult Dow for priming recommendations on other materials. Should a primer be required, apply it before installing the backer rod. Applying a bead of silicone sealant directly to the substrate material to test adhesion effectiveness prior to its general use is always recommended. A good piece of advice is to perform a test using a sample of this product to ensure compatibility.


Areas adjacent to joints should be masked to ensure neat sealant lines and to avoid contact with polished granites, metal, or glass. Never allow masking tape to come in contact with clean surfaces where the sealant will adhere to. Masking should always be removed immediately after gunning.


Install backer material or joint filler, setting blocks, spacer shims, and tapes, as specified. Apply silicone adhesive sealant in a continuous motion using a steady pressure adequate enough to properly fill the void and seal the joint.


Dow Contractors Weatherproofing Sealant is neither tested nor represented as suitable for medical or pharmaceutical uses.

Dow Contractors Weatherproofing Sealant is not recommended for:

  • Silicone structural glazing
  • Application in confined areas where ventilation is not adequate
  • Joints under constant water submersion

DISCLAIMER: These instructions are from the product manufacturer. PK Supplies Inc. makes every effort to ensure that these instructions are accurate. By following these instructions you agree that PK Supplies Inc. is not liable for any damages or losses caused by these instructions.

Instructions can be used for...