Proper Sealant Application for Pre-Finished Colored Claddings

OSI proper fillet sealant bead


Successfully applying sealant over joints that involve pre-finished color cladding such as fiber cement or engineered wood requires an understanding of substrate reliability, dependable joint construction, sealant choice and skillful application. Because a coating of paint can disguise some sealant errors, primed cladding has more tolerance, but pre-finished colored cladding does not allow for that, so attention to detail is required.


Substrate Reliability

Sealant adheres to a clean cladding surface and may not adhere well over surface contaminants, including:

  • Contaminants such as dust, dirt, oil and even adhesive backing on protective films, can all create a thin residue that can compromise sealant performance. This includes the even dust created by cutting the cladding itself.


  • Oils and other residues, which can often be removed with a 25/75 mix of soap and water mix, followed by a good rinse. If you use a degreaser, follow it with a 50/50 mix of isopropyl alcohol and water.


Dependable Joint Construction

When sealant doesn’t adhere as it is supposed to, it may have to do with one of the following:

  • Cladding movement. All cladding is designed to move. If cladding movement exceeds its design limitations, it can impact sealant performance.


  • Joint design. The joint gap is determined by the movement of the materials that form the joint. If there is an error in joint design, it can affect sealant performance.


  • Fastening. Cladding should always be fastened directly to the structural framing or wall systems. This secures it and prevents it from moving more than it should.


OSI fillet bead sealant siding installation


Sealant Choice Application  

For sealant to perform well and hold up aesthetically, it’s important to:

  • Choose the correct sealant for pre-finished colored claddings is essential for a dependable and long-lasting finish.  The sealant must provide reliable performance in three areas.

            ○  Adhesion strength

            ○  Movement capability

            ○  Precise Color Match Characteristics and Durability


  • Apply sealant to pre-finished colored cladding joints with the correct skill and accuracy.


The cut angle of the spout (nozzle) at 3/8” and positioning of the gun must support the finishing of the bead  to maintain balance.


Using the gun with balanced pressure and speed to ensure consistent contact to both substrates while dispensing a smooth sealant bead.


Do not tool or smear the bead. Tooling or smearing will reduce any ability the sealant has to withstand UV exposure and joint movement, causing premature joint failure and color fading. The challenge is that there isn’t enough depth of the sealant left in the joint to function as a sealant.



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