Why Your Fairing Compound Keeps Shrinking and How to Stop It

Proven Strategies for Filler Shrinkage Repair That Lasts

Few things are more frustrating than spending hours on a repair or fairing job, only to come back later and see the surface has sunk, cracked, or pulled away. Filler shrinkage is one of the most common, and costly, issues in body and marine work. The good news? Shrinkage isn’t inevitable. By understanding what causes it and how to prevent it, you can save time, rework, and wasted materials.

At Smooth Tech Co., we’ve seen it all. That’s why we’ve formulated products like FairTech VE, FairTech PE, and FairTech EX to stand up against the usual culprits behind shrinkage. Here’s what you need to know.

What Causes Filler Shrinkage?

Shrinkage happens when the filler material continues to cure or outgas after it’s been sanded, coated, or painted. Common causes include:

• Excess resin or solvent content that evaporates over time
  

• Incorrect hardener ratio during mixing (too much or too little catalyst)
  

• Improper surface prep, leading to weak adhesion and pull-away
  

• Environmental conditions, like high heat or humidity accelerating cure rates
  

• Rushing the process, sanding or overcoating before the filler is fully cured

Each of these issues can compromise the integrity of the repair, leaving visible defects that mean extra work down the line.

How to Prevent Shrinkage in the First Place

Prevention starts with process. A few best practices can dramatically reduce the risk of shrinkage:

• Measure carefully: Follow the recommended hardener ratios! Guessing leads to inconsistent cures.
  

• Prep surfaces correctly: Clean, sand, and decontaminate before applying filler.
  

• Apply in layers: Build up material gradually instead of laying it on thick.
  

• Respect cure times: Allow each stage to fully cure before sanding or topcoating.
  

• Control your environment: Work in stable conditions to minimize external stress on the curing process.
  
  

Smooth Tech compounds are engineered to minimize shrinkage, but even the best product needs proper technique to perform at its peak.

Choosing the Right Product for Filler Shrinkage Repair

Not all fillers are created equal when it comes to shrink resistance. That’s why Smooth Tech offers multiple chemistries tailored to specific conditions:

• FairTech PE (Polyester): Affordable and quick-curing, best for repairs where speed is critical but long-term shrinkage resistance may be less demanding.
  

• FairTech VE (Vinyl Ester): Stronger chemical resistance and reduced shrinkage compared to polyester, ideal for marine and automotive applications under stress.
  

• FairTech EX (Epoxy): Maximum bond strength and the lowest shrinkage potential—perfect for demanding structural repairs.
  

• FairTech EX-LW (Lightweight Epoxy): Provides the same epoxy-level shrink resistance while reducing sag in vertical or overhead applications.
  

By matching the product to the job, you avoid the “one-size-fits-none” approach that often leads to shrinkage problems.

The Bottom Line: Shrinkage Isn’t Inevitable

Shrinkage may be common, but it doesn’t have to be the standard. With the right process and the right compound, your repairs will stay smooth, strong, and reliable long after the job is done. Smooth Tech compounds are built to eliminate the guesswork so you can focus on delivering results that last.

Ready to stop fighting shrinkage? Shop Smooth Tech Co.’s full line of fairing compounds today.