A repair that holds its shape perfectly the day it’s made can slowly bulge, thin out, or shift months later under a constant load it was never truly designed to carry alone. That gradual, permanent deformation under sustained stress is called creep, and for polymeric repair putties it is a critical failure mode in joints bearing a continuous load — structural members, pressurized lines, or support components.
Eliminate or Bypass Continuous Load
The most effective way to prevent creep is to ensure the putty is never the primary load-bearing element in the joint or repair.
If a repair is under constant tensile or shear load, that stress needs to be transferred to the metal substrate directly. Mechanical reinforcement — bolts, metal stitching plates, or internal pins that bridge the defect — carries the actual load, leaving the putty to function only as a seal and filler around the load-bearing elements. In a bolted flange repair, the bolts themselves should bear the load and maintain the gap, not the cured putty; the putty should be compressed but not subjected to continuous, high-shear stress on its own.
For a filled cavity, preparing the geometry so the putty is mechanically locked in a way that converts external load into a compressive force on the putty, rather than a tensile or shear force, matters a great deal — putties are significantly stronger and more creep-resistant under compression than under tension.
Managing the Cure and Operating Environment
Temperature is a major accelerator of creep, since higher temperatures soften the polymer and make it deform more easily under stress. Ensuring the putty is fully and properly cured, including any recommended post-cure heating cycles, matters directly: a fully cross-linked polymer matrix resists creep far better than a partially cured one, and the post-cure process raises the material’s glass transition temperature (Tg), letting it maintain rigidity under load at higher operating temperatures.
Where the load itself is unavoidable, reducing the component’s temperature in the repair area helps meaningfully — even a 10°C reduction can noticeably slow the rate of creep, and techniques like heat shielding or improved local airflow can achieve that reduction. Never subject the putty to its maximum mechanical load while it is also at its maximum operating temperature, especially right after cure — introduce load and heat gradually rather than simultaneously.
Controlling Thickness and Geometry
The shape of the repair influences stress distribution and, in turn, susceptibility to creep. Use the minimum effective thickness: thick sections of polymer are more prone to creep than thin bond lines, since the bulk material has less surface area contact with the rigid metal substrate to restrain its movement. Spreading the load over the largest possible area of the rigid substrate — by feathering the repair edges and overlapping the defect significantly — decreases the stress per unit area the putty experiences, which reduces the driving force behind creep. As with other loading failure modes, use radii and fillets rather than sharp 90-degree corners in the repair geometry, since stress concentrations accelerate creep by overloading a small portion of the material.
Distinguishing Creep from a One-Time Cure Shrinkage Event
Because both creep and cure shrinkage produce a similar visible result — a repair that sits slightly lower than it did originally — it’s easy to misdiagnose one as the other. The distinguishing factor is timing: shrinkage occurs once, in the days immediately following the cure, and then stops entirely once the polymer has fully cross-linked. Creep, by contrast, continues gradually for as long as the sustained load remains, and a repair still slowly deforming months or years after cure is exhibiting creep, not shrinkage. Tracking the repair’s dimension at two points well after the expected cure and post-cure window — say, at 30 days and again at 180 days — separates the two: no further change between those two readings rules out creep, while continued gradual movement confirms it and signals that the load path needs to be redesigned rather than the compound simply re-applied.
Recognizing Creep Before It Becomes a Failure
Email Us if you’re monitoring an existing repair for early signs of creep — a simple dimensional check against the as-cured profile, repeated at a fixed interval under normal service load, catches slow deformation long before it progresses to a sealing or structural failure. Creep and thermal cycling often interact in the same joint, so it’s worth reviewing how CTE mismatch between a repair compound and its substrate contributes to bond failure alongside a creep assessment.
For genuinely load-bearing repairs where creep resistance is a primary selection criterion, compare epoxy and UV-cure adhesive chemistries for heavy-duty repair strength before committing to a compound.
Incure’s Epo-Weld line of metal repair compounds is formulated for strong creep resistance once fully cured, but load-bypass design and correct post-cure conditioning remain essential for any repair under sustained mechanical stress. Contact Our Team if you need help designing a load path that keeps a repair compound out of continuous tension.
Visit www.incurelab.com for more information.