ᐅ Seeking Experience with Yellowing in Epoxy Resin

Dear House Building Forum,

Regarding my current project, I couldn’t find much information online. Maybe it’s because this isn’t commonly done.

I want to seal some concrete slabs with clear epoxy resin. I was able to apply a test slab quite well by rubbing it in with a sponge and removing the excess, so that only a very thin layer remains on the slab.

My question:
Does the combination of epoxy resin and sunlight always turn yellow?
The layer on the test slab is less than 1mm (0.04 inches) thick—will it also turn yellow?
The slabs will be permanently exposed to sunlight.

I would really prefer not to have yellow-colored slabs later on.

Kind regards,
Ben

BenBenBen schrieb:

My question:
Epoxy resin combined with sunlight always turns yellow, right?
The layer on the test panel is less than 1mm (0.04 inches) thick; will it also turn yellow?
The panels are constantly exposed to the sun.

Answer to question 1: YES
Answer to question 2: YES
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Even UV-resistant modified epoxy resins yellow when exposed to sunlight, regardless of the film thickness.
Regards, KlaRa

KlaRa schrieb:

Answer to question 1: YES
Answer to question 2: YES
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Even epoxy resins modified to resist UV exposure yellow under sunlight, completely independent of film thickness.
Regards, KlaRA

There are also UV-resistant options, but these are not weather-resistant. Such composites generally do not adhere well. If water gets between the epoxy and the concrete, combined with freezing conditions, delamination occurs faster than you can say “whoops.”

Myrna_Loy schrieb:

There are also UV-resistant materials, but these are not weatherproof. Such composites do not hold up well anyway. If water gets between the epoxy and the concrete, combined with frost, delamination occurs faster than you can say “oops.”

UV resistance and weather resistance are two material properties that are unrelated. There is no justified connection between the two.
If a synthetic resin layer shows signs of failure, it is not due to the material combination in this case, but rather due to improper application of the composite system by unqualified personnel. The manufacturer’s instructions regarding intended use and application areas are decisive!
There are plenty of coating resins known that are suitable for outdoor use and also UV-resistant.
Furthermore, the original question focused on UV resistance, which cannot be answered by purely speculative damage mechanisms of a completely different nature.

With differing coefficients of thermal expansion (concrete vs. epoxy) and non-chemically reactive bonds (epoxy organic to concrete inorganic), there are always problems under changing conditions. Manufacturer warranties for plastics typically cover a maximum of 20-30 years under ideal processing and application conditions.

Incidentally, the connection was based on the previous claim that all epoxy resins yellow, which is why I pointed out that there are indeed non-yellowing variants, for example, those used in glass restoration; however, these are not weather-resistant due to their composition. Transparent epoxy resins, for instance, are generally less durable than pigmented ones, as the pigments and fillers protect the resin and hardener components.

KlaRa schrieb:

UV resistance and weather resistance are two material properties that are unrelated.
Any link between them is unfounded and does not exist.
If a synthetic resin layer shows failures over time, in this case it is not due to the combination of materials but rather to unprofessional application methods of a composite system! The manufacturer's instructions regarding intended use and application area are decisive!
There are sufficiently available coating resins that are suitable for outdoor use and still UV resistant.
Furthermore, the primary question referred to UV resistance, which cannot be answered by purely speculative, entirely different damage mechanisms.