Epoxy Resin Won't Dry

Hi everyone - I recently have been experimenting with epoxy resins
and have run into a problem. I made these little box shaped
components in silver, filled them with colored epoxy and left them to
dry - that was a few days ago and they are still not fully dried. I
am worried I am doing something wrong.

I used 90-minute epoxy, and two types of tints to make the colors I
wanted. (1) Castin’ Craft Color Pigment (says it is for epoxy resins)
and (2) Tints All (used for coloring latex, alkyds, oil, acrylic). I
left the pieces to dry on top of bookshelf out of the way but in the
open air. Also - they are about 1/4 inch deep and I filled them in
one sitting.

Any ideas why they aren’t drying?


Hi Molly,

Epoxy doesn’t actually “dry”… it cures. It is a chemical reaction
between the two components, resin and hardener. Cure time should be
no more than 24 hours under normal conditions. Ambient temperature
has an influence, curing faster in a warm environment.

My suspicion is that the resin and hardener were not mixed in the
proper proportions, which is really important. Judging by eye can
usually get you by if you’re careful, but people who must have it
right will actually weigh the two components before mixing to ensure
the proper ratio.

All the best,


Dave Sebaste
Sebaste Studio and
Carolina Artisans’ Gallery
Charlotte, NC (USA)
dave@sebaste.com mailto:dave@sebaste.com

   Any ideas why they aren't drying? 

Epoxy doesn’t “dry”. It cures when the hardner and resin react
with each other resulting in a new material, the cured fully
polymerized (hardened) epoxy resin. Usually, heat is generated by the
reaction, and external heat will speed the reaction. Epoxy does not
need fresh air or the like to cure. But it may need a little warming.
Try putting it in an oven at, say, 100 (nice Kuwaiti air temp)
degrees. Just enough to get it gently warm to the touch, and see if
that helps it out. If it doesn’t, then:

  1. Perhaps your epoxy is way past it’s shelf life and the componants
    have, (oh, for example) oxidized to the point where they no longer
    react correctly,

  2. Something in your pigments is inhibiting the reaction. Perhaps
    you used too much? Some pigments (liquids, rather than dry powders)
    have upper limits in terms of how much you can add to the epoxy before
    it interferes with curing.

  3. You mixed the epoxy insufficiently, or in the wrong proportions.
    In general, epoxies can be very sensative to the wrong proportions
    of hardner to resin. While many consumer types are optimized to be
    forgiving (at the expense of strength, usually), they still need
    proportions reasonably close to the stated one for that type. In
    many a difference of as little as 10 percent error in the ratio can
    cut the bond strength and hardness of the cured resin in half.
    Measure the two parts carefully. For small quantities, often the
    best method is to use a scale to weigh the two parts. The small
    electronic carat/gram scales sold to jewelers are not accurate
    enough, usually, to be legal for trade in gems, but they’re fine for
    weighing epoxy resins.


G’day Molly It may well be that the last pigment that you described
is for acrylic resins as opposed for epoxy resins…you could try
subjecting the articles to ultraviolet light this may help speed up
the hardening process. (John Burgess where are you?) Cheers Will
Francis Melbourne

Is the resin soft or just sticky? If sticky, it could be the type
of resin you used. Polyester resins tend to have a tacky/sticky
surface when cured. This can be greatly reduced by adding a "wax"
sold specifically to stop the tackyness.

If the resin is soft, it could be old resin/hardener/catalyst, mis
mixed (Epoxys have a very narrow margin of mix error compared to
polyesters), used the wrong catalyst, poor mixing (if you use paper
cups for mixing and put in the catalyst first, the paper the cup is
made of can absorb a good deal of the catalyst and the material will
not cure or you didn’t scrape the sides and bottom to get it "all"

Just a for potential reasons for the problem.

John Dach

Another possibility could be that the epoxy is old. If you’ve had
it more than a year or so, it probably never will cure.



First of all epoxies really do not “dry” they instead harden due to
a chemical reaction, usually through the use of a catalyst. When you
introduce coloring agents to the mix, you alter the usual chemical
balance for normal hardening. My only suggestion is to heat the
items in your oven, at low temps., and see if that will accelerate
the hardening or set up process. Trial and error is what you are up
against since you have introduced additional variables into the
chemical formula of the epoxy and have changed the working
properties of the mix. Good luck.


This will happen if you put too much coloring or don’t mix the two
parts of the epoxy equally. When I have added acrylic paint to Epoxy
333, I have found that the very smallest drop of paint will color
the epoxy but not upset the ratio of the two epoxy components.

J. S. Ellington

My suspicion is that the resin and hardener were not mixed in the
proper proportions, 

My first thought on this is was that the coloring agents had diluted
the mixture. I have only ever used “dry” coloring agents in epoxy.

Christine in Littleton, Massachusetts

       you could try subjecting the articles to ultraviolet light
this may help speed up the hardening process. (John Burgess where
are you?) 

G’day; You rattled my cage? Well, I am not too sure about UV
helping ordinary epoxies to harden. Even if it did where would you
get the UV generator - other than the (sometimes) bright sun which is
high in UV radiation (which is why one lies on a beach to get a sore
back). Actually epoxies harden well at room temperature in total
darkness, but a little heat will considerably speed things - say from
an incandescent (filament) bulb a few inches away.

I personally find an easily available and cheap material for
colouring epoxy resin is TEMPERA POWDER. It is sold by most artist
supply shops, is a pigment, not a transparent dye, mixes well and
easily with properly proportioned epoxy and hardener, and doesn’t
interfere with the hardening properties. All the colours are mixable
so one can get the exact colour and shade one needs. I use only
red, blue and yellow, plus black or white to mix with the epoxy get
exactly what I want. A room temperature of 22 C will cure the resin
nicely overnight and it can then can be filed and sanded. Use wet
’n’ dry papers with water to avoid clogging. Attempts to use a buff
to polish epoxy are doomed - but you will get a good shine with 400
grit paper, followed by hand polishing with ‘Brasso’ metal polish on
a soft cloth. If a good transparent, colourless lacer is put over
the epoxy an enamel like finish is obtained. BUT: that will soon
wear off and look cheap and nasty. The metal polish finish suits
most people. Now will you reopen my cage door please?

Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ