[Shop-talk] Plastic epoxy/solvent weld

[Ian McFetridge]

You're probably right that they were solvent welded, that's fairly common
with acrylic pieces (what I see my wife's clips appear to be).  Maybe buy a
couple test clips that appear to be there same material for testing as
solvent welding can deform really if not done in just there right way.

Here's there AI scoop on welding the two plastics I see clips are mostly
made from:
Both cellulose acetate and acrylic can be solvent welded
, but they require different solvents to fuse the plastic together. The
solvent essentially melts the surfaces of the plastic pieces, which then
bond to form a seamless, single piece as the solvent evaporates.
Solvent welding cellulose acetate

   - *Solvents:* The most common and accessible solvent for welding
   cellulose acetate is pure acetone. Nail polish remover is not recommended
   as it contains emollients and other additives that interfere with the
   welding process.
   - *Method:* A thin coat of acetone is applied to the clean surfaces of
   the cellulose acetate. The pieces are then pressed together and held firmly
   while the solvent evaporates.
   - *Considerations:* The process for welding cellulose acetate can be
   slow and requires significant pressure for a successful bond.
   - *Best for:* Eyeglass frames, tool handles, and film materials.

Solvent welding acrylic

   - *Solvents:* Acrylic solvent cements, such as Weld-On #3 and #4, are
   specifically designed for bonding acrylic. These cements are typically a
   fast-drying, water-thin liquid based on chemicals like methylene chloride.
   - *Method:* The process relies on capillary action. With the pieces held
   together, a small amount of the liquid cement is applied along the seam.
   The solvent is drawn into the joint, melting the two surfaces together.
   - *Considerations:* It is crucial to have perfectly flat, smooth, and
   clean edges, as the watery solvent will not fill gaps. Clamping or taping
   the pieces together beforehand is recommended for precision.
   - *Best for:* Projects requiring a strong, clear, and seamless joint,
   such as display cases, signs, and aquariums.

Key differences between the two
Feature  Cellulose Acetate Acrylic
*Common Solvent* Pure Acetone Specialized acrylic cements (e.g., Weld-On #3)
*Bond Speed* Slow, requiring hours and pressure to cure Very fast, with an
initial set in minutes and a full cure in 24–48 hours
*Bond Clarity* Can be clear, but is prone to blemishes if not done
carefully. Excellent, capable of producing very clear, seamless, and
bubble-free joints.
*Application* Acetone can be brushed or sprayed on, but careful application
is needed to avoid damaging the finish. Typically applied with a
needle-nosed applicator to let capillary action draw the cement into the
joint.


If you just want to try glue....From my experience I would rule out super
glue (cyanoacrylate) as it is better for static adhesion, like a figurine,
not loads.  Polyurethane glues like Gorilla glue are tougher (absorb stress
by flexing a little more).  I'd definitely rough up the surfaces and
ideally if you could drill holes for small pins to couple them like dowels,
you'd get the strongest combination with mechanical and chemical bonding.

Best
Ian




On Sun, Oct 5, 2025 at 6:43 PM Jim Stone <1789alpine at gmail.com> wrote:

> My granddaughter asked me to fix her favorite hair clip and I’d like to
> keep my reputation as Grandpa Fixit intact.  The part that came off will be
> under stress when the clip is used.  The plastic didn’t break; the larger,
> decorative part of the clip came loose from the spring clip.  It looks to
> me like it was originally solvent welded, not glued.
>
>
>
> I have never had tremendous luck gluing plastic but never tried solvent
> welding. Does anyone here have a recommendations for either a strong enough
> plastic glue or a readily available solvent that I could use to bond the
> two pieces and keep my reputation intact?
>
> Thanks,
>
> PaG, aka Jim_______________________________________________
>
> Shop-talk at autox.team.net
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