How To Glue Acrylic

Which glue gives the strongest bond joining two pieces of 3 mm acrylic sheet?

For an L-shaped bookend made from two pieces of 3 mm acrylic, you should achieve good results with Selleys Multi Grip, listed on this site as Selleys Fix & Go Multi Grip. Multi Grip is a clear, solvent-based general purpose glue and it bonds very well to acrylics and Perspex, PVC and similar plastics.

The two properties that matter for this job are that it is solvent based and that it dries clear. Solvent based is what makes it work on acrylic; clear is what makes the joint acceptable to look at on a transparent object.

Why a solvent adhesive suits acrylic

Acrylic is a thermoplastic, which means a solvent can soften its surface. A solvent-based adhesive applied to two acrylic faces slightly softens both, and as the solvent evaporates the two softened layers set together. The result is closer to a weld than a glued joint, and it is why solvent adhesives outperform far "stronger" products on this material. An epoxy, by contrast, sits between the two faces as a separate layer and can only grip the surface.

That same chemistry is the reason for the biggest constraint on the job: the joint must be close fitting. A solvent adhesive has almost no gap-filling ability. Two square, flat edges pressed together give a strong, nearly invisible joint; a joint with a visible gap gives a weak, cloudy one.

Getting a good L-joint in 3 mm sheet

A butt joint between two thin sheets — the edge of one against the face of the other — has a bonded area only 3 mm wide. That is the practical limit on this design, and there are three things you can do about it.

Get the edge genuinely square and flat. A saw-cut acrylic edge is rarely either. Draw-filing the edge or running it over fine abrasive on a flat surface makes a large difference to both strength and appearance. Do not polish it to a gloss — a lightly matt, flat edge bonds better.

Remove the protective film only at the joint. Peel back a narrow strip either side of the bond line and leave the rest of the film on until the job is finished. It protects the faces from adhesive marks and from handling scratches.

Support the joint at 90 degrees while it sets. A set square held with tape, or a block clamped inside the angle, keeps the corner true. Acrylic has no forgiveness once the solvent has flashed off.

How to make the joint

1. Make sure the surfaces are clean and dry. Fingerprints on the bond line will show.
2. Test on offcuts first. Solvent adhesives affect different acrylic grades slightly differently, and a test tells you both how strong the joint is and whether the surface has crazed.
3. Apply a thin layer to one surface. Thin is correct — an excess of solvent adhesive gives a cloudy joint and can craze the surrounding surface.
4. For a faster bond, apply the adhesive and leave the surfaces open for 1 minute before pressing them together.
5. Press the surfaces together and hold or clamp them square.
6. Allow it to set undisturbed. Full cure takes several hours.
7. Leave it clamped and unhandled while it cures. A solvent joint that is flexed early stays weak.
8. Replace the cap immediately after use.

Limitations

• Not suitable for polyethylene or polypropylene. If the sheet turns out to be a polyolefin rather than acrylic, this is the wrong product and Selleys directs you to All Plastics.
• Not for polystyrene foam. The solvent attacks it.
• Not for underwater use or constant moisture.
• Use on clean, dry surfaces only.
• There is no published technical data sheet for this product, so there are no cure-time or strength figures to quote. Allow generously rather than assuming.
• Solvent adhesives can craze acrylic if applied heavily or if excess runs onto a visible face. Keep it off the show faces and test first.
• A thin butt joint in 3 mm sheet has a small bonded area. For a bookend that will take real load, consider a design with a larger overlap.

Alternatives worth knowing

If the joint has to fill a gap, a solvent adhesive will not do it. An epoxy such as Araldite Super Strong fills irregularities, dries clear, and holds up to 150 kg/cm² — though its bond softens above 60°C, it may discolour if exposed to UV, and it will not bond PTFE, polyethylene or polypropylene.

If the acrylic is being fixed to a wall rather than to itself — a splashback, say — that is a different product. See how to glue an acrylic splashback to a wall.

If you cannot identify the plastic, test in a small hidden area first. Selleys repeats this instruction across the range because two plastics that look identical can behave completely differently with the same adhesive.

Common questions about gluing acrylic

What does Selleys recommend for acrylic?

Selleys Multi Grip, a clear solvent based general purpose glue that bonds very well to acrylics and Perspex, PVC and similar plastics.

Will the joint be clear?

Multi Grip dries clear. A close-fitting joint with a thin film of adhesive gives the clearest result; excess adhesive gives a cloudy one.

How close-fitting does the joint need to be?

Very. Solvent adhesives have little gap-filling ability, so square, flat, well-mated edges are what produce a strong joint.

Should I leave the adhesive open before joining?

For a faster bond, apply the adhesive and leave the surfaces open for 1 minute before pressing them together.

How long until it is strong?

Allow it to set undisturbed; full cure takes several hours. There is no published data sheet for this product, so allow generously.

Will it craze the acrylic?

Solvent adhesives can craze acrylic if applied heavily or allowed to run onto a visible face. Apply thinly, keep it off show faces, and test on an offcut first.

Can I use an epoxy instead?

An epoxy will bond acrylic and will fill a gap, but it forms a separate layer rather than partly fusing the surfaces. Selleys nominates the solvent adhesive here.

What if my sheet is polycarbonate rather than acrylic?

Test first. Polycarbonate and acrylic look alike and react to solvents differently.

Is the joint waterproof?

Multi Grip is not for underwater use or constant moisture.

Should I remove the protective film?

Only along the bond line. Leave the rest on until the job is complete to protect the faces.