Short answer: To glue acrylic to acrylic, use a solvent cement, not glue: run water-thin cement such as Weld-On 4 along a tight, flat joint with a needle bottle and let capillary action pull it in. Weld-On 4 fixtures in about 3 minutes and reaches roughly 2,400 psi in 24 hours; use thicker Weld-On 16 where parts don't fit perfectly, and two-part Weld-On 40 or 42 for the strongest, gap-filling joints.

What is the best glue for acrylic?

For acrylic to acrylic, a solvent cement beats any glue. It doesn't sit between the parts as a layer. It softens a thin skin on each surface, the softened plastic fuses, and when the solvent evaporates you have a joint that is acrylic all the way through. Done well, it's nearly invisible.

Key facts

  • Weld-On 3: water-thin, fixtures in about 2 minutes, about 2,825 psi at 24 hours on acrylic. Fastest, but can blush (turn white) in humid air.
  • Weld-On 4: water-thin, 1 to 2 minutes working time, fixtures in about 3 minutes, about 2,430 psi at 24 hours and 2,600 psi at one week. More blush-resistant than 3.
  • Weld-On 16: medium-bodied (about 800 cps, like motor oil), 5 minutes working time, 10 minutes fixture, about 3,090 psi at one week.
  • Weld-On 40 and 42: two-part reactive cements, 15 to 20 minutes working time, 2 hours fixture, about 4,000 psi at one week.
  • Capillary reach: thin cement wicks about 1/4 in. into a tight joint.
  • Temperature: Röhm wants the adhesive at room temperature, 64 to 77 °F (18 to 25 °C), before use; cold slows the solvent action.

Bond strengths are IPS's typical values for 1/4 in. acrylic with a 1 sq. in. bond area. SCIGRIP sells cements under the same numbers (SCIGRIP 3, 4, 16) with similar behavior.

TypeExamplesUse it for
Water-thin (capillary)Weld-On 3, Weld-On 4, SCIGRIP 3 and 4Tight, flat, square joints. Boxes, display cases, stands. The cleanest look.
Thickened (bodied)Weld-On 16, SCIGRIP 16Joints that don't fit perfectly, small gaps, curved or bent parts, quick repairs.
Two-part reactive (polymerizable)Weld-On 40, Weld-On 42The strongest, clearest gap-filling joints. Outdoor parts, aquariums, structural work.

Thickened cement is forgiving, but it isn't a true gap filler: Röhm's joining guide notes that solvent adhesives are not gap-filling. For real gaps, or joints that must stay perfectly clear and strong, use a two-part reactive cement.

How capillary bonding works

Water-thin cement behaves like water in a paper towel. Put the two parts together with no gap, touch the needle to the seam, and the cement runs along the joint by itself. You don't paint it on the faces first. You assemble, then feed the seam.

That only works if the joint is tight. A visible gap breaks the capillary pull, and the cement runs out or leaves dry spots and bubbles. That's why joint prep matters more than the brand of cement.

How do you glue acrylic step by step?

  1. Prepare the edges. The bonding edge must be flat and square to the face. A routed or machined edge, or one sanded flat on wet 400 to 600 grit paper on glass, is ideal. Don't polish or flame-polish an edge you're going to bond; polishing rounds the corners and leaves stress that can craze.
  2. Peel the film back about 1/2 in. from the joint on both parts so cement doesn't run under it.
  3. Dry-fit and hold. The parts should meet without forcing or flexing. Hold them with a square, a block, or a simple jig and painter's tape. Use only light pressure; clamping hard squeezes out the softened plastic and starves the joint.
  4. Apply the cement. Use a squeeze bottle with a fine needle (around 20 to 25 gauge). Hold the seam horizontal, touch the needle to it, and draw it slowly along. The joint turns clear as it fills.
  5. Leave it alone. Don't move the parts for at least 2 to 5 minutes. Moving them while wet is the most common cause of bubbles and weak spots.

How long does acrylic cement take to dry?

  • Fixture (parts hold themselves): about 2 minutes for Weld-On 3, 3 minutes for Weld-On 4, 10 minutes for Weld-On 16, 2 hours for Weld-On 40 or 42 (all at 73 °F).
  • Handling strength: IPS says 65 to 80% of the ultimate strength comes within 24 hours for Weld-On 3 and 4.
  • Full strength: 72 hours for Weld-On 40 and 42, and solvent joints keep gaining strength for several weeks. Don't load a shelf or fill a tank the same day.

Cold rooms slow everything down. Work at about 65 to 80 °F (18 to 27 °C), and in humid weather choose Weld-On 4 over 3 to avoid white blush.

Can you glue laser-cut edges?

Yes, but with care. Laser-cut edges look ready to bond, yet Acrylite notes they carry high stress from the heat of cutting and recommends annealing after laser cutting. Flame-polished and heat-bent areas carry the same kind of stress. The stress can show up as fine cracks called crazing, sometimes days later. Annealing first (Acrylite's rule of thumb: 180 °F for one hour per millimeter of thickness, then cool slowly for at least 2 hours) lowers the risk. For small craft parts, laser edges usually bond fine; for display cases, a routed edge is better. More on laser vs routed edges.

When to use CA glue or epoxy instead

  • CA (super glue) is handy for tiny parts and quick fixes. It's brittle, and its fumes can leave a white frosting ("blooming") around the joint.
  • Clear epoxy fills gaps and bonds acrylic to other materials, but it's a visible layer, not a weld, and some epoxies yellow. See gluing acrylic to wood, metal, and glass.
  • Avoid household glues and solvent-based contact cements on visible faces. They're weak on acrylic and some craze it.

Is acrylic cement safe to use at home?

Treat it as a hazardous chemical. Current Weld-On 3, 4, and 16 no longer contain methylene chloride, but their data sheets still list them as highly flammable, harmful if inhaled, and suspected of causing cancer, and IPS labels them for industrial and professional use. Work with cross-ventilation and a fan pulling vapor away from you, keep the can closed, wear safety glasses and chemical-resistant gloves, and keep it away from flames and kids. Read the safety data sheet for the exact product you buy; formulas change.

Tip: Practice on two offcuts first. Five minutes of practice tells you how fast your cement flows and how much is too much.

Want it done for you?

We cut parts with edges ready for bonding, and we build solvent-bonded boxes and display cases ourselves. See acrylic fabrication, or get an instant quote on cut parts you'll glue yourself. Planning a box? Read how to build an acrylic box and how to get bubble-free joints.

Questions

Can I use Gorilla Glue or regular super glue on acrylic?

Super glue works for small, hidden joints, but it's brittle and can leave a white haze. Expanding polyurethane glues are a poor fit for clear acrylic. For acrylic to acrylic, solvent cement gives a far stronger and cleaner joint.

How strong is a solvent-welded acrylic joint?

IPS lists about 2,400 to 2,900 psi at 24 hours for Weld-On 3 and 4 on acrylic, and about 4,000 psi at one week for two-part Weld-On 40. That's a good fraction of the sheet's roughly 10,000 psi tensile strength; Röhm puts the best reactive-cement joints at up to 75% of the sheet. Bubbles and gaps cut that a lot.

Can I use acetone to glue acrylic?

Acetone attacks acrylic (sheet makers rate it "not resistant"), but it tends to leave weak, cloudy, crazed joints. Proper acrylic cement is made to bond cleanly and is worth buying.

Weld-On 3 or Weld-On 4: which should I buy?

Both are water-thin and reach similar ultimate strength. Weld-On 3 sets a little faster; Weld-On 4 gives you an extra minute and resists white blushing in humid conditions, which makes it the easier choice for most people.

Sources