How To Adhere Perspex to Wood
What is the best sealant for adhering Perspex to wood?
Selleys nominates two products for gluing Perspex to timber, and for a cubby house either will do the job:
- Selleys 3 in 1 Adhesive, Sealant and Gap Filler
- Selleys 650FC Fast Cure Adhesive Sealant, for the gaps and joints
Both provide excellent adhesion, both are water and weather resistant, and both are paintable with water-based paints. That combination is what makes them right for an outdoor structure a child will use.
Why an elastic adhesive rather than a rigid glue
This is the part worth understanding before you start, because it explains why a strong rigid glue would be the wrong choice here.
Acrylic sheet and timber expand and contract at different rates, and outdoors they do it every day. A rigid bond between them concentrates that difference into the glue line and into the sheet itself. An elastic adhesive absorbs the movement instead. 3 in 1 has a movement capability of ±20% (ISO 9046 modified) and elongation at break over 250%; 650FC is rated at ±20%. That elasticity is a feature, not a compromise.
The second reason is that both products double as sealants. On a cubby window you want the sheet bonded and the perimeter sealed against water, and one bead can do both.
Comparing the two
| 3 in 1 | 650FC | |
| Technology | Moisture curing SMP | Silane modified polymer (SMP) hybrid, high modulus |
| Colours | White | Grey, Black, White |
| Packaging | 480g cartridge | 300mL cartridge, 600mL sausage |
| Skin time | 15 to 30 minutes | 20 minutes |
| Cure rate | 3 to 4mm per 24 hours | ≥ 2.5mm per 24 hours |
| Movement capability | ±20% (ISO 9046 modified) | ±20% |
| Application temperature | 5 to 30°C | Do not apply below 5°C |
Indicative data only, not intended for the preparation of specifications.
In practice: 3 in 1 is the simpler single-product choice for a small job — it bonds, seals and fills gaps, comes in one white cartridge, and can go on wet or dry surfaces. 650FC gives you a colour choice and a sausage format if you are working through a lot of joints, and its 20 minute skin time is more predictable than a range.
Test the acrylic first
One caution that applies to both. Neither data sheet names acrylic or Perspex specifically among its substrates. 3 in 1 lists glass, metal, timber, brick, concrete, tiles and most plastics; 650FC has broad primerless adhesion to common building materials. Both explicitly exclude polyethylene, polypropylene and Teflon.
Acrylic sheet is not in that excluded group, but it is also not individually named, so run a test bond on an offcut before you commit. Bond a scrap of the same sheet to a scrap of the same timber, let it cure for the full time, and try to pull it apart. Ten minutes now saves rebuilding a window later.
How to bond the sheet
- Make sure both surfaces are clean, dry and free from dust, grease and any old or crumbling sealant. Leave the protective film on the acrylic until the last moment, then peel back only the edge you are bonding.
- Cut the tip, attach the nozzle and cut it to the size you need. Insert into a caulking gun.
- As an adhesive, apply to one surface — beads every 30cm for broad surfaces, dots for small ones. Press the surfaces together.
- As a sealant around the perimeter, force the product into the joint so it makes good contact with both faces.
- Tool with a soap solution before skinning occurs — within about 15 minutes for 3 in 1.
- Support the sheet until the adhesive cures. Larger, heavier panels need to be held or propped.
- Clean up uncured product with mineral turps; cured product needs scraping, sanding, or a silicone remover.
Painting and limitations
- Both are paintable with water-based paints. 3 in 1 cannot be painted with solvent-based paints unless a water-based paint is applied first, and 650FC may affect the drying of alkyd or oil-based paints.
- Neither is suitable for polyethylene, polypropylene or Teflon.
- 3 in 1 cannot be applied over paint without allowing at least 7 days drying time.
- 650FC needs atmospheric moisture to cure, should not be applied below 5°C, and should not be applied in the presence of curing silicone or polyurethane sealants. Avoid contact with solvent cleaners during cure. White 650FC may yellow slightly with age and sun exposure.
- Neither is recommended for continuous submersion or below water line use.
Common questions
Which of the two should I use?
3 in 1 if you want one product that bonds, seals and fills. 650FC where you want a colour match or a sausage pack for a bigger run of joints.
Will it stick to Perspex?
Selleys names both products as suitable for gluing Perspex to wood. Neither data sheet lists acrylic individually, so test on an offcut first.
Can I paint over the bead?
Yes, with water-based paints. Solvent-based paints need a water-based paint applied first over 3 in 1.
Is it weatherproof?
Both are water and weather resistant, and 3 in 1 is UV resistant. Neither is for continuous submersion.
How long until it holds?
3 in 1 cures at 3 to 4mm per 24 hours; 650FC at 2.5mm or more per 24 hours. Support the panel until it has cured.
Does the timber need to be sealed first?
The surface must be clean, dry and free from dust and grease. On a cubby house, painting or sealing raw timber before assembly gives a more durable result overall.
Can I work in cold weather?
Apply 3 in 1 between 5 and 30°C, and do not apply 650FC below 5°C.
What if the acrylic already has a coating or film?
Remove it from the bond area. Adhesives bond to the surface they touch, not through a film.
Is there a related answer for acrylic sheet?
Yes — how to glue acrylic covers acrylic-to-acrylic bonding.
What is the best sealant for adhering Perspex to wood when building a kids cubby house?
Liquid Nails Exterior is a suitable option for adhering Perspex to wood, though it's recommended to do a compatibility test first to ensure optimal adhesion for your specific application.
Should I test the adhesive before applying it to my whole project?
Yes, compatibility testing is recommended before proceeding with your project when using Liquid Nails Exterior to adhere Perspex to wood, to ensure optimal adhesion performance.
Can I use any sealant to adhere Perspex if it will be exposed to water?
No, Perspex cannot be used with certain sealants under water. Sealants like Marine Flex are not suitable for Perspex, particularly in underwater or submerged applications.
What surface preparation is needed before adhering Perspex to wood?
Both surfaces should be clean, dry, and free from dust, grease, and oil before adhering Perspex to wood.
What should I do if my Perspex-to-wood bond needs to withstand water exposure?
If you require a bond that will withstand water exposure or underwater conditions, you should consult product datasheets for alternatives specifically formulated for these demanding applications, since products like Marine Flex are not suitable for Perspex in submerged applications.