I have a 1:24 scale model car and the decals keep peeling off after a few weeks. I've already tried gluing them with white glue but it doesn't work. Is there any trick or specific product to keep them stuck properly?
White glue (like school glue) just isn't designed to last on smooth plastic surfaces, so it makes sense that your decals keep peeling off. What actually works with decals is using a stronger adhesive specifically formulated for this kind of job. Look for contact cement (like Poxipol or similar) or even better, a hobby model decal adhesive - some come in tubes and others in spray. Spray is easier to apply evenly without getting air bubbles.
Now, the important trick is preparing the surface before you glue. Clean the area where the decal goes really well with alcohol or a degreaser so there's no dust film or residue left - that's what most people mess up. Let it dry completely. Then apply the adhesive in thin layers and press the decal down for a few minutes without letting go, and if you can, use a flat object to distribute the pressure evenly.
Some people also seal the decals afterwards with a clear matte or glossy varnish (depends on the finish you want) - that not only protects them but helps lock them down better. If your model is going to be somewhere with temperature or humidity changes, that's especially important because plastic expands and contracts, and the varnish acts like a kind of "shock absorber" that keeps everything stuck. Try this and you'll see it lasts way longer than just a few weeks.
I've had the same problem with my models, and honestly, white glue is never going to work on smooth plastic 😅 What I'd recommend is using a decal adhesive like Microscale Decal Set or something similar - it comes in two parts and sticks way better. Another cheaper option is to apply a thin coat of matte or gloss varnish over the decal once it's on, so it gets sealed and won't peel off as easily.
After I messed up applying decals on a model years ago, I found out what really works is sealing the decals with a matte or gloss varnish on top, not trying to glue them better underneath. Once the decal is in place (even if it's just with temporary white glue), a coat of acrylic varnish fixes it completely to the surface and keeps it from lifting over time, plus it protects it from dust.
Before applying the decals, lightly sand the plastic area with fine-grit sandpaper (like 400-600) so it loses that slippery shine, then clean it well with a damp cloth and let it dry. After that, use a contact adhesive or a model glue like Tamiya Extra Thin Cement, which dries fast and holds way better than school glue. The trick is preparing the surface, not just picking the right glue.
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