From Wired How-To Wiki

There’s a reason why Lego has sold somewhere north of 400 billion of those colorful little plastic blocks. People love assembling the models, taking them apart again and making their own creations. Repeatedly. Even the wildly successful licensed model kits like those in the Star Wars or Harry Potter series will eventually make it into the collective tub of Lego bricks found in many homes (whether kids live there or not).

So if one of the biggest reasons for Lego popularity is the ability to continually reuse the bricks to build new creations, why on earth would you want to glue it? Even mention gluing Lego in the wrong forum and you’ll pay for it with a stream of “Are you crazy?” themed comments — or worse.

However, despite the general rule that you never glue Lego, there are actually some practical reasons for doing so. The professional model builders who create pieces for the various Lego theme parks get a free pass, obviously (you can’t have those gigantic models at Legoland collapsing and injuring a guest because kids removed some key pieces). But there are other times when gluing your personal Lego creation together makes sense as well. For example, my family has a Lego train that runs beneath the Christmas tree every year. That set isn’t going to be broken up for pieces, and everyone gets tired of reassembling it after a Catzilla attack. Time to glue it. I have a complex Lego model that decorates my office. It’s been knocked off the desk several times (catzilla again), and gluing means not having to scramble for missing pieces and putting it back together again for the umpteenth time. Maybe you want to preserve your kid’s first Lego creation for posterity — you could take a picture, or you could glue it.

What You'll Need

Gluing Lego involves adhesive (duh), but depending on the condition of the Lego bricks, there are a few other items you should have handy, including:

• Compressed air
• Isopropyl alcohol
• Cotton swabs
• Toothpicks
• Tweezers
• Razor blade

In terms of which glue to use, there are multiple choices. Epoxy should hold, but it can be messy, smelly and difficult to work with. Clear ABS glue (used to fasten sections of ABS pipe together) works great —after all, Lego is made of ABS plastic — but it has a very unpleasant smell during application and takes a day to fully set. Gorilla Glue is favored by some, but with a caveat that you have to be very precise as the glue expands as it dries. Hot glue could be used, but it tends to be less rigid and can be very messy to work with. Some folks recommend plastic model cement. The option that seems to offer the best compromise between permanence, cost and ease of use is super glue, although you do have to work fast and be careful not to glue the bricks to your hands.

I used Krazy Glue brand super glue and opted for a package of mini tubes rather than one large tube. This way, if the applicator got gummed up or I left the project for a few days, I could just start a new tube of glue. One of these 4-packs was sufficient for a 1,000-piece project.

Are You Sure You Want To Do This?

Now that you have all your materials (I’m assuming you have the Lego kit too), time for a gut check. Still want to go though with it? There’s no shame in backing out now and legions of Lego geeks will applaud your decision to leave your bricks au naturel.

Let The Gluing Begin

Lego is a toy, but that doesn’t mean you should approach gluing a model together without some serious planning. After all, you’ll be working with super glue and a lot can go wrong if you take a half-assed approach.

If this Madalorian trooper looks pissed, it's not because he's missing his helmet — that can be fixed. It's because I was in a rush and too much glue was used to attach his head and backpack, leaving him with a permanent case of ring-around-the-collar.

Pre-Assemble The Kit

What is it carpenters say about cutting wood? ‘Measure twice and cut once’ or something like that? Apply the same logic to your Lego kit. Put the thing together once so you’re familiar with assembly. Finding out you attached a piece facing the wrong direction is going to be a real burn when you’ve super glued it. A trial run at assembly also helps you to pinpoint any tricky areas where applying glue might be more challenging.

Clean the Bricks

If the kit you’re building is fresh out of the box, you can skip this step. However, if the Lego you’re gluing has been in circulation, you’ll want to clean it first to ensure the glue adheres properly. If it’s filthy, considering subjecting it to a good wash, otherwise give everything a blast with the compressed air to get rid of dust, then use cotton swabs and the isopropyl alcohol to clean any surfaces that will be bonded.

Approach the Model Strategically

Gluing the entire model isn’t away a good idea. For one thing, you may want to retain the ability for adjustable sections of the model to move, wheels to turn, that sort of thing. And remember that Lego train from the introduction? The one part that’s likely to eventually need replacement is the electric motor, so it was important not only to pass on gluing this component in place, but to avoid gluing any pieces that would interfere with its removal.

There are also structural considerations to account for. When you use glue to permanently bond pieces of Lego together, you introduce the possibility of parts of the model snapping if stressed (for example, if it topples over). Normally, this isn’t a problem — the Lego model falls down and pieces fall off. However, if the pieces are glued together with a rigid glue, it’s possible that a section could snap, breaking pieces instead of just falling into easily reassembled components. A large lump of a model isn’t likely to be problematic, but if you’re gluing together a kit with limbs, legs or other protrusions (like General Grievous in the photo), leave out the glue in strategic points so that if the model falls, it has stress points where it can naturally fall apart instead of shattering.

Lego's General Grievous kit is a prime example of why strategic gluing is important. If this model were completely glued together, a fall could easily snap one of the thin, fragile limbs or light sabers. Instead, the circled joints were assembled without glue to provide natural breaking points — putting a half dozen pieces back together is a lot easier than sourcing the parts and rebuilding a shattered arm.

Apply Glue Carefully

With super glue, a little goes a long way. You want enough to secure the two pieces of Lego without having excess squeezing out between the bricks. You’re going for an invisibly glued look, not a melted-wax-dripping-down-a-candle effect. Applying too much can also potentially affect moving pieces (the glue can run down an opening to an adjacent piece, locking its mechanism) and it looks unattractive with clear pieces.

Most Lego pieces fasten together via small studs and have very tight tolerances; a small drop of glue on one or two of the studs so that the top and at least some of the side surface is covered should ensure a secure bond. Cover multiple studs if you are gluing a large piece. There may be odd pieces that are inserted into openings, in which case a small dab of glue on the piece to be inserted should take care of it.

Pro tip: Avoid getting glue on your fingers. This could result in your fingers being glued together (unpleasant) or smudgy glue prints on the Lego bricks (unsightly). If it helps, a toothpick can be used to more precisely apply the glue and tweezers may be useful for manipulating small pieces.

One of the advantages of super glue over other methods is its quick bonding time. When you glue two pieces together, apply pressure for 30 seconds, then they should be fine and you can move on to the next piece. Final curing takes 12 hours or so. A small drop of glue on one or more studs is all it takes in most cases. A slight drip down the side of the stud is good, but avoid the possibility of excess glue squeezing out where it will be visible by applying glue on the inside edges of the studs instead of outside facing edges.

Pro tip: If you find yourself in the unfortunate position of having made a boo-boo, the razor blade might be able to save you. Carefully insert the blade between the bricks (remembering this thing is literally razor sharp and will damage plastic as well as your fingers) and, so long as you weren’t too generous with the glue, you should be able to pop the pieces apart.

General Tips

• Any glue can be toxic and give off toxic fumes (even though they may not be obvious), so always work in a well-ventilated area.
• If you have a few pieces of extra Lego, practice your gluing technique before starting the project.
• Make sure bricks are fully interlocked. If you don’t press them together firmly, you’re left with a gap. This looks bad enough at the best of times, but with super glue, your carelessness is on permanent view. In a worst case scenario, pieces further along in the model assembly may not fit (remember those tight tolerances), leaving you with a real problem.
• I said it earlier, but it’s worth repeating — a little super glue goes a long way. If you ere on the side of caution, it’s easy enough to glue the piece back on with a bit more glue, but if you use too much you risk a mess.
• Be especially careful about glue placement and use the minimum possible amount with clear pieces. Where possible, place glue closer to inside facing surfaces to reduce the likelihood of any excess being visible.
• If you end up with extra glue oozing out of a joint between pieces, don’t give in to the temptation to wipe at it with a paper towel or you’ll end up with an even bigger and uglier problem. You’re better off waiting for it to harden, then mechanically scraping the excess with a razor blade, or using fine sandpaper.
• Know where to find replacement pieces. If you accidentally mess up, you may have to put the project on hold while you wait for replacement parts. If you aren’t near a Lego store, Bricklink is a good resource for buying individual pieces.
• If you get glue on your fingers, call a time out until it’s dealt with. Don’t touch any Lego pieces or you’ll end up with a glue fingerprint that captures your shame for eternity. Check here for tips on how to get the stuff off your hands.

Original article by Brad Moon, Wired.com.