what to use to bond hard plastic item, when superglue doesn't work?

me1000uk

Hi there,

I have this plastic item, it's one of those height measuring things that you see at doctors. Handy for keeping track of kids heights. Unfortunately my toddler sat on the measuring bit (it's a hard plastic bit that rests on the head to show the height) and broke it. 

 I've attached a photo to get a visual for the area that needs glue (you can see the left side is pointing down slightly because the area with the arrow is broken.

No spare parts available as discontinued, and I tried gorilla super glue which did absolutely nothing.

Any ideas for what type of adhesive to fix this?


Appreciate any suggestions!! thanks in advance.

Section62

me1000uk said:

Any ideas for what type of adhesive to fix this?

It depends on the exact type of plastic.  Are there any markings anywhere which indicate plastic type?


Also, it is probably a case that rather than just applying glue to the break, you need to add some extra material to add strength and reinforce that section.  For example gluing some 'blocks' into the corner on both sides so the total surface area of the glue join is much greater.

Could you repost the picture without the arrow so we can get a better look at the break?

Belenus

Epoxy resin, perhaps plus reinforcement as above, should work.

FaceHead

Are there any markings on the product that indicate what type of plastic it is? Looking at the component, there's a decent chance it's ABS, which - along with the gap there - would have me reaching for the araldite, or any sort of two part epoxy that will fill that gap.

victor2

As Section62 says, it depends on the type of plastic.

Many superglues list certain plastic types they will not stick, such as polyethylene or polypropylene. I had to glue some perspex together and got this. It worked well on a test piece, but the actual pieces glued came apart after a little use and they weren't under a lot of stress.

Another vote for reinforcing the joint, if you find some adhesive that sticks!

531063

JB Weld                                                      .

grumbler

Some plastics are next to impossible to glue. In such cases a small soldering iron with the right tip at the right temperature can help, possibly with a small piece of the same plastic taken from some unimportant place. This does require some skills.

twopenny

Have you tried aroldite? The original version with 2 parts.
I've seen it stick a loo seat to great effect and that takes a lot of sitting on!

Bendy_House

That's a crack that's due to the LH piece having been bent downwards in relation the RH section?

The problem with superglue in this situation is not only that it might not adhere well to such 'waxy' plastics, but that the actual contact area is so small. And S-G relies on a good close contact too.

Can you pull the LH bit 'up' so's to close the gap? If so, that's your starting point so that the part is 'straight' when fixed. Perhaps a strip of sticky tape pulled firmly along the whole top will hold it tightly closed during the gluing process?

As said above, the strongest repair will involve having extra adhesive added along the corners either side of that crack. That won't get in the way of anything, will it?

Before adding the chosen adhesive, I'd use a craft knife or similar to scrape the surface along that corner in order to remove the worst of the shiny plastic surface, and even consider 'keying' it further by scratching it or using coarse sandpaper - that should really help the adhesive to stick.

And then a nice bead of epoxy-adhesive (Araldite-type stuff) or even - and simpler - a slow bead from a hot glue gun, either side.

Do you have one of them? No?! And you have kids?!!! (Mind you, the first lesson they'll learn is how to burn themselves...)

Section62

Bendy_House said:

Can you pull the LH bit 'up' so's to close the gap?

This will be necessary in any case, otherwise the measure will be incorrectly reading.  Ok, it will only be by a small amount, but imagine the potential trauma involved in discovering you've grown 0.5cm in the space of a couple of days.

Bendy_House said:

As said above, the strongest repair will involve having extra adhesive added along the corners either side of that crack. That won't get in the way of anything, will it?

Just for clarity, I wouldn't suggest putting extra adhesive in the corners, as the adhesives most likely to work won't add much strength if used like a fillet weld.

What I was suggesting is to try using is some additional (plastic) material to be bonded into position acting like a fillet. The glue joint is then working over a much larger surface area and the fillet material provides additional strength.

If the manufacturers have used ABS then my ideal choice would be some uPVC angle trim (or modesty blocks) bonded in place with uPVC solvent... but other options are possible using stuff people are more likely to have laying around the house than angle trim and uPVC solvent.  Could be time to raid the box of 'spare' Ikea parts.

me1000uk

Hi All,
Thank you so much for the responses. I'll address some of the questions raised below and I've posted a couple of photos.

- type of plastic? Not really sure, nothing to suggest the type of plastic on it. It's not got much flex to it. I would suggest it's the same kind of plastic you'd find on a brightly coloured cheap kid's toy that cracks easily or maybe a remote control or cheap mouse.

- The contact points are quite small as can be see from the whiteish area where the crack happened. There is some further stress a few cm below at the bend, but the main crack is a small contact. I do think however the if something is applied to the red part as well as the crack, then it becomes a much larger contact surface to work with. The red part below the crack can be held against the blue part adjacent providing added reinforcement if the right adhesive is used.

I was hoping theres something like a liquid that cures hard almost like a type of cement that can be held in place for a few minutes? Or something more suitable than the superglue. If I need to rough it up a bit then it's fine, as the superglue definitely struggled with the glossy finish it was as effective as putting water on it.

- The soldering option or anything involving melting the plastic could well work but was hoping for something I can buy for less than a tenner from amazon or screwfix and involves a low risk. 

- yes the crack was from pressure on the big 'head' rest' being sat on and flexed it downwards. In terms of adding more adhesive it's not really an issue as it won't affect it operationally. It's essentially a sliding measure where a rectangular hole simply goes on to a large ruler and moves freely. The repair isn't impacting that function, and is mainly to prevent further damage and of course straighten it so the measure is accurate.

Hope that helps refine the glue required? Many thanks again. As mentioned the replacement part is discontinued and the new model is north of 70 quid so the money saving repair is the much preferred method!