Repairing and strenthening thin moulded plastic

What type of plastic? It's difficult to glue things to polyethylene and polypropylene (for example), even though "sticky tape" of various sorts will stick well.

Such a lot also depends on the loadings and requirements.

Traditional fibreglass kits use polyester resin rather than epoxy. It's cheaper, more brittle, and does not stick quite so well to many things. Epoxy plus fibre glass is good, provided it has the basic adhesion. "Mechanical keying" is also a big help.

I'm not sure how to tell what kind of plastic it is.

It is hard rather than soft+flexible.

Cheers

Dave R

A crude guide is if it feels waxy then it is probably HDPE which almost nothing will stick to reliably. If you can shave a piece off and try it with various solvents and gentle heat that will distinguish cured resin one time cure plastics from thermoplastics after that it is guesswork.

If you don't know what it is then slow epoxy is the least likely to cause adverse solvent effects and be reasonably strong. Thermoplastic glue sticks can be effective in the right circumstances too.

If you need a bit of flexibility and the load isn't too high I have had some luck mending torn door seals with black Sugru (sp?).

Try to find out what the plastic is. There may be a symbol moulded into it. If not, you could try Floplast SC250 solvent cement or similar, an internet search will show you loads of suppliers.

A picture of the fitting might be helpful. If it's a plastic called ABS, then the above will fix it "as new", and allow you to stick on more similar plastic as reinforcement.

Hopefully you will be able to see these.

I can't see any markings on the moulding but there could be some on the inside. However taking it all apart could lead to more problems.

The edge of the plastic at the bottom of the door measures 3mm on my digital callipers. I can't get the jaws in the hole but I assume that the thickness is consistent.

Cheers

Dave R

Eurgh. I'd *guess* it's some sort of foamed PVC. Floplast 250 sticks that as well as ABS. You could experiment with some acetone, e.g. nail varnish remover if you know anyone that uses such stuff, you could get some on a clean rag and see if it dissolves any of the material when you rub it on. If it does, solvent cement would be useful (the MEK in it is rather more aggressive than acetone), but you still have the issue of what to bond to it (maybe a ring doughnut shaped piece of stuff). More of the same sort of material, or ABS.

However, is it either of those two plastics is the question!

Do you think it would be foamed at 3mm? I'd be more inclined to suspect PE or PP, unfortunately.

But I agree with the rest. Given the geometry, after solvent testing it would not be hard to do a little trial somewhere away from the damaged area.

I can't really figure out the problem from those images but, if there is space behind, it might be possible to shape a piece of thin aluminium to back up the whole damaged area. Then, if you attach that using pop rivets from the front it's sometimes possible to make a fairly inconspicuous repair even on polyethylene. (I have a heavy duty wheelbarrow that I repaired that way). If you sandwich Sylglas tape between the plate and the original that should give you quite a strong repair.

Is it strong or brittle or bendy or what? What does it do? Myself I'd have a bash at doing it and see what happens, if its naff now it assumedly will be no naffer afterwards! Brian

The problem is that on one side the locking rod came out of the hole when unlocking (design issue) and then went through the plastic when locking.

You should be able to see most of an off-round hole (to allow the fixing to be adjusted) with shattered plastic below.

On the good side you can see a round metal guide clamped to the plastic by two bolts so you can't see the hole.

The metal guide for the broken side isn't visible in the picture.

Looking at the whole thing - a very large sheet of black plastic with various bends, lumps and bumps, I assume that this was probably made by vacuum moulding a flat piece of plastic when warm and pliable but this is just a guess.

My main concern with pop rivets and the like is not fouling anything, but there does look to be some leeway, especially if the rivet heads are on the inside. The main issue is access as I'm trying to work from within a bulge so getting at the inside part may be tricky.

If I run out of time short term I plan to cut up a plastic container, cut the hole, and duct tape it into place so that at least the end of the locking rod is supported and pointing in roughly the right direction.

Thanks to all for the help so far.

Cheers

Dave R

It's a vacuum moulding for sure

Another option if you want to fasten something to the *visible* side is rivnuts (which are like pop-rivets but with a thread inside them). Much used in kit-cars and the like, there are cunning tools that let you position them without enough access on the visible side for a conventional pliers or lazy tongs type tool.

The top hinge on my fridge broke the other day. May well have been my fault - leaning on the top of the door.

It is made out of a semi rigid plastic. Being old, it may well have been more flexible when new. But not very different from the sort of PVC guttering etc is made of.

Luckily the break was in the top plate, rather than the hinge pin. So I cut a piece of 1.5mm steel to cover the top plate and glued the whole lot with Gorilla super glue. Left it a day to set fully, then painted the steel to match the plastic. Seems to have worked OK.