The 'E' Type Forum

just a general request here. I have some old plastic trim on an early Range Rover that has cracked and wondered whether anyone on here has any experience of welding plastic? There are a number of kits available on E any and whilst they are not overly going to break the bank I don't really want to buy one to try it out if they are rubbish. The plastic is about 2 mm thick and black. It would need to be "dressed" somehow as it is on show. Not sure whether they can be filed down afterwards or not

I bought one (butane) to try and repair a cracked brake fluid bottle (epic fail!). However I have managed to use it to repair more modern plastic although getting a smooth finish takes time. Once you have filled the crack you can file the excess down but I have not tried it. They are great for repairing broken plastic bits though. Bear in mind there are many different types of plastic - PP, PE ABS etc - so you need a kit with a choice. The butane versions work by contact, electric ones work with hot air.

I've repaired plastic using an electric soldering iron with a fine point. I used the point to melt and then mix both edges of the break.

I've successfully repaired plastic parts (on show cars and prototypes) using different methods.

When working with a visible surface I've used a proprietory 2-component plastic repair adhesive (which flexes much more that a traditional epoxy) together with correct primer for the type of plastic involved. This method allows sanding, and subsequent painting. Typically used in car workshops to repair split bumper facias.

For non visible (but still functional) parts I find that the good old hot-melt glue gun works well, especially with the typically more slippery plastics such as PP and PE. For example washer bottles and other fluid reservoirs not under pressure, wheel arch liners and such. Again, the key is to select a suitable glue, not all hot melts are equal.

I've also hot-welded rotationally moulded (thick) PP and PE parts, using a proper hot air gun with feed nozzle and 'filler cord' (as in metal welding wire). It's an art, a bit like TIG vs MIG, where MIG is point and shoot, TIG is a skill to be learned.

Regarding repairing visible trim on an classic RR, I would tend to avoid welding, and go with a cold repair on the rear surface (e.g. 2K adhesive, even consider a bit of glass fiber weave) to mate the parts, and fill any cracks, then repaint the entire section with a colour matched paint.

The bigger problem is it not to identify the plastic to repair?
The plastic is not a matter it is only a genertic name, and you don't repair PVC like PE or ABS.
Do you know somebody who sell these different kind of kit ?

I got "BONDIC" it's liquid plastic which cure with a little UV lamp.
Very easy to use but with limited use.
What do you think about it ?

I've got a Bondic set. I find it quite useful for repairing instruments and switches and such. It sticks quite well to brass (if you roughen the surface with #120 sandpaper) so if a part needs reinforcing you can embed a bit of sheet or wire to strengthen the original and hold/seal that with Bondic. It has mostly replaced 5 min epoxy for me, as it is much faster and a lot easier to build up an area with. I also use the UV diode that came with it with leak detection fluid.

I have also seen here a system for repairing plastic trim with which one heat welds a series of staples across the crack to stabilise the crack mechanically before filling, either by welding or epoxy filler.

I have had mixed success with the dash repair kits where you mix a coloured filler then clamp a textured release sheet to match the surface texture. Here you need to cut back the edge of the plastic far enough that the oxidised foam underneath gives a good surface to bond to.

The key with plastics is to choose a filler/glue which will bond to the plastic, and to make sure that the repair isn't subjected to mechanical strain.

Andrew

Good knowledge out there again! Thanks guys, not sure what type of plastic my trim is. It's the sill that runs along the bottom of the door and wings. It is a complex moulding made in two parts and bonded together, so hollow. The rear ends always crack due to a weak fixing on the rear wing which if knocked takes the plastic with it. They are unobtainable. There is a number on the part which I don't think is a part number so maybe some sort of id. I will photograph the item as one or two of you maybe able to point me in the right direction. Apologies it's non E type but I feel sure it's a useful thread for others as well.

Here is the broken bit

Not quite sure where this part is on the RR, is it a visible sill moulding on the outside of the RR, or a trim panel visible once the door is opened ?

Anyhow, my money is on it being a PP or an ABS material, quite possibly a PC-ABS blend, commonly used on exterior trim parts, however I'm not sure when the blend became widely used. It's good a definition of shape and it's quite robust and self supporting for large panels. The PP is much tougher (resilient) but is poorer on shape definition and self support (e.g. needs more clips, or more 'shape').

To differentiate the PP from the ABS theory you could thoroughly clean the loose part and drop it into water. If it floats then it's PE or PP. If it sinks, then you can drop it into glycerin / glycerol (e.g. from Boots the chemist), ABS (and PS) will float, whilst PVC would sink. But I' sure it ain't PVC and it ain't PS.

Of course if the part is painted and not just through-coloured then the paint will alter the results.

If you have a good nose and a spare piece you can do the burn test. The odour and the type of burn, drip and soot will tell you more. Don't laugh, I've seen plenty of engineers do this when they're stuck, although usually a bit of finger feel get's them pretty close.

There's a nice interactive animation on this link, leading to a step by step process.

http://www.doitpoms.ac.uk/tlplib/artefact/polymers.php

Thanks to Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

If you can get the part off the car it will be marked as to the type of plastic. You can tell the diifference between PP and PE with a flame test.

The sill finisher is off the car but I have not seen a coding yet. Will take a look again. So are we thinking welding it or using the bondic?

To weld, or even bond it, there will need to be reinforcing material added such as metal mesh. There are several plastic welding video's on Youtube so you can see the process. Might also be worth taking the part to a body specialist and get their advice - they repair bumpers using mesh and plastic welding.

Hi Andrew

An idea to repair this part.
First of all I finish to cut it.
It seems to have some foam inside and on the round part remove it on a small length on the two parts with a Dreumel.
I make also a chamfer on the edges of the two parts.
After that I'll insert a small rond piece of stainless steel and will glue it ( epoxy ) to reconstruct the straight of the part.
At that state we are strong in the length but not in the width.
Remove a thickness of plastic on the rear face of the hole and glue a small flat part ( 2 mm ) of stainless steel where you drilled the oval hole in it again.
After that refit the part and put some epoxy glue to fill the depth of the chamfer.
To finish the esthetic you can sand the excess of glue chamfer and put some mat black paint on a rag and dab slowly.
Hope it's help you.
Mich

thank you for the advice and Mich , David and others. There is no foam inside it actually, its about 40mm in diameter and that is all hollow.

I am sure this can be done successfully I just have to work out which is the best tool and procedure for the job. I will check the material and start from there.

If I am correct, it seems the collective view appears to be the it will not glue or weld without some structural rigidity into the part with a filler. It was suggested to me that on the blind side which cannot be seen, one could drill say four holes and stitch it together diagonally with lock wire and a twist plier.

Would be so much easier if I could buy a new one!