best thing to fill a bumper hole?

[PranK]

I have a new bumper for my car in trying to prep and paint. It didn't have holes for the headlight washers but the cutout was marked on the back and I cut them both out. The problem is I probably went a little wide on one side and I'm not sure the hole will be properly covered when the washers are off.

What I'm going to do is to try and close the hole a little bit but I'm not sure what I can use to do this. I tried filler but it just wasn't strong enough. What should I use?

Thanks guys

Christian

[GTSBoy]

Take the bumper to a crash repairer or a plastic welder (the sort that the crash repairer would use if they don't have their own guy) to stitch a little plastic into the hole and sand it back.

[HCD Velcra]

Obviously the most common thing when working with bumper plastics: Use fiber glass stuff from the inside, put some layers on, then fill from the other side and make a new hole. Youd still need to cover the color difference though, but surelly the cheapest way

[Unzipped Composites]

12 hours ago, HCD Velcra said:

Obviously the most common thing when working with bumper plastics: Use fiber glass stuff from the inside, put some layers on, then fill from the other side and make a new hole. Youd still need to cover the color difference though, but surelly the cheapest way

 

Fibreglass isn't going to stick long term to a plastic bumper, even with very good mechanical key. 

 

@PranK if you want to do the job yourself, look for a plastic bumper patch kit for a 2-sided repair. Something like this: 

https://wholesalepaint.com.au/products/3m-flexible-bumper-plastic-patch-automotive-repair-kit-05888

 

Personally I prefer the kits that use a thermoplastic or aluminium mesh patch that is bonded in place with a 2k polyurethane adhesive, but these self adhesive patches work OK too - just make sure the surface is VERY clean first, which means wipe with isopropyl alcohol, then sand with 240 grit (ignore the instructions not to sand), then wipe again with the isopropyl. 

Then you can use a flexible plastic filler (Isopon is good, 3M better) like any generic body filler and fill from the back before sanding smooth. 

[PranK]

I'm trying to DIY this as much as I can so I think that 3M patch kit looks the goods.

Thanks guys!

[PranK]

@Unzipped Composites found this one, looks too easy ! https://www.ebay.com.au/itm/174576698610?hash=item28a59504f2:g:RxkAAOSwh-df67kj&frcectupt=true

 

 

[Unzipped Composites]

55 minutes ago, PranK said:

@Unzipped Composites found this one, looks too easy ! https://www.ebay.com.au/itm/174576698610?hash=item28a59504f2:g:RxkAAOSwh-df67kj&frcectupt=true

 

 

Yeh thats the stuff. It is very easy, you just need to use the right materials.

Plastic being a low surface energy and very high flexibility makes it difficult to bond to, so rigid resins like polyester or epoxy (your two typical fibreglass resins) will struggle to bond and will eventually delaminate. These plastic-specific repair products are just as easy to use (even easier in fact), but will do a good job of a permanent repair.

[PLYNX]

I have also had great success using vinyl ester resins for these sort of repairs over the years.

Vinyl ester resin tends to be a little bit more flexible than polyester resins used in most fiberglass

But as Martin ( Unzipped Composites ) states prep work is very important for the best adhesion.

With ABS type plastics first washing the affected area first to get rip of dirt and grime first.

Sand area as required

Then cleaning the area down with acetone will begin to "soften" the plastic and make the surface sticky or tacky to the touch.

And then finally a wash down with styrene monomer being sure not to touch the area after the wash down to avoid contaminants on the fresh plastic surface.

This will give the very best adhesion between the plastic and vinyl ester resin on application.

So ends today science lesson !

[Rusty Nuts]

On 6/5/2021 at 10:01 PM, GTSBoy said:

Take the bumper to a crash repairer or a plastic welder (the sort that the crash repairer would use if they don't have their own guy) to stitch a little plastic into the hole and sand it back.

I do my own plastic welding, use a cheap as sh#t chinese welder off Aliexpress, I use good quality welding rods, and source patch pieces from other Nissan plastic bars. Then the repair is smoothed with flexible plastic filler available from repco. I have a collection of repaired R33 S1 and S2 and M bars which were discarded by their previous owners. I also make my own ABS filler paste, very easy and ingredients available from Bunnings.

Edited June 9, 2021 by Rusty Nuts
additional information

[PranK]

Thats super cool @Rusty Nuts - sounds like a good DIY topic!

This front bar is the first time I've ever tried body work. I've already cut these holes too big and my prep work is terrible with paint and primer not even sticking to some parts and then theres the mess!!

Thanks guys, I'll try these 3M patches as they are probably the easiest for a simpleton like me, then I can just pack filler over the top. Then I get to prep and prime again.

 

[Unzipped Composites]

4 hours ago, PLYNX said:

I have also had great success using vinyl ester resins for these sort of repairs over the years.

Vinyl ester resin tends to be a little bit more flexible than polyester resins used in most fiberglass

But as Martin ( Unzipped Composites ) states prep work is very important for the best adhesion.

With ABS type plastics first washing the affected area first to get rip of dirt and grime first.

Sand area as required

Then cleaning the area down with acetone will begin to "soften" the plastic and make the surface sticky or tacky to the touch.

And then finally a wash down with styrene monomer being sure not to touch the area after the wash down to avoid contaminants on the fresh plastic surface.

This will give the very best adhesion between the plastic and vinyl ester resin on application.

So ends today science lesson !

 

I still wouldn't consider this a permanent repair man. Vinyl esters aren't really more flexible than polyesters*. Realistically vinyl has better cross-bonding properties which is why it works better than polyester, but epoxy is even better again so if you had to choose a regular laminating resin to attempt to repair ABS with then it would be epoxy all day long. 

 

Fact remains though, ABS is a low energy plastic and is difficult to bond to. Not completely impossible like some others types of plastic, HDPE and Polypropylene are virtually impossible to bond, but still difficult enough that even an epoxy bond will only be 'moderate'. You can improve it slightly by increasing the surface energy of the ABS through flame treatment, though this is more difficult than just waving a butane torch around for a few minutes. There is a precise moment when the flame treatment increases the open sites on the ABS and it becomes bondable, but take it too far and those open sites break down again and the surface actually becomes 'greasy' and even more difficult to bond to. So really to do it properly requires proper equipment, and is a bit beyond the realms of repairing a vehicle panel.

 

*they are, but you're talking ~5% elongation of vinyl vs 3.5% elongation of polyester - ABS is around 50%. This can be part of the problem, because the laminated fibreglass patch will fail long before the ABS does, meaning any patch will always delaminate without much strain. Obviously this is only really an issue if the patch is in an area where the ABS is constantly moving around (try to patch an ABS mudguard and see how long it lasts), on a component that is rigidly mounted and doesn't move much like a front bumper, then the patch will mostly stay in place unless it experiences a large degree of flex at some point (like pulling the bumper off). Trouble is, on a vehicle all panels are subject to vibration, which can start to break the bond and make the repair visible underneath your paint job. It may not actually fall off completely, but it is less than ideal to have a repair showing up later once you've gone through all that effort and expense.

 

All of this is largely irrelevant simply because products exist that are more suitable for the job. 

[Rusty Nuts]

On 6/9/2021 at 1:30 PM, PranK said:

Then I get to prep and prime again.

There are some good guides for prep on YouTube. Wax and grease remover use before starting any work, use before and after sanding and use a plastic etch primer if you're using cans Septone make one I've used.

[Unzipped Composites]

Just now, Rusty Nuts said:

There are some good guides for prep on YouTube. Wax and grease remover use before starting any work, use before and after sanding and use a plastic etch primer if you're using cans Septone make one I've used.

 

Also wash with soap and water. Wax and grease remover will remove oil based contamination but not water based. Best to use both.