Repair with JB Weld - mould release coat?

[GLK]

I'm going to attempt an adaptation of a W176 black Mercedes bonnet star to the W169/R230 type of fixing.

This will involved taking a mould from my original bonnet badge and forming a copy on the back of the new one.

If I use a silicone rubber mould, what would I need to release the formed JB Weld part?

Any spray, like PTFE or even WD40, etc, or will the silicone mould be "immune" to epoxy all by itself? The mould is a food grade high-temp type.

I also have Araldite and Abro Steel, but I think JB Weld is better for the job?

 

[wu56Shoozz]

A Coating of talcum powder in the mold usually works, just make sure that the mold is properly coated all over...

 

[Marku]

It depends what you are going to finish the item with. If you use talc make sure that you rub it over the surface with your finger and empty out any loose. You can get spray release agents, silicone sprays and I have even used spray silicone furniture polish. However you should have no problem with a silicone mould I have not used JB Weld but I have had no problems with casting resin.

 

[GLK]

Thanks chaps!

I bought a silicone mould releasing spray - SILICONE RELEASE SPRAY 500ML MOULD RELEASING AND LUBRICATION OIL | eBay, as a number of people recommended that, specifically for epoxy compounds, and particularly for JB Weld.

PS I don't think the mould I have in mind (thin pins) would be suitable for powder agent, not with my skills anyway

 

[Spitfire]

If you are casting epoxy resin components in a silicone rubber mould, you will not need any kind of release agent. Silicone rubber is (should) be self releasing when used with epoxy (it will wear out and deteriorate after time though, after multiple castings).

The silicone release spray is, I would suggest, for use on 'hard' surfaced moulds, i.e: non-flexible ones with no undercut, in order to release the moulded item from the mould. In a similar way to GRP (glass fibre) components are released from moulds.

Not sure why talcum powder would be anywhere near any of this, you do not need it. Unless you are casting components in White Metal, when talc is often used in conjunction with the appropriately heat-resistant moulds, to aid release of the cast metal (after being poured in, when molten).

I ran a company specialising in cast resin components using silicone rubber moulds for the best part of 20 years, have you considered using PU (polyurethane) resin instead? PU resin can be incredibly versatile, regarding quality of surface finish, cost effective, durability, strength etc etc. Depending on which resin is used of course.

Could you give an idea of which moulding silicone you are using? More specific details on the epoxy you may be using?

Also, without fail, ALL of the components I manufactured were cast using a vacuum chamber too, to totally eliminate air pockets and voids in the final castings, for an optimum surface finish.

As stated previously on these forums, I am currently involved with the manufacture of Carbon Fibre components, but still keep my hand in now and then with cast resin components in silicone moulds as I still have all the equipment in my workshop at home.

Could you post a pic of the component you intend to mould, just out of interest?

 

[GLK]

Thanks, great stuff - just what I needed.

I want to mould the back of the bonnet badge, so I can fix the newer black one (different pins - will cut them off) onto my car.

This is the back / pins I need:

This is what I have, and would like to add a JB Weld mould to:

I bought this kit and spray:

Mouldcraft Fast-Sil 16g-1kg Mould Making Silicone Putty RTV Food safe Sugarcraft | eBay

SILICONE RELEASE SPRAY 500ML MOULD RELEASING AND LUBRICATION OIL | eBay

 

[Spitfire]

I think I see what you are trying to do. Instead of going to the bother of moulding, instead you could ......


1. Remove/grind off the pins on the Black badge, remove/grind off the surface detail on your existing bonnet badge, then bond the Black badge on top of your existing bonnet badge.

2. The method I would take .... remove your existing bonnet badge, remove or grind off the mounting pins on the back of the Black badge and fix it in place of your original badge, using 3M Automotive Double Sided Acrylic Tape, part No. 06384. It is designed for the automotive industry to attach badges, body panels, trim, spoilers etc. The badge will NOT accidentally come off. Any excess tape can be trimmed with a sharp blade.

This is the tape, below:

 

[GLK]

I like the approach number two - that way I can eBay the existing badge, which is less than two years old, and is like new.

I have 3M VHB tapes and pads, so will have a look, if any are 06384.

Right, it appears I do not have 6384 - I have 4910; 4930; 9473 & 4646 ...

 

[KeithJG]

Best to see what chemicals are in the product you are using for producing the part from the mould.
It is important to use chemicals or compounds that are not in conflict with one another.

In the late 60's i was lucky to of been involved producing the Sparkman & Stephens designed GRP yacht Morning Cloud for Edward Heath.

Using any release agent containing silicon in those days damaged the Gel Coat of the grp layup. It became wrinkled on curing.

We simply used a car polish which did not contain silicon for mould polishing and a blue release agent.

 

[Spitfire]

Right, it appears I do not have 6384 - I have 4910; 4930; 9473 & 4646 ...

The spec info/manufacturers data supplied with those tapes should give you an indication as to if they are applicable/up to the job of securing badges or trim items securely.

Unfortunately I do not have the spec sheets/info for those particular tapes to hand. I can only vouch for 3M 06384, from personal experience.

 

[GLK]

The spec info/manufacturers data supplied with those tapes should give you an indication as to if they are applicable/up to the job of securing badges or trim items securely.

Unfortunately I do not have the spec sheets/info for those particular tapes to hand. I can only vouch for 3M 06384, from personal experience.

Thanks. I'll get off my lazy behind and go check on 3M website

I did a similar thing for my old W168, but there was no choice - no factory bonnet badge, so only 3M VHB tape option existed. Lasted nearly four years before I sold the car, have no doubts it's still okay today.