A modder's guide to filler selection and use.

[Pug]

Originally posted at Ars C&CF (http://episteme.arstechnica.com/eve/ubb.x?a=tpc&s=50009562&f=77909585&m=7960946865&r=7960946865)

Well, I've meant to make a repository for this kind of information for a while but was waiting until I could take some good pictures to illustrate my points better.
As it is, I guess the information will be useful and pics can always follow.
All contributions welcome. http://arstechnica.infopop.net/infopop/emoticons/icon_smile.gif

I'll try and add expanded guides with pics to the following various types as I go through them as parts of my current project.
I'll also try and incorporate how I pulled off my modded cheiftec bezel (http://episteme.arstechnica.com/6/ubb.x?a=tpc&s=50009562&f=77909585&m=5980958165&r=6880932565#6880932565) too.
^^^^ link also includes basic modder's guide to primers (http://episteme.arstechnica.com/6/ubb.x?a=tpc&s=50009562&f=77909585&m=5980958165&r=5940931365#5940931365) http://arstechnica.infopop.net/infopop/emoticons/icon_wink.gif


But to start with...

Common basic filler types and applications -

Glass Fibre (Fibreglass) mat and resin (or GRP - Glass Reinforced Plastic) - Normally used for bridging holes and making new structure (ie. filling 3.5" slots and making ducts or scoops).
Often used in combination with aluminium mesh or perforated metal sheet to give structural strength and rigidity.

Heavyweight, Premium or Fibreglass Filler - Normally used for filling larger recesses and grooves which are deep but closed (ie. not a complete hole).

Lightweight Plastic or polyester based filler - Normally used to fill light recesses or lend shape and smoothness to applications of fibreglass or heavyweight filler. Good for general purpose use except for the caveats mentioned where the metal based filler makes a wiser choice. Common variations are normally very easy to sand. (I think Bondo falls into this category)
Sub type - Aluminium metal based filler - Consists of aluminium powder mixed with polyester resin and dries much harder, and is more stable, than the typical talc based body filler. Used on flexible base applications such as plastic bezels or mixed material applications where ordinary fillers would crack due to flexing.

Stopper or knifing putty - A finishing compound used where the depth of fill is less than 2mm.
Commonly used to cover sanding scratches/blemishes, cracks or air bubble craters in filler.

[Pug]

Glass Fibre (Fibreglass) mat and resin (or GRP - Glass Reinforced Plastic).

This filler type is very useful for bridging holes and/or creating non-stressed panel features.
It is light, non-corrosive, cheap, easy to work with and is strong enough for just about any PC modding duty. Bezels, panels, scoops, ducts, stealth mods, you name it.
Hell, you could even make a complete case from this stuff. With funky looks too! http://arstechnica.infopop.net/infopop/emoticons/icon_biggrin.gif
It can be carved, drilled and even tapped for threads after setting.

It doesn't require any specialist tools or equipment, either. You can normally buy a kit that will just require you to purchase extra mat and/or resin/hardener at a later date as you need it.

The main common components are
a) Polyester resin
b) Hardener BPO (Dibenzoylperoxide)
c) Fibreglass Matting
d) Aluminium mesh (optional)

The basic application of this consists of cutting the desired shape/size of matting ready for your chosen task, then mixing up 2-3cm of hardener as a catalyst to 10ml of resin (may vary by brand - read instructions on your chosen product), which is then applied to the mat to impregnate it and bond it to the area you are repairing/enhancing.

Preparation
Using a medium/coarse flatting paper, rough up the area around the hole on both sides of the piece to key the surface ready for bonding.
It's ok to remove material around the edge from the front side here, as this will allow for an easier blend and greater security of the repair after final sanding.
Try to aim to create a slight taper inwards if possible, so that the area around the hole is dished slightly.

Cut up two or three of pieces of matting, slightly oversize (about 1cm) for the hole and set them to one side.

If you are dealing with a large hole or aperture, you will probably need to reinforce it by means of aluminium mesh to prevent sagging that would require copious amounts of extra filler to overcome.
As long as you have access to both sides of the workpiece, you can turn the piece over to apply the mesh to the back side, making sure that none protrudes proud of your desired final surface (2mm deep would be a good depth to aim for, or use the thickness of the surrounding panel as a guide.).
Cut the mesh about 1cm oversize for the hole.
If your hole is part of a box section, don't despair, cut a piece of mesh that you can feed through at an angle and insert a screw into the middle of it. You can wind this screw against the blind section to pull the mesh against the desired surface, bond round the edge, remove the screw and fill over it.

Working on the back side, apply activated resin or filler around the edge of the aperture to hold the mesh in place, apply the mesh, then allow to set.
You now have the equivalent of a perforated dent, instead of a hole.

Application
Mix up a batch of resin - stick to about 10ml to begin with until you get a feel for how quickly it sets.
Apply this to the mesh and edges of the hole (where you prepared earlier) and lay down a single cut piece of matting on top. (the heaviest weight piece if your kit includes more than one grade).
Coat this with more of the activated resin, using a stippling action to work it right into the fibres and get all the air out (if your kit came with a roller wheel, that's good for getting all the air out properly too).
If your resin hasn't yet set or turned gel-like, get another piece on there and repeat this step.
Otherwise, mix up another 10ml while the first stage sets and repeat until you have the desired strength and thickness.
Allow to set until hard and no longer tacky. (Test with a fingernail pressing into it, there should be no mark).

Finishing
If you have access to a surform (aka dreadnought - looks like a long cheese grater with handles) you will find this to be the best method for achieving the desired profile prior to sanding.
Otherwise, use a good sanding block and coarse to medium paper.
Let your sanding action carry you from one side of the piece smoothly to the other until it begins to follow the original shape of the piece.
Once you have got it all down to the original level, you can fill any depressions with lightweight filler.

[Starbuck3733T]

Sticked, for great justice!

[Pug]

Aww, now you just make me wanna add pics and finish the guide... :o
*adds to to-do list* ;)

Thanks mate. :)

[Frodo]

Good guide

i personally disliked using fibreglass reinforced filler, due to its hard arsed ishness nature, its VERY stuborn once dried

then again, i was being lazy and trying to do it by hand, now ive FINALLY got a dremel clone it may be easier

i find polyester based products easiest to work with, especially for shaping, if im making LARGE shaping difference i would recommend making the general shape with fibreglass, and then mix a big batch of polyester based, and just go over the fibreglass based filler, and get the real shape, then sand!

if you want i can help write up a guide, with pictures n' all, as ive got alot of filler work to do on one of my older cases (which im just modding for fun really - not much use for it otherwise!)

[mnpctech]

i can help write up a guide, with pictures n' all, as ive got alot of filler work to do on one of my older cases

That would be great! Thanks for sharing

[Marquee]

Pug nice guid, I have been looking for a nice guide like this one. Maybe with the pic add what grit sand paper. Good Job

[Pug]

Cheers guys - no probs.
Hope to get the opportunity to revisit this soon. :thumb:

[Frodo]

well, im starting a new mod soon, and it will involve alot of bondo/filler work

my inspiration is the front of your cheiftec, as im using a cheiftec aswell, but im going to use that style mesh uptop :D

filler can be alot of fun once you learn how it handles, then its a breeze to work with!

[lbreevesii]

lookin good so far, just kepe writin. btw, where i can i buy some of the aliuminum reinforced body filler? I haven't seen it at the auto stores and i could definantly use some...right now i'm using bondo and bondo hair...

speaking of which...back to sanding...