Sanding paintwork - by hand or machine?

[Quack]

I sanded/polished/waxed one panel of my herald yesterday by hand to remove orange peel, and it looks great, but i feel it could be better.

I have ordered a little polisher/sander (this one to be precise https://www.ebay.co.uk/itm/125160723570) but im not sure if i should use it for sanding or not. Do we think it will be better? There are some minor visible scratches from my hand sanding work, and im wondering if using an electric sander will help to prevent this, and cut away the orange peel better.

I'm also curious, as im using 2000grit followed by 3000grit (taking no chances by going lower, my paint is quite feeble in some areas) would it be possible for me to go right through if i just...kept sanding? Or does it not work like that? In other words is the 2000grit made to take away a layer of bumps, but wont go any further than that, or will it just keep removing layers if i keep applying it?

 

 

[NonMember]

Any sandpaper of any grit will remove as much as you keep going for. The very fine stuff is just rather slower at it because it takes tiny nibbles instead of big bites.

Were you sanding wet or dry? I don't think I'd use anything mechanical for sanding of top coat paint. It's too thin and delicate. Stick to fine grit, wet, on a block. Nothing wrong with a machine for polishing, though.

[Paul H]

I prefer to wet sand by hand and find these  Toolstation sanding pad  useful and for orange peel I start at 400 grit going up in 200’s to 1000 . 
Paul 

[Quack]

I was wet sanding, maybe I just didn’t polish the scratches out enough.

Christ I think 400 grit would wipe my paint clean off Paul!

[Quack]

Okay that sounds like a good plan thanks, yeah I used 1500 as a test and it blitzed right through so definitely won’t be going that low again.

[chrishawley]

There is so, sooo, much that could be said on this topic and a wide range of practices according to experience and operator preferences. But to tackle a just a few points:

Electric polishers ('mops') are pretty much a standard requirement for getting a bright finish when refinishing. But an essential feature is that the tool must be powerful enough not to stall on the worked surface or burning results. A professional Rupes polisher is £300 - £500 and a £27 tool may not perform up to this level.

While 1200, 1500, 2000 (etc) grit abrasive discs can be used  (with a suitable soft interface pad) on a mop, this is precarious without considerble experience. Safer to stick with hand flatting and not risk sanding through to primer (or basecoat, if applicable). Avoidance of scoring marks when flatting involves: absolute cleanliness, cicular motion, constantly soaking-wet paper and rinsing the paper in a bucket of very soapy water every thirty seconds.

Having flatted to the desired degree then comes mopping. First step is a flat, hard, foam pad with a fairly severe-cutting compund. The advertising blurb for the polisher you've chosen rather sidesteps the fact that a litre of cutting compound will cost about as much as the tool. Farecla G6 is a widely accepted standard. Starting tips for cutting include: liberal application of compound to the work (not the pad), working on limited areas at a time (e.g 1 sq foot), mop head to be continually rewetted by dunking in fresh clean water then spinning off and consistent moderate pressure into the work.

The finish can then be titivated using a fine grade compound (such as Farecla G10 or 3M Finesse but more ££s) on a soft mop; but quite often the finish with G6 wil be nice enough to proceed directy to hand finishing with one's favorite wax polish.

2-pack cuts and polishes best while still soft (e.g. 24 - 48 hours after application). Older, fully hardened, paint is more challenging and harder work.

 

[Quack]

Thanks Chris, very detailed response! Maybe I should just stick to hand sanding then. Am I able tl use a small chunk of wood as my block? As I don’t have any actual sanding blocks currently 

[PeteH]

6 hours ago, Quack said:

Thanks Chris, very detailed response! Maybe I should just stick to hand sanding then. Am I able tl use a small chunk of wood as my block? As I don’t have any actual sanding blocks currently 

I would be reluctant to use a Wooden block, most vehicle surfaces have curves, so the block will only flat a tiny section at one time, making the potential for cut through greater, If you dont have access to a "proper" block, consider hard/stiff foam?. I did once use a block cut from a sheet of "kingspan" (urea foam) for example. My father had several Cork blocks which had a modicum of flexibility too. which he used on timber surfaces for finishing.

[chrishawley]

Yup. Wood much too severe. I use:

• flats (not tips) of fingers for for general, light, correction

• foam block for faster work on wider areas (upcycled from an old foam kneeling pad cut to handy shapes/sizes)

• water-soaked cork block for ocassional 'severe' situations (e.g nibs. runs, sags)

[Quack]

Roger that, I’ll head in to town today to get a proper block!

[Clive]

Rubber sanding block under £2

https://www.toolstation.com/sanding-block/p45873?store=RN&utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=_dc&pcrid=558676913905&pkw=&pmt=&gclid=CjwKCAjw4ayUBhA4EiwATWyBrn6v9tYEzEgUw_-E-kWRQw92GT_xJcZze4r6eexc2hZPw83m_4CS6hoC8eYQAvD_BwE&gclsrc=aw.ds

And like others, I have also used a cut up kneeling pad for curved surfaces. Even a flat faced bit of polystyrene would do.

And if you really get into it a long bed sander is a fantastic bit of kit, but for shaping rather than refinishing.

[daverclasper]

20 hours ago, chrishawley said:

Having flatted to the desired degree then comes mopping. First step is a flat, hard, foam pad with a fairly severe-cutting compund. The advertising blurb for the polisher you've chosen rather sidesteps the fact that a litre of cutting compound will cost about as much as the tool.

All great info, thanks.

Any cheaper alternatives as such, eg toothpaste/baking soda (not Vim, maybe too abrasive), or cheaper brands of compound, for a reasonable shine (not mirror finish)?

[Clive]

2 hours ago, daverclasper said:

All great info, thanks.

Any cheaper alternatives as such, eg toothpaste/baking soda (not Vim, maybe too abrasive), or cheaper brands of compound, for a reasonable shine (not mirror finish)?

Farecla G3 is excellent. And I have also used Upol 333 (a copy methinks) which was very budget friendly. T cut is a bit mild, but has its uses.

[chrishawley]

Possibly 'Best Buy' would be 1kg of G3 at £15

https://www.ebay.co.uk/itm/113803020298?epid=1228449864&hash=item1a7f30480a:g:A1YAAOSw5ZRdEK2M

G3 is a somewhat finer grade than G6 but still pukkah stuff. 1kg will do a whole car.

Beware cheapies claiming 'quantum nanotechnology infused with sustainable gravitational waves...etc' - likely to be false economy.

[Quack]

That’s very cheap. I currently use Autoglym polish (see pic) right after sanding. Should I use g3 before applying that do you think?

 

[chrishawley]

I like Autoglym SRP: It's really a final polish but does have a very fine cutting action as well. But it's a big jump from 1500 or even 2000 grit wet'n'dry to a final polish. So to get a fair finish in a realistic amount of time an intermediate mopping step with G6 or G3 would be a usual thing to do. So, yup, G3 after the wet'n'dry.

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I'm mindful though that the final finishing of paint is a whole art in itself and every operator (pro and amateur alike) has 'what works for them' according to requirements, resources, budget etc etc. A mate of mine is an automotive painter knocking out several jobs a day and his standard process is:

1200 wet'n'dry by hand > G6 by mop > 3M Finesse by mop  > Any wax by hand

I'd be interested ot know what other processes members use.

 

[Quack]

Okay I’ll get some g3 in, that should complete my process! Thanks.

final question, how many layers of compound and how many layers of polish would you normally use? I’ve been applying 4 layers of polish to get scratches out but I’m guessing now I’m using compound I’ll only need one layer of polish at the end?

[Clive]

Compound, a dab, keep it damp (sprayer bottle is very useful) and that covers a fair area. It can remove paint quite quickly, so be cautious and check regularly. One happy with the finish, then make sure all compound residue is removed, and a quick polish or wax. Job done.

[chrishawley]

Just to embellish Clive's answer a bit:

If all has gone well then 95%, say, of the shine shoud be evident at the compounding stage leaving a polish with only a little work to do: a single application just to brighten the finish.

Similarly; the more any defects (nibs, orange peel, fisheyes, scracthing etc) are corrected at the wet'n'dry stage the less work the compound has to do. An ideal situation is where the flatting stage has yeilded a defect free, even, satin, finsh and then a single going over with compound will suffice.

The 'dose' of G3 or G3 is probably about half to one teaspoon per sq foot (ish)

Do let us know how you get on.

[Quack]

Excellent info, thankyou. I’ll report back in a couple of weeks as I’m away next week.

[Wagger]

There are polishes in several colours. I used the closest to my Cosmos Blue on my old 'Modern' before selling. It disguised blemishes quite well.

[Phil C]

Bit late to the scene but if you are not already aware Trev's Blog on YouTube is a very useful mine of bodywork/paintwork information.