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FYI - I am in the UK

I am wanting to do a few upcycling jobs on pieces of furniture that have some interesting compound curves and details (think of beaded panel doors etc). My goal is to paint them a new colour to give a bit of a wow factor, and I know the first job one must do is to sand and scuff the existing paintwork in order to help the new paint/primer adhere to the surface.

Now, we all know that hand sanding is tedious, time consuming and sometimes painful; so my question is regarding how I can more efficiently do the job of scuffing the surface of my pieces such that I don't spend an exorbitant amount of time doing this tedious process.

Just FYI - I currently have a mouse detail sander from Black and Decker, and a 125mm random orbital sander from Bosch.

Any help and advise would be much appreciated.


Research

Having watched many a YouTube video on this process from different creators, it seems that the best solution (at least from the rave reviews) would be the SurfPrep sanding system, with their famous spongy sanding pads (approx 10-15mm thick) being the key to the issue. However, from all of my searching, I can't seem to find a reseller in the UK. Maybe I've not Google'd hard enough?

Possible solution - Interface pads

I have also looked into "interface pads" and it seems these can be somewhat thicker and spongy for such a purpose and have seen that Mirka make one that is 10mm thick for a 125mm sanding pad, but only a 7mm one for the detail sander; so I'm not entirely sure I would get the same amount of flex as something that SurfPrep would offer.

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  • I know what you've asked for specifically but linear profiles are generally sanded by hand for good reason. With power sanding I can't imagine it done successfully with anything other than a linear sander, which no longer seem to be common (and apparently in some places are unobtainable). Obviously the major alternative is to scrape, which will either save all or most of the sanding.
    – Graphus
    Sep 4 at 22:32
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    I just watched one of the SurfPrep videos on YT and oh my lord, you do not want to sand cabinet doors this way!! Literally the very thing you seek to avoid when sanding — an uneven result, with bare wood exposed in places — is proudly displayed as the desired outcome O_O If you're intending to refinish using paint this piebald effect may not seem important but you're also at least one step along the path to changing the original contours of the piece, with edges dubbed and corners rounded over <shudder>
    – Graphus
    Sep 5 at 7:40
  • @Graphus I know what you mean. I'm not particularly wanting to do all of the sanding with this method - I'm thinking more for upcycling a piece of furniture with compound curves, just to do some basic scuffing of the surface such that primer/paint will adhere more easily. I have some pieces already that have basic kind of curves and I have hand sanded them in the past as you say, I'm just looking (hoping) for a slightly more productive method.
    – physicsboy
    Sep 5 at 8:57
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    May I suggest editing the Question to ask about good methods to achieve the end goal then? As it stands this is perilously close to a shopping question anyway and if you're basically seeking an efficient scuff-sanding technique then that makes a good Q for here, and one that's long overdue. Although it has been mentioned in passing quite a few times I don't think it's a subject that we've had a specific query about (I just did a search to check and found no previous Qs).
    – Graphus
    Sep 5 at 11:07
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    Good edit. I'm working on an Answer which I'll post later in the day. I want it to be as complete and comprehensive as possible (i.e. cover all the bases, including things I don't personally do) so it's taking a while. It'll be worth the wait I promise. "As for your last message about the person's lack of ability to do a good hand sanding job... I fear that I may fall into that category also ;-" We all have to start somewhere, nobody is a pro straight out of the gate..... and not to state the obvious but even if you are not good at hand sanding it's not like you made the opposite claim :-D
    – Graphus
    Sep 6 at 7:16
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and I know the first job one must do is to sand and scuff the existing paintwork in order to help the new paint/primer adhere to the surface

Actually the first job should often be to clean the piece if the goal is to provide the best base for uniform adhesion of the subsequent paint coats.

While sanding or other abrasion can remove dirt and surface contamination it's not a reliable way of doing so in certain situations. If the piece has been waxed, or is oily/greasy from use, sometimes you just end up spreading a thin layer of the contaminant over the whole surface as you scuff it. So clean first for safety.

Plain soapy water (at least warm preferably) is enough to do a basic cleaning; you can mix in some alcohol to increase its power if you don't mind the odour. But if you know or suspect there's wax on a piece wiping with white spirit (US: mineral spirits) may be the thing to rely on. Finish maker General Finishes recommend scrubbing with a 50:50 mix of water and denatured alcohol to clean surfaces prior to refinishing or overcoating. It's also very much worth trying some old-school things including sugar soap, but the cheaper and much more widely available washing soda can have the same cleaning power from what I've seen firsthand using both to clean greasy kitchen cabinets. Additionally, both sugar soap and washing soda may dull the finish you're cleaning; more on this below.

And now to sanding, or at least abrading.

  • First thing to keep in mind is you're not in any way trying to sand off the previous finish. The very opposite in fact.
  • Don't only think sanding.

While you can cover a multitude of sins with paint, including various stains and sand-throughs where bare wood has been exposed, to successfully recoat an existing finish1 all you should be aiming for is to scuff it up just enough to 'key' its surface, to give the next finish something to grip (i.e. form a mechanical bond). In addition to only needing to sand a little, relatively fine abrasives are all that it is necessary to use. And although you do seek to make the surface uniformly matt you don't need to go crazy; small missed spots and remaining shine in tight recesses aren't a big deal, as long as they're clean.

  • The key to adhesion of new finishes to old is clean and matt, or as sometimes expressed clean and dull.

As Bob Flexner put it in one article:
"An old finished or painted surface should be clean and dull for successful recoating. If there is grease or dirt on the surface, or if the surface is glossy, a fresh coat of paint or finish might not bond well. But if an old surface is clean and dull, any new paint or finish should bond fairly well." My emphasis2.

And furthermore, you don't need to just sand, i.e. we're not just talking sandpaper. By sandpaper here I mean all the various sanding products (paper, cloth, films and screens), commercial sanding blocks/sponges and the various sanding pads made for power sanders of various styles.

In short, be open to using the two other chief abrasive types: non-woven nylon abrasives (e.g. Scotch-Brite, but don't limit yourself to just that) and steel wool. Steel wool may be old school, but it's a superb conformable abrasive (I would argue personally that it's still the best conformable abrasive3 ) that still has a valuable contribution to make in finishing and refinishing.

For turned legs especially nylon pads or steel wool are a really good alternative to sanding, even power sanding. For abrading the classic in-and-out profiles of spindle turnings, one of the things demonstrated poorly by SurfPrep in one or more videos, I'd argue you'll do a better and faster job abrading by hand. The reason is you can wrap the entire outside of the spindle with the abrasive, grip it with your hand and then rotate — effectively you abrade the entire circumference in one go. Since, as already covered, you're only looking to lightly scuff the surface this can be the work of moments per section; a whole leg might take less than a minute.

Now last but not least....

  • In some cases NO sanding or scuffing is required.

As briefly touched on above and as mentioned in various refinishing guides a cleaning process may leave the surface dull. If it's dull enough you may not need to abrade at all.

Bob Flexner has covered this in various articles and in his books, mentioning that both ammonia and TSP (tri-sodium phosphate) in water can dull finishes. So cleaning solutions of sugar soap, washing soda, ammonia and TSP4 may sometimes save you the entire scuffing step.


1 Be it shellac, lacquer, varnish or paint, doesn't really matter.

2 This should be borne in mind by anyone who holds to the view that you can't put new poly over old, or can't apply poly on top of other finishes.

3 If it's decent quality and not overly greasy. If you find a brand that holds up to use fine but is a little oilier than you'd like it's not difficult to degrease by soaking in solvent, and the same solvent can be used again and again for this task.

4 Note that these are all basic or alkaline.

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There is no efficiency to be had here. If you want decent results, you will have to hand-sand using a selection of sanding blocks and sponges.

But it depends on what you want. If you want a rougher "rustic" patina, you can use smaller power sanders with various fixtures and try to get most of the finish, leaving marks and going down to bare wood in other places. Some people like this look.

Or you can hand-sand to get some consistent finish to build from. This is where you get the best results for your time, in my opinion. It creates a surface that provides a good bond for the new finish, and a consistent surface so the finish goes on relatively even.

Or you can go all the way and use a chemical stripper and remove all the previous finish, and then use hand sanding to get to bare wood.

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