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I'd like to "re-fresh" a balance bike.

enter image description here

According to the constructor, its laminated body is made of

Simply superply™. Nothing but hand-picked, grade a veneers bonded with the finest marine ply "WBP" glue (water & boil proof) for maximum weather resistance

Unfortunately, five years of usage damaged it (some parts are worn out, and a bit of rust got where metal parts are in contact):

enter image description here enter image description here

I'd like to sand and re-varnish (parts of?) it, but I'm not sure what kind of produce to use. The varnish needs to:

  1. Protect the wood against all kind of exterior strains (dust, rain, shock, …),
  2. Not be toxic (the skin of a child will rub on it), and tolerate sweat.

I was thinking to use "Cabot Clear Wood Protector", the safety data sheet states, under the "Potential acute health effects" section,

Skin contact: No known significant effects or critical hazards

and it should be sturdy enough for outdoor use. But what do you think?

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    There should be no issue with skin contact in the main, but it's impossible to predict for any extended contact. They don't test generally test for that with exterior products, and the Cabot product you name would likely make a point of saying so if it was the case. On the other hand it is intended for outdoor furniture, which presumably means they do have confidence of it in that general use. It could be fine, but if you want to use this type of product (a "deep penetrating" exterior finish) they only work right on bare wood, so you'd have to get off ALL the existing finish. [contd] – Graphus Jun 7 at 7:04
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    This should ideally not be done entirely by sanding, it's better to strip and then do a light sanding as needed. Sanding off old finish risks damage to contours and removing too much material overall, plus it converts the finish into a fine dust which is a health hazard. If you don't have 100% dust extraction on any power sander you use it's v. important to wear a good dust mask, at minimum. – Graphus Jun 7 at 7:07
  • @Graphus Thanks a lot for your comments, I've updated the question. The finish is already mostly gone on the parts I'd like to restore. Of course, if there is sanding involved, I'll protect myself: thanks for the reminder! – Clément Jun 7 at 17:27
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    The use of the word "varnish" in this question is at odds with the finish that is intended to be used, which as far as I know isn't a varnish. (Even if that word has migrated to mean a great number of potential finish types.) – jdv Jun 7 at 18:01
  • @jdv Thanks a lot for your updated answer, and for those additional comments. English is not my native language, and I'm not too familiar with the woodworking lingua, so my usage of "varnish" may indeed be at odds. Feel free to edit it if you feel that it would make it clearer. – Clément Jun 7 at 18:03
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You could consider another option: don't refinish it at all. Depending on how damaged the existing finish it (you don't say or show) in most case light scuffs and dings are just part of the charm, and don't represent any problem with ability of the material to resist moisture.

That veneer is very stable, with very good natural water resistance. On top of that, it was probably finished with some sort of decent outdoor spray polyurethane. So, unless it has been treated with complete disregard, it'll be fine as-is.

You wouldn't want to leave this out in the elements permanently or seasonally, but the occasional ride through a sprinkler or being caught in the rain isn't going to harm it. But the assumption is that most of the time this bike is brought into a porch or garage.

Outdoor furniture has to be refinished regularly because it is left to the tender mercies of 2-3 seasons of weather, and hundreds of hours of UV light exposure. Unless this bike has had the same treatment, it's probably fine.

That all being said, if you want to refinish these pieces with most finishes, including the penetrating finish you mention, you will have to remove all of the previous finish.

  1. Take everything apart.
  2. Mask or remove the hardware. Some of those bearing surfaces might be screwed in, or be a really tight interference fit. However you do it, you want to get these as clean as possible and maybe even remove the rust.
  3. Using an appropriate remover, remove all the old finish completely.
  4. Repair the damage. This is not going to be easy, but you might have to get clever with epoxy and canoacrylate glue and clamping.
  5. Hand-sand to a smooth finish. The idea is to sand for comfort of the person using it, at least with the finish you have indicated you want to use. Penetrating finishes don't really require any surface prep, other than it being bare wood.
  6. Apply, re-apply the finish as directed.

Of course, all those decals will be removed, and the hardware and fit might not be very tight. In some cases you might even have to rebuild up some wood "bearing" surfaces with epoxy or a wood insert that is machined back to nominal size. As mentioned before, you are going to have to make sure the metal bearing surfaces don't spin where held in wood, and are nominally the right size to meet each-other.

A note on finishes:

There are pros and cons to using a penetrant finish vs. a sealing finish, like a harder exterior polyurethane (or varnish). The former is intended to be re-applied regularly, and is also intended to age and patina over time. A sealing finish will need to be refinished less often, and is intended to cure hard on the surface. Penetrating finishes need to be applied to clean, absolutely bare wood. Polys (and varnish type finishes) are slightly less fussy in this regard.

But the majority of the attention you will be spending on this project is removing the old finish, prepping the surface, and making sure the mechanical interfaces are nominal after years of use, exposure to the elements, finish removal, and surface prep. Try to stay away from the edges.

As for toxicity, pretty much any finish, once cured, is essentially non-toxic and completely safe. With penetrant finishes you have to make sure it isn't the same stuff that they use in pressure treated lumber, but they usually say that on the label. Those tend to be oil solvent based, as well.

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  • Thanks a lot for your observations. I've added a couple of pictures: the finish is completely worn out in some parts, and some rust started to go into the wood. So, even if I don't refinish it completely, I'm still under the impression that at least partial restoration could be useful. – Clément Jun 7 at 17:28
  • Oh, and yes, the bike was in a shed most of the time, it's the shocks that damaged it, mostly. – Clément Jun 7 at 17:40
  • Point #2: "you don't want to keep these as clean as possible" you don't??? – FreeMan Jun 8 at 18:46
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Thanks a lot to jdv and Graphus for they precious answer / comments. I thought I would post as an answer a description of what I've done, in case somebody faces the same issue.

  1. Take everything apart,

  2. Clean with soapy water,

  3. Apply a mix of 1/2 vinegar, 1/2 water, to the parts that were rusted, let rest 10 minutes and scrub lightly, following this advice,

  4. Scrub with steel wool,

  5. Lightly sanding with fine paper, not removing all of the previous finish, but easing the damaged parts,

  6. Applied one coat of "Cabot Clear Wood Protector" uniformly,

  7. Let rest ~24 hours,

  8. Re-assemble.

I'm only at step 7, I'll probably post pictures once I'm done. I'm not completely satisfied with the rendering, but that should do.

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    +1 If you ever want to remove rust staining from wood again using vinegar, don't dilute it. Vinegar is already a dilute mixture of acetic acid and water, and most household strength vinegars are very dilute already (5-6% is fairly typical). It makes no sense to make it any weaker! – Graphus Jun 17 at 15:54

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