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In 2020 my father-in-law made a sandbox for our daughter. In 2021 he passed away, so this has become an important item to us to remember him by. However, he made some mistakes in building it. For one, he painted it but did not put a sealant on the wood, so it has started cracking some already due to weathering (one piece has cracked along a screw hole and needs to be replaced). He also didn't use galvanized hardware, so the screws and hinges (he made it so the seats fold down as a cover over the top) have significantly rusted. We want to save it to make sure it lasts for many more years for our daughter to remember him by. Here's what I presume I need to do:

  1. Disassemble it into pieces
  2. Sand each piece down to remove the paint as well as the top layer of weathering
  3. Apply a sealant to weather-proof the wood
  4. Repaint it
  5. Reassemble it with galvanized hardware

Except I have pretty much zero woodworking experience, so that's why I'm here. I can handle disassembling and reassembling it (it's pretty simple), but here's what I don't know:

  1. First, do I have the above right? Is this the right way to go about preserving it?
  2. I've borrowed a sander, but what kind of grit sandpaper should I use for this kind of work? Do I need to start with a low grit and finish with a higher one, or can I get by with a single grit for this? I have some 120 grit paper already and don't know if that's appropriate or not.
  3. When using a belt sander, what is the proper pressure to apply while sanding? Do I just let the weight of the sander do the work, apply a firm pressure, or somewhere in between?

Any and all help is appreciated.

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    Hi, welcome to StackExchange. In lieu of a formal Answer which I don't have time for right now (middle of the night where I am) I wanted to quickly touch on a couple of points. Painting v a sealant was not a mistake — think of the exterior woodwork on your home, that just has paint on it (or if you're lucky primer then paint). This is the norm. Also paints are actually the best protectant for wood, hands down. But it needs to be the right kind of paint and the wood matters — photos would be v helpful. Now since this is a sandbox, I presume it's sitting directly on the ground, on soil I mean?
    – Graphus
    Apr 17, 2022 at 3:33
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    Ideally you wouldn't want to sand off the previous finish. As I touch on in many Answers sanding is the worst way to remove previous finish. The best method overall is a chemical stripper, since this is of course what they're for. Last thing, galvanised hardware definitely the right call! Absolutely critical for exterior projects to use galvanised (or stainless steel, or bronze) screws and hardware. If you go with galvanised which are by far the easiest to get and likely cheapest you want to shop for hot-dip galvanised if poss.
    – Graphus
    Apr 17, 2022 at 3:41
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    A belt sander is often described as the best tool to ruin a perfectly good piece of wood. So be light with the pressure. You could try starting with 120, but I doubt you’d get good results. 80 then 120 (or maybe not even the 120, depending on what you want) is probably better. Apr 17, 2022 at 15:29
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    I wouldn't even remove the paint unless you really had to. Scrape off the rough flaky bits and maybe a light ing to feather the edges and scuff up the mating surface then repaint.
    – user5572
    Apr 18, 2022 at 16:47

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Take pictures of the paint job and possibly assembly.

I suggest disassembly and cleaning it. Paint remover probably would be best as no experience is needed. Use a different sander or use the belt sander lightly before applying the epoxy. Not much sanding is needed. Paint will gum up sand paper. I don't like belt sanders, either use sparingly with finer paper 120 220, or better use a different sander. Belt sanders, as all sanders, use their own weight, keep it moving though. You can also sand by hand as not much is really needed for the epoxy. Coat everything you can with 2 coats of 2 part epoxy. Epoxy cures by producing its own heat so mix small batches, one at a time.

The epoxy should fix most if not all the cracks. Unless the board is rotted it shouldn't need to be replaced. It may need to be clamped or a filler mixed with the epoxy to make it thicker. You can buy filler (silica, microspheres...) or use sawdust. Filler allows you to make the epoxy as thick as syrup, mayonnaise or even peanut butter. Replace the board if needed though.

Paint it to protect the epoxy from the sun. Paint it before you reassemble it. its easier and will allow you to ensure it is completely painted. You will need to repaint every so many years as the paint degrades.

Put it back together with either hot dipped galvanized or stainless steel.

The epoxy is pricey but we're talking not only an outdoor wooden thingy but one that will contain wettish sand. It will basically bullet proof your project for many years as long as you keep up with the paint and any repairs that may crop up. You mentioned it is only two years old and already has problems. AND you want it to last for some time. This is why I recommend Epoxy. Oh I would also coat the inside of any bolt holes as they can/will allow water to penetrate the wood. But I am a bit anal about this kind of thing.

After your daughter outgrows it you might want to dump the sand out of it and store it someplace... for your granddaughter.

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