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I have purchased wood in order to make some basic furniture:

  • One of these will be placed outside (simple table),
  • One inside the bathroom, (basic chest of drawers)
  • And another in the hall way (shoe rack).

I've already done some work, ie, cutting the wood to size, preparing parts for joining the pieces etc.

Currently I'm in the process of trying to find what materials I will need to finish the wood (and learn how to) for each of these items I'm building.

My question is:

  • When do I need to "treat" / finish the wood, ie, sand and apply these coatings?

  • Is it before I join the pieces, or after once everything is assembled?

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I recommend you apply any finishing products before final assembly, but after any gluing or other permanent assembly.

Surfaces that are going to be glued together don't need (and shouldn't have) finish as this will weaken the bond, and the glue itself and adjoining wood should protect the wood (choose a suitable glue for the environment).

Surfaces that will never be taken apart but will not be glued (some joinery, for instance) probably don't need finishing prior to joining them. This is a gray area, and will depend on the joint. The primary goal is that exposed wood that isn't intentionally exposed will be protected.

However, other parts that are fit together using other fastening methods should be finished before assembly. Even small spaces admit moist air, and those spaces may expand or contract based on humidity, so may admit water or other environmental contaminants. Without protection on the interior facing pieces of the wood you risk visible damage over time in some environments.

Finishing as a step to preserve the wood in the environment it is going to be placed should help guide your decision as to when to finish. If you do it solely for looks, you may be happy with the results if you perform it after assembly, but time may show that protection should have been your goal during finishing, and not just looks.

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  • Thank you @AdamDavis. All brilliant answers and excellent points. I'm choosing this as the solution though as it tells bit more and gives bit more ideas for newbies like myself. Cheers to all. – Phil May 13 '15 at 15:00
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You can apply finish at whatever time is easiest to do so. Sometimes you will want to sand and finish one side of a board before final assembly, if it would be difficult to reach afterwards. The insides of small boxes are much easier to sand as flat boards than after they are assembled. You do have to take more care in handling already finished boards.

If you choose to apply a finish prior to glue up, remember to tape off the area of the joint that will receive the glue - glue will not bond well to a finish.

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  • Also, since glue will not stick well to the finish, it is easy to remove any surprise squeeze-out. No trying to sand away glue where two pieces come together at a right-angle (it will pop off with the flick of knife edge) and no worry about finishing over a thin layer of glue remaining from squeeze-out that you thought had been totally wiped away. – Ast Pace Feb 18 '16 at 22:45
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There is a reason it is called 'finishing' it is the last step to complete or 'finish' your project.

Sanding can be done at different stages, usually you won't sand a piece before you glue a flat surface together. So if you are gluing a table top you will want to glue all the pieces together first, then sand them all, because often you will need to sand after to make all the joints flat and even. However, sanding the rails under the table before you attach them is a good idea because it is easier to do it before you get more corners to worry about.

Now where you might put a finish on before final assembly is when item in question breaks down and the parts are often separate. Say the leaves from a dining table or the legs that are attached by bolts. But anything that will be permanently put together should have the finishing last.

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  • Typically finishes are not applied underneath furniture or where people are not looking. That is harder to see before assembly. – Matt May 13 '15 at 14:30
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    You should always seal both sides of a piece of wood. Unfinished wood gains and loses moisture faster than finished wood. Having a totally unfinished side to a board can lead to warping. – LeeG May 13 '15 at 14:33
  • @LeeG That is a good point. Comment is based on looking at the underside of chairs and what not. More meant for stains. – Matt May 13 '15 at 14:36
  • Thank you @bowlturner. I don't understand one thing though: why not sand before gluing? Wouldn't it help to bond easier if sides were coarsely sanded? – Phil May 13 '15 at 15:00
  • @Phil When I'm gluing two boards side to side, I use my joiner to make the sides a nice flat and smooth before gluing. To coarse a job and you get voids that fill with glue instead of bonding the fibers of both pieces together. – bowlturner May 13 '15 at 15:21
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The answer is usually "it depends." In some cases where you might need an even finish (like in a waterproofing situation) you might want to finish the pieces before final assembly. I'd argue that for most situations, I wait until the end of the project to finish it, except if visible surfaces would be hard to finish when it is assembled.

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    The inside of cabinet boxes are a good example- I always finish them before assembly, carefully keeping stain / finish off gluing surfaces. I also try to at least stain surfaces that are likely to be exposed due to seasonal contraction / expansion. (e.g., the tongues and grooves on a panel, or the tenons on a mortise and tenon joint. – TX Turner May 13 '15 at 19:07

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