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I have nearly finished making a small table which will be placed in a bathroom. I am concerned about protecting the wood in a humid/damp environment.

The bathroom can get quite humid while people are having showers etc, and in winter it can take some time to fully dry out. I want to avoid any mould growth or other damage from moisture.

The table is made from softwood - partly reclaimed pine from an old patio door, and partly non-specific softwood from a big DIY store. I want to keep a natural wood look, so no paint or opaque finishes. Ideally, I would go for something not too glossy - a silk or mid-sheen finish.

I have had good results with Danish oil before, but for this I want something more hard-wearing.

I see polyurethane varnish used as the default finish for a lot of things these days. However, I find that (where I live anyway) there's a wider range of non-poly varnishes available than polyurethane varnishes.

Specifically with regard to protection from moisture, what are the advantages or disadvantages of polyurethane or other kinds of varnish? Are there any differences between oil based and water based varnish? Are there any other kinds of finish that I should consider?

  • For future projects, consider using woods that are inherently resistant to moisture/decay, such as white oak, cedar, etc. – PProteus Jun 23 '17 at 14:19
  • Yes, I would but this was kind of a practice project using some wood I already happened to have. – MarkH Jun 27 '17 at 17:17
  • No need to feel you've compromised on the wood here Mark. There's no need to favour naturally rot-resistant species for indoor applications involving higher-than-normal moisture levels. In older DIY and woodworking guides written for the UK market furniture and fittings for the bathroom were regularly made from pine or something like it. And many of those things are still in use in those bathrooms oday, 40 and more years later! – Graphus supports Monica Jun 28 '17 at 6:53
  • was the emmets applied over an oil stain as a sealant? Matt, was the WaterLox applied over an oil base stain as a sealant? – Erika Sherrell Mar 19 at 19:38
  • I've got a small shelf that my wife & I built in college out of a couple of pine boards, some angle brackets and some stain (something cheap like Minwax - we were in college). It's been in our bathroom for more than 2 decades. It's survived that time and 3 kids with nothing much more than a couple of toothpaste stains. – FreeMan Mar 19 at 20:39
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As always "what's the best xxxx" is not a good Question. In almost all cases there isn't a best but instead multiple good options to pick from, and that is very much the case here.

I am concerned about protecting the wood in a humid/damp environment.

You don't have to be. People worry about this sort of thing a lot these days (I did too early on) but there's no reason to — things were made from wood and used in damp, sometimes very damp, environments for centuries before modern finishes came along and they lasted well.

You can even leave the thing bare and it'll do just fine. Although obviously most people would prefer the wood to look 'finished' and for it to be protected a bit from stains etc. the wood itself just sitting there won't be harmed by steamy air once or twice every day and the occasional splash of water.

I see polyurethane varnish used as the default finish for a lot of things these days. However, I find that (where I live anyway) there's a wider range of non-poly varnishes available than polyurethane varnishes.

Poly is nearly the default choice these days because most consumer-level varnishes are poly, including when it isn't specified on the labelling. And it is the toughest of the common varnishes (by quite a margin) anyway, making it the superior choice if durability and waterproofing are desired.

Specifically with regard to protection from moisture, what are the advantages or disadvantages of polyurethane or other kinds of varnish?

I'm presuming here you're asking largely about protection from water vapour/humidity rather than liquid water, and there isn't a lot between varnishes at a typical coat thickness used today. But referring back to my earlier point you don't need to worry about this particularly so it doesn't matter much here.

Are there any differences between oil based and water based varnish?

Yes. Very broadly speaking the former are better and the latter not as good. But, waterbased finishes have improved greatly over the years and some are now much better than they used to be, equalling the performance of oil-based varnishes in direct comparative tests..... old timers take note!

In addition to the functional aspects of the finishes, waterbased finishes are mostly "water white" once dry and change the look of wood minimally as a result (on pine and other lighter woods, they can give a 'cold' cast to dark woods).

Are there any other kinds of finish that I should consider?

I don't think so no. Totally a judgement call of course but there's no reason you need to look beyond common consumer-level finishes for something like this. I'm not a fan of them but commercial "Danish oil" finishes would probably be fine for this, unless where it's sited it will be frequently splashed with water in which case varnish would be a better bet.


Just a final bit on this since it has more general applications to finishing:

Ideally, I would go for something not too glossy - a silk or mid-sheen finish.

All gloss finishes can have their surface modified after they've hardened to a desired sheen level. This was commonly done on shellac in the past and it works just as well today on varnishes and other coatings. I've even done it to paint.

The idea is very simple, you're just scratching the surface very finely, usually following the grain, and being careful at corners and along edges not to rub through. The coarser the scratches (this is relative, they're still tiny so you won't perceive them as scratches if you do it well) the more matt the finish.

For a satin or semi-gloss finish you can sometimes merely buff the surface with a cloth to knock sheen back one notch from fully gloss. On fully cured polyurethane varnish because it's very tough you'd usually have to resort to abrasives, so a gentle rub over with 0000 steel wool or the finest grade of Scotch-Brite will do the trick.

For something more mid-sheen and approaching matt you can use 000 / 00 steel wool or a coarser grade of Scotch-Brite.

  • I might need to ask a follow-up question, but when you say 'waterbased finishes are mostly "water white" once dry and change the look of wood minimally as a result', do you mean that they don't have the "yellowing" effect that sometimes comes with oil-based finishes? I know it's sometimes seen as undesirable, but some of the wood I've used is very pale, almost white, and a bit of yellowing here would be welcome. – MarkH Jun 23 '17 at 9:45
  • yes that is correct. – aaron Jun 23 '17 at 10:58
  • "do you mean that they don't have the "yellowing" effect that sometimes comes with oil-based finishes?" yes. *Always* comes with oil-based finishes by the way, not sometimes. I agree on very very pale woods that the added colour is sometimes desirable, but be aware the wood will naturally change colour by itself over time. It'll move towards an ochre/deep yellow with light exposure, so sometimes softwoods can end up extremely yellowish with a full varnish job on them after a couple of years. – Graphus supports Monica Jun 23 '17 at 15:58
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    I can fully support the claim that "you can even leave it bare". My bathroom furniture (upcycled pine and spruce) is now a little over 7 years old and doesn't show it a bit, despite our bathroom being so humid that towels won't fully dry during the day. – Stoppal Jun 28 '17 at 5:30
  • I would disagree with this answer and the idea that any finish can be used. Any finish that absorbs water will do poorly in a bathroom. For example, a French polish will both water spot from individual drops of water and get cloudy and dull from generalized high moisture levels. I don't know, maybe you think having a big, ugly gray water spot on your cherry table is Ok, but I think most people would not like that. – Treow Wyrhta May 7 at 18:15
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This is a tough problem to solve, and similar to what finish should be applied to wooden kitchen countertops. Overall, the difference between finish types is less significant than the difference between film- and non-film-forming.. with the possible exception of shellac, which i wouldnt use in any wet environment. The issue at heart is:

  1. A film-forming surface (shellac, poly, "varnish," lacquer, or epoxy) will initially be strong, resilient, and protect the wood. However, over the years the inevitable scratch will develop and allow water in to penetrate... that will look quite bad, and repair is difficult if not impossible without a complete refinish.

The exception to this is "bar-top" epoxy - epoxy put on in a very thick layer. That will be tough as nails and should never need repair. however, it's a unique look that you may not want.

  1. On the other side is a penetrating/drying oil - those offer significantly less protection in terms of both mechanical and moisture damage to the wood. However, they are incredibly easy to maintain (if needing frequent renewal).

I speak from experience - my kitchen countertops have poly on them, and the poly has been scratched/worn through in many spots and looks piebald. I have considered refinishing with BLO, but haven't been able to bring myself to it yet.. so, my sympathies to you.

  • Good points about maintenance/refinishing. I think it's going to be unavoidable though. I do want a somewhat hard surface skin for protection from my toddler, so penetrating oils are probably not the best here. – MarkH Jun 23 '17 at 11:53
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For what it's worth, I made a towel rack out of wood and finished it with a few layers of shellac. It's only been a few months, but I see no evidence of water damage. (I thought I might get water spots.) The moisture of a damp towel poses no problems. If shellac can withstand mild dampness for 6-12 hours each day (humid climate), any film-forming finish should tolerate the humidity of a bathroom. (However, I would definitely not use water-based shellac!)

Aaron mentioned the fact that film-forming finishes are harder to repair. That may be true for those that cross-link, but shellac repair is as easy as the initial application. Lacquer repair is similar, but you need spray equipment (or very high skill, if brushing).

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I recently installed a kitchen counter and farm sink. The counter was mahogany butcher block and the finish was a product called "Emmets good stuff".

I love that stuff. It was easy to apply and looked great. It is a gell, Applied like a stain, wipe on in the direction of the grain let it sit for a few minutes and wipe off with the grain. The kitchen has been in use for less than a year but i see no issues at all. I love the satin finish.

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I'm late to this post, but wanted to add that I've tried a product called Waterlox, that has held up quite well for our wood kitchen counter.

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The best option is a water proof wax. The gold standard for water proof waxes is carnauba. Using raw carnauba flake is optimal, but not necessary. If you use flake, it has to be warmed to apply it because it is very hard at room temperature. Carnauba has a beautiful luster. It can be given a matte finish by rubbing with tack cloth, or buffed to produce a deep mirror finish or anywhere in between.

Second best choice would be a semi-permeable wax like a beeswax/paraffin type wax. You make this by melting a pound of beeswax into a pint of linseed oil. It can be thinned with spirits of turpentine, but the less thinning the better.

You can also use clear epoxy. Epoxy is very tough and waterproof. Some mumbo jumbo terms for clear epoxy formulations are "clear coat" and "sealant".

In the old days they used "spar varnish" which is a generally a resin-tung oil distillate. Making this stuff is pretty hard, so epoxy is probably a better choice.

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