Fix moldy/stained wood counter top?
December 6, 2010 7:09 PM   Subscribe

Did I just ruin my kitchen wood block counter top thanks to moisture/mold/poor use of cleaning products?

Photos of my once decent looking counter top: one two three four
Here are two "control" photos from an undamaged area: one two
What happened: Dishwasher broke so we started washing by hand. Laid a kitchen towel down on the counter top and put the wet dishes on top. Was working out fine until we left the moist towel on the counter for several days. When we finally picked up the towel, we noticed dark/black areas (mostly in the spaces between boards and in places that may have been existing cuts/scratches) and thought it was mold. Freaked out and sprayed 409 on it. Result was that we still had the black areas but also seem to have bleached the wood around it. Also, it seems as though the spaces between the blocks are larger, but it could be some combination of the moisture and dry heat of the apartment in winter (?) Final note is that it's been over two weeks now and we haven't seen any real change, for better or worse.
In any case, looking for ways to get the counter top back to "normal."
posted by gwint to Home & Garden (12 answers total) 2 users marked this as a favorite
You're going to have to do some serious restoration here. Sand to get the surface finish off. Then bleach with oxalic acid per directions here. This will lighten up the black lines which appear to be in the seams even in the control areas. You could refinish with a polyurethane, but I'd suggest just using mineral oil. You'll have to refresh it every now and then, but it will repel water. And if any staining occurs in the future, it's easy to scrub off and re-oil the surface.
posted by beagle at 7:19 PM on December 6, 2010 [1 favorite]

Yeah I think that's going to need some quality time with a sander to fix. And I think you were right, that it really was mold growing in there ... the 409 probably killed it, in the sense that it's no longer a living organism, but it's still there. Killing mold doesn't magically make it go away, it only makes it dead.

Once you've sanded it down, then you'll need to think about some sort of finish. I'd probably go with polyurethane and stop using it as a cutting board (a cutting board should be something you can easily refinish or replace!), but if you're hell-bent on using it as a cutting surface, some sort of oiled finish like the mineral oil beagle suggests is probably the way to go.

But if you go that route, you will definitely need to keep oiling it regularly, since what let the moisture in (leading to the mold) was almost certainly the absence of some sort of water-repellent finish on the surface. Without regular oiling, you'll just be back in the same place in a few months or years.
posted by Kadin2048 at 7:48 PM on December 6, 2010

The answer all depends on what you are willing to do. If you are a DIY money smart person; this will take a few hours and a good idea of varnish or oils. If you are a non DIY with money to spare it is ruined.

I (being poor) would never replace this. You need a sander and some time, it is super easy to fix, just google sanding and refinishing butcher block. The part you are not going to like: all the wood should be sanded so that the new varnish matches.

Most woods are naturally mold repellent. I wish I was good enough to ID the wood from the photos, but i'am not. Point being I would suspect the damage not deep at all.

Oh and next time use a cutting board, it takes 10 min for me to resand and oil my boards, it takes 2 days to properly resand and varnish a kitchen counter.
posted by Felex at 7:59 PM on December 6, 2010 [1 favorite]

Being a DIY person, beagle got it right, and next two suggestions are good expansions on that.

Finish-wise: My maple countertops are heavily polyurethaned with spar varnish, and so far are holding up fairly well. But I also don't cut directly on them, I treat them basically like a table surface (that does, at times, get really really wet).

Looking at your pictures you definitely cut on yours, so I'd both get used to re-sanding occasionally (for this I'd get a basic quarter-sheet sander, the square form-factor will let you get the corners, unlike a round random-orbital sander), 100, 150, and maybe 220 grit, then mineral oil or walnut oil, and re-oil regularly. Like get in the habit of drying your counters when you clean up, and re-applying oil every night for a while.

Why walnut? Like mineral oil, it doesn't go rancid at room temperatures, so no off flavors (don't let extra virgin olive oil anywhere near your boards). Unlike mineral oil, it actually dries hard, creating a really nice solid finish that you can easily touch-up.

I can't speak to food allergies from it, but my wife gets canker sores if she eats walnuts straight up and is just fine with us using walnut on all our wood cooking utensils and cutting boards.
posted by straw at 9:06 PM on December 6, 2010

Sanding is pretty much your only option to restore the surface. However, please make sure you wear very good dust protection. Inhaling mold dust can lead to a serious respiratory infection. Please post some "after" photos when you're done!
posted by killy willy at 10:15 PM on December 6, 2010

Dry wood wants to suck up water. Wet wood goes grey.

Polymer finishes like polyurethane work by drying to a waterproof film that keeps water away from the dry wood underneath. Dry wood tends to shrink, and if it has many joints, shrinkage can crack the protective polymer film. Knife cuts and scratches can also breach the film and let water seep underneath. Once water has got underneath a polymer film, it quickly starts to look bad.

The only way to make damaged polymer-protected wood look good again is to sand off all of the old finish and start over.

Oils will seep into wood, displacing and repelling water. Oil also swells wood and makes joints tighten instead of loosen. Mineral oils stay liquid. Some vegetable oils, like walnut, linseed and tung, partially polymerize and harden to a tough, flexible, durable, semi-gloss finish. It takes them quite some time to do that, during which they will penetrate and swell the wood they're protecting. Hardening-type vegetable oils, or mixtures of those with mineral oils or solvents, can be burnished to a pleasing sheen by rubbing them over hard with a steel wool pad about an hour after application.

Knife cuts and scratches still create weaknesses where water can enter the wood surface, but will usually not be anywhere near as deep as the penetration of the oil finish. That means that not so much water goes in the wood. An oiled wood surface with scratches and cuts can be restored to looking good simply by pouring on a little more oil and rubbing it in hard with steel wool.

If your countertop were my countertop, I'd rip all the old polyurethane off with a belt sander and 40-grit paper, then go over it with a 120-grit belt, then finish it with a 300-grit sheet under an orbital sander. I'd then apply a thick coat of a tung oil based finish, leave it for a couple hours, burnish it with steel wool, and avoid using it for three or four days. After two weeks of regular use I'd rub it dry with a towel, wait a couple hours, apply another coat of oil finish, let that sit for a bit and then burnish it in again with the steel wool. Then I'd transfer the remaining oil finish to a smaller can to minimize the amount of air it's sealed up with, and keep it around to touch up the occasional scratched or dull patch.

My own house has exposed hardwood floorboards, and this is exactly what I've done to them (I used this range of tung-based finishes, now unfortunately no longer available retail, and did the burnishing with a big industrial floor polishing machine). They've held up very well to foot traffic for about seven years now, and are just starting to show some worn patches e.g. under chair legs; I will get around to touching those up at some stage. The floors have never been re-oiled, just swept and given a weekly vac and mop. I'm completely sold on oil finishes for wood surfaces, and can think of no reason at all why I'd ever choose urethane again.
posted by flabdablet at 10:27 PM on December 6, 2010 [2 favorites]

And yes, do wear a decent mask when sanding and do use sanders with dustbags and do ventilate the room. Polyurethane dust, wood flour and mold spores will do your lungs no good at all.
posted by flabdablet at 10:29 PM on December 6, 2010

Pro woodworker here.

Your counter is made of beech, which is good wood in many ways -- hard, smooth, consistent color, pretty to look at -- but is extremely reactive to moisture, by which I mean that it expands and contracts a lot when its moisture content changes.

The glue lines between pieces of your counter are unusually fat and have opened in many places, even in the "undamaged" areas; it looks more like flooring, which is rather problematic. The material may have been built-up at a home shop by someone underequipped to do the job right, but more likely it just came from a discount supplier (IKEA) that doesn't sell the best stuff. It's also likely that the counter suffered a lot of repeated wetting and drying before it ever had a finish on it, or perhaps the finish was never heavy enough to protect it from the use it gets.

What happens is that the wood at the surface expands when it gets wet, but is restrained by the still-dry wood a little deeper in. So the expanding surface gets compressed beyond the point from which it can recover its original dimensions when it dries again ("compression failure"), and when the surface does dry out, the joints open, tearing any film finish that might've been bridging the joint, thus making the whole thing even more vulnerable to the next wetting/drying cycle. Progressive compression failure is the reason the cracks have gotten wider in the damaged area.

I would not expect 409 to kill the mildew. I would use a mild bleach solution to do that.

I don't think you've beached any color out of the wood. The light areas appear to be sections where the amber-colored finish is totally worn away. The absence of that finish, combined with the color of the mold, are most of what you're seeing there.

You have a bunch of options, depending on how fussy you are about the state of the kitchen. As was mentioned above, if you've got cash to spare and are at all fussy then you should just replace the countertop. At the other end of the spectrum, if you're poor and not fussy, you could bleach the molded areas, let them dry, and apply a few coats of wiping varnish to give it a little protection and shine. In-between are various levels of restoration, including stripping, filling in the gaps, refinishing, etc.

Regardless of what route you take, you should change your habits a bit. Leaving a wet towel on the counter for even an hour, let alone several days, is a bad move unless the counter is refinished with a heavy film finish like polyurethane or epoxy. If you do apply a film finish, you can NEVER EVER cut on the surface because you'll just cut through the finish and start the cycle all over again. Your wood countertop is never going to be bulletproof. Unless you baby it, it will continue to degrade.
posted by jon1270 at 3:26 AM on December 7, 2010 [1 favorite]

If you're already planning to sand and refinish, I would suggest giving it a go with a magic eraser first and see how that works. I stupidly used a magic eraser on my hardwood floor scratches and quickly took the finish off my floor (but got rid of the scratches!). Going over the damaged area with a magic eraser might be all you need to dig down deep enough to clean the crud out of your scratches and isn't quite as involved or messy as a real sanding.
posted by jrichards at 7:24 AM on December 7, 2010

A relevant question is whether this is butcher block or a finished countertop. Butcher block is meant to be unfinished and oiled, countertop is meant to be finished and never cut on.
posted by gjc at 7:32 AM on December 7, 2010

At the other end of the spectrum, if you're poor and not fussy, you could bleach the molded areas, let them dry, and apply a few coats of wiping varnish to give it a little protection and shine.

I'm most certainly not a pro-woodworker, but I was going to suggest the same thing as a start. That should keep your countertop protected while you figure out how badly you want to learn about refinishing.

Also, FWIW, from those pictures and my experience, it looks to me like the gaps on the moldy portions may not really be larger, they may just appear larger because the whole gap is being highlighted by a fuzzy black line.
posted by desuetude at 1:13 PM on December 7, 2010

Tung oil is just fine for a floor, but I wouldn't use it on a counter where it can come in contact wtih food, particularly if it's being used as a butcher block. 100% pure tung oil may be ok, but do not use a tung oil based finish as that will be poisonous.

I would avoid it entirely by using a mineral oil or other food grade oil.

As repeated many times above, all you need to do is sand it down and oil it repeatedly for a couple of days. After that, oil it down a few times a year and you'll be fine.
posted by Jupiter Jones at 7:45 AM on December 8, 2010

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