Need help with mold on MDF

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Forum topic by kirbi69 posted 03-27-2018 02:43 PM 917 views 0 times favorited 12 replies Add to Favorites Watch
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83 posts in 2193 days

03-27-2018 02:43 PM

Ok so I have a mold problem now somehow.

It’s growing on my MDF router table extension on the side of my table saw.

I built it about 2 years ago. And coated it with about 6 coats of wipe on poly.

I’ve never had any mold problems with ANY of the MDF in the shop. But now everything is growing mold?

What can I do to stop it from coming back? Laquer? Something else?

12 replies so far

View Fresch's profile


460 posts in 2530 days

#1 posted 03-27-2018 03:00 PM

No, you need to fix why you have mold.
Sounds like you have a moisture problem, need dehumidifier or at least fan for constant air flow.
Tell us about your shop, no rust on your metals?

View bondogaposis's profile


5607 posts in 2961 days

#2 posted 03-27-2018 04:50 PM

The finish is not the problem. Moisture is the problem, you shop is overly humid. Fix that and your mold problems will disappear.

-- Bondo Gaposis

View kirbi69's profile


83 posts in 2193 days

#3 posted 03-27-2018 07:29 PM

Well I live in Aransas pass Texas. Right next to the water. And right where they eye of hurricane Harvey came through. Never had any mold before even when the shop flooded from the hurricane.

Now all of a sudden in the last two weeks. I got this mold. It’s always very warm and humid down here.

My best guess is that I haven’t gone into the shop in the last couple weeks and so all the doors and windows have been shut up. And created a stagnant air that allowed the mold to take root.

So no amount of polyurethane or laquer or something g will prevent this in the future?

I’m not really concerned about my other pieces of MDF. Because they are mostly just scrap. Or whatever. But I don’t want my router table molding!

I’ll try and keep the shop more ventilated :)

View Woodknack's profile


13025 posts in 2990 days

#4 posted 03-27-2018 08:27 PM

Fresh air and sunshine (if possible) will work wonders.

-- Rick M,

View Fresch's profile


460 posts in 2530 days

#5 posted 03-27-2018 08:47 PM

Has the “wood” started to swell? Google mold/ mildew if I recall you need more than bleach or alkyhawl.

View CaptainKlutz's profile


2263 posts in 2104 days

#6 posted 03-28-2018 12:15 AM

Permanently killing mold underneath a finish is hard. Heat (160F+) is about only way to kill it, without removing the finish, using chemicals, the re-apply finish? Even with heat, you still have a stained wood underneath.

+1 Need to figure out how that much moisture got underneath the finish, and reduce the moisture in your shop.

Another thing to consider:
MDF is produced using lots of water, typically laced with chemical fungicide to stop mold from growing during processing. If you have other pieces of MDF purchased from same source, near same time; that all are showing mold; your continuous moisture levels may have simply exceeded the ability of fungicide to stop mold growth?

While I have not had issue here in Arizona, have seen reports of sub-standard MDF developing mold during transport and storage. Most of this product came from China. (surprise!) They had similar issues with moldy dry wall years ago, that is still being ligated by the lawyers today. So your problem may not just be moisture in your shop, but the quality of MDF in shop?

Best Luck!

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

View AxkMan's profile


65 posts in 736 days

#7 posted 03-28-2018 01:35 AM

Could be the lumber yard you got it from. Sometimes they throw the wood outback on the ground that can pick up mold, especially the bottom ones. They are not always wrapped or tightly at that, just exposed. If you had a storm and picked up MDF after that, that might be an explanation. Most lumberyards just throw ‘em.

View Kelly's profile


2639 posts in 3554 days

#8 posted 03-28-2018 02:47 AM

Heat will do wonders for mold, but it takes at least 115 degrees or more.

In a fit of genius, I washed the carpets of my car (kid food stink). I didn’t get it dry enough and that coupled with that I lived in the Pacific Northwet (Pacific Beach, Wash), I got mold. Lots of it.

Fortunately, I visited a friend in Eastern Washington, in the dead of summer. One hot day with the windows rolled up and the mold was cooked away. The smell never came back.

I never checked the temp, but it was over 110 outside, so inside the car had to be like the face of the sun.

View Woodknack's profile


13025 posts in 2990 days

#9 posted 03-28-2018 03:50 AM

UV will kill mold, which is what I meant by sunshine.

-- Rick M,

View woodbutcherbynight's profile


6054 posts in 3019 days

#10 posted 03-28-2018 03:55 AM

A fart fan in a window or small hole in wall that cycles on a timer for a few hours each day will keep enough airflow to eliminate the problem. Dealing with the mold that has already formed, not so much fun.

-- Live to tell the stories, they sound better that way.

View kirbi69's profile


83 posts in 2193 days

#11 posted 03-28-2018 06:31 PM

Thanks for all the helpful replies y’all!

I ended up opening some bay doors and running my big fan for several hours yesterday evening.

I also soaked a rag in bleach and wiped the mold off the top and bottom side of the MDF as best I could. Let it dry a little and then put another couple coats of polyurethane on the top for good measure .

Also while I was at it. Sanded down the cast iron top and coated it with a thin layer of poly too.

I’m very good about keeping the rust off my saw top using either wax or corrosion x. Because of the humid air. It’s a constant battle. But I never figured my MDF would mold from just humid air.. especially with so much polyurethane on it.

Anyways I’ll keep the shop more ventilated and we’ll see what happens.

Thanks again!

View Fresch's profile


460 posts in 2530 days

#12 posted 03-28-2018 07:22 PM

I have a 52” paddle fan runs 24/7 replace it about every 4yrs. when it burns out. Use paste wax too.

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