How to Get Rid of Black stains on an Exterior Door

Within the October, 2017 problem of Widespread Woodworking, web page 10, I answered a query from a reader regarding how to deal with paint on an exterior door that was starting to raise on the cross-grain joints the place water was in a position to get in and work its approach beneath. This impressed one other reader to ask how to take away black stains on his clear-completed exterior door (a minimum of one coat of polyurethane) and stop them from recurring. Right here’s what I responded.

Right here’s an image of the outside door with the black stains the reader needs to take away.

To get rid of the black stains you’ll want to strip or sand off the end. Stripping is often simpler, however the polyurethane could also be deteriorated sufficient in order that sanding is simpler. Most strippers ought to work OK however they could be sluggish. The quickest appearing will embrace methylene chloride listed on the can. Slower appearing will embrace n-methyl pyrrolidone (NMP) and be packaged in a plastic container. The whole lot I’m suggesting right here might be simpler when you can take the door off its hinges and lay it horizontal on noticed horses or one thing comparable.

When you will have eliminated the end, you want to bleach out the black stains. A deck brightener may work, however I all the time use oxalic acid crystals, which I dissolve in scorching water, the warmer the higher. I hold including crystals till no extra dissolve – that"s, the crystals sink to the underside. Oxalic acid may be troublesome to discover anymore, however you will get it from Amazon. The model I exploit is Savogran. I’m not acquainted with the opposite manufacturers, however they could work simply positive.

This can be a fairly dangerous case of black water stains.

After remedy with oxalic acid the black stains are utterly gone. To be efficient, the end should first be eliminated so the answer can get into the wood.

So with the end eliminated, brush on the dissolved oxalic acid. Brush it on extremely popular for the best effectiveness. Let the liquid dry on the wood in order that the crystals reappear. Then hose or wash them off. Don’t brush them off as a result of they"ll choke you up in the event you breathe any.

You"ll be able to apply the answer once more as soon as the wood has dried if all of the stains aren’t eliminated. There"s typically somewhat brown stain remaining however it"s superficial and straightforward to sand off.

Selecting the most effective end to apply is essential. If the door will get direct daylight, you must use a marine varnish from a marina, not from a house middle. There are tons of marinas close to the coast. In any other case, you possibly can mail order from an organization akin to Jamestown Distributors or from Amazon. Typical manufacturers are Pettit, Z-Spar, Interlux and Epifanes. They include UV inhibitors that block the UV mild. Widespread manufacturers from residence facilities are nugatory for blocking UV.

If the door isn’t uncovered to daylight, you need to use any end. However the concept is to block the water penetration that has brought on the black stains. So whichever end you employ, you need to apply at the very least three coats.

– Bob Flexner