How to bleach out black staining on Mahogany rails?

[Bob Quinn]

Does anyone have an effective way to bleach out black stains on the mahogany rails?
The left two pictures are of areas I have already redone with awlgrip. You can see the heavy staining near the stainless fittings. Overall they turned out pretty good, but would like to be able to reduce or eliminate the stains.

The right most picture is of the aft deck railing after sanding. It's wet from rain in the picture but the rain highlights some staining on the top/side radius.

On the front rails I experimented with two part teak cleaner / brightener to no effect.
I also tried the Oxalic acid mix method and it didn't seem to do much either. I only left it on for a few minutes though.

Just wondering if I need to use the oxalic acid mix with a paper towel and keep it wet for a longer period of time?

Is there a better method to get rid of the stains?

In some of the areas I tried sanding deeper but it seems the stains are pretty deep and didn't want to end up with pencil sticks for rails!

Also on the center picture you can see some very light patches. What did I do wrong here? Maybe I didn't sand off all the original varnish or?

 

[SEVEN]

The only thing that I’ve found that (sometimes) work is the part A and part B wood bleach. Part A turns the wood almost black. The Part B neutralizes the bleaching and brings the wood back to the natural color. Again, depending on how bad your staining is, it may or may not work. It will definitely help, but it may not completely bring it back to natural. The issue in California is it is no longer available for sale. Hopefully in your area it is still available

 

[doc g]

Source of the problem is water getting into the end grain of the Teak railing. Need to remove the end cap fittings and use Te- Ka two part teak cleaner , maybe a few times ,and then sand and seal off the end grain. I used west system thinned . Then proceed with the finish of your choice. I have heard that black stain is called blue mold .......Pat

 

[Bob Quinn]

Thanks guys I will try the two part teak cleaner again. I think I was too impatient with it as the directions say leave on for 2 to 3 minutes and move on. I'm thinking soak it on with wet paper towels and let it sit / sink if for a while. Maybe then followed by the oxalic acid method. I think that might be what's in the teak cleaner but I will research. Patience I guess!

 

[tom5518]

First, it’s not mahogany it’s teak. Big deal as you must treat the two differently. Is there still finish/varnish on the rails? It must be stripped off before any treatment will work. The black is underneath the finish. A chemical stripper will work if it’s varnish. If you refinish with varnish or a variety of other finishes you must use a sealer before varnishing. The oils in the teak will lift the varnish off without sealing it first.

 

[Bob Quinn]

First, it’s not mahogany it’s teak. Big deal as you must treat the two differently. Is there still finish/varnish on the rails? It must be stripped off before any treatment will work. The black is underneath the finish. A chemical stripper will work if it’s varnish. If you refinish with varnish or a variety of other finishes you must use a sealer before varnishing. The oils in the teak will lift the varnish off without sealing it first.

Oops, I thought I was told they are Mahogany.
I like the sealer idea. I just ordered some penetrating epoxy sealer. Is that the right stuff to use before awlgrip coatings?

 

[metama]

I just used total boat varnish "primer" sealer. No sure I am happy with it. The wood got a touch darker then if I just used thinned the first few varnish coats. But, given that I stripped the aft rails back and removed all the dodgers, I though a few sealer coats under varnish was a good idea.

 

[tom5518]

Oops, I thought I was told they are Mahogany.
I like the sealer idea. I just ordered some penetrating epoxy sealer. Is that the right stuff to use before awlgrip coatings?

I don’t know. Best to ask Awlgrip what to use as there likely is a specific sealer to use. Same goes for varnish.