Refinishing Exterior Mahogany

by Doug
(Stevensville, MD USA)

Sanding older varnished mahogany on the outside of my boat cabin. (Boat is under shed at marina)

I re-varnish with 'Captains'.

Edges have bare spots that are gray color.

I sanded them to natural wood color.

When the varnish hits the bare wood, the wood turns black!

Several smaller edge places, but looks terrible!

I have washed bare wood with solvent and water thinking microscopic dirt in the pores of the wood.

Did not work.

Need to email me at...

Thank you......... Doug B.

Comments for Refinishing Exterior Mahogany

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Mar 27, 2014
Mahogany left without protection
by: Anonymous

My boat sat for some time without any varnish in areas.

Despite many different attempts to lighten it via cleaning all the dirt off first and allowing it to dry then sanding... it still had dark areas that would indeed look black when wiped over with mineral spirits or alcohol.

It seems that some of that was stain from water and the elements.

I did not want to sand it down much further.

As much of my mahogany turned yellow and faded due to no protection, I did end up staining it.

I sanded then stained to help the wood have a consistent look.

Also the stain would give it some UV protection from turning yellow again.

Feb 10, 2014
after thought
by: Glynn

If its one of the central american mahagonies (they tend to be very dark naturaly) and treated with raw linseed oil it will go nearley black, the sun darkening it first, however it will lighten after a time, also some of the modern varnish compositions have a uv filter, making bleaching dificult.
This "seems" to contradict my first comments. This just goes to show that the age old method first try the finish out on a part of the boat where it doesn't show.

Feb 10, 2014
refinishihing exterior Mahagoni
by: Glynn

It's allways difficult to diagnose from a distance not knowing the mahagoni(type) involved.

If you can possibly avoid useing Bleach do so ,it can lead to problems later.

I'll recap on what you wrote.

1:-the edges and a few spots have shed their varnish.
2:-the've turned grey.
3:-you sanded them down and applied a new finish.
4:-now all the newly prepared surfaces have gone very dark.

If this is the case it could be one of two things,the newly sanded wood came in contact with a highly alakali (very high ph,or you rinced it off with water from a rusty bucket)fluid or most likley the newley sanded parts have reverted back to their natural colour.

What happens is this, as most natural varnish has no ultra violet filter the mahagony bleaches out naturally(the varnish also gets more golden in colour)this leaves the mahagony with this golden red brown that's so cherished.

If up to now I've got it right the you've got to sand down the compleat section(the finer the sanding medium the better the final finish)uintill the colour is even, that means bare wood, there is no way around this the wood is going to get dark (I think your Black is likley to be very dark red)varnish like normal then just wait,the sun and the weather will do the rest.

If you've used a bleaching agent the natural pattina will be impossible to achive and your only option is dye.

Hope this helps, if you've got problems drop me a line.


Sep 19, 2012
Black Mahogany Edges
by: Anonymous

The black is due to moisture getting into the mahogany which is why you are getting it on the edges.

Try going over the affected areas with a heat gun to get them thoroughly dried out.

If that and sanding doesn’t cure it then you might have to resort to bleaching and restraining.

If you do use a bleach it must be neutralised, thoroughly cleaned off and the wood allowed to dry thoroughly before re-varnishing.

If you use a wood stain try it out on a spare bit of wood first and use it sparingly as it can turn out darker than expected.

When you re-varnish make sure the edges are well sealed.

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