# Forum Home Renovation Retaining Walls  Removing merbau stains on retaining wall

## ozizu

Ho to all. After the succesful completion of my retaining wall and merbau decking timber on top for seating, ive had some bleeding from some areas of the merbau down the front  of my boral blocks. Even though i had excessively cleaned and weathered the merbau to remove the bleeding, when i momentarily flipped the underside of the merbau to fill up my retaining wall with sand (for extra stability) ,it started raining. Unfortunately i hadnt fully weathered the underside of it since i thought it would never be exposed underneath. 
Have tried oxalic acid, soapy water, turps, clc but to no avail. Havent yet tried napisan, chlorine, hydrocloric acid or bleach like some other posts i read said that bleach worked wonders on rendered walls.  
Any other info would be appreciated. thanx

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## JulianH

Bleach or a gel based toilet cleaner should work OK, but it depends how porous the materials are.  I used some gel based toilet cleaner just this morning on redgum wood chip tannins that had leached onto an exposed aggregate driveway. 
Hydrochloric Acid will also work, but can be very tough to balance with the downside - it can quickly eat into porous surfaces, resulting in significant pitting.

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## ozizu

> Bleach or a gel based toilet cleaner should work OK, but it depends how porous the materials are. I used some gel based toilet cleaner just this morning on redgum wood chip tannins that had leached onto an exposed aggregate driveway. 
> Hydrochloric Acid will also work, but can be very tough to balance with the downside - it can quickly eat into porous surfaces, resulting in significant pitting.

  Thanx julian, will try the bleach (white king i presume) and hydrochloric acid sometime this week. Just really annoys me that i weathered and sealed the top side of the merbau but hadnt sealed the underside and yet, a bit of water and severe disappointment. Being a first time novice home landscaper, will definitely learn from these mistakes.

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## Planned LScape

I had this problem last year on a job where the carpenters had left a pile of merbau on sandstone, which looked black after heavy rain. 
I tried oxalic, hydrochloric and a few other acids to no avail. What did the trick was a cheapo $3 bottle of household bleach. Let it sit for a bit, scrub in then hose off

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## ozizu

> I had this problem last year on a job where the carpenters had left a pile of merbau on sandstone, which looked black after heavy rain. 
> I tried oxalic, hydrochloric and a few other acids to no avail. What did the trick was a cheapo $3 bottle of household bleach. Let it sit for a bit, scrub in then hose off

  Just had planned Lscape had mentioned, simple potion of whiteking done the trick. Applied it with a old toothbrush, let it soak it for 2 minutes, scrub and pressure hose off and VOILA. Thanks to all.

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