Removing merbau tannin stain from cement render

Hey all,

I've thoroughly enjoyed reading all your posts in this forum as the advice has been priceless.
I've just finished my merbau deck which looks great. 1 week after completion the first rain came and so did the well documented 'bleeding issues'. I was astounded by the amount of colour that leached from the merbau. I immediately hosed down the entire deck the next morning but was unable to wash away the stains from my newly rendered walls.
This was only days ago and I've since given the deck another hosing as per advice from other members. From the sounds of it, I've got a good 3 months to wait before the tannins have stopped bleeding from the timber.
So now I am completely paranoid about any future damage that may occur to the rendered walls. I've tried to remove the stains with detergent, napi-san, sugar soap, etc. All with no success!
The walls are a light colour and I'm concerned that the stains are there for good. If I can't remove them I'll be forced to wait a few months until the deck is cleaned and oiled at which time I'll get the walls 'touched' up. This is obviously the expensive option so any advice on the best method to remove the stubborn stains would be greatly appreciated.

Cheers

Hi Luckysack

For starters even though you have decided to not coat your deck for 3 months there is nothing stopping you flushing 90% of the tannins out with napisan wash and scrub now and lesson your head aches.... You will have to do it again when you coat but it will greatly reduce your stainage..... The stains on the render if its bare to be painted then who cares ....i have used domestos when on jobs to clean it off if i need to take it off with what the customer has at home... Other wise you can mix up a mild phosphoric acid solution.......

cheers utemad

www.dialadeck.com.au

Oxalic acid.
Available from Bunnings.

Al :)

Thanks for the advise guys,

I'll try the napisan wash straight away and attempt to budge the stains with oxalic acid. I've already tried bleach which I'm pretty sure is the same as Domestos??
I've got a good 80m2 of decking to scrub down so I'll be busy. I'll get some before and after photos of the stain cleaning. I've seen other stains before but nothing quite like this. The walls already have the final coat of acrylic render on them so I have to be a bit careful.
I'll see how I go.

Cheers

Well I've washed the entire deck down with napisan and my shoes and clothes are stained a rich blood colour. It definately got some colour out of the timber but I'm sure there is more to come seeing as the boards have only been down for about a week.
On the other hand I tried some oxalic acid on the render stains and had NO luck. I tried varying strengths and let the acid soak on the render for a good hour. It didn't even lighten the stain or mildly bleach the render.
I think I'm resigned to putting a scratch coatof render on the walls after few more months.
Once again thanks for the advise.

I had some tannnin stains from blackbutt flooring on some tiles once. I had left some of cuts on a tiled deck and it rained overnight. The next day their was stains left on the tiles. I went down to bunnings and brought a bottle of deck wash that claimed to remove tanninan stains. I poured it on the stains and left it for about 10 min, i used a stiff bristle scrubing brush and washed it down with a hose. It all came of, in some parts i had to do a 2nd and 3rd go untill all of the stain had gone. Check out bunnings and some of the washes that are are avail, you may have success.

Nappisan seems to work for me, I use it in a bucket of hot water, with a scrubbing brush and some elbow greese.
Check out my topic on merbau bleading http://www.woodworkforums.ubeaut.com...ad.php?t=50152

I have scrubbed it all away, problem is it will just keep coming back when the timber gets wet until all the tannins are gone

I've finally found something that gets rid of the tannin stains on the render. Plain old bleach!

I simply used a paint brush to paint on domestos (undiluted) and allowed it to dry. I was amazed to find the walls looking like new the next day.
Other washes such as napisan and every acid under the sun will not even budge the stains once they dry. If you can get to the stain before it drys its relatively easy to remove but once it drys bleach is the only solution. Otherwise known as sodium hypochlorite. I was also surprised that the colour of the render was not affected by the bleach.
Sydney is currently experiencing severe storms and flash flooding so I'm sure the tannins will make their way out of the timber soon enough. The colour leaching from the decking timber is definately getting lighter.

Hope the wait is worth it.

Hey Lucky;

Did you wash off the bleech after it dried or did you just leave it on to come off in the next rain?

cheers.

Quote:

---

Originally Posted by luckysack

I've finally found something that gets rid of the tannin stains on the render. Plain old bleach!

I simply used a paint brush to paint on domestos (undiluted) and allowed it to dry. I was amazed to find the walls looking like new the next day.
Hope the wait is worth it.

---

THE DOMESTOS DOES IT ALRIGHT HEY !!

Utemad

Well I tried the old bleach trick and to my surprise it worked, seems to do the same as napisan but alot less effort....