Thread: Merbu "leaching". How bad is it?

It looks like rust stains. We have it all over the joists and bearers of our verandahs and about 3 or 4 inches up the posts (splashed by falling rain I presume). It's also on the cement footings below.

I've never tried to remove it, not sure if you can, as I'm eventually going to paint. But I think I would want to avoid getting it on anything permanent, especially if you're talking about light colours.

Dave In Oz reported good results from some chemical wash that was spruiked on here a few years ago. It was an outdoor bench seat he made. I tried to search for it but can't find it. He mentions it in his post about the seat but doesn't give details of the product. There was another post somewhere that gave an email address or something. Anyway there are probably other products around. Have a look at some of the posts about merbau decking in the renovation forums.

Yep, tannin stains.

Oxalic acid. (I think! ) I used to know that stuff!

It's easy to get via a builders hardware shop, and works instantly.

Make sure you have PRIMED all the joins in the timber before assembly, EVEN if you are going to clear finish the outside bits (pink primer can be scraped off the exposed bits later). That will stop a lot of the problem as the water can't get into the end grain.

Keep the rest oiled/stained or whatever and you won't have much of a problem.

Cheers,

P

Originally Posted by bitingmidge

Yep, tannin stains.

Oxalic acid. (I think! ) I used to know that stuff!

It's easy to get via a builders hardware shop, and works instantly.

Make sure you have PRIMED all the joins in the timber before assembly, EVEN if you are going to clear finish the outside bits (pink primer can be scraped off the exposed bits later). That will stop a lot of the problem as the water can't get into the end grain.

Keep the rest oiled/stained or whatever and you won't have much of a problem.

Cheers,

P

Thanks Midge. We are going to paint it so as long as I at least prime it straight away it should be o.k?

Originally Posted by craigb

Thanks Midge. We are going to paint it so as long as I at least prime it straight away it should be o.k?

Yep, although you may get some leaching through shrinkage cracks, but prime EVERY joint before assembly. Have I said that before?

Use an oil based primer and all will be fine.

Cheers,

P

Craig we have used it on an exterior rail and have sealed it with a marine grade sealer using the hardner which makes the surfuce water resistant. I would recommend priming and selaing or your cuts as I have found from rain a small amount of run but only from the seals on the posts.