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How to paint a Merbau laminated/finger jointed outdoor structural post?

I have a newly installed - 3 months ago- 115mmx115mm Merbau laminated/finger jointed structural post which I now want to paint to match the colour of the adjacent walls. It has seen a lot of wet weather - I'm on Sydneys Northern Beaches - and has leached brown liquid which now seems to have stopped. It is bolted to brickwork and stands on the heads of 4 gal screws screwed into the bottom of the post and stands about 4mm off the supporting brickwork. It has about a 2mm gap between the back of the post and the wall to which it is bolted.

What is the best way to prepare the post for painting? Should I Sikaflex the gap between the post and the wall and also the bottom of the post and the supporting brickwork?

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JacobZ

Hi @mikiep91,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Merbau is a beautiful, dense timber, but it’s notorious for tannin bleed. The fact that your post has been in place for three months and the heavy leaching has slowed is good news, because the biggest risk of staining is usually in those first months. Giving it a good scrub with some Cabot's New Timber Prep, which is designed to remove naturally occurring timber oils in preparation for coating, can help ensure that there is no tannins remaining. If you are confident the leaching has stopped, then you can skip this step.

Regardless of the leaching, you'll want to give the post a really thorough scrub with a decking cleaner such as Cabot's Deck Clean to neutralise any remaining tannins on the surface. Rinse well and let it dry completely, ideally, for a few days of fine weather.

Once dry, lightly sand the surface with 120-grit sandpaper to remove any raised grain and to give the paint a good key.

Then, apply a stain-blocking primer such as Zinsser Bulls Eye. This step is crucial—if you skip it, brown bleed will almost certainly come through your paint.

After priming, you can paint 2-3 coats of a high-quality exterior paint, tinted to match your wall, such as Dulux Weathershield or Taubmans Sunproof.

It’s generally better to leave a small gap at the base so air can circulate, and the bottom of the post can dry. If you do seal it there, water could get in and not escape, leading to rot in the long term. If you are aware of this risk and still want to seal it up, I'd suggest using a suitably coloured silicone sealant after the paint has been applied and it has fully cured.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

mikiep91

Hi Jacob,

Many thanks for this comprehensive reply.

The only problem is that Cabots New Timber Prep and Deck Clean are only available in large quantity packs and as I have no other timber which would require them I may be left with a whole lot of stuff in stock that I won’t need!

I don’t want to appear as tight but I hope you’ll understand what I mean?

Can you suggest any other material to meet the prep and cleaning challenge? In any case, per your comment I can probably skip the New Timber Prep stage.

Would a wash down with clean mineral turps do the job?

Thanks in advance for your advice.

Kind regards,

Mike Pollard

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/57128#Comment_57128

Hi @mikiep91,

I completely understand. I've got a shed with several products where I only used a small amount, and a whole lot remains.

A good scrub and a wipe down with some mineral turps should do the trick as long as you are confident the oils have stopped leaching.

Let us know how you get on, and don't forget to post some pics to show the result.

Jacob

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