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How to stain an old timber pergola?

Finding My Feet

How to stain an old timber pergola?

Hi all,


I'm wanting to do some maintenance on the pergola. It is built on concrete with (I think is) pine with a tin roof. We've had it for 15 years and have not had it oiled or painted in the meantime. 

I did some research and ours just lots of checks in the wood. I have already used the deck cleaner to give it a good scrub down on the wood, though not the best timing as the rainy season comes in...


I have a few questions:

1. As I have cleaned it, is it best to cover the wood from the rain before it is stained? Do I need to wash it down again and wait for the wood to dry before I do anything else or can I just use a broom to get rid of the dust?

2. If I want to stain the wood. Is there an all-in-one that I can use to stain it that is suitable for different weather conditions or it would be best to have a base and a top coat? 

3. What can I do for the checks that are in the pillars? There are a few that are quite deep and I've noticed that some bugs hid in it when I was cleaning it. Is there any recommendation to fill it that will also take the stain?

4. Additionally, some wood is not exposed to the sun or rain but is under the tin roof. Can I just oil it as part of the maintenance?


Thanks in advance!

Bunnings Team Member
Bunnings Team Member

Re: Pergola wood maintenance

Welcome to the Bunnings Workshop community @sky31. It's wonderful to have you join us, and many thanks for your question about wood maintanence.

You might like to start by sharing some images of the timber showing the issues you've described. That way, our members would have a much better idea of what you're working with. Let me know if you need a hand uploading pictures.


It's probably best to stain the timber prior to it becoming wet again, but that isn't an issue as long as you allow it to fully dry out before staining it.


Plenty of stain and oil combination products can be used; there is no need to stain separately with a base and topcoat.


Cracks and checks can be filled with an exterior timber filler. Ensure you select a colour that closely matches your timber.


You could just oil the timber that is not exposed, but to achieve a consistent finish, coating all the timber would be the best approach.

Please let me know if you have any questions.


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Re: Pergola wood maintenance

Hi Mitchell,


Thank you for your reply.

Here are some pics of the pergola and the checks in the pillar. Upon closer look some run quite long and some fairly deep so I'm not sure if that would be of structural concern. If its just cosmetic aspect 

Also just want to check whether the woods under cover are the same type as the rest of the pergola. I've only used deck cleaner to scrub down the ones exposed to the elements and the wood under cover was only washed down with a hose. I'm not sure if they are the same type of timber or different as the colours are quite different. 

So is it sufficient to just use a broom to clean before staining even after some heavy rains? 


Appreciate your time and patience. 


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Home Improvement Guru

Re: Pergola wood maintenance

Good Evening @sky31 

Nice looking pergolla and its in decent condition as well :smile: Id like to say Welcome to the community :), definently a fun place to hang out and just take a wander through all the projects. 


As nothing has been done to the timber for 15 years I dont think there will be any problems with having to clean anything again. The only bit that I noticed was that first photo of the post in your last batch of photos. If its green mould I would clean any that I find first. I would think cleaners should kill whatever is growing there, if its the old colour of the timber I wouldnt worry about it.


As to the splits in the timber, Another one I wouldnt worry about as timber ages it does split naturally. If its to a point it concerns you then you could support the area first and replace the post but thats a long way to go for a cosmetic repair.


When you say "checks" do you mean notches in the timber or the knots in the timber?



Bunnings Team Member
Bunnings Team Member

Re: How to stain an old timber pergola?

Hi @sky31,


I'd also like to welcome you to the Bunnings Workshop community and say I'm excited to see your project and would like to help you get the best result possible.


As @Dave-1 has said, the structure looks very good for 15-year-olds. Nothing jumps out at me that would be a structural concern. If there are any sections where you can see horizontal splits, this is something to evaluate, but vertical splits along the grain are perfectly normal and not a point of concern. This happens naturally over time as the timber ages. The fault line opens up due to the changing moisture and the breathable nature of timber.


The frame of the roof structure, and the lattice are H3-treated pine. H3 treatment allows for external use, without direct contact between the timber and earth. 


The posts for your pergola are similar to these H4 poles. These poles are H4 treated, meaning they can be used externally and in direct contact with the earth. 


These are rough pine products that use CCA treatment. The copper in this treatment gives them a greenish tinge, which unfortunately means they are not great at accepting stains as the green colour is impregnated into the timber and can show through lighter stains. 


My advice if you would like to go with a stain, is to clean the posts thoroughly to remove any obvious green from the surface and to use a dark stain such as EXTERIOR STAINS CETOL SIKKENS 4L HLSE WNUT 10 - Walnut, followed by a clear coat varnish such as Bondall 1L Satin Monocel Gold Marine Clear Timber Varnish. The darker-coloured stain will help to cover the green better than a light stain will.


Please note that CCA treatments are toxic, and you should take all preventative measures to ensure it does not become airborne and is inhaled. I don't advise sanding them back for this reason. Any cleaning should be done with the use of a mask and gloves to prevent any possibility of ingestion.

Please don't hesitate to let me know your thoughts and if you have any further questions, I am more than happy to help.




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