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What is the best foundation for posts in a high salt environment?

I need to replace 4 supporting posts under 2 verandahs. The old posts are steel and have corroded as we are in a high salt environment. I have purchased four 4X4 Merbau posts for the job and am going to raise the foundations for the posts slightly to keep the posts out of the ground. I am going to use bricks or concrete blocks as foundations for the posts (or should I pour concrete). The foundations vary from just w few cm to as much as 30cm high. My idea is to support the posts on steel styrups which I will fix into the bricks ( or with bolt heads set into the concrete onto which I will put a nut and washer to hold the posts down). This method, I am hoping, will make the replacement of the styrups in the future a simpler swap and the posts should not be degraded by the environment.

1. Do you agree with my methodology? Please make any suggestions.

2. Also, should I coat the posts (and with what) or should I leave them uncoated?

3. If i am to use a concrete pad, should I set up the posts in situ first and then pour the concrete into a "box"?

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Comments

EricL

Hi @Russ42

I think your idea of using a concrete footing is perfect. It makes replacing the posts in the future a straightforward swap. However, before you begin, I suggest consulting either a registered builder or engineer on how deep and how big the footing should be. The metal posts currently holding your verandah has been calculated to hold a certain weight and to withstand inclement weather. If the footing is not correctly calculated, it could produce unwanted consequences.

Because you're in a high salt environment any extra protection you can apply to the timber posts would be a plus. I suggest using Dulux 4L Exterior Paint Weathershield Low Sheen Vivid White tinted to your preferred colour. I recommend a minimum of three coats to provide maximum protection against the environment. If you have any other questions we can help with, please don't hesitate to post them.

Please keep us updated with your progress, we look forward to seeing your verandah posts repaired.

Let me tag our experienced members @ProjectPete, @tom_builds, and @TedBear for their recommendations.

If you need further assistance, please let us know.

Eric

Russ42

https://www.workshop.bunnings.com.au/discussion/comment/18112#Comment_18112

Thanks Eric. You have reminded me: one or 2 of the steel posts have sunk a little so a concrete pad would be good. It would need to be larger than the existing so perhaps put some screws (?) into the top of the existing footing to help attach the new footing to the old, and a wider new footing? Getting someone else involved is just time consuming, expensive and (IMO) unnecessary if I over-cater (larger pad/ some reo. etc.).

Also I read ...somewhere.....that the salt crust which forms on the surface of wood protects it very well from rot and insect attack.....?

btw, would Quickset be OK for the footings?

EricL

https://www.workshop.bunnings.com.au/discussion/comment/71713#Comment_71713

Hi @Russ42

I was thinking more along the lines of Pryda Post Anchors for anchoring the post to the footing. Yes, you can use Easy Mix 20kg 32MPa Quick Set Concrete. However, it's better to use MaxPRO 20kg Concrete Mix or similar. It will take longer to go off, but its overall density is better than Quick Set Concrete. The standard concrete mix will trap fewer air bubbles as it has time to settle. Compared to Quickset which immediately starts to activate as soon as you add water to it. This tends to trap air bubbles in it, making it less dense and more likely to fracture when stressed.

Salt is like a drying agent on wood and causes the timber fibres to dry faster making it less flexible. This causes the timber to splint and break. Although it offers protection from predation, it does however exact a heavy toll for that protection.

If you need further assistance, please let us know.

Eric

Russ42

https://www.workshop.bunnings.com.au/discussion/comment/99152#Comment_99152

Thanks again, Eric! I have the Full Styrup Anchors ready to go. Excellent advice on the concrete! I have been wondering about Quickcrete ("if it seems to good to be true, it probably is") I am thinking of leaving the post of the old anchor in to bind the new concrete with the old pad. Will have to cut the top off and treat the rust but should make an excellent locking point for the new to old pads... Will paint the posts.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/116368#Comment_116368

Hi @Russ42,

It's great to see you've received some excellent advice from @EricL. Please reach out if you need further assistance or have questions.

Mitchell

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