How to replace verandah support posts?

Russ42

I am in the process of replacing steel posts supporting tiled verandahs with timber posts (90x90 cm Merbau). We are located close to the coast so the steel is rusting where fixings for hand rails etc. have removed the galvanizing, hence the change to timber. I have several questions:

I have had to excavate the buried post in the photo as they were buried during some yard work. My plan is to excavate to the top of the concrete pad and add the 30cm or so of concrete to the top of the pad so the new stirrup and timber post are well clear of any soil. i have questions about this:

1. Should I drill holes in the old pad and put 4 (?) pieces of steel rio, old bolts, into the holes to tie the new concrete to the old pad.

and bondcrete the top of the old pad

2. Is it OK to screw the bearer to the Merbau post (the photo with the old bolt holes in it) or will it weaken the post?

3. The old steel post is bolted to the old concrete pad. Can I leave the bottom 15cm of post in the hole when I fill the hole with new concrete, or am I making it vulnerable to rusting in the new concrete ( concrete cancer)?

4. I have found there to be conflicting opinion regarding using Treated Pine screw as opposed to Gal screws when fixing treated pine. The chap I spoke to in Bunnings said the treated pine screws were necessary as there is still some copper in the treatment of the pine timber but another hardware in Forster said they don't stock treated pine screws as the are not necessary. Since Bunnings Forster have insufficient stock of the TP screws I am inclined to use the Gal ones I have already ordered. Is it necessary to use the TP screws or are Gal screws sufficient?

MitchellMc

Hi @Russ42,

Before you go any further, have you determined whether this steel post is a structural member for the roof above? I see it continues through the verandah and is attached to the roof. It would be unwise to remove the post without careful consideration or assessment from a builder. The post might be a non-structural element above the verandah, but if it's been used to achieve the span on the roof joists, your new timber post will also need to continue through and support the roof. In the interest of safety, I feel it would be best to consult a builder before moving forward.

There are various post supports that will allow you to connect directly to the old concrete footer. You could then pour concrete around them to prevent contact with the surrounding soil. It would be far better to connect to the old footer than to a new pad poured onto of the old one. The alternative would be to break up the old footer and concrete your post support into a new one.

You can bolt the bearer to the new Merbau post, but you might like to employ a joint that bears the weight of the verandah on the post as opposed to only bolts. The type of joint will depend on if this post is continuing through the deck to the roof above.

If you can remove the old steel post, that would be best. However, you'll likely find that you'd need to break up the entire footer to retrieve it.

It's important to use appropriate fixings in treated Pine. Fixing failure due to corrosion is the leading cause of deck collapse. It's recommended by our supplier to use Techshield bolts, specially formulated to protect the bolt from the chemicals found in both CCA and ACQ-treated pine. These are hot-dipped galvanised bolts that have then had an additional coating to prevent the galvanisation from coming in contact with the treated Pine. They are designed to last up to four times as long as traditional hot-dipped galvanised bolts. Given your existing fixings seem to have rusted extensively, I think it would be a good choice to select a superior bolt to what was used previously. 

I see Bunnings Forster has a number of Techshield bolts in stock. If you can let me know what size you're after, I can check availability.

Please let me know if you have any questions.

Mitchell