Repairing my fence - timber onto galv steel posts?

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jasonpklee

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#293164 3-Jan-2022 00:32

Hi Everyone, new to the forum and relative rookie in DIY, so looking for some help here.

My fence is in a pretty sorry state, and the horizontal timber planks (75x50 fence rails) are falling off the square (50x50) galv steel fence posts. Turns out the builder took a nailgun to it and nailed the planks onto the posts from the outside, but the nails are corroded after around 8 years and shearing off, causing the planks to fall.

My original idea was to drill through and put a couple of galv bolts but I would then need to drill all the way through so that I can lock the other side with a nut, which obviously ruins the looks of the fence (at the moment the inside face of the posts are clean without holes).

Any ideas on how else I could affix these timber rails onto the metal posts?

Bung

6327 posts

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#2842226 3-Jan-2022 05:38

You can get self drilling screws for metal. Do they just have to hold the rails to the metal posts or do the rails have fence palings attached?

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wellygary

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#2842228 3-Jan-2022 06:37

If you are worried about keeping the “face” of the steel posts clean, how about drilling them “laterally” on the sides in line with the rails???

Drill all the way through and then bolt on an angle bracket on each side

https://www.mitre10.co.nz/shop/bowmac-angle-bracket-no-gusset-b50-hot-dip-galvanised/p/170408?gclid=EAIaIQobChMI2rKQ1cyT9QIVszdyCh2D8QksEAQYASABEgKzCfD_BwE&gclsrc=aw.ds

Then hang and bolt the rails onto the brackets..

you could even slice a recess into the rail and then drill and bolt through the wooden rail if you really wanted To make it seem flush...

eracode

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#2842235 3-Jan-2022 07:25

Sounds like you have: Steel posts, horizontal 75x50 rails attached to the posts top and bottom, then vertical palings attached to the rails - is that right? (You don't mention palings).

Assuming the posts are square tube, the steel is probably about 3-5mm thick. Self-drilling screws (i.e. no pre-drilling required) are intended for fixing sheet steel like roofing onto timber (i.e. they drill first through the sheet steel). They may not work well fixing timber onto much thicker steel - I don’t think they are designed for that.

You could use the bracket idea mentioned above but that's a lot more work and expense and not necessary IMO.

I would simply re-attach the rails to the posts using stainless-steel self-tapping screws. You will need to pre-drill a hole in the steel about 1mm smaller diameter than the screws and they will tap into the posts and hold the rails firmly.

https://www.placemakers.co.nz/online/fastenings-general-hardware/fastenings/wood-screws/product/self-tapping-screw-10g-x-50mm-pan-head-square-drive-t302-stainless-steel-spqt4052002/p/4516595

Clamp each rail to its posts at each end, in the position where you want it. Drill the hole through the timber and the steel all in one go, so that you get it easily all lined up - then put the screws in.

Sometimes I just sit and think. Other times I just sit.

Bung

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#2842237 3-Jan-2022 07:32

The length of the drill point on a self drilling screw governs how thick the material can be. The posts are probably only 3mm wall thickness and there are screws designed for thicker steel than that. What hasn't been specified is the weight the fasteners will be holding.

jasonpklee

3 posts

Wannabe Geek

#2842396 3-Jan-2022 11:02

Hi Guys,

Thanks for the feedback and discussion, starting to get some ideas on how to tackle this.

To clarify, no palings, just multiple horizontal rails placed somewhat closely together to achieve a semi-look-through fence. Fence posts are around 2m apart, but some of the railings span 3 posts (one on each end, one in the middle), while others span only two (one on each end). Browsing on Mitre10 for comparable materials, looks like radiata like so: Radiata Fence Rail - Fencing Timber | Mitre 10™

Metal posts sound hollow so should be square tube, unable to confirm thickness but 3-5mm sounds about right.

I wasn't sure the self-tapping screws would work, but I don't have much experience with this so maybe I'm just worrying over nothing. Assuming 50mm thick rails and 3-5mm thick metal walls, does that mean I should be looking at self-tapping screws of around 60mm length? Will the 10g screw suggested above be strong enough for this purpose, or should I look at a bigger gauge to be safe?

eracode

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#2842405 3-Jan-2022 11:45

75mm might be better because with 60s you may have the taper part of the screw holding the rails into the steel. Depends on the actual thickness of the rails. If they’re dressed to 45mm, 60mm should be fine.

How long is the fence in total? Would you consider just reattaching rails at the top and bottom (and maybe at half-height) then put vertical palings on the rails. Fence palings are cheap as chips and it may be easier and not much more expensive to do it this way.

Sometimes I just sit and think. Other times I just sit.

jasonpklee

3 posts

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#2842457 3-Jan-2022 14:33

Yeah good point, I was looking at this earlier and the websites all don't show the length of the taper so I'll have to check it out in store.

To be honest I toyed with the your suggestion of putting vertical palings but the rails are actually all still in pretty good condition and 70% of them are still in position so it's easier to just reattaching in the same manner, and just fix up any that fall off later in the same manner. Not to mention our residential area has some rules in the covenants preventing excessive modifications to the external visuals (annoying to be honest) and I'd much rather avoid the hassle of dealing with the residents society rep and a couple of nosy neighbours.

eracode

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#2842479 3-Jan-2022 15:23

It might be worth re-fixing all of the rails because if some have come loose due to corroded nails, the other 70% are likely to do the same sooner or later.

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neb

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#2842545 3-Jan-2022 18:57

Just a general comment, check what you can put through treated pine without it corroding away too quickly.

eracode

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#2842555 3-Jan-2022 19:54

neb: Just a general comment, check what you can put through treated pine without it corroding away too quickly.

Stainless steel - as recommended above.

Sometimes I just sit and think. Other times I just sit.

MikeAqua

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#2843357 5-Jan-2022 08:43

eracode:

neb: Just a general comment, check what you can put through treated pine without it corroding away too quickly.

Stainless steel - as recommended above.

I'd go with galv self tapping screws, unless stainless is the look you want. Stainless (esp 316) into galv risks galvanic corrosion, which would cause the post to rust around the screws. If you do go with stainless, use tef-gel or similar on the threads. Also you may need to go with a thicker gauge in stainless.

With a nail punch you should be able to punch the nail remnants into the post clearing the nail holes. You can then use the nail holes in the timber and the steel pots as pilot holes for your self-tappers. You may need to widen/tidy them with a drill bit. If you do, take it slowly and don't use too much pressure. It's very easy to break drill bits widening holes. Remember not to let your drill bit get too hot. Some cutting spray like CRC's CDT would help with this.

Mike