# Forum Home Renovation Sub Flooring  Screwing Merbau to steel joists

## Al Kilgour

Hey guys, 
My deck is coming along nicely however i just wanted to get some advice on screwing/nailing Merbau to steel joists. What type of screws would you suggest and what is the best way to do it. 
I am not afraid of hard work and i figure pre drilling all the holes then screwing it down would look the best.  
I have no idea what type of screws to use so any advice and links to pics of screws would be greatly appreciated. 
Also the joists are RHS Gal..

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## Big Shed

Hi, I did a deck on our houseboat, merbau on C channel, but same principle. 
I used self-drilling countersunk metal screws, but pre-drilled them with a drill bit just under the size of the drilling tip on the screw. I also countersunk the merbau so that the screw head would sit just under the top.

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## Al Kilgour

Thanks Big Shed: I am certainly going to countersink the Merbau so the screws dont sit proud.   http://www.jamestowndistributors.com...tainless+Steel  
Do you think these screws would be good for this job? If not can you link me to some that would so i know what to get. 
Thanks in advance.

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## Dirty Doogie

Those screws wont hold in steel.

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## Al Kilgour

Thanks Doogie. Anyone able to link me to something that will?  http://www.redboxhardware.com.au/ind...id=84&gid=1241 
These look like they might do the trick. Can someone confirm this for me. Also what size screws should i get? The Merbau will be 90 X 19 and the joists are 2mm RHS Gal.

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## Dirty Doogie

My reference site is playing up  - http://www.kjbolt.com.au/products_cat.php  
cant get you a link to the exact screws you need atm

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## Al Kilgour

No worries doogie. When you can access it that would be greatly appreciated mate.

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## Dirty Doogie

How big is your deck - a lot of ppl are now gluing decking down to duragal joists - a bit slower but very easy and durable. There seems to be some issues with penetration of the joists. These KJ bolts people have decking glue which is being used more and more.

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## Dirty Doogie

http://www.kjbolt.com.au/newproducts_02.html  
the screw at the top is the sort you might want to use - notice the drive tip for going through metal - these go in much easier if you drill a pilot hole through the timber and through the steel.

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## Al Kilgour

Thanks Doogie, The deck is huge and call me old fashioned but i like the idea of screws. I just dont trust glue   :Frown:

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## silentC

OK I got sick of constantly having this debate, so I've rung the OneSteel technical guy and asked him why they don't recommend screws on outside decks and verandahs. So here's what he told me: 
1. You put a joist tape on the top of the joist which seals against the nail as it penetrates - this doesn't work with screws. Using screws can therefore allow moisture into the joist. 
2. When the decking expands, screw heads have been known to snap off. Timber joists allow for a bit of expansion, steel doesn't. 
He said that their preferred fixing method for external applications is a stainless steel twist nail. 
If you insist on using screws, he says you can put a blob of silicone under each screw, or counter sink and then fill the holes - but this wont help with the head snapping problem. 
With their own products, they wont assist in warranty cases if the decking has been screwed down.

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## Dirty Doogie

Hi Silent - did the onesteel dude say anything about gluing decking down.?

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## silentC

Didn't ask him, hadn't read your post! 
The only thing I'd say about it is that you wouldn't be able to put a joist tape down first... 
There's a type of deck fixing available that grips boards from the sides - no through nails. I reckon if you could tek-screw that to the side of the joist with a bit of flashtak behind it, that would be the Rolls Royce.

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## Dirty Doogie

Yeah I agree Silent - a batten of some sort down the side of the duragal joist sealed with nuetral silicone seems to me to be the best way. The KJbolt site which I gave a link to above lists a decking glue suitable for duragal joists - but I cant get into the site proper atm. Interesting stuff and links there also.

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## Tools

I think what Silent is referring to is a fixing that is screwed in between the boards and slots in to a slot in the side of each board. 
Tools

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## silentC

Yep that's the one, someone on here has used them. Takes a lot more work but looks good.

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## hansp77

I used countersunk stainless hex head bolts on my boat... looks great (though you can't really see any details in these shots), could get a bit expensive though :Rolleyes:

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