low deck steel joist extra protection

hi everyone,

I'm build what will end up being quite a low deck in one area. there will be about 50ish mm between the ground and the bottom of the joists. the red line is roughly the bottom of the joists and the green is area with low clearance. I will end up chucking a layer of gravel over the whole thing just incase a noah's ark flood comes and washes under there.

Attachment 537545


The joist are C section and zinc/gal and a solid top will going on top so no actual rain or run off water will really hit the area. But I can see it just always being damp under there so I'm looking at some options to ensure everything has longevity as replacing joist or bearer later won't be easy. any coating will really only apply to about 3m worth of joists as the ground tapers off after that giving plenty of air flow.


this is just for reference of what the deck is built from:
Attachment 537546

1. just paint it in the same paint (dulux under coat + dulux rapid coat monument) my other 2.7m high deck is going to be painted in.
2. use something like a bitumen paint and just coat EVERYTHING with a coat or two. The area won't get sun light so UV is not a problem.
3. cold gal spray/paint... not sure if it will grip to the zinc coating though.
4. something else?


digging down isn't really an option as i'm already pushing it with having to retain area's just to get the 50mm I have now, plus dealing with the clay etc etc

Quote:

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Originally Posted by havabeer69

hi everyone,

I'm build what will end up being quite a low deck in one area. there will be about 50ish mm between the ground and the bottom of the joists. the red line is roughly the bottom of the joists and the green is area with low clearance. I will end up chucking a layer of gravel over the whole thing just incase a noah's ark flood comes and washes under there.

Attachment 537545


The joist are C section and zinc/gal and a solid top will going on top so no actual rain or run off water will really hit the area. But I can see it just always being damp under there so I'm looking at some options to ensure everything has longevity as replacing joist or bearer later won't be easy. any coating will really only apply to about 3m worth of joists as the ground tapers off after that giving plenty of air flow.


this is just for reference of what the deck is built from:
Attachment 537546

1. just paint it in the same paint (dulux under coat + dulux rapid coat monument) my other 2.7m high deck is going to be painted in.
2. use something like a bitumen paint and just coat EVERYTHING with a coat or two. The area won't get sun light so UV is not a problem.
3. cold gal spray/paint... not sure if it will grip to the zinc coating though.
4. something else?


digging down isn't really an option as i'm already pushing it with having to retain area's just to get the 50mm I have now, plus dealing with the clay etc etc

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Slope the ground away from the deck as much as possible even to the extent of installing aggie drain with an open run off pipe to drain any seepage where ever possible.
Remember water does flow downhill but if you have a situation where you create a dam then moisture will most always be present, so getting rid of the seepage is a good start.

As to painting the gal steel, as you have stated it is only as good as the sticking power of the paint which, on gal is very limited and then you will drill through the top anyway so ???.
One problem I see using gal steel is the swarf caused by drilling/ screwing will lay on the gal steel and in the bottom lip and this will cause premature rusting.
Maybe have a serious look at bonding the decking to the gal steel instead but it may be cost prohibitive..
Sika FC11 comes to mind for that purpose but take advice from the Sika people (not Bunnings) or the makers of T Rex which is an alternative to Sika..
But then again it would rid you of the problem of drilling so many holes, so horses for courses.

yeah I think i've pretty much settled on the bitumen paint idea and I'm just gonna slap a thick coat or two on everything. Its meant to be rated for water proofing zincalume water tanks ETC so should give the deck a heap of longevity.

Attachment 537551

got the stirrups concreted in the other day but you can see how low the end is, the beam is actually sitting on some old bit of timber concreted in the ground (plus a wedge). Should be enough room for a layer of gravel, and i'm going to trench an ag drain on the house side of the stirrups just to try and move any water that comes down from behind the sandstone wall.
as you can see it actually sits HIGHER then a 45mm thick piece of timber.... but its also currently a boggy boggy mess from walking around on the sloppy clay
Attachment 537550

Attachment 537552