Board logo

Universal Columns / I Beam / RSJs outdoors
gregs - 23/1/16 at 09:24 AM

Simple question - I need to complete a project (at home) involving UC's buried in the ground with sleepers between to act as a retaining wall in the garden.

Simple question - do I need to galvanise them (they will be ~23kg/m) - or is this really cosmetic for something of this 'mass' over a lifetime of say 50 years?

Could be quite a cost saving if I only need to do the ones that are 'in view'.


monkeyarms - 23/1/16 at 09:42 AM

Need to galv.? I would say no.
a coat or two of Hammerite or similar would be my choice.

BigFaceDave - 23/1/16 at 09:55 AM

We do quite a bit of steel work at work and if anything is ever being buried in footings or underground we will just paint them (or at least the bit going in the ground) with bitumen paint.

v8kid - 23/1/16 at 10:05 AM

On the other hand 50 years is a long time.

hkp57 - 23/1/16 at 11:04 AM

I assume the bottoms will be in concrete so there will be no issue down there as everything such as re-bar in concrete does not need coating as there is no oxygen to rust it out.

The problem area is usually where it comes out of the ground and it is constantly wet / dry cycled in air it will rust out.

If you don't galvanise or as a minimum paint a good quality bitumen based coating on it with the right surface prep (sand blasting) it will rust and quite quickly.

The parts where the beams are are open to the elements and damp also.

I would galvanise every time.

Depending on sizes of your sections many good fencing companies stock pre-cut posts already galvanised.

ALLAN 14 - 23/1/16 at 12:21 PM

Hi Greg
I would use a damp proof membrane on the back of the structure with a perforated drain throgh the bottom,
with drains through the wall, Drap teram type material up the back of the structur and over the earth bank.
Back fill with small gravel and fold it over the top before you put the earth back on.
If you Google French drains you will get more info.
If you get the beams supplied with high build oxide undercoat make shure its waterproof and paint with good
quality bitumen before you put the timbers in and after.

Hope that helps a bit.

zilspeed - 23/1/16 at 01:48 PM

Concrete carbonation is a very real thing.

The alkalinity in the concrete becomes compromised over time and cease providing protection to the steel with which it has contact.

(Window sill with rusted reinforcing being a classic example)

Proceed carefully if any of the steel is encased in concrete and might be exposed to carbon dioxide..

907 - 23/1/16 at 03:30 PM

I would use bitumen. I believe there's a product called chassis black.

The pic shows the RSJ leg of a Dutch Barn that for the last 70 years has been used to store straw bales.
You can see a hole corroded in the centre web, which is always rolled thinner than the outer webs. Loose straw
has collected at the base and held moisture, hence the rust. The barn is now to be used for the storage of wood chips.

My "temporary" repair was to dig either side of the existing concrete 1m deep and drop M20 studding through the holes
in the base plates. My customer is in his 70's and thinks it will still be standing when he isn't.

Paul G

centre web rusted through
centre web rusted through