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[Gaffers]

Tomorrow night I will be taught how to weld by a colleague while we rebuild the trailer for Jenny.  I have a lot of new box section mild steel and my thoughts are now to painting it.  Obviously it will get immersed in salt water several times a year thus a good coating in and out of the box sections is vital.  There seems a lot of info about painting the outside but nothing about the inside of box section mild steel.  Some will be closed off from the welding but some will be open.

Any thoughts?  I was thinking of using a wad of cloth dragged up vertically through it with some string which has been soaked in the necessary paint. 

Also, I assume hammerite is ok for this type of application?

P.S. Mega thanks to Shackeng for the welding equipment, I shall no doubt pass it on myself one day once done with it

[aaronjb]

I hear that Hammerite is too 'brittle' at least for the outside of a chassis and very prone to stone chips - Por15 is meant to be better.

As for the inside.. not sure a rag will give you good coverage - perhaps waxoyl? Or see how much it is to get it dipped?

[Gaffers]

I thought about getting it dipped but afraid of the cost.

the sections internally are 1.2m long so not easy to do with waxoyl.  Maybe I could weld plates onto the open ends?

[Andy B]

I thought about getting it dipped but .....

If you do, don't forget that you'll need to drill the box section where another welds to it ie no closed off sections so that whatever youre dipping it into can flow through out. Same applies if you galvanise it.

[Gaffers]

Galvanising would be a waste of time if it is going near sea water, surely?

[05omegav6]

There are ways of waxoyling the insides , iirc used to be common on MGs and the like to make sill changes last a few years rather than the typical every other service

Also, try screwfix et al for plastic plugs similar to those found in metal table legs etc

[Andy B]

Galvanising would be a waste of time if it is going near sea water, surely?

Galvanising would be ideal for something going near/in the ogin. 

How about sacrificial anodes like a grey funnel liner 

[Gaffers]

Surely the zinc coating would be the sacrificial element in this case?

[Andy B]

Surely the zinc coating would be the sacrificial element in this case?

I'll have to pass on that, but there were various chassis that were galvanised ................ 

[aaronjb]

According to the second site I found, hot dip galvanising is "£7-10 per m2, dependent on weight, size and quantity of material" - see if you can find somewhere local that'll slip it in on a bigger job and take cash.

The zinc corrodes, of course, but incredibly slowly compared to steel - the same site suggested 40 years of protection in 'harsh' environments..

[Gaffers]

And about 1 hour in salt water lol

[aaronjb]

Corrosion rates of galvanising in seawater: http://www.galvanizeit.org/aga/about-hot-dip-galvanizing/how-long-does-hdg-last/in-water/water-corrosion-data//#seaWater

[belldarr]

I have a jetski and a 20 foot boat that both have trailers that regularly get dipped in the sea, both trailers are fully galvanised and I rinse off the trailer and the boat/ski as soon as I recover them and they have been fine.

I would advise doing all your welding, drill all your holes then diss-assembel and spend the money getting the whole lot galvanised and then paint if you wish - or it will just rot from the inside out as you probably suspect. 

Darren

[Tony H]

I have a jetski and a 20 foot boat that both have trailers that regularly get dipped in the sea, both trailers are fully galvanised and I rinse off the trailer and the boat/ski as soon as I recover them and they have been fine.

I would advise doing all your welding, drill all your holes then diss-assembel and spend the money getting the whole lot galvanised and then paint if you wish - or it will just rot from the inside out as you probably suspect. 

Darren

Agreed if you intend to keep the trailers any length of time this is the only way to go