Rebuilding car trailer and welding/bolting galvanized frame

I have the chassis of an old trailer tent that I intend to re-purpose as a multi-functional trailer for my own use. The chassis is in good condition and is mostly constructed from U-section galvanized steel. All my previous fabrication projects have used plain mild steel.

Some of my modifications / add-ons will require securing to the chassis. Can I bolt and/or weld mild steel fabrications to the chassis or will this be problematic? I'm thinking of various connectors for removable sides, mudguard supports, ladder/kayak rack, tie down points, etc. I would also like to reinforce the frame in a couple of places. I presume it's good practice to grind off any galvanized first when welding, but please correct me if I am wrong. If I do weld mild steel to the galvanized frame, what finish should be applied?

Would it be okay to fabricate some parts from mild steel, apply an appropriate paint, and then bolt to the galvanized steel frame? In this situation, are galvanized fixings required or preferred?

I should probably mention the trailer will be stored outside covered by a tarpaulin.

I'd say galvanised fixings and fittings are to be preferred, but most importantly, if you are welding to the galvanised chassis, be sure to grind off the zinc coating for a good few inches around the weld area as zinc fumes are poisonous. Probably OK if outdoors with a bit of wind, but be careful.

As a finish, one of the so-called "cold-galvanising" sprays would do, or just a good primer and suitable paint - but that way you'll probably end up painting the whole thing.

Rob

Paint ground surfaces/welds, etc with cold galvanizing paint and use galvanized fittings. Cold gal is not as wear resistant as hot dip but gives good rust prevention.

As Rpb has said, Zinc fumes are not good for you, but having welded galv many times and founded much brass It will not be zinc that kills me. a good paint system will keep the oxide at bay. If you have access to stainless then it can often be cheaper than galv and can be welded. If using stainless nuts/bolts grease them before tightening as they may cold weld and then you could be in the ---- ! Good luck, Noel.

Go ahead and weld (with precautions as above), fabricate in MS, and send the job to the galvanizers - better than spray-on Zn-rich paint.

**LINK**
This thread brings up some of the pitfalls of building a trailer these days. Hope this is helpful if you were not already aware.

Mike

Hi Ajax, apart from welding fumes from the galvanizing being poisonous, the galvanizing must be removed by a good amount each side where you need to weld and where the weld penetrates through, otherwise the zinc will contaminate the weld metal and will produce a weak weld and it is likely to be porous, so weld only where really necessary.

Regards Nick.

Hot dip galvanizing after your modifications is is the best option but is expensive. The trailer. has to be chemically cleaned to removes organic contaminants such as dirt, paint, grease, and oil from the metal. Then pickled in acid which removes mill scale and rust (oxides) from the steel. Then dipped into a flux bath which prevents oxidation of the metal prior to entering the galvanizing bath and also aids the galvanizing reaction in developing the hot-dip galvanized coating.

I recently modified my standard box trailer (already hot dip galvanized) into a tilt trailer and considered having the new parts galvanized but cold gal coated instead because of the price.

Paul

Is it really worth using a trailer tent frame? They're even flimsier and smaller than a caravan, which are are virtually useless once the body woodwork rots away. The suspension and wheels on trailer tents tend to be the lightest components available too.

I say this having recovered the wreckage of several such things that weren't up to the job they were being used for.

Has the use of a suitable mask as a precaution against fumes been mentioned?

I think a mask to the FFP3 standard would be suitable.

Your trailer will be plated for the weight it was as a trailer tent and no more, don't add so much weight that you can't carry anything in it.

Based on some of the comments here, plus what I've now read online, I will probably opt for mechanical fixings rather than weld anything on. I remember gas-cutting galvanized tubing in a milking parlour as a young man, and I'm still alive today, not to say that is an endorsement of the practice!

I rather suspect that would make it an expensive build. My other trailer (now almost 50 years old) seems to have done okay without a zinc coating.

I don't think that would help, would it? I have FFP3 masks and filters for particulates and vapours, but they won't filter the gas.

Perhaps that's why no one mentioned it!

Someone on here must know?

Thanks for raising this, but I expect it to be well within the limit. The trailer (Conway Products Ltd, model number CDX/93) is plated 650kg maximum gross weight and appears substantial enough for my intended uses which will mostly be limited to carrying bulky but not particularly heavy items (e.g. kayak, family bikes, sheet materials, fencing posts and rails, etc.) It happens to be braked which is nice, but maybe not essential for my intended uses.

All valid comments and I agree that some caravan / trailer-tent frames are unsuitable for conversion, but this one seems adequate for my needs. With some modification, mostly a small amount of bracing, a flat deck and some hold downs, I think it will be adaptable enough and safe to use. I plan to fabricate some bike / kayak / material carriers that can be added/removed between uses.

This trailer frame is plated 650 kg max gross weight. I don't know whether this assumes some structural integrity from the tent box framework which has been removed, but I don't plan to go anywhere near this weight.

The Al-Ko axle and 145R10 tyres seem more substantial than most I've seen on small box trailers (e.g. Erde) with the added bonus of a working brake system.

Of course, I could be wrong!

Brian

One thing I might mention is that after collecting this trailer with my existing lighting board, I realized that due to it's width (over 1.3 m) the lighting requirements are different to a smaller box trailer - e.g. fog lights are required, side reflector requirements, etc. Braked trailers manufactured after October 2012 also require a reversing light, which I think would be a good idea for this trailer, but perhaps not a legal requirement as I suspect it is older. In fact, since checking these rules I'll have to take another look at my nearly 50-year-old "skip" trailer to check that it is road legal.

I would not weld to a galvanised chassis,welding and zinc do not mix,when grinding the zinc coating off I have found that the zinc appears to have penetrated into the base steel and it takes further grinding into the base material to get clean material,this is ok with say 10mm thick plate,but the welding will still spit and bang occasionally,so use bolted construction and only drill holes into the centre line of the channel, do not drill the flanges of the channel,it will serious ly weaken them, If you are converting to a box trailer the way to stiffen the trailer is to make sides from angle iron ,welded at the corners then fill the frame with 12 mm ply and make it a really tight fit so that it becomes a girder section, on light trailers the weakest point is where the trailer "box" meets the drawbar and it may pay to to add some plate to the channel section drawbar , make sure the wheel bearings are well greased and get a spare wheel nearly all trailer problems are old tyres and bearings failing. Also make sure that you inform the car insurance company that you have a tow bar fitted,they are regarded as accessories. some time ago I checked with Direct line about my Discovery ,although it had been fitted from new with a towbar Direct line needed to know,as they regard it as an accessory and must be declared,and updated the policy though there was no extra cost .

I recently replaced the rotting wood base on my farm trailer with salvage steel 'planks'. 2 coats of farm oxide appear to have given it a surprisingly durable finish. Also discovered that the stuff can be sourced in a rainbow selection of colours with minimal prep.

pgk