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Protecting The Chassis


mechs
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Just wondered something, This caravan i've got now hasn't got the galvanised chassis like my last one :( but looks ok however was going to give it the once over with a wire brush then wondered what, if anything to coat it with to protect it from the elements?

 

I'm sure I read on here somewhere NOT to use underseal, if so any recomandations?

 

Thanks :)

Compass Shadow 1988

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Do you know who made the chassis too?

 

Caravan chassis's - even steel ones - are not as prone to rust as car chassis are.

 

Cars are more frequently used, and get wetter often so rust appears if the metal is exposed.

 

A caravan chassis does not get wet so often and dries out quicker because of underdraft, and a high percentage of moisture evaporates so reducing rust.

 

Personally, I would not bother to underseal. Doing that might cause more risk of rust than leaving it exposed if not done professionally.

 

Underseal can hide a multitude of damage too and if I saw a caravan that had been undersealed, then I would not touch it with a barge pole - and a very l - o - n - g one at that.

 

I studied the rust and effects of in BT for cables and metal surfaces, so I know all the above to be true,

 

Regards

 

Pete

Edited by Bailey Oklahoma
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I would tend to use something like hammerite. Although it claims to be able to used over rusty metal I would still clean off as much rust as you can. The old red oxide paint used to be good but the last time I got some it did not seem to adhere as well, presumably the product changed. I think Halfords have changed their stock holding as my local one had several tins reduced so it might be worth a look in your one.

 

Underseal was always applied to prepainted surfaces, not to bare metal so even if you went down that route you still need to paint

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I have seen others and owned one Al-Ko chassis caravan with extensive surface rust and seriously depleted galvanizing. It is a myth that they don't rust even when galvanized. I put it down to winter use where I know we encountered salted/gritted roads. My handbook said to wash the chassis after winter use but doing this after each tow onto a site is not practical and even at home difficult to do 100% effectively.

Subsequent vans I have treated the chassis from new and periodically with Waxoyl and Dinetrol products and this has allowed us to continue winter caravanning without the issues we had earlier. I carefully brush these on to avoid risk of "overspray" getting on the treatment the maker applied to the underfloor as I suspect these petroleum based products would do that no good at all.

I would resist any form of painting as experience is that rust can spread and possibly be accelerated, under the surface of the paint. I would directly Waxoyl the cleaned up but rusted surface you have in reasonable confidence that it would check its further degradation.

Edited by JTQ
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Painting a already rusty chassis with a paint or underseal will trap moisture and it will rust behind the paint . As said Waxoyl will protect it by keeping moisture out and it also mends itself if it scratched .

 

 

 

Dave

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Thanks, i'll probably just leave it reading some of the posts on here. It's an Elddis caravan, not sure who made the chassis, how do I find this out? I'll investigate later :)

 

It's not overly rusty considering its age plus the previous owners were tourers but i'll be on a seasonal pitch, always am, so it won't be towed much at all.

 

I'd just wondered if it was worthwhile coating it with something but reading the posts might do more harm than good trapping mpoisture etc so if it's best just to leave it I will.

 

And yes, my now old caravan chassis is galvanised. I'll have another look but don't think this one is at all.

Compass Shadow 1988

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Hammerite Paint is good for metal parts. It can be expensive and it is best to use an old brush when applying.

 

You do not brush/clean of the rust before using it.

 

The cost of the cleaning solvent to clean the brush is more than a new brush!

 

I use it on a wrought iron gate and it is exposed to all weathers. It is two years since it was last painted.

Ford C-Max and Coachman Festival 380/2 SE 2006    Motto  Carpe Diem

Still trying to find the perfect pitch. ..110 amp Battery+ 65 watt roof mounted Solar and 25 watt Wind Turbine. LED lighting. Status Aerial 315. Loose chattels marked with UV,. Safefill Gas Fitted.

 

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Thanks.

 

I just took a very flimsy wire brush (Poundland so rubbish!) attatched to a pole and gently rubbed over the underneith. Not much came off to be honest, just a few flaky bits and dust.

 

Near the end however (at the other side of the caravan near the a-frame I found a plate that read "B&B Trailers, Leamington Spa" and the number under it so had a quick google search and just about to have a read of this http://www. thomson-caravans. co. uk/advice/maintenance/pdf/bbhandbookchassis72-83. pdf as that's my chassis :)

Compass Shadow 1988

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My first caravan had that chassis, its got proper suspension, coil springs and dampers!

 

If you use Hammerite make sure you buy the correct grade, normal Hammerite is not suitable for direct application to a Galvanized finnish, i cant remember if it was galvanized. But Hammerite do a dearer product suitable for applying direct to a galvanized finnish.

 

If its rusting already i would just paint brush some engine oil on, this will slow it down.

 

I would only use Waxol on a new chassis.

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Thanks xtrailman, not applied anything yet. I don't think it's galvanised and I couldn't see it in the "instructions", Is the suspension, coils and dampers a good thing?

 

I just took the flaky bits of rust off but will look into the Hammerite, it's still solid anyway and nothing wrong looking at it, I was just wondering about keeping it that way

Compass Shadow 1988

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The best thing to do is to attach a sacrificial anode. We don't do this much on land, but sailors do it all the time. Essentially, when you galvanise an iron item, you are applying a coat of zinc to it. Zinc is higher in the electrochemical scale than iron so will preferentially react with oxygen. Thus, your iron won't start rusting until all the zinc has gone. If you attach a few fillets of zinc to areas that are likely to go rusty the zinc will preferentially oxidise and protect the iron. Google for sacrificial anode, wirewool the appropriate parts of the chassis and bolt on.

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Interesting, thanks! Got a few options to explore I see, i'll have to google alot! :)

Compass Shadow 1988

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Thanks xtrailman, not applied anything yet. I don't think it's galvanised and I couldn't see it in the "instructions", Is the suspension, coils and dampers a good thing?

 

I just took the flaky bits of rust off but will look into the Hammerite, it's still solid anyway and nothing wrong looking at it, I was just wondering about keeping it that way

 

I found the Monsa 1200s the best tow i have ever had, towed by a 1. 6 90bhp cavalier with complete composer. While i'm not sure about the rubber suspension.

 

The best thing to do is to attach a sacrificial anode. We don't do this much on land, but sailors do it all the time. Essentially, when you galvanise an iron item, you are applying a coat of zinc to it. Zinc is higher in the electrochemical scale than iron so will preferentially react with oxygen. Thus, your iron won't start rusting until all the zinc has gone. If you attach a few fillets of zinc to areas that are likely to go rusty the zinc will preferentially oxidise and protect the iron. Google for sacrificial anode, wirewool the appropriate parts of the chassis and bolt on.

Rolls Royce used to use anodes, don't know if they still do?

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I'm never sure about painted galvanisation. It is protected from the iron by the paint it is suspended in, and so can't bond chemically. How can it work?

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GALVAFROID®

ZINC-RICH COATING

Technical Description

GALVAFROID Zinc-Rich Coating is a brush or spray-applied anti-corrosion coating containing 92-95% zinc in the dried film which confers electro-chemical protection on ferrous metals. It may be used as a primer or self-finish.

 

Explanation of protective mechanism: GALVAFROID treatments of iron and steel base their corrosion inhibiting qualities on the galvanic action which develops in corrosive conditions between the zinc and the substrate.

 

The latter is protected even in scratch lines and at points of abrasion, since the zinc surrounding the break is immediately reactivated and corrodes sacrificially in preference to the underlying surface. Zinc corrosion products, which are largely insoluble and impermeable, soon form, sealing the break and protecting the substrate. The lateral spread of corrosion is thereby prevented.

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According to the guide i've got the chassis is not galvinised in the link above I posted, that's why I wasn't sure wether to treat it or not

Compass Shadow 1988

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http://www. zinga-uk. com/files/Zinga_versus_Galvafroid. pdf

 

I have no idea if this is the case but it accords with my understanding of paint chemistry. The zinc HAS to be in contact with the metal, which is why ingots are so good. Sounds as though Zinga have solved this? http://www. zinga-uk. com/

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I've used Galvafroid when i was electrical contracting, we used it to paint mild steel frame works that we fabricated, its an excellent product.

 

Also used it on cut joints on galvanized tray work, its been around to my knowledge 40 years.

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Thanks blueflightmedic for the links, will more than likely try and get some of that. If only I could pinch some of the paint they use to paint the Forth Rail Bridge! :D

Compass Shadow 1988

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Not been in touch yet Rita but also will do that too. Like I say it's not in bad condition, just want to keep it that way but I know some say to treat the chassis and others it's a no-no so thought i'd ask on here too :)

Compass Shadow 1988

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