Trailer painting questions

ProDave

ProDave

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I was having a look at the boat trailer today and it's in desperate need of a strip down, scrape and sanding and then re painting. It's not galvanised, just painted box section steel.

Two questions. having scraped and sanded, what to paint the outside with? and what primer to use first so it stays rust free for longer? I'm torn between hammerite type paint, or under body sealant (I don't care much what it looks like!!!)

And second question, what about the inside of the box sections? I can't paint them with a brush, or do much in the way of scraping, but I feel it's worth pouring something down them, paint? or just old engine oil?
 
The underbody sealants that I’ve seen and used have all been waxy and would rub off or transfer onto anything they touch, leaving greasy smears. For that reason I’d go for Hammarite with a zinc rich undercoat. Old engine oil would creep acros the inner surfaces of the box section and help to keep some of the metal moisture free, and perhaps reduce the speed of corrosion. It is also likely to easily emulsify and get washed away.
If the outside is in such a state then the inside will be worse where moisture has been trapped. I’d want to be 100% sure of the integrity of all the metal work before investing time in painting or sealing it.
 
ProDave said:
I was having a look at the boat trailer today and it's in desperate need of a strip down, scrape and sanding and then re painting. It's not galvanised, just painted box section steel.

Two questions. having scraped and sanded, what to paint the outside with? and what primer to use first so it stays rust free for longer? I'm torn between hammerite type paint, or under body sealant (I don't care much what it looks like!!!)
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Hammerite isn't great, because it's very brittle and chips off easily. In theory I think the best thing is proper chassis paint (POR-15 do a good one) but I repainted my mild steel Hunter 490 trailer with a glossy red oxide paint by Coo-var and it's holding up very nicely.

And second question, what about the inside of the box sections? I can't paint them with a brush, or do much in the way of scraping, but I feel it's worth pouring something down them, paint? or just old engine oil?
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I'd suggest drilling holes and then injecting Dinitrol rust proofing wax. Waxoyl is a lousy second best.
 
I'd be inclined to use a rust killing primer and Hammerite, although the modern formulation ism't a patch on the original. The trouble with underseals is that the best ones don't quite set and can seriously mark your clothes every time you strap the boat on - and will probably rub off with the tie downs.

If you have access to the tube ends it would be an idea to do what you can to remove internal rusting by attaching a wire brush to a set of drain rods and rodding it through. Again, if you have sufficient access you could also consider treating it with Waxoil (sp?) which is likely to last longer than old engine oil and won't dribble out on the driveway! All at a price, of course.

Rob.
 
ProDave said:
So a good coat of zinc primer and some chassis paint looks like what's needed.
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POR-15 chassis paint contains anti-corrosion stuff and goes straight onto the metal; th einitails stand for Paint Over Rust. Many paints dislike zinc primers.

For the inside I only suggested old engine oil as I have plenty.
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It's maybe better than noting, but if it's well used it can be quite acidic and it does run off in time.
 
My trailer had a box section draw bar which parted after just 2 years from new. The rust was from the inside and not obvious. So as said box sections are a real concern. Since then I have put as much old engine oil as I can into box sections drilling small holes in the top of sealed areas. I just use a metal type paint over rust areas. Plus lots of oil in tight spots. A constant concern and problem. olewill
 
There is a galvanisers at Elgin, run by a forumite. I got my anchor chain done there last year for something like £25.
Obviously there would be work in stripping everything off the trailer, and you'd probably then need to borrow another trailer on which to transport it to Elgin, but it's far and away the best option in the long run.
 
Agree 100% about Hammerite. I've been using Rustoleum - just done the chassis on a pick up truck - as it seems to keep rust at bay pretty well. Expensive, though.

rob2 said:
I'd be inclined to use a rust killing primer and Hammerite, although the modern formulation ism't a patch on the original. The trouble with underseals is that the best ones don't quite set and can seriously mark your clothes every time you strap the boat on - and will probably rub off with the tie downs.

If you have access to the tube ends it would be an idea to do what you can to remove internal rusting by attaching a wire brush to a set of drain rods and rodding it through. Again, if you have sufficient access you could also consider treating it with Waxoil (sp?) which is likely to last longer than old engine oil and won't dribble out on the driveway! All at a price, of course.

Rob.
Click to expand...
 
I am a fan of Jotun paints, my last cradle was painted with Vinyguard 88 (an underwater primer originally purchased to go between epoxy and antifouling.) I never overcoated it but the cradle was still rust free when I sold it ten years later. Easy to apply with a 4" roller and dries in an hour or two, great adhesion.
The new cradle is going to get a coat of Jotamastic 87 which is a two pack epoxy coating claimed to be good on rusty surfaces, probably overkill but I have the stuff and it is about to go out of date, I might defer it for a while and coat the iron keel at the same time.
 
I have rolled it into my garage today (very tight fit) ready to be worked on. The main reason is to keep it dry while I am stripping sanding and grinding before the new paint goes on.

I have already had a good scrape of the worst looking bits, and it does appear just to be surface rust from the outside where the paint has failed and water has got in. the bits I have scraped look to be sound metal underneath so I don't think it's rusted through from the inside. So hopefully I have caught it in time to stop the rot.
 
As a one time professional trailer builder, it is the insides of the tubes I would worry about. Use a sharp object to tap the underside of the tubes, esp any low points that might trap water.
Couple of recent cases in my w/shop from friends. One looked good and had been painted often. Bottom of tubes completely gone from the inside. Second was a 7yrs from new and galvanized, except that the square tubes inside the rubber in the 'torsion' suspension were not galvanized and one was failing. Trailer started to lean a bit and he bought it over to ask why. Axle was scrapped and a new one €350.
 
Use a sharp object to tap the underside of the tubes

I'd second that and I'd "thump" the underside of the trailer at the low and suspect points with a centre punch and lump hammer. If the steel is good you'll just get a punch mark, if it's gone from the inside, it'll go right through.

The consequences of a trailer failing whilst towing even a small yacht, could be quite serious.
 
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