During my resto I have been doing the unenvyable task of getting rid of the rust on the underside of my bus using combinations of wire brush on drill, wire brush on grinder and wire brush in hand as a last resort !!! A lot of you will be familiar with that same epic battle against the tin worm, and, after all your hard work you want to give it the best long lasting protection you can there are a number of different products on the market and the question is always asked whats best .......que Harry Hill. I have used in the past underseal....by underseal I mean the sticky black stuff. I have used a couple of different brands, usually with added waxoyl. What I have found over the last 6years of daily use on my MG is that it doesnt last. By being sticky it attracts dirt and salt etc and will eventually be worn off by road grit. Thoses bits which dont get worn off will eventually go hard and crack which will trap moisture against the metal unseen to rust. When you come to remove the last stubbon bits to repair the rust it can be difficult to get the last traces off to make a good weld....I now no longer use the stuff Waxoyl (or other brands) are essential IMHO but only after proper painting has been carried out first, it is also a must to do inside all the box sections etc Next was hammerite metal paint and similar brands. Looks good, gives a shiny appearance....but doesnt last. I had rust reappearing within 3 months due to paint flaking Next then is POR15. my initial use of it was to grind back the rust give it a clean with white spirits then acid etch primer then POR15. after a month or so I found I could peel big bits of it off. not to be put off I bought (at great expense) all the other POR15 products for preping the metal TO THE LETTER of their instructions. I had some mixed results, some areas it stuck well, gave a good finish ....but accidently running over it with a wire brush in the drill removed it I thought it was supposed to be stronger than that . I did apply it in the Autumn so it is possible that moisture in the air affected adhesion. I will give it another go in the summer for a fair trial but I feel that it is very picky when it comes to preperation before painting. ......So eventually I came across epoxy mastic 121 from rust buster http://www.rust.co.uk/epoxy-mastic.cfm it is a 2 pack paint which contains no isocyanates so you can use it at home with out the air fed mask, you should still wear a fume mask but they are cheap enough to buy. As it is a 2pack product it cures by chemical reaction rather than solvent evaporation thus making it less prous or susseptable to moisture ingress and hard wearing It has won a few practical classic magazine product tests. It resists stone chips well due to its high solids content. I have found that it can still be worn away with the wire brush in the grinder but it does not come away in big flakes like some of the other products. With 2 coats it is durable enough for a stand alone underside protection...althou gh I will be dousing it in cavity wax when Im finished. I have found that (even though I meticulously get rid of the rust) it is not too picky about surface preparation either, it will quite happily go straight over rust with good adhesion, as it is a 2pack product it forms an air tight/water tight barrier on the metal It sets quite hard and seems to be a cross between paint, rubber and stone chip, but is not soft to the finger nail like some stone chip paints are I have also found that it acts like a seam sealer, I squidge it into all the nooks and crannies and where any panels join forming a lip. I really dont think I will be needing any seam sealer after using it it comes in black, red oxide, green, buff, aluminium and grey I highly recomend the stuff...just check out my resto!! they also do a 2 pack epoxy primer which I will be using on the body work of the bus, it also contains No isocyanates so can be used at home. Can be sanded like conventional primer but isnt porus so it has got to be a good thing. It can also be over painted with any 2pack or 1 pack (cellulouse) paints. I've not used it yet but I have bought it ready http://www.rust.co.uk/popup.cfm?p_i=501025&p_n=501025
So far (including the 3/4 full tin -2ltr, I'm still using) I have used 6 litres. That has included painting inside all the sills and other panels before welding in place (ground off local areas to weld to), inside the petrol tank bay and some external bits just to give some protection until Im ready for painting because I am doing the resto out side I needed to protect it all with something non porus like most primers. every thing so far has ....or will get, 2-3 coats of it and Im going to do the petrol tank too I've still got the cab area to do as well so I think I will probably need another 2ltrs. I recon if your just doing the underside and not inside any panels your welding in place then 5 - 6ltrs should do it. They do 5ltrs for £85 but I think it is just as important as final top coat paint .......probably more important to protect the underside as best as you can as that will be the area which is most valnerable, so its not some thing I want to scrimp on and have to end up doing all that welding again in 5yrs time. I have been buying it in 2ltrs at a time as Im not sure if an opened container has a shelf life. When painting my bottom (ooo err Mrs) I mix up no more than I can paint in an hour as it starts to go off after an hr or so. This is usually about one plastic water cooler cup's worth....which is what I mix it up in. I save my used plastic cup's from work (honest : ) to use as paint containers as you can throw them away after and it's not cost you any thing - I use 2 cups inside each other for strength as I have had one cup split before. I use some little measuring scoops which I bought for under £1 to measure out the paint - 1 scoop of paint to one scoop of hardner (1 to 1) you could also try using coffee scoops ....same sort of thing. I use a searate one for paint and hardner, this way Im not scooping up paint with a scoop covered in hardner other wise the paint you leave in the tin could start to set.
I'll be taking the easy route and send my bus to these guys http://www.before-n-after.co.uk/ Taking it to them, at least I know it would have been done right. I think they charge 500 quid and you get a 5 year guarantee of no rust. That's a lot of dollar, but reckon it's more than worth it.
Diddy as usual your threads are excellent. Is the epoxy any good as a rust inhibitor, I can see that it prevents new rust, but does it inhibit any exisiting surface rust that may be left even after ones best efforts at removing it? I would send you some Karma if I knew how.
Thanks diddyman, excellent info. I am about to start my resto in earnest and I have been following your excellent resto thread closely. Hope you had a great day in London. Now get back to the bus. Karma coming when I can. Peebee
thanks Peebee .... London was pretty good good luck with your resto ....looking forward following your resto thread ;D
I've been wondering what to do to my underside, Great thread, i also need to bump up my posts to give Karma ! ;D
