Undersealing

Paul gurgled happily, sounding much like they were saying:

Clean it all up first - rotary knotted wire brush in a drill, back to shiny metal. Then paint it with some DECENT primer (I like Rustoleum

769), and if you've got access to a compressor, the stone-chip stuff that comes in the 1l schutz cans (can probably get in aerosols otherwise), and finally some underbody wax, as well as cavity wax in any and every box section - most structural rust comes from within.

The old '70s style rubbery-tarry underseal is horrible stuff. It dries and cracks and lifts, holding moisture. It's even worse than Hammershite.

A mate mentioned getting a Shultz gun and there are one on Ebay from £8.99 to £39.99 for what looks like exactly the same item - are they just better made ones or just chancers going for better price?

I have a genuine shutz gun think made by 3M. Also bought a brand x gun and it works much better.

What you have to look for is the cap size of the container to which the gun fits - they do vary.

I think it should work in conjunction with the material liquidity/density (what ever the word)

But get the gun to suit the sealer can lid its more comfortable to work with than hand holding the can under the gun. Cans have changed over the time.

Personally there is now better stuff than 3M Shultz around - water based easier to clean up better to paint over plasticised etc.

I use a water based stone chip stuff and then paint over that with black chassis lac.

Paul gurgled happily, sounding much like they were saying:

Mine came from MachineMart - but can I find it on their site now? I'd have thought it would have been nearer the tenner end of the price range than £40, though.

Since they're theoretically a standard fitting (kinda the whole point), the difference is probably one of how much shit they'll put up with before sulking.

cheapo ones work indefinitely, there is really nothing to go wrong with them as they are so simple inside.

"Mrcheerful" gurgled happily, sounding much like they were saying:

I was thinking in terms of withstanding being stood on/dropped/driven over etc - the usual workshop abuse...

Years back, I didn't bother to look closely at a friend's schutz gun before connecting it to an airline and spraying. The nozzle had got squished very flat which, combined with the hardened paint in there, had created an effective air-tight seal. The can turned (briefly) into a football before the seam let go.

I've still not decided if it was a good thing or bad that the seam was pointing at me rather than the car. Once my trousers had dried, we broke and folded them into a bin.

which meant the breather hole must have been blocked too!! probably it is best to have the very cheapest if you know you are the sort to abuse things, after all at 10 pounds it is throwaway territory in any case.

I have a classic car which I spray the underneath of every two to three years with old engine oil. Costs nothing and works a charm. OK, the underside is oily, but does that matter if it keeps the rust off? Furthermore, if there is already rust there, it stops it getting worse.

Rob Graham

I have no experience, but I did some reading of similar threads a while back and came to the conclusion that the best kind of underseal is Dinitrol (and not Waxoyl).

They do various grades. What Dinitrol recommend is using Dinitrol 3125, which is a light penetrative fluid to make a waxy film, and then Dinitrol

4941 which is a heavier non-penetrative waxy coating on top.

Anyone have any opinions on the subject?

From what I read, spraying any of this stuff on the underneath is a pain. Possibly paintbrush is easier for the underside if you don't spray into the cavities (and if you do spray the cavities, you might have to drill holes to get into them).

Theo

Applying anything to the bottom of a horizontal surface is a pain.

Not if you extend the suction tube on the gun (with plastic tube) and hold the can.

Theo Markettos gurgled happily, sounding much like they were saying:

From the people who brought you Hammershite. 'nuff said...?

Rob gurgled happily, sounding much like they were saying:

Compressor and schutz gun - the pumpy-uppy sprayers are just utterly useless. It's going to get messy, whatever you do - you can buy huge rolls of thick plastic sheet from a builder's merchant dirt cheap. Roll out a couple of layers of that to park on.

It still drips & goes everywhere, I reckon the sprayer's far easier than the paintbrush though.

Waxoyl works quite well inside box sections and doors also as a light pre treatment underneath if you spray a heavy underseal over the top.