Silly question about temporarily stopping local rust

[paydase]

Sorry to ask that question, I haven't found a clear and simple answer in this forum.

I would like to know what is the best approach to temporarily fix a locally rusted area without having to dismantle a panel or a component if that is not possible for some time.

I am thinking in particular of pieces not easily accessible for removal in the engine bay and of external body areas where paint was locally damaged because of dents.

I know that the good approach to fix rust is to totally remove the rotted material by grinding down to sound bare metal and/or to put some kind of deruster or phosphate primer, then paint.

Any advice on how to do it correctly and of suitable deruster/primer/paint (I am not knowledgeable)?

[malcolm]

In the engine bay, if things aren't seriously rusty, you can use POR 15 paint - it stands for "Paint On Rust" and the surface needs to be slightly rusted to work. If it's not, then you treat the surface to give a fine rust coating before painting. This paint is impervious to oil and petrol, so good in the engine bay, but does not stand up to continuous UV, so no good on exterior. Hammerite by comparison is good with UV, so great on fence railings etc, but no god with oil and petrol; it just peels off.
I know it's not a proper solution, but I've used POR 15 on a couple of lightly affected areas under the bonnet, and it sets like concrete and gives a realy hard finish that doesn't seem to deteriorate.
It has very limited colours; black, grey or silver largely! Here's a link on Amazon:

[mgcjag]

Hi Serg.......have had very good results with Kurust.....its a thin milky ligued that converts the rust (Light surface)to a stable black base for primer, undercoat and topcoat...very easy to use.....as with all these rust products they are a holding measure only......have used por15 but be aware that once the tin has been opened its reaction with moisture in the air is what starts its hardening so is not reusable once the lid is put back on, also u need special primers to top coat...also quite a lot of surface prep with other products needed before u apply por15....stear clear of hammerite used it recently but its started to peel off... others i know have had the same happen...think they changed the formula recently...Steve

[paydase]

Thank you Malcolm and Steve.

I had looked at Por15 and similar products.
I noted its sensitivity to UV, its hardening when opened and also that it's not healthy (need preferably to wear a protective mask).

I also understood (but I may be wrong) that actually it "encapulates" rust underneath rather than transforms it. So that sufficient preparation to remove most of the rusted material is needed beforehand not to risk that the trapped oxygen/water continues weakening the metal. That being maybe the reason why some challenge Por15.

I also understood that the remaining rusted layer (metallic oxides) is transformed by rust converters, but also in some way by Por15.
In the case of Por15 it seems that the transformed layer helps binding Por15 to the base metal underneath while for some other rust converters (including phospating treatments) it may lead to a loose layer that has to be removed before putting a primer.
Am I right or did I completely miss the point?

Now, Por15 becoming very hard and solidly bound when time is passing, will it be easy to remove it later on if/when a stable/comprehensive repair for putting a new paint is undertaken? Probably necessary to grind down to bare metal?

[mgcjag]

Well there u go.......or do a proper job rub down to bare shiny metal to get rid of the rust, epoxy prime then topcoat......Steve

[christopher storey]

I use phosphoric acid at about 10% dilution ( the "raw" product is often 81% which is too thick ) , available from agricultural merchants, putting several coats on the rusted areas, and then after it has cured - about 24 hours - thoroughly wire brushing until most of the rust has gone, and then retreating with several more coats. Allow that to dry, wipe the surface over with a damp rag, and allow that to dry. The surface is then fit for any paint you wish to use. POR 15 is ok, but is devilish stuff to remove and not a good basis for any subsequent paint, so I tend to stick to cellulose or acrylic primer and topcoat

[paydase]

Here we go:

That is the typical kind of uneasy component to treat.
It's my seat runners. One of them is rusted because it was bolted directly on the floor without washers and because some humidity ingress:



I know they are difficult to dismantle because of dimples, which would be necessary because some rust is trapped between the two parts of the runner and also because there are rollers with rubber o-rings inside that may be damaged if washed by phosphoric acid.

So, in that case, probably needed to flatten the dimples, dismantle, brush the rust and go the phosphoric route...

[Geoff Green]

I use "Feed Molasses" (not human consumption molasses) mixed with 4 parts water to remove rust. Fill a container, with lid, to cover the parts and let soak for a week. Remove and wash off the film, dry and wire brush any areas that were rusty. Repeat as needed. The solution lasts for about 6 weeks with constant use and the lid keeps it from evaporating and the smell does not escape.

When the rust is gone I use a small hand wire brush (tooth brush size) and soapy water to clean then rinse with fresh water and try quickly as it will begin to rust immediately. Primer as soon as possible.

The hidden rust will be converted / removed although being able to access the rusty area for brushing speeds things up.

[malcolm]

With POR 15, you are supposed to brush off all flaky rust first. My understanding is that then, when painted, there is no further rusting that takes place under the paint. You don't need to use special primers or treatments first, unless you are painting on shiny new metal.
It is true that you cannot put normal topcoat on top of POR without further treatment. The POR is supposed to be the final coat.

[SteveG]

With POR 15, you are supposed to brush off all flaky rust first. My understanding is that then, when painted, there is no further rusting that takes place under the paint. You don't need to use special primers or treatments first, unless you are painting on shiny new metal.
It is true that you cannot put normal topcoat on top of POR without further treatment. The POR is supposed to be the final coat.

You can paint over POR15 with a similar product made by the same company, Chassis Black. If applied properly or even sprayed onto the surface it dries to a satin black finish not dissimilar to powder coating. It protects from UV and is supposed to be a long term treatment.

[mgcjag]

According to the POR data sheet there own tie coat primer is needed to paint over por15 then any top coat.....Steve