welding project Juular's Scandi Noir. Volvo C70, 240 &122. Earth day.

[junkyarddog]

Apparently the Bosch set up is more economical that the Lucas CAV setup.

I've no idea if this is true,but I've been told it a few times by different people.

[juular]

Half heartedly took the broken 240 strut off last night.

Two things.

1) Fucked, M7

2) That Bilt Hamber stuff is utterly useless.

The old shock failed in a strange way, in that it would only compress halfway.  This is as short as I could get it. As you can imagine the ride was a bit rubbish.

 

[Lacquer Peel]

16 hours ago, junkyarddog said:

Apparently the Bosch set up is more economical that the Lucas CAV setup.

I've no idea if this is true,but I've been told it a few times by different people.

I've heard the opposite. 

[juular]

Nug keeps flinging stupid, but fixable problems my way.

Glow plugs stopped glowing. As you can imagine, running 100% veg in Autumn without glow plugs can be entertaining.

Tracing it back, it was clear the relay was buggered. I kind of suspected it might be that when it started smoking.

Part of the relay contact on the right was making intermittent contact, causing an arc and then overheating. With that cleaned up then bent back into place, that sorted the glow plugs.

Next, I noticed that it was occasionally not wanting to turn over. If you pressed on and kept turning the key, smoke could be seen coming from the negative cable on the battery.  

It was pretty fucked. I replaced that and doubled it up for good measure.

What next, an injector leak?

That was a dick to sort, as the copper washer was not for coming out of the injector seat. I eventually got it out and replaced it. No more leaks.

I thought I was winning at this point, and was even deliberately going out aimless drives in the evening just because it's such a fun little thing.

Then it started doing this.

 

Not really sure what's going on there. I think I am either getting air in or I need a bit more advance on the pump. 

I attached the cold start cable to the pump (forgot to do so when I swapped it) which made a little bit of difference. I tightened all the hose clamps up and checked for leaks - none.  However it does seem a little bit happier now so I'll see how it goes. Still could do with being a bit less surge-y when cold.

Finally, I was greeted to a puddle of oil on the drive under the right wheel.  Looking closer, it has gone all over the inside of the wheel arch and is running down the strut, so it's clear the shock has had it.

Then the top mount fell to pieces. Like poetry.

In the process I have also mangled the lower ball joint cover.

I thought it would be easy enough to replace the boot, but all I have succeeded in doing is stabbing myself in the hand with a screwdriver. Getting those clip rings in place is a nightmare.

And honestly, I don't know why I didn't just buy a new control arm in the first place. 

Might sort the rest of that out next week.

There's a point in there somwhere, that the fuel cost maybe isn't the biggest factor in the cost of ownership, even when control arms are 3 quid?

[reb]

Fuck me for £2.80 is it even worth trying to superglue the pinhole tear in the boot on the freshly fitted unused arm on mine 😂

[juular]

Not much to report on the 240 front. It's simultaneously a really nice semi-classic, and a lovely, comfortable, reliable An-Car. I've been getting decent economy out of it too, well, decent for an old RWD block of pig iron. Around 35mpg on my daily commute using E10. At the moment that makes it cheaper than running any of our diesels except the 205, which is on the veg.

The 240 does need a front wheel bearing done. This isn't a big deal as bearings are cheap and fitting takes about half an hour.  However I'm currently playing parts bingo with that, as here's how far I got.

I was ready to tap the bearing on when I found that it was just marginally the wrong size.

The next attempt, ordering a good quality OEM new old stock part resulted in this, which is so rusty it's useless.

So I'm just waiting on a replacement for that to turn up before I can get on with it.

All of the bits arrived for the 205 to rebuild the driver's side suspension.

Started by cleaning up the spring seat and top mount as they were mega rusty.

Then a good brush over with phosphoric acid and some paint.

While painting I noticed that one of the top mount studs had sheared off. It's been like this for a long time by the looks of it.

Drilled out the remnants, then welded a bolt in place.

 

The £3 control arm looked alright, and it was cheaper than trying to find a replacement ball joint boot that actually fits.

This corner is looking lovely and shiny now.

A few other things were tackled. The rear boot trim rattles like fuck, as most of the clips are extremely tired.

This was sorted with some new clips that have spacers on them to give a bit more pressure and prevent rattles. These were kindly donated by @davidfowler2000 who did the same on his 205.

Next up I wanted to check over the fuel lines and filter housing as I was still getting bad surging and cutting out on a cold start when running on the veg. My thoughts were that air was getting into the lines due to the extra strain put on the system trying to lift cold and thick oil.

Pulled off the lines and emptied the filter housing.

This got a good clean out, then the base of the housing was scrubbed up with a pad.

I also padded out the big O-ring groove and then cocooned it in RTV before refitting.

I also replaced the O-rings inside the water drain tap and the heater thermostat as they're known leak points. Everything was reassembled with new hose clamps.

I've had quite a few mornings to test this out, and it does seem to be a lot better. It still surges, but it's easier to keep alive and the symptoms tail off much quicker.

Next plan is to try and modify the fuel system to be more veg-friendly, following advice from @Lacquer Peel.  The mod list currently looks like this:

- Replace 8mm fuel lines with larger bore 10mm lines.

- Loop the fuel return back into the inlet to allow heated fuel to recirculate

- Delete the filter heater thermostat so that the filter housing is always heated

- Fit an electric lift pump that runs on a cold start to help move the fuel.

[Shirley Knott]

I'm still disappointed by the poor performance of Dynax UB, I honestly used to consider it the holy grail of rust prevention, that being said everything I put it on ended up being sold in less than a year so I couldn't attest to a long term positive experience either TBH.

These days I'm using Comma 'wax seal', it's much cheaper, but needs re-application as it's softer stuff, time will tell... 

[juular]

It's been almost a year since the 240 passed its MOT after being welded back together.  At one point I mooted the idea of doing a post-mortem of sorts on the whole project, to have a look one year on and see what worked and what didn't. Since I'm now at the point of going over the car again for its upcoming MOT, this is as good a time as any to do this.

I think the main thing you'll probably want to read about is how well it has held up to rusting further, and if any of the expensive chemicals with big promises actually did anything useful to help.

It's important to mention that I haven't babied the 240 in any way whatsoever. It's been driven in snow, ice, deep water, on beaches, along forest roads, and I've never bothered my arse to wash any of the mud or salt off after use. I absolutely love the 240 as a car, but I've followed Volvo's marketing advice and Drove it Like I Hated It.

It gets stored outside permanently. I've put around 6000 miles on the car since December last year so I don't reserve it as a weekend classic either.

I'll break this down into sections, and I may slot in some more photos after I'm finished with the text and have a chance to upload them.

Rust-proof primers / zinc primers

Screwfix Galvanising Spray Paint

First up is this stuff from Screwfix.  If the description is to be believed this is a zinc-rich cold galvanising spray which is also spot-weldable.  This sounds ideal for coating panels before you get back to top coating them properly. The idea is that the zinc is a sacrificial layer which corrodes in a harmless manner before the steel itself can be attacked.

I used this on the external surfaces of the passenger side A-pillar and sill repairs while I got on with repairing the rest of the car. I also gave most brackets, bolts and nuts a quick blast with this after bathing them in acid to remove the rust.  I also gave the steering rack a quick coat of this to freshen it up a little.

Unfortunately, it's a bit shit.

The first sign that it isn't really up to the job is the weight of the tin. If the paint really is zinc-rich, it would be much heavier than it is, plus it would dry a fairly cloudy, matte grey.  In reality this appears to be nothing more than shiny silver spray paint.

Most of the bits I painted in this began to rust again within a week or so. That's just putting up with atmospheric moisture, never mind abrasion, water and salt spray. In fact, the unprotected inner surfaces of the steel I welded on didn't look any worse than the bits I painted with this.

Verdict : 1/10.

Bilt Hamber Electrox Primer - Aerosol

This is the so-called professional version of the above zinc spray and as such costs over twice as much. However, you can tell right away it's a better product as the tin feels significantly heavier.

I did some sections of the floor and chassis outriggers using this.  This dries a much more believable matte grey colour (ie: it looks like zinc).  The outriggers were left painted in this while stored inside the damp, leaky car for months without any signs of rusting. It does appear to do what you expect it to.  

The outriggers were then welded on and overcoated with some underseal. After a year, they look just the same as when I repaired them.

I've also painted the leisure battery enclosure on my campervan in this, which is quite exposed underneath and comes into contact with all sorts of spray, grit, salt and mud.  That has been on the van a couple of years now and shows very little signs of corrosion except where the coating has been damaged. I have to say I'm quite impressed.

The major downside to this is the cost. £40 per Litre for the brush on version is eye watering, and I find that coverage is a bit disappointing so you tend to use quite a lot more than you expect. 

I also find that this flakes / chips very easily so you'd probably want to topcoat it, although it seems to stand up to the claims that it can 'self heal' going by the campervan battery housing.

Verdict : 6/10

 Zinga cold galvanizing system - brush on.

Being impressed with the Electrox but not the price and coverage of it, I thought this would solve both problems.  Zinga are careful not to call this a paint or a primer, and are keen to reinforce the image that electricity pylons across Europe are painted in it.

This was (back in 2020) much cheaper than Electrox - around £45 for a 2.5L tin, although this is sold by weight rather than volume.  This is a good sign as it means you are buying actual zinc by weight rather than fresh air and binders. The tin itself is spectacularly heavy for its size, another good sign.

I used this to paint the insides of the rear wheel arches, the insides of the sills, and the internally facing sides of repair panels. I also used it as a primer for the outer rear arches and the front windscreen surround (after giving up on another product).

I've also used this as a primer coat for the inner arch and boot floor repairs I did on the 205, coated with some underseal.

This stuff works really well. It brushes on nicely and dries quickly. It's easy to topcoat despite Zinga being coy about calling it a primer of any sorts.  I also find it gets into crevices and holes much easier than the Electrox spray, purely because you can coax it into place using a brush.

There's less wastage as you don't have overspray to deal with, so the tin lasts a surprisingly long time when brushed on carefully.

After a year of this being on the car, I'm very impressed with it.  I haven't spotted a single sign of rust breaking back out anywhere where it has been used. I have some offcuts of panels that have been lying around my garden exposed to the elements that were coated in zinga before being chopped.  None of those have started to rust either.

It 'self-heals' very well, and in fact if you take a wire brush to it, you can see how it has bonded with the steel underneath and changed its colour.

The repairs on the 205 have also stood up to a similar level of driving it hard without giving a shit. Recommended.

It gets negative points for being an absolute pain in the arse to clean off of brushes as it's not dissolvable in white spirit - you need to get 'Zingasolv' to thin or clean it and it isn't cheap.

I also find it's a bit fragile. In some places you can scrape it off with a fingernail and minimal effort, which doesn't inspire confidence. It does seem to hold up though which is the main thing.

Verdict : 8/10

Rust-Anode Cathodic Protection

I found this while looking for another tin of Zinga, which seems to have rocketed in price over the years. This is around 25% cheaper than Zinga for the same size, yet the technical data seems very similar.

I've used this only on the Amazon so far but I'm mentioning it here because it's relevant.  I've not had a full year to test it out, however the Amazon is sitting outside being battered by wind and rain and sleet, with shit door seals and big holes in the engine bay. 

I've painted the Amazon floor in this and despite it regularly filling with water which lies for days, there is not a single speck of rust to be found, even where the floor was previously a bit rusty!

I'm convinced this does the same job as Zinga but is a fair bit cheaper. I also find that this covers better and is less prone to flaking and scratching (it feels more paint-like). You can also thin and clean with white spirit which makes life less complicated.

Verdict : 9/10

Plastikote Zinc-Rich primer

I bought this as a stop-gap when I ran out of Zinga and just needed to finish off a couple of bits of welding. The tin isn't very heavy for its size, which suggests to me it's not as Zinc-Rich as it claims to be. 

I didn't do huge amounts with this, but it does seem to have worked fairly well. The shock absorber top mounts are a notorious rust trap on the 240s and I used it here before covering in underseal.

So far there's been no rust breaking back out there.

I have used it in a couple of other locations where the results weren't quite so good. Admittedly the metal had previously been rusty, and as such had been cleaned and treated before this was sprayed over.  Zinga and Rust-Anode managed to keep the rust from breaking back out, but this stuff struggled a bit, showing blebs of ginger in places.

It would be fine for clean new steel, but not for anywhere you had to de-rust.

Verdict : 6/10

Rust converters

Bilt Hamber Hydrate 80

I had really high hopes for this as it seems to be highly regarded in restoration circles. The idea with this is that you wire-brush off the worst of the rust, then paint this over it in two coats, one perpendicular to the other. In theory it should form a stable barrier that smothers the rust and prevents oxygen from continuing the corrosive reaction.

It comes out of the bottle a sort of milky white colour, and then as it reacts with rust and steel goes a very dark blue.  It's quite mesmerising to watch and sort of gives you the impression it's doing 'something'.

I used this on nearly all of my original suspension parts which were heavily surface-rusted.  I first went over everything with a jetwash, then several rounds of degreaser followed by wire brushing, then more jetwashing, finally finished off with a wipe down with panel wipe.  This is to get rid of any contaminants as most of the suspension parts were covered in grease and oil.

Some parts of the suspension I ran a finger sander with a 40 grit belt along to get rid of heavier corrosion and provide a nice keyed surface. On top I applied 2 coats of H80 at perpendicular angles. This was done at around 18C as I've heard anecdotally that cold weather can prevent the converter working properly.

Once this was completely dry it was then topcoated with Bilt Hamber Epoxy Mastic, which is also touted as an amazing product and the ideal thing to topcoat H80 in so that it never rusts again. Allegedly.

Frankly, this is all complete horse shit. H80 really does fuck all except ruin your day.

It doesn't seem to be remotely waterproof despite it claiming to be ok to leave it uncoated.  On the bulkhead of the 240 the areas I coated in H80 while I worked elsewhere rinsed off in the space of a few days, leaving huge levels of surface rust to break back out.  It also isn't a very tough  barrier and the slightest knock or bump seems to cause it to fall off in great big lumps, exposing plain old untreated rust underneath.

Below you can see where I have painted perfectly clean brand new steel in H80. The reason for this is that where clean steel meets rusty steel, you're supposed to paint the whole lot in H80 to keep a uniform coating.

It seems to have done nothing much except added rust where there wasn't any. The image above is pretty much typical for anywhere I've used H80. You get a week or two of 'hey that looks alright', then it all goes to shit and leaves you worse off.

The passenger floor is another good example. Here it was used to prime the floor which was half pitted steel, half brand new metal, then topcoated with Bilt Hamber 2 pack epoxy.

It hasn't done much either on the clean or already rusty steel. It has flaked off in places, taking the top layer with it. In other places it has bubbled up and it looks like a light wire brushing would take most of it off.

I've been through a whole 1L bottle of this and had to remove and redo pretty much all of it.  No amount of experimenting with this gave me a decent result. I even contacted BH who gave me a list of things to try to improve it, none of which really helped. 

Verdict : 0/10

Vactan

This is essentially the same idea as H80 - an acid based rust converter mixed with an agent that sets over the top for a waterproof / airtight barrier. A lot of people here swear by it, so I thought it was worth a shot.

Admittedly I've not used huge amounts of this as the H80 experience really put me off these all-in-one rust converter products. However I did touch up a few areas here and there where I noticed rust breaking out due to damage, or me simply missing out a few bits.

So far the touch-ups I've done here and there have been so-so.  On the LS400 I treated the radiator crossmember before refitting the undertray. 8 months later, it's still holding up, although I can see a few areas where rust has already started to poke back through.

I treated a couple of areas in the engine bay and boot floor of the 240 with this. In the engine bay it has held up nicely (perhaps the heat helps?), but on the boot floor it has simply cracked and began to flake away exposing rusty steel.

I've found that this is very dependent on what temperature you apply it at. If you apply sub 15C it has a tendency to form a powdery white substance which just brushes off.  Above that, it does seem to activate in the way that H80 does - it progressively gets darker as it dries.

I find that it won't stick to non-rusty steel at all, no matter how well cleaned and keyed it is. 

Use it to tidy up some underbody areas before undersealing? Yes - and it'll probably work quite well.

Use it on bodywork I wanted to paint and look good in the future? Probably not. 

Blob it on to prevent a rusty scab becoming a great big hole in 6 months time? Definitely. But expect to have to redo it.

Verdict : 6/10

Concentrated Phosphoric Acid

I came across this by accident as @Lacquer Peel dropped off a bottle of it. It's branded as Bonnyman's Rust-Off, but it's pretty much just concentrated Phosphoric Acid.

The idea behind this versus the other rust converters is that you let it do its job, working it into the steel with a wire brush, and then you're expected to topcoat it.  The difference is that the acid isn't diluted by the other ingredients, and you can be a bit more confident that it's actually doing its job before you put paint over it. Being able to work and agitate it into the rust seems to be the key here.

This works really well. As you work it into rust you can clearly see the surface going darker and harder. When it dries, which only takes a few minutes, the rust is very well contained in a hard layer (iron phosphate?) which in theory stops oxygen getting in. If you take something sharp and scrape away at this layer, you can see that it has soaked much deeper into the rust than either of the rust converters above.

I tested this on a few places on the 240 but didn't really document it with photos, sorry. I wasn't particularly confident it would do anything but I seem to have been wrong.  Even on rust which has broken out on an external surface, I've dabbed some of this on and forgotten about it. Months later despite water being able to run down the panel, the rust stayed a dark blue/brown colour and didn't spread.

I've used this mostly on the Amazon where the results have been surprising. Here I've used it on a heavily rusted part of the scuttle. This is after being open to the elements for a few weeks without any topcoat, which alone is a decent test given how long the H80 lasted.

And after about 7 months of being exposed to the elements. Ignore the extra holes, I made them deliberately.

Yes, some orange has returned, but this is a really unfair and unrealistic test. It has done a surprising job given that it has had water pooling on top of it for months on end and hasn't been topcoated. Plus, I've been dragging the bonnet on and off weekly, scratching both the scuttle and the tops of the inner wings essentially taking chunks of the protective layer off.

A fairer test is probably on the Toledo, where it was painted on the very rusted chassis leg and left for around 3 months.

I've got a lot more faith in that than in the H80 or Vactan. I think it's as close as you'll get to killing off rust without cutting it out.

Verdict : 9/10

Next up, I'll list the topcoats and underseals I used, but I need to get some before and after photos arranged, as the contrast is really interesting!

[Sunny Jim]

Thanks for taking the time to document all that. I'll invest in some Rust Off and await your update on top coats.

[JMotor]

11 minutes ago, Sunny Jim said:

Thanks for taking the time to document all that. I'll invest in some Rust Off and await your update on top coats.

Wot he sed.

I'm also experimenting with a red oxide primer called Bonda. Brush on stuff and seems to be quite good so far. A bugger to remove which could be a good thing? I've used it when doing the repairs on my  Corsa project. 

Not fully sure on how it'll last at the moment.

[Jim Bell]

Great reviews. 

Clear, concise, helpful and submitted with photographs. 

9/10. 

[mat_the_cat]

Interesting stuff, and bears out what I've found on the products I've also used. With the Zinga, you can leave the brush to go hard, and after immersion in the tin for a while it will go soft again as the solvents go to work. I've also found that it hardens after 'weathering', but generally use it as a base coat before further protection.

[captain_70s]

Great write up, mega handy! 👌

[rainagain]

Really interesting write up, it's good(?) to see that others are having problems stopping the ginger returning and it's not just me. I used Vactan on the tow bar of my 307 and never got round to top coating it and it held up fine, however I used it to treat the rust on the arches of my saab early this year and rust is already starting to come back through. 

[captain_70s]

Vactan seems very situation/environment dependant.

I sanded/brush painted the Dolly's front valance and spots on the sills with it one summer as it was rusty all over. Stuck on and lasted well with no top coat, the ginger didn't bleed back through for over a year despite being left with no top coat outside on an exposed bit of the car. You can see the dark patches in this picture:

Eventually it came back through, but I reckon with a top coat it'd have been pretty robust. Really has to go on pitted metal to adhere decently.

I did some bits of the Acclaim one winter and it was rusty again within a week or so, presumably due to lower temps.

I think @GingerNuttz is a big fan of aciding everything as the best rust removal method.

[GingerNuttz]

Acid is only a temp solution tbh and anything rotten or rusty can only be fixed by cutting it out.

Can hold it back foir a while with acid and a decent primer then top coat tho.

[GingerNuttz]

https://www.jennychem.com/products/biosan-super-concentrated?variant=15420606545969&currency=GBP&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic

One I use gallons of.

[grogee]

6 hours ago, juular said:

 

A thousand thanks for these observations. Virtually all the information you might find online or in print about these products is not based on any science - it's either magazine promos where they basically got a freebie, and don't give it any decent time in the elements. Alternatively it'll be Man On A Forum who will swear blind it's got to be chip fat/vinegar/monkey spunk otherwise don't bother m9.

I wonder if that fella on YouTube who tests oil additives/glue/thread repair etc has done anything about rust treatment and/or protection? He sets up some fairly scientific (but still appealingly shed-based) tests and doesn't seem to have any axe to grind. Search Project Farm on YT.

[grogee]

Here he is doing underside protection test:

 

https://youtu.be/lyWHF4NoNVk

[grogee]

Rust remover:

https://youtu.be/6-MC_ZEXQbw

[tom13]

1 hour ago, GingerNuttz said:

https://www.jennychem.com/products/biosan-super-concentrated?variant=15420606545969&currency=GBP&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic

One I use gallons of.

Do you cover the rust in this neat then leave and primer over?

[grogee]

Where do you get Bonnyman's from, @Lacquer Peel?

[GingerNuttz]

4 minutes ago, tom13 said:

Do you cover the rust in this neat then leave and primer over?

I mainly use it for tiny pits in steel like on the manta roof etc.

I just douse it in it then I sand what I can back to bare steel leaving it in the bits I can't sand, shoot some primer then whatever top coat. 

Acid etch primer is just phosphoric acid in a primer so the acid may well be able to be painted over without sanding it back but I can't take that chance 😂

[Lacquer Peel]

15 minutes ago, grogee said:

Where do you get Bonnyman's from, @Lacquer Peel?

It was in the implement shed at my granny's, my aunty gave it to me. It is probably quite old. 

[artdjones]

With the Vactan/Hydrate 80 two coats are needed, with the second at 90 degrees to the first. I've had  some bare metal with two coats of Hydrate 80 on in a steel shed for 2 years with no breakthrough so far. The large areas I covered with Hydrate followed by  Löwe zinc primer are still perfect.

But a small can of Löwe is very heavy.

So for me 

Hydrate 80  8/10

Löwe 9/10

[juular]

On 12/6/2022 at 4:19 PM, tom13 said:

Do you cover the rust in this neat then leave and primer over?

I normally brush it on neat, get a stiff steel brush and work it into the metal, then leave for 15 minutes. I then wipe it off with a clean towel, then prime with zinc.

If left for longer it can form a sticky layer. So far I haven't found this really affects how the next coat sticks, but with any zinc primer it's better than it's actually in contact with the steel for it to do its job properly.

[juular]

On 12/6/2022 at 4:27 PM, GingerNuttz said:

Acid etch primer is just phosphoric acid in a primer so the acid may well be able to be painted over without sanding it back but I can't take that chance 😂

An easy way to get rid of the excess after it has dried in, is to paint some more acid onto it. This recombines the dry layer into liquid, which you can then wipe off, leaving the treated pits intact without having to sand it.

[juular]

On 12/6/2022 at 2:57 PM, captain_70s said:

Vactan seems very situation/environment dependant.

I sanded/brush painted the Dolly's front valance and spots on the sills with it one summer as it was rusty all over. Stuck on and lasted well with no top coat, the ginger didn't bleed back through for over a year despite being left with no top coat outside on an exposed bit of the car. You can see the dark patches in this picture:

Eventually it came back through, but I reckon with a top coat it'd have been pretty robust. Really has to go on pitted metal to adhere decently.

I did some bits of the Acclaim one winter and it was rusty again within a week or so, presumably due to lower temps.

I think @GingerNuttz is a big fan of aciding everything as the best rust removal method.

Pretty much my experience too. It's really odd how in some places it just falls off, yet in others it sticks tenaciously for a long time.  Strangely I find it works better the less you prepare the surface. Sanded, degreased, wire wheeled, panel wiped - it'll just turn to powder. Lather it on top of a rusty scab you haven't bothered to deal with at all and it seems quite happy.

[juular]

On 12/6/2022 at 5:20 PM, artdjones said:

With the Vactan/Hydrate 80 two coats are needed, with the second at 90 degrees to the first.

That's how I used it in every case, confirmed with Peter Hamber himself that the prep and painting I'd done was exactly as it should have been.

[GingerNuttz]

9 minutes ago, juular said:

An easy way to get rid of the excess after it has dried in, is to paint some more acid onto it. This recombines the dry layer into liquid, which you can then wipe off, leaving the treated pits intact without having to sand it.

I need to fill over shit usually so I need to sand it anyways to get the mechanical bond with filler, used a wire brush a couple of times too and that worked well before sanding it.