Stone chip top coat - cracking need to fix

[Rocketman]

Hello all.

First post on here but have spent quite a lot of time in the past reading up on the forum and learnt a lot.


Anyway my problem.

Spent ages renovating a inner wheel arch. Welding, removing rust ect. So used upol seam sealer where required all good there. Unfortunately I have used hammerite stone chip which has reacted in some areas badly with the top coats and left large cracks.

Really annoying because I took several days over spraying this to try and avoid it. Misted the first coat of colour let to dry. Finished off the colour and let to dry. Looked fantastic still - no reaction. Then started on top clear coat and initially for the first few hours it looked great and really felt the time I had spent on it not rushing it was well worth it.

But then I started getting the cracking and the stone chip had basically gone to mush in areas under the paint.

Now what to do???

Some areas look great and have set fully and all it fine.

Other areas are now hardening off (days after the top coat) but have terrible cracking.

First thing I'm not going to use the hammerite stone chip again.

I think using the upol gravi-gard sounds like a much better option for over-coating with paint???

Moving on to how to do this again - would it be possible to wait for the top coats on now to fully dry then roughen and go over with the upol gravi-gard. Let that fully dry and then top coat again???

Would that work or do I need to strip this some how?

Thanks for any help

 

[steveo3002]

id roar it all off ...letting it all set up might work or might not , stonechip is full of solvent so chances are it will attack it

 

[richie00boy]

Sounds like one of the coatings (probably the stonechip) had not given off its solvents fully and reacted when other solvents on top built up. You may be able to leave it, resand and reapply, but it will take days maybe weeks for the solvents to come out before you can start. I would rub it all off and start again.

Aerosols have very high solvent content and need plenty of flash off time and only putting on thin coats each time. In this colder weather it's especially important and I would say 15-30 minutes between coats. A small fan heater will help.

If you are expecting and trying to achieve a rippled factory finish then that is probably where it's going wrong as this stuff won't build like that and if you try to make it like that it will be full of trapped solvents. The u-pol will be just the same. You need a compressor to get that finish.

 

[Rocketman]

Thanks for the replies. I've spent a bit of time now this afternoon reading around and rang a couple of paint suppliers up. The general consensus is the hammerite stone chip is fine by itself for protection but when it comes to over coating what has happened to me is a common problem. No matter how long you leave the stuff it often softens and top coat cracks.

For example even old hammerite stone chip touched with white spirit instantly goes to mush, where as other stones chips/seam sealers have reasonable solvent resistance.

I have been recommended this afternoon hycote or upol stone chip as much better alternatives for over coating.

But yes it does come down to what to do now.

Oh yeah the hammerite before over coating had fully hardened off, over a week before over coating. It wasn't that thick and was in a dry garage.

Jes if the wife finds out I'm ripping all that off she will go up the wall. She is not to happy with the time I'm spending on the car!!
But it looks like that may well have to happen.

 

[langy]

Use Gravitex, you won't get any problems with that

 

[Rocketman]

Yeah heard that Langy (well found that out today - bit late). I will need a compressor for Gravitex .

From what I can tell though Upol Gravigard is the same stuff as Upol Gravitex but in an aerosol. As it's in a aerosol you don't quite get as much ripple effect?

That's doesn't bother me as it's only the inner wing and as long as it looks good and does the job I don't care if it doesn't exactly match the original ripple effect as long as it looks consistent.

But yeah if I hadn't just bought a torque wrench I would be looking at a compressor.

 

[Rocketman]

Started ripping the cracked stuff off tonight. Demoralising after all the work to get within touching distance of finishing the inner wheel arch but it had to be done.

 

[Rocketman]

Finished it now and it worked perfectly with the Upol gravigard. Top coats look as good as you ever would want for a inner wheel arch.

 

[Rocketman]

Hello back again on this

Another problem. OK one inner wing is spot on now with the graviguard system/top coats.

But unfortunately I had previously also done the N/S inner wing in hammerite stone chip and not top coated it yet.

So going by the last experience the hammerite couldn't cope with the amount of solvents in the top coats I would guess I used.

Thinking on this would a isolator coat stop the problem and save me having to rip all the hammerite stone chip off?? (would the isolater coat stop the solvents attacking the hammerite stone chip??)

 

[richie00boy]

It might do. I would brush on some epoxy primer as an isolator though, it's far better than 1k Barcoat, which just relies on a different solvent rather than crosslinking to provide resistance.

 

[the snooper]

ive used that hammerite stone chip on a job (came with the job) and I had the exact reaction, the stuff is terrible, the slightest whiff of thinners and it softens up so get some thinners on a rag and wipe it off it wont be hard, and get a better make. that's your only real option

 

[Rocketman]

Thanks for the input

It might do. I would brush on some epoxy primer as an isolator though, it's far better than 1k Barcoat, which just relies on a different solvent rather than crosslinking to provide resistance.

I see. Do all epoxy primer have no solvents in? Is there one you would recommend for the job - I assume some are better for brush on applications than others or is it much of a muchness?

ive used that hammerite stone chip on a job (came with the job) and I had the exact reaction, the stuff is terrible, the slightest whiff of thinners and it softens up so get some thinners on a rag and wipe it off it wont be hard, and get a better make. that's your only real option

Snooper I would really like to do this and might still but I did a pretty good job in the first place not just the bits you can see. Put it this way I think it took about 16 hours to get the other side back to having stone chip on again - took a long time getting it out all the nooks and crannies (though it might be faster this time as I haven't top coated it)

Yeah the upol stuff is well a million times better in my opinion now. Def won't be using hammerite stone chip ever again.

 

[DrNik]

Sorry to jump on the thread, but what primer goes under the gravitex, I only ask as it sticks like ..... To a blanket from my experience

 

[Rocketman]

It goes on bare metal or existing suitable coats.

For info graviguard is the aerosol version of gravitex virtually the same tech guide from upol for both products.

edit - here you go

http://www.u-pol.co.uk/documents/datasheets/tds/GRA-TDS-EN.pdf

http://www.u-pol.co.uk/documents/datasheets/tds/GRAVA-TDS-EN.pdf

 

[DrNik]

And how far does 1 ltr go, used the 2 pack 3m stuff, that's brill stuff but expensive and don't go far

 

[Rocketman]

And how far does 1 ltr go, used the 2 pack 3m stuff, that's brill stuff but expensive and don't go far

I'm using the graviguard aerosol version at the moment so can't tell you on the 1 litre gravitex.

richie00boy should be able to advise on it.

 

[richie00boy]

Epoxy contains solvents, but Barcoat contains a lot more as it's at a viscosity to be sprayed. Epoxy needs thinners adding to be sprayed. So using epoxy you are less likely to face a reaction. It's no guarantee of no reaction though and maybe it's best to remove the stonechip, given that epoxy primer is not cheap. It's not really expensive but it's not cheap. Also, if you do brush it on and it starts softening the stonechip it might make a mess.

 

[Rocketman]

I think we are back to stripping the hammerite crap off then. To much of a risk on time on money to do anything else.

 

[the snooper]

Epoxy contains solvents, but Barcoat contains a lot more as it's at a viscosity to be sprayed. Epoxy needs thinners adding to be sprayed. So using epoxy you are less likely to face a reaction. It's no guarantee of no reaction though and maybe it's best to remove the stonechip, given that epoxy primer is not cheap. It's not really expensive but it's not cheap. Also, if you do brush it on and it starts softening the stonechip it might make a mess.

Bar coat doesn't use solvents as far as I know it uses spirits which is why it doesn't react when sprayed and once dry forms a good barrier I've neve had anything react after I've had to use it

 

[Rocketman]

Snooper do you think it would react with the hammerite stone chip though?