Cellulose shrinkage problem

[Mark Wilson]

I'm part way through spraying my panels before reassembly. The panels were all media blasted and etch (I think) primed by the blasters and are in a generally good condition. There were a couple of small areas of accident damage which I stripped back, filled with body filler and reprimed the whole panels with high build celly primer. I thought at that stage I'd got the repaired areas pretty much perfect, but the areas are quite clearly visible through the celly top coat. I'm assuming this is the dreaded shrinkage, but is this likely to be in the body filler or in the cellulose stopper I used for fine finishing? The shrinkage is very shallow - can I fill with more stopper or high build above the top coat, or do I need to strip back to the body filler or bare metal?

Mark

[les]

I've found filling panels is not as easy as I may seem, the filler needs to extend beyond the area being filled to avoid the 'ring' that can appear around the perimeter, when sanding down a wooden blocks keeps the filler flat. When priming I've also found that the paint should be left to harden befor top coating.

[Mark Wilson]

Thanks Les, definitely not easy on double curvature wings! The last coat of primer had been on for a week, so I suspect that I've gone a bit heavy on the fine stopper. After a bit of googling it looks like I would have been better using a two pack stopper such as Dolphin glaze - didn't know there was such a thing! I'm going to rub back to the bodyfiller and either use just filler or the two pack stopper, if I can get some this weekend. I've been using rattle can high build primer when I've had to go back over these areas. Is this OK?

[les]

I've been wondering why you use stopper, you should get a good finish with the filler. I personally only use cellulose stopper for small imperfections that may appear in the finished filler or elsewhere, certainly not in any larger applications. High build sounds good, the rattle cans seem to work better held from a distance, you don't get such a wet surface on the panel. Good luck!

[Mark Wilson]

These were awkward bits which I had to have several goes at to get right, so when the guide coat showed there was still a depression I coated it with stopper as I don't think filler should be applied over primer, and I didn't want to go back to square one. Wish I had now, though. Just bought some Dolphin glaze from Halfords so I'll let you know how that goes, if I'm allowed back to the garage this weekend which is looking doubtful.......

[kennatt]

its the age old problem of celly,it will always do just as you describe,the best solution is to use two pack primer on the repaired bit it never lifts or shrinks into the filler.don't worry about the exaggerated health, risks ok if you are just doing a small area as you are. In the old days when all you could get was celly,we used to spend more time flatting repairs down than anything else involved,when two pack paint came along ,it cut our time by hours.Mind we had full air fed respiration systems. By the way celly stopper is just thick primer,and is used to skim over a small nick or mark ,its too thick to cover depressions as then its too thick and makes the lifting and shrinkage worse good luck with it

[chickenjohn]

You can use a different filler / primer to cellulose. No need to use the nasty 2K, ask at your local paint suppliers. 2K should only be used in an extracted booth and with an air fed mask with a clean air supply.

I've recently used Lechler 1k filler primer over etch on a traveller roof and on the rear wings as a base for cellulose with great success. No sinkage at all around a couple of filled areas.

[Mark Wilson]

Good to see you back on here CJ! Good and timely advice from you and Kennatt - most of the car is now done, with celly high build with only minor problems, but I've run out of primer and still need to do doors and rear (Trav) roof, so I'll see if I can get hold of some Lechler 1k. I replaced the celly stopper with Dolphin Glaze which is harder to sand but looks ok - haven't top coated it yet but it looks ok with primer.

[Mark Wilson]

John, can you give me the precise name of the Lechler 1k primer/filler please? I'm struggling to find it online and Leeds is a black hole as far as "local paint suppliers" goes. I've found Hydrofan water based, but I don't think that is what you were referring to.

[kennatt]

k2 has an unfounded bad reputation,the problem is not with the cyanide in the hardner,it very quickly oxidizes in the air,its the prolonged use which causes asthma ,since on breathing in, the vapor hardens in your lungs. hence the need for air led masks in commercial booths. Celly is just as bad,without a good mask. for a once in a lifetime use ,no problem as long as you have a good mask,3m do one. Its no use going to water based since they are a clear over base and the clear laquer is 2k

[Mark Wilson]

I'm no chemist, but I believe isocyanate isn't the same as cyanide. HSE advise, however, that even short term exposure can trigger asthma, and advise airfed masks even for outdoor short burst SMART repairs

http://www.hse.gov.uk/pubns/guidance/mr5.pdf

Everyone can make their own decisions and as with all risks not everyone will suffer ill effects. However, I'm extremely aware of the effects of asthma, as my younger brother has had his life just about ruined by it (nothing to do with paint spraying) so it isn't a risk I'm prepared to take. I wear a 3M twin filter mask for celly spraying.

Mark