Underseal Problem ... Shrinking ?!

[DamirGTI 342]

Please i need a diagnose of this problem : while finishing the floor panel from underneath , after seam sealing and painting i applied one coat of underseal and after it's dried off it ripped the surface and made "craters" but only on the areas where the seam sealer was underneath the paint .. ok. i said maybe i need to spray one more coat , i did that the other day when the first one was fully dry (after 24h..) and again after it's dried off :

 

 

 

 

 

can someone enlighten me please : why is this happening ?! what surprises me is that there was - 2 coats of primer and 2 coats of paint (all cellulose based) on entire floor surface underneath and over the seam sealer (but i didn't brush on the seam sealer on the bare metal..one coat of zinc rich primer was under the seam sealer and celly primer/paint on top ..) before spraying underseal and now i can see the seam sealer (was some 1pack white color seam sealer .. and it0s not a cheap one !!) down inside in these cracks ?!

 

Been thinking how and with what to fill these cracks and to be honest i'm not sure anymore which option will be best :

 

1 fill the cracks with the underseal , again , but this time not with the spray gun but with the brush

2 fill the cracks with PU sealant

3 fill the cracks with ... dunno , paint ?!

4 ?!

 

Damir

Edited March 9, 2009 by DamirGTI

[pugdamo 111 2 Cars]

Its reacting to whatever paint you used. Try using something called Shutz,it doesnt react with anything,if thats stonechip type stuff youre using it can be awful for reacting.

[omega 82]

was it a hot or cold day when you did this ?just thinking that it might be shrinkage

[DamirGTI 342]

Yes this was stonechip type underseal (body) what's a "shutz" then ?!

 

Damir

[DamirGTI 342]

was it a hot or cold day when you did this ?just thinking that it might be shrinkage

 

Well , yes it was a bit cold (around +10C could've been even a 2 or 3C lower i'm not sure) .. and , dunno if this might be a problem : i "heated" all the underseal cans in the bucket of warm water before spraying/applying on the floor surface ... i did the spraying with the UBC gun and at 3.0 to 3.5bar pressure settings ..

 

Damir

Edited March 9, 2009 by DamirGTI

[pugdamo 111 2 Cars]

Shutz is an underseal aswell but it doesnt react with anything,we used to use it in a garage i used to work at,we used it for all welding repairs,its in a can the same as stonechip so it gets sprayed on in the same way,try a web search on it. Hope it helps

[DamirGTI 342]

Crap

 

 

 

.. bloody thing peels off

 

Damir

[de Noir 0]

Damir, this is surface treatment problem.

 

Either surface isn't healthy, or you 'contaminated' it with somehing, or paint system you used doesn't mix with stonechip protectant.

These things happen.

 

Stone chip protectant sticks like glue, it just does not peel off!

 

The right way is to brush everything away and do it all over again. I am sorry for your effort man.

Edited March 16, 2009 by MH_

[philfingers 5]

I had a similar thing with paint on the wing. use an etch primer first on the bare metal, then primer and underseal would be my best guess

[DamirGTI 342]

Well i'm 90% sure that this was reaction in between the seam sealer and underseal as the underseal is lifted only on places where the seam sealer was underneath ...

 

Anyway i cleaned off all the areas where the underseal didn't hold on firmly on the surface and stuffed PU sealant (some expensive rubber based for car bodywork) inside the gaps and overcoated entire floor surface + wheel arches with non hardening bitumen based underseal and it seems fine now

 

Damir