what makes bog crack???

[ari666]

so i have re done my boot 3 times now, and each time i get it all flat and nice, but after it gets a coat of black and is left to dry for a few days, cracks appear in the bog.

also i just noticed a crack in the rear windscreen filler panel. this crap is doing my head in, what have i done wrong?

when the boot cracked the first time it was more like a bunch of blisters, i got a paint scraper and removed all flaking bits of bog all the way to the metal, went over it thoroughly with 40 on the wizzy so all lifting bog was completely gone. then i filled the holes with more bog, finished it off with fine filler, puttied, blocked back, etch primer, then matte black

cracks appeared 2 days later but they were more like cracks than the blisters from the first time, but still the cracks went pretty deep. so i die-ground out the grooves and re filled with fine filler, re puttied, re primed then resprayed. soon as the black went on it f'ed up and started bubbling (lots of tiny bubbles) in spots and some of the cracks became visible where the fine filler was. and since then its been in the sun and has gotten worse.,

i only just noticed the rear window panel today and if i am going to set to it, i want to know what i have done wrong so it doesnt happen over and over again. especially there cos there are 3 or 4 angles i need to get right.

 

[ari666]

pics.

windscreen panel:

little bubbles/crack:

more:

and more:

 

[soop]

Moisture. And its probably too thick.

 

[lemusa]

try building it up, looks like your puttin it on way to thick. Make sure the area is moisture free like soop said too

 

[calais_cruzin]

I go with the too think, heat still trapped in the middle, with the outside cold, when it fully cools, its cracks.

Have a look on youtube about how the make big dam walls, they have to do it in small layers so it cools even, stopping the cracks.

 

[Philthy]

Looks too thick to me too. Rather than layering the bog on a bit at a time, can I suggest trying to straighten out the panel a bit more before simply bogging it up? More work now, but less pain in 12 months when it cracks up again

 

[soop]

Yeah pretty much, don't bog dents ya dodgy bastard.

 

[ari666]

lol, i think that sounds like a resounding "too thick" answer. is there an easy (temporary) fix to get this car through rwc? or will the cracks pass?

this boot is FKEDUC the bog is insanely thick, but its just a short stop till i get another boot that isnt damaged/rusted out/stretched. the rear panel however isnt really that thick. well it may be, i didnt do it, my "mate" did. the whole rear panel needs to be readressed anyway cos its wobbly as hell. but im just annoyed cos the whole point of slappin this thing together was to get it to rwc and reg and it seems to be falling apart faster than i can save the $$$

 

[wildss]

what brand of bog is it?
my old boss used to let it sit overnight before he touched it with 40grit.
he used septone and eagle which he never had a problem with.
ive seen some pretty big/thick bog work and it didnt crack in such a short time like yours has....

 

[soop]

Go to a paint and panel shop (not a repairer a retailer) and get a Speed file ffs.

you'll get it flat no worries.
Cracks will pass rego unless the guys a tool kit.

Wild SS - Thick bog wont neccisarrlly crack if its done right. But if you slap 10" of bog in a dent and sand it, it will. Because as it dries it shrinks.