Gassing off- How long for Bondo (and other GRPs)to set?

[Gorminrider]

How long should Bondo set before painting?
...My question arises because I discovered new bubbles in the paint of a heavily bondoed tank that had to have been "done" three years previous. I've already "fixed it" but I am still wondering if mine won't fail the same way in a few years and, MAINLY, if that is the cause....gassing off under the paint.
I have always tried to do fg (Fibreglass, or GRP GlassReinforcedPlastic) in the warm weather outdoors and used gelcoat over so it's never really been an issue before, but on cars and bikes, with the different paint going on, well it's a question.

This reminded me. Plainly good advice it is too but doesn't quite answer my question.
jbird7262
http://www.thegsresources.com/_forum/showthread.php?231988-gs450-cafe-build&p=2182917#post2182917

Just a tip... 36 years of bodyshop repair, try to keep the bodyfiller 1/16th to 1/8th thickness if you can, the thicker it is the more expansion happens with temp changes, could cause some cracking.....

I

 

[nvr2old]

If you use a good quality filler, you should have no problems spraying primer after just a few hours. Make sure the filler and it's hardener is mixed thoroughly. If it isn't, you'll have problems like you described. The filler shouldn't really be more then a 1/4" thick. The thinner the better.

 

[Gorminrider]

Thanks,nvr'.
Thin it is from now on. I guess the PO really globbed it on all at once to fill the dent. But amazing it took three years to start pimpling the paint over just one deep ding. Maybe the glob got somewhat sealed by thinner layers that dried harder over it ?...the PO's thinner surface patches were ok.

 

[posplayr]

I'm not an professional, but have been doing bondo for some time to remember the old days when bondo shrinkage was a problem. Back in the 70's you would see guys driving around for months waiting for the bondo to settle under grey primer. Nowadays, it is much less important with water proof glass reinforced bonds. You have seen those car make over shows? They do a whole car and massive amounts of bondo over the weekend.

THIS IS THE WRONG STUFF: It it will absorb water and probably shrink as well.
http://www.amazon.com/Bondo-261-Lightweight-Filler-Pint/dp/B0007ZG9TO

THIS IS THE RIGHT STUFF
http://www.walmart.com/ip/Bondo-272-Bondo-Glass-1-Quart/17056865

There is also the long hair stuff if you are trying to fill gaping holes. I fill as required (if you have no other way by working with teh metal) then go over the top with the finer short hair stuff.
http://bondo.com/bondo-hair-long-strand-fiberglass-reinforced-filler-762.html

You do a final skim coat with a non reinforced filler for feathering the metal, bondo and any existing paint before primer.

There is probably some small amount of shrinkage (of the modern products) after 1/2 hour but it is almost non existent. It is also waterproof stuff is much stronger. If the surface is properly treated then bond between metal and bondo should hold for years. I like to crosshatch the bare metal with 30 grit to give the filler better bite.

So the question becomes, how do you avoid any rust under the bondo? You certainly dont want to do what this guy did, applying bondo and leaving the bare metal tank out to rust.

http://www.thegsresources.com/_forum/showthread.php?231988-gs450-cafe-build&p=2182887#post2182887

You either strip and etch it and use a metal prep like phosphoric acid, or if it is clean and dry out you can just power sand the metal to, cross hatch scratch it , wipe it down with a moist cloth (something that will not leave a residue or promote rusting; water if you work fast, alcohol would be safe) , blow dry and apply the bondo. If this is a whole tank that was stripped, it should have gotten a metal prep treatment.

 

[Gorminrider]

aha. Good stuff, Pos. And a mystery solved--I've wondered what those guys in the primed jalopies were up to!!

Yes. it was indeed all "pinkstuff" bondo filler per your first link. About 1/3 of the tank was somewhat faired all around a large deep dent on the side, near the tank emblem(a Honda). The rest had original paint in ok condition with a few more little places bondoed. It hadn't cracked but was certainly thick enough to so Maybe at least a couple of layers and he kept it clean enough in between because I couldn't see layers when taking it off. ..no flaking etc. PO's job had very good adhesion too. And the overall paint was good enough to fool the eye it was OEM... except those peculiar blisters starting to show up.

It's the permeability of bondo that got me wondering about the gassing-off idea, because otherwise it was holding up pretty well...
Now, Microfibre! THAT IS A GOOD good idea! If my version of a fix fails, I will use it the next time to "build up". (I used a little fg matt to build up my version but it was tricky and messy making little batches of resin and was more nuisance than it was worth in this instance)

 

[Guest]

As mentioned, use pro filler and etch property before application. There must be no silicone around while doing this type of work.

 

[posplayr]

If my version of a fix fails, I will use it the next time to "build up". (I used a little fg matt to build up my version but it was tricky and messy making little batches of resin and was more nuisance than it was worth in this instance)

Being an Ex windsurfer, I have also done my share of fg work, although I tend to stay away from "matt". Kinda funny story, maybe you will not make teh same mistake.

Back in early 1980's I was taking off on a trip to Baja and while at my friend's newly opened shop, he had this 8' 0" windsurfer naging on the wall; I had to have it. $400 grabbed it off the wall and took off to Baja the next day. For the time this was super small board made by a San Diego surfboard company; knew nothing about WS (as I came to find out). Bottom line was the entire bottom shape was that of a surfboard and not a WindSurfer! I even took the board to Maui in 1984 and came back and just pitched teh board in teh corner as it was worthless generating huge spray due to the bad bottom design.

After about a year, I figured what the He%%, nothing to loose so I reshaped the entire tail of the board to be more hydrodynamic (as per the books by Hoener Aerodynamic Lift and Aerodynamic Drag) https://en.wikipedia.org/wiki/Sighard_F._Hoerner

I reshaped the new tail, using bondo and then spray painted it with white paint and then fiberglassed it. It worked really well, amazingly well. I was out siding in a spring wind one day and I noticed more drag, I looked under the board and the fiberglass was peeling back. With the kelp out on teh reef it make for a noticeable stopping power. Anyway, I was not going to stop and fix the board; that had to wait. Next trip out, I crash going over the handlebars (that's what we say anyway; no handlebars on a WS) I looked under the board and the entire Fg skin had ripped off but left the bondo.

The bondo was applied to the bottom of the fg board and it was even the pink stuff. Well I just ripped off whatever was remaining and since there was no damage to the original Fg around the clark foam core, I just kept riding like nothing had happened. The obvious problem was the adhesion of the Fg to the painted surface; it did not hold, but the Bond held to the fg underneath it.

After I got home, I tried to figure out how to repair it. Since the pink stuff takes on water I needed to do something. I ended up just putting a finish coat of polyester resin to seal the bondo and said screw the color. You could only see it when the was board flipped up. That is it, the G&S, on the left. I rode it for another couple of years after that.

What's this got to do with Fg and bondo, well it is a story about Fg and bondo and they did not go well together. On a metal tank I figure it is alot easier to feather bondo that fg anyday so there is really no reason for fg especially matt. Nowadays teh epoxies are so much better. Put a little 10 oz cloth down if you have to, but no matt.

The other tip, when doing glass is to tape it down; it squeezes out much of the resin making the part stronger and then will require zero sanding.

 

[nvr2old]

Fiberglass and metal don't really work together. They expand and contract very differently. Modern plastic fillers are what to use with metal repairs. The fiberglass will hold for awhile, but eventually will fail. Think of how many fiberglass hood scoops have been applied to metal hoods, but soon start to crack at the joints. Fiberglass is meant to use on fiberglass. Modern products/fillers/primers/paints have come a long way and they're designed to work as a system. Used correctly and the repairs will last for many, many years.

 

[posplayr]

Fiberglass and metal don't really work together. They expand and contract very differently. Modern plastic fillers are what to use with metal repairs. The fiberglass will hold for awhile, but eventually will fail. Think of how many fiberglass hood scoops have been applied to metal hoods, but soon start to crack at the joints. Fiberglass is meant to use on fiberglass. Modern products/fillers/primers/paints have come a long way and they're designed to work as a system. Used correctly and the repairs will last for many, many years.

20 years? 30 years, 40 years? Unless it starts to rust underneath or the clear coat goes not sure shay there is to fail.

 

[Gorminrider]

ha! I've got too many stories like that! And matt has crap in it..a starch to hold it together..maybe I would have been better off to snip some fibres off some fine cloth into the bondo but there I go... I see my biggest mistake is persisting in using up the ol crap I have kicking (off!) around.
Yes, I've seen fg "constructions" peel off metal for sure. I would expect to make a thing like an air scoop separately and bed it in something with rivets,screws, or bolts.
But bondo can stick wonderfully well to a gas tank that is shiny and roughed up per pos' post above. even over rusty pits for awhile ,being as the surrounding is attaching well.
I think rust sticks very well to steel at the topmost oxidation but rust in any thickness has little strength and probably is full of voids too I guess. (Something to look into on wikapedia? at molecular level)

added..which brings me to rust converters. Will they bond with filler?

 

[posplayr]

ha! I've got too many stories like that! And matt has crap in it..a starch to hold it together..maybe I would have been better off to snip some fibres off some fine cloth into the bondo but there I go... I see my biggest mistake is persisting in using up the ol crap I have kicking (off!) around.
Yes, I've seen fg "constructions" peel off metal for sure. I would expect to make a thing like an air scoop separately and bed it in something with rivets,screws, or bolts.
But bondo can stick wonderfully well to a gas tank that is shiny and roughed up per pos' post above. even over rusty pits for awhile ,being as the surrounding is attaching well.
I think rust sticks very well to steel at the topmost oxidation but rust in any thickness has little strength and probably is full of voids too I guess. (Something to look into on wikapedia? at molecular level)

added..which brings me to rust converters. Will they bond with filler?

Personally if it was me, unless you are trying to save some time, it is too easy to use AC stripper and have an entire tank down to bare metal in 1 hour, the find a tub and put the whole thing in something like acid magic. You can dilute it 4:1 and it is only $10 a gallon. Just get rid of the rust. We are talking primarily about a MC gas tank here, not an entire car body.

After soaking, rinse and use a metal prep like POR15 or CASWELL have that gives you enough protection to avoid flash rust before you do the bondo. Bondo goes off in 15 minutes and you should be doing the second coat of Bondo to fill in anything you might have left. Then comes the primer 1/2 hour later so there should be no rust on that tank period. Basically in 2-3 hours max (after the petal prep dried overnight), you have a striped , tank bondoed and primed with a sandable primer. No rust.

BTW I have never used Jell coat and not sure what that is adding to the mix that quality paints will not do? IIR there is an epoxy primer that goes over the sandable primer that would basically act like Jell coat but it is specifically made for paints. What happens to a jell coat when you sand it to apply top coats?

 

[Onthebar]

done bodywork for several years & will offer my 2 cents. Weve commonly used fiberglass resin in our bondo when having unexplainable pinholes or porosity when applying bondo straight out of the can. usually theres a reason your getting inperfections, dust on surface or even your spreader or technique. Depending on how much is added, it offers a viscosity, application & finish compareable to very high end "finishing puty" which allows you to use your "high build primers" as they were intended, thickness & absorbsion/shrinkage being maintained as manufacturer recomends. Remember, to much of a good thing, leads to compromising every product from that stage on. Tip for you. Try to effectively mask/plug fill hole leaving seal area exposed to primers & sealers, then mask only seal surface for the color & topcoat, remove masking while topcoat is curing, apply w/a brush on mask line, working it in hard. No fuel under paint situation... done. hang in there.

 

[posplayr]

done bodywork for several years & will offer my 2 cents. Weve commonly used fiberglass resin in our bondo when having unexplainable pinholes or porosity when applying bondo straight out of the can. usually theres a reason your getting inperfections, dust on surface or even your spreader or technique. Depending on how much is added, it offers a viscosity, application & finish compareable to very high end "finishing puty" which allows you to use your "high build primers" as they were intended, thickness & absorbsion/shrinkage being maintained as manufacturer recomends. Remember, to much of a good thing, leads to compromising every product from that stage on. Tip for you. Try to effectively mask/plug fill hole leaving seal area exposed to primers & sealers, then mask only seal surface for the color & topcoat, remove masking while topcoat is curing, apply w/a brush on mask line, working it in hard. No fuel under paint situation... done. hang in there.

Anybody painting their gas tank should figure out the right way to address this. You do not want gas to eat under the paint at the filler. An easy way to get this to happen is to coat your tank and forget to open the breather/vent hole in the neck. Ask me how I know.

 

[Gorminrider]

pos, I've only used gelcoat on boats it is pretty much just thinned old-school bondo in my comprehension but there might be additives for non sag beyond just it's viscosity BUT an IMPORTANT DIFFERENCE from bondo is the WAXED Gelcoat. Most you can find is waxed. I would not use this anywhere near something I was going to paint. The wax can be stripped somewhat after hardening but really I wouldn't want to take paint any gelcoat that hasn't aged a long period- the unwaxed gelcoat is rarer and is tacky for quite awhile. It is a good clue as to how long it can take fg to really fully cure I think.

Weve commonly used fiberglass resin in our bondo when having unexplainable pinholes or porosity when applying bondo straight out of the can.

that's Good to know! But I would add that resin commonly found is waxed resin.

Tip for you. Try to effectively mask/plug fill hole leaving seal area exposed to primers & sealers, then mask only seal surface for the color & topcoat, remove masking while topcoat is curing, apply w/a brush on mask line, working it in hard. No fuel under paint situation... done.

Good idea! I wish I had done this exactly so but, just as a whine, for (learner) spraybomb guys like me getting a little liquid paint to use with a brush is tricky and noxious...I've done it before .The aerosol sprayed into a cup dries really fast ... a special jar is needed so the paint doesn't all blow back out into my face from the jar.( breathing protection is required!) Still, I will try it.

 

[nvr2old]

I've been suggesting for several years now about the paint edge at the filler neck. A simple swipe of JB Weld over the paint edge will completely seal off the paint from gas/fumes seeping under it. Just mask a line about 1/8" back on either side of the paint edge so it stays neat. So much discussion here for what is essentially a very simple repair job. Get the dent to bare metal, rough it up with 80 grit so the plastic has some tooth to stick to, use a quality plastic filler, block sand it with 36 grit, smooth on another thin coat of plastic if needed, sand with 80 grit, primer, sand with 180, primer again, sand with 400 grit. Make sure the surface around the repair is prepped and clean, maybe 2-3 final coats of primer over the whole tank, sand with 400, followed by the base coat and clear coat. My way may not be the only way, and it's certainly not the cheapest, but I've used this system for 100's of quality paint jobs that've stood the test of time. If someone wants to skip many of these steps, especially if you don't have the tools (sanding blocks, paint/primer guns, compressor, etc.) or don't/can't spend the money for the materials..because they are expensive..then I certainly understand. It's all in what you're satisfied with as a final product. Spray can jobs with (sorta) high-build primers and base coats can be done with decent success, especially when topped off with modern spray can 2K clear coats, but the steps getting there should be the same.

 

[Gorminrider]

good idea per epoxy and it Might do for a fast "saviour" if it starts to lift too...I'm saving these pages of advice so if it comes to my Suzukis, it'll be better. ... I still don't know what caused the pimple blisters in the PO's otherwise seemingly ok paint job (and I apologize for not taking pix)...but anyways, this is what it is now. The 2K clearcoat scared me just reading the directions, so I went with spray enamels, and brushed varnish after experimenting with various coatings and paints. I am pretty happy with job I did and it Survives gas spills very well so far. and no blisters yet.


View attachment 41724

 

[60ratrod]

for those interested in rust and corrosion, here are a few excerpts from volume 1 of the corrosion control manuals that I use. basically all corrosion is, is metals trying to return to a baser, more original state, as they are naturally found in the earth. here are the types of corrosion that we encounter on motorcycles:

this one is what we normally see on frames, inside and outside of tanks, and on engine blocks:
UNIFORM SURFACE CORROSION. Uniform
surface corrosion is probably the most common type of
corrosion. It results from a direct chemical attack on a
metal surface that proceeds uniformly over the entire
exposed surface (see Figure 3-7). The metal gradually
becomes thinner and eventually fails. On a polished
surface, this type of corrosion is first seen as a general
dulling or etching of the surface and, if the attack is
allowed to continue, the surface becomes rough and
possibly frosted in appearance. An example is the
etching of metals by acids. The discoloration or general
dulling of metal created by exposure to elevated
temperatures is not considered to be uniform surface
corrosion. Coating/sealing the exposed surface will
protect it from this type of attack. Also, corrosive elements
may be removed through air movement and drain holes.

this is the type I warn about when using stainless fasteners in aluminum blocks:


GALVANIC CORROSION. Galvanic corrosion
occurs when different metals are in contact with each
other and an electrolyte, such as sea water. It is usually
recognizable by the presence of a buildup of corrosion
deposits at the joint between the metals. For example,
aluminum skin panels and stainless steel doublers,
riveted together in an aircraft wing, form a galvanic
couple if moisture and contamination are present.
Figure 3-8 shows galvanic corrosion of magnesium
adjacent to steel fasteners. The potential for galvanic
corrosion is greatest when the two metals are well
separated from each other in the galvanic series and are in electrical contact.


both of the above types can and will lead to this type:

INTERGRANULAR CORROSION.
Intergranular corrosion is an attack on the grain
boundaries of the metal. A highly magnified cross
section of any commercial alloy (see Figures 3-11 and
3-12) shows the granular structure of the metal. It
consists of quantities of individual grains, each having
a clearly defined boundary, which chemically differs
from the metal within the grain. Frequently the grain
boundaries are anodic (tend to corrode more easily) to
the metal within the grain. When an electrolyte is
present, rapid selective corrosion of the grain
boundaries occurs. High strength aluminum alloys,
which depend on precipitated phases of alloying
elements for strength, are particularly susceptible to
intergranular attack. Figure 3-13 shows how
intergranular corrosion progresses in 7075-T6
aluminum alloy adjacent to steel fasteners. In this
example, the grain boundaries are anodic to both the
metal grain and the steel fastener.



this is what most corrosion leads to if not addressed, but usually takes a while depending on the metals involved. best example is when you find an old sheet of steel on a car and find that it's flaking off:

EXFOLIATION CORROSION. Exfoliation (see
Figures 3-14 and 3-15) is an advanced form of
intergranular corrosion where the surface grains of a
metal are lifted up by the force of expanding corrosion
products occurring at the grain boundaries. The lifting
up or swelling is visible evidence of exfoliation corrosion.
Exfoliation occurs on extruded, rolled, wrought, and
forged high strength aluminum and magnesium parts.
This type of corrosion most often occurs on extruded
sections of metal and is found primarily in aluminum
sheet around steel fasteners. Its prevention involves
separating the aluminum and steel by a barrier, such as
zinc-chromate primer or sealant.