Roadster Tank Rebuild / Slosh Coating Concerns

T95 · Oct 10, 2011

Anatomy of a Roadster Tank and Slosh Coats

I have a fiberglass roadster tank that I have cut open to both repair and recoat for use with modern fuels. The tank was an ebay purchase that came with plenty of issues, but I believe it was put out of service prior to the ethanol fuels of today. I am taking my lead from Jean, but plan on altering a few steps along the way to suit my style tank. I'll add to this post as I make progress.

First off I decided to cut the top open rather than the bottom. In studying the bottom I found it had way to many contours to cut. I also liked the idea that the seam would be high and out of constant fuel contact. So my cut was made about ½” inboard of the side of the tank so I would have room to blend the seam. I am comfortable working with polyester resin/ fiberglass on a small scale as I have made numerous repairs to surf and windsurf boards over the years. I have never worked with vinyl ester, so I do have a lot to learn. If you have some pointers send them my way.

Roadster Tank Rebuild / Slosh Coating Concerns

Tank Anatomy:
After opening the tank I now have a good understanding of how it was constructed. I can also see some obvious areas of concern that might lead to the failure of a slosh coat.

Basically the tank is constructed of two pieces:
The top shell or the visible portion of tank. This side has the color applied gel coat and because it faces the mold when release it has a nice smooth and shiny surface.
The bottom shell- This piece cradles the frame and it houses the petcocks and mounting studs. I was surprised to find the gel coat, shiny side, on the interior and in my case it was still intact with a high gloss to it.

The bottom piece has a large lip that is turned up roughly 90 degrees and sits inboard of the lower edge of the outside shell. Copious amounts of putty, or what I believe is thickened fiberglass, were applied between these surfaces to act as the bonding agent. This same putty is used to bond the mounting studs, fuel neck and petcock bungs
The exterior of the tank was painted black over the original red. In these photos the red shows as the interior of the top shell with black paint on the exterior. The bottom shell is fiber-glassed black. I recently sanded off the black paint.

Slosh Coating Concerns:

Prior to cutting open the tank I filled the tank with a couple handfuls of sheet rock nails and agitate the tank for some time in an attempt to clean the inside. I found this to be a random process at best with limited benefits in removing scale due to degradation or delaminating. In my case little or nothing was accomplished.
Also, if you chose to use this technique count the number of nails or screws you put in the tank. Your screws or nails can easily get lodged in the voids in the seams.

I found that the filler neck does not fit flush to the inside of the tank, as I had expected, so removing the nails was really difficult. This protrusion would also make emptying the tank of fuel difficult.

The interior seam is an obvious area of concern for slosh coating. First off this is a generous seam and overlaps on the inside by as much as 1” . I am guessing the wall thickness of the shell to be around 1/8”. When sloshing a coating I believe this thin seam edge could present bonding issues.

The interior bottom of the tank is by no means flat or level. To my surprise I found the petcocks are not at the lowest point in the tank. They sit up on a tray with small recessed areas alongside the tray. This may be a built in spot for debris to settle out. Regardless you won’t have and indication of the tray or the recessed areas by looking at the bottom of the tank, it appears to be flush from the outside. Unfortunately, this arrangement guarantees that you can never drain all the fuel from the tank by simply opening the petcocks. Additionally my petcocks appeared to be bonded to the putty used to hold the petcock bungs in place. This putty sat another 1/8” above the tray height leading to additional fuel retention.

Photos show petcock tray/ recesses

Finally, as I stated above the gel coat was still intact on the interior bottom piece. This high gloss surface could present slosh coat bonding issues.
It also brings another unanswered question to mind. Because the tanks have both a rough and smooth surface on the interior I am wondering if either is more prone to failure over the other. Are this tanks failing on the sides or bottom?

nortriubuell · Oct 10, 2011

Good info on Fiber tanks for sure ... many thanks for posting. I've had several fiber tanks over the years, but will never own another. My last one was my first ebay purchase back in 2002. A beautiful "Fireflake Emerald Green" ... not a Norton "factory OEM color", but it was gorgeous and looked like it was !!! After about five years the modern fuel did it's damage, and it started to get what looked like "air buubles" in some spots on the sides and top. Just made me sick too, as I loved that paintjob. The tank had what looked like some kind of silver color coating inside when I got it. And this just pealed right off after the first couple tanks of fuel and I'd fish it out. Though the tank still didn't leak, the "air bubbles" just infuriated me. :evil: ... so I sold the tank on ebay. I was honest about its issues, and surprised it sold for so much.

I admire your courage to fix one, cheers ...

T95 · Oct 10, 2011

nortriubuell said:
Glad you liked the Post!
and it started to get what looked like "air buubles" in some spots on the sides and top.
Years ago my friend had a sailboat the was covered with small pimples in the gel coat. The theory at the time was that moisture was trapped between the application of the gel coat and the underlaying top coat of fiberglass. If I recall it was more of a problem on boats that were fabricated in humid environments. I understand that the ethanol can eat right through the fiberglass and I am sure the first sign would be bubbles!

The tank had what looked like some kind of silver color coating inside when I got it. And this just pealed right off after the first couple tanks of fuel and I'd fish it out. Though the tank still didn't leak, the "air bubbles" just infuriated me.
I have no idea what the silver coating was, hopefully not Caswells!

I admire your courage to fix one, cheers ...

Courage or more likely insanity considering the odds of successfully containing ethanol base fuels in a fiberglass vessel! Oh well, it will be a fun project!

Hobot · Oct 10, 2011

I for one enjoyed and learned from your clever tank dissection. Polyesther resin is prone to ethanol attack d/t the phytates[sp] in it. If was me I'd redo with vinylester and a couple of heavy coats of Casswell's Novolac set up with help of heat for a few days or more. Actually is has been me and also my pal Wes, we both did serious thick long tedius tank tumbling till Caswell's set up stiff enough not to sag anymore. That was like 7 yr ago and plenty of ethanol spiked gas run through and stored up over break downs or winter months.

http://www.compositescentral.net/showthread.php?t=5737

I`ve had a hell of a time trying to find an appropriate resin. I`ve had a couple of tech reps from epoxy companies tell me that a vinyl ester or hybrid epoxy vinyl ester would NOT work but a pure Novolac resin would.

Hortons Norton · Oct 10, 2011

Thanks for the pictures and tips, I sealed a fiberglass tank with 2 heavy coats of Caswell's some time ago and so far so good. I do know it won't last forever but it was all I had at the time. I do plan on replacing it soon as it is also like playing with a loaded gun riding with one, They can be dangerous. Sorry T95 for the short highjack of your thread but I need to ask nortriubuell a question, Do ya know who this guy is?????? the one in the middle.

Matt Spencer · Oct 10, 2011

The used to tip a can of Pliobond , inside according to the early 70s artical I browsed utiliseing a rusty ! :shock: :lol: ( call that rust :roll: )

Dunno if it still holds up on this Ethanol feul , ' Aucklands premier motocycle worshop ' used and recomended it as sealant , for the machanical componentry .

Why you kids , I'll Boil You In Oil . Yes indeed " Pliobond " could take the heat , oil and they said in ' motorcyclist ' U.S. ( I think ) The Fuel Too .

Carbonfibre · Oct 11, 2011

Cutting a hole in the top of your tank means almost certainly its irreparable now..............unless of course you are not worried about always being able to see a visible ring where the cut out section has been joined back in?

If you intend to section a tank to apply a proper chemical resistance layer, the proper way to do the job is to remove the bottom by cutting along the centre of the bonding surfaces (if anything gets cut away it can be easily repaired with new GRP), then remove any previous failed tank "sealer" using mechanical abrasion. Ideally the interior surfaces should then be blast cleaned, using a relatively aggressive media, but being careful to keep the blast gun moving all the time. Next scour the surfaces with acetone, and then apply a chemical resistance layer using novalac vinyl ester resin, and synthetic veil (or tissue).

Finally, and ideally when the chemical resistance layer is still "green" (before it has hardened fully and is chemically inert), the two parts of the tank should be bonded back together using a bonding paste made using the same novalac VE which has been used for the chemical resistance layer. Subsequent to the bonding process, a small quantity of resin needs to be introduced into the tank and run around all the seams that have been bonded to seal any small pinholes.

Its not a good ideal to use any type of epoxy "sealer" for this type of job, as these products are generally very brittle, and as GRP tends to move quite a lot through vibration and also contracts/expands due to heat when bikes are being used, cracking of epoxy type sealers is very likely to occur, which is the main reason to avoid using them in any composite tank, as failure will most certainly occur very soon after the "sealer" film has cracked.

bwolfie · Oct 11, 2011

And here we go, Mr. CF has chimed in once again. How about Mr. CF start posting some pictures and details of the work he has performed and the bikes he rides before any further coments are made. I am sure that many of us would like to see that.

DogT · Oct 11, 2011

Carbonfibre said:
Cutting a hole in the top of your tank means almost certainly its irreparable now..............unless of course you are not worried about always being able to see a visible ring where the cut out section has been joined back in?

Bondo and sanding primer on the outside?

Dave
69S

bwolfie · Oct 11, 2011

Same as if you were replacing a fiberglass panel on a car, easy fix.

Hobot · Oct 11, 2011

After seeing how much boozed gas has been inside Wes's tiny fiber tank sealed with Caswell's for years now, I'm feeling pretty darn confident my IS tank and any one else's using Novalac will be just fine in the long run. Finishing the outside is actually the fun part and will turn out as if never injured. Might add a sight glass too.

Acetone with clean the insides of anything interfering with a bond but rough texture even better, just make sure any acetone is cooked out the surface and don't leave in but a few moments.

debby · Oct 11, 2011

My experiences with two glass tanks, both of which had been coated, makes me tend to believe that carbonfibre's theory of the coatings cracking with vibration is indeed correct. In both cases, all was well for a couple of years, then bubbles appeared on the exterior surface of the tank - big bubbles on the tank that had been painted, small bubbles and raised areas on the tank that still had its original gelcoat finish. Neither tank leaks, neither has soft spots, the coatings in both tanks appear to still be in perfect condition, but the ethanol seems to be getting through somehow.

It's possible that there were voids in the coatings, because you can't really see inside the tank to tell if you're getting complete coverage, but with two coats of the Caswell product applied there shouldn't be any voids, I would think. It seems more likely to me that the coatings are cracking as he has suggested.

I think it's basically hopeless to expect a fiberglass tank to last more than a couple of seasons regardless of what you do to it. "Steel is real", as they say in the bicycle world :!:

my two cents,
Debby

T95 · Oct 11, 2011

Ahh! Mr Carbonfiber,
I was waiting for you to pounce on my little project. I really do appreciate that you took the time to give me your opinions, but you need to work on your delivery, its a bit abrasive! I agree, you may be correct that the tank is irreparable, but it won't be due to a visible seam. Blending the seam is really the only part of this repair I am confident about!

Carbonfibre said:
Cutting a hole in the top of your tank means almost certainly its irreparable now..............unless of course you are not worried about always being able to see a visible ring where the cut out section has been joined back in?

I see your confident about the," right way to do the job", but I thought I was clear on why I chose to cut the top rather than the bottom. When I made the decision I wasn't aware how the seam was formed. Now that I can see all the putty that was used to bond the two halves I am even more confident I made the right decision. This tank was not previously sealed.

If you intend to section a tank to apply a proper chemical resistance layer, the proper way to do the job is to remove the bottom by cutting along the centre of the bonding surfaces (if anything gets cut away it can be easily repaired with new GRP), then remove any previous failed tank "sealer" using mechanical abrasion.

Now thank you for the good advice on cleaning, I appreciate that! I was going to use vinyl ester but I am not sure about the Novalac. I'll research your previous post on this subject to see if its the same product you have been touting. I know one of them was basically unobtainable in small quantities.

Ideally the interior surfaces should then be blast cleaned, using a relatively aggressive media, but being careful to keep the blast gun moving all the time. Next scour the surfaces with acetone, and then apply a chemical resistance layer using novalac vinyl ester resin, and synthetic veil (or tissue).

I agree, bonding a green seem is probably ideal, but it may be unrealistic in my case.
Finally, and ideally when the chemical resistance layer is still "green" (before it has hardened fully and is chemically inert), the two parts of the tank should be bonded back together using a bonding paste made using the same novalac VE which has been used for the chemical resistance layer. Subsequent to the bonding process, a small quantity of resin needs to be introduced into the tank and run around all the seams that have been bonded to seal any small pinholes.

Anyway thanks for the input and I know the odds of sealing this tank successfully are not exactly in my favor.

Its not a good ideal to use any type of epoxy "sealer" for this type of job, as these products are generally very brittle, and as GRP tends to move quite a lot through vibration and also contracts/expands due to heat when bikes are being used, cracking of epoxy type sealers is very likely to occur, which is the main reason to avoid using them in any composite tank, as failure will most certainly occur very soon after the "sealer" film has cracked.

T95 · Oct 11, 2011

bwolfie said:
Same as if you were replacing a fiberglass panel on a car, easy fix.

I know polyester resin is really forgiving. We see how I do with the vinyl ester!

T95 · Oct 11, 2011

hobot said:
After seeing how much boozed gas has been inside Wes's tiny fiber tank sealed with Caswell's for years now, I'm feeling pretty darn confident my IS tank and any one else's using Novalac will be just fine in the long run. Finishing the outside is actually the fun part and will turn out as if never injured. Might add a sight glass too.

Acetone with clean the insides of anything interfering with a bond but rough texture even better, just make sure any acetone is cooked out the surface and don't leave in but a few moments.

You know Hobot! The fact that you have had success with Caswells gives me hope! I think I have read a couple dozen post on this topic and know its a gamble. I thought the guys who were draining the tank after every ride were holding the secret to success until I looked inside my tank. You can open up the petcocks or even take them petcocks off and your still going to have an 1/8" of fuel laying in the tank.

T95 · Oct 11, 2011

debby said:
My experiences with two glass tanks, both of which had been coated, makes me tend to believe that carbonfibre's theory of the coatings cracking with vibration is indeed correct. In both cases, all was well for a couple of years, then bubbles appeared on the exterior surface of the tank - big bubbles on the tank that had been painted, small bubbles and raised areas on the tank that still had its original gelcoat finish. Neither tank leaks, neither has soft spots, the coatings in both tanks appear to still be in perfect condition, but the ethanol seems to be getting through somehow.

It's possible that there were voids in the coatings, because you can't really see inside the tank to tell if you're getting complete coverage, but with two coats of the Caswell product applied there shouldn't be any voids, I would think. It seems more likely to me that the coatings are cracking as he has suggested.

I think it's basically hopeless to expect a fiberglass tank to last more than a couple of seasons regardless of what you do to it. "Steel is real", as they say in the bicycle world :!:

my two cents,
Debby

Thanks Debby,

Who knows if the coating is cracking due to vibration or just loosing the bond. After looking into my tank and seeing that glossy surface and the ragged seaming I think voids in the coating and poor bonding could be a real widespread issue with slosh coating!

Anyway, by the time I get ready to put fuel in this thing Jeans test tank will have a couple of years of service.

Steel is real, but I like my light plastic bikes as well!

Gary

Carbonfibre · Oct 12, 2011

debby said:
My experiences with two glass tanks, both of which had been coated, makes me tend to believe that carbonfibre's theory of the coatings cracking with vibration is indeed correct. In both cases, all was well for a couple of years, then bubbles appeared on the exterior surface of the tank - big bubbles on the tank that had been painted, small bubbles and raised areas on the tank that still had its original gelcoat finish. Neither tank leaks, neither has soft spots, the coatings in both tanks appear to still be in perfect condition, but the ethanol seems to be getting through somehow.

It's possible that there were voids in the coatings, because you can't really see inside the tank to tell if you're getting complete coverage, but with two coats of the Caswell product applied there shouldn't be any voids, I would think. It seems more likely to me that the coatings are cracking as he has suggested.

I think it's basically hopeless to expect a fiberglass tank to last more than a couple of seasons regardless of what you do to it. "Steel is real", as they say in the bicycle world :!:

my two cents,
Debby

The fact that its pretty much impossible to ensure uniform film thickness when applying any type of epoxy "sealer" inside a tank, linked to the difficulty of properly preparing the interior surfaces to provide a good secondary bond, suggests that while epoxy "sealers" may provide something other than a short term solution in some cases, that failure is a distinct possibility over an extended period in most instances.

Use of anything which has little degree of flexibility as a slosh coat inside a composite tank, which does flex and vibrate in use, is a recipe for disaster, and the continued sales of these product (none of which has been properly tested or is supplied with any form of chemical resistance data), is due to the fact that there are very large profits to be made, and failure can easily be blamed on poor application, or any other nonsense that the sellers might dream up.

Carbonfibre · Oct 12, 2011

T95 said:
Ahh! Mr Carbonfiber,
I was waiting for you to pounce on my little project. I really do appreciate that you took the time to give me your opinions, but you need to work on your delivery, its a bit abrasive! I agree, you may be correct that the tank is irreparable, but it won't be due to a visible seam. Blending the seam is really the only part of this repair I am confident about!

I dont feel its of an awful lot of help to anyone who has a GRP tank to read a thread on here, which effectively details a very good way of destroying a moulding which was probably savable!

There have been other similar threads and again these are of no real help to anyone who owns a GRP tank and has concerns over Efuel corrosion.

Carbonfibre · Oct 12, 2011

T95 said:
debby said:

My experiences with two glass tanks, both of which had been coated, makes me tend to believe that carbonfibre's theory of the coatings cracking with vibration is indeed correct. In both cases, all was well for a couple of years, then bubbles appeared on the exterior surface of the tank - big bubbles on the tank that had been painted, small bubbles and raised areas on the tank that still had its original gelcoat finish. Neither tank leaks, neither has soft spots, the coatings in both tanks appear to still be in perfect condition, but the ethanol seems to be getting through somehow.

It's possible that there were voids in the coatings, because you can't really see inside the tank to tell if you're getting complete coverage, but with two coats of the Caswell product applied there shouldn't be any voids, I would think. It seems more likely to me that the coatings are cracking as he has suggested.

I think it's basically hopeless to expect a fiberglass tank to last more than a couple of seasons regardless of what you do to it. "Steel is real", as they say in the bicycle world :!:

my two cents,
Debby

Click to expand...

If you apply a chemical resistance layer as I have outlined, and are able to make sure this is applied properly to all interior surfaces, then your tank will be quite able to resist all commonly available pump fuels.

Thanks Debby,

Who knows if the coating is cracking due to vibration or just loosing the bond. After looking into my tank and seeing that glossy surface and the ragged seaming I think voids in the coating and poor bonding could be a real widespread issue with slosh coating!

Anyway, by the time I get ready to put fuel in this thing Jeans test tank will have a couple of years of service.

Steel is real, but I like my light plastic bikes as well!

Gary

Roadster Tank Rebuild / Slosh Coating Concerns

Similar threads