TOPIC SPLIT Was: 1970 s2 0453R Reassembly - Now: Fiberglass Repairs

[dakazman]

Sadly Started repairing the blisters that popped up in paint. Just as it states in the lotus manual,  cut out and fill in , repaint. This still holds true . Here are some pictures that document the fix.
Dakazman

[Certified Lotus]

Bummer! So the big question is how do you prevent that from happening?

[surfguitar58]

That's a drag. I doubt it was a problem in your prep work, I can't imagine a more thorough job that you did. My friends who paint boats with Awlgrip are anal about humidity and dryers on their compressed air lines. Failure to do so causes blisters, they say. And you do live in ultra-humid Florida. Hopefully you can blend-in the repairs. What kind of paint are you using?

[dakazman]

These were all fractures deep into the glass and not blisters caused by contaminants. They were all slowly picked open and inspected , then grinded out with a dremmel . Then refilled with glass matting cut up and mixed with resin.
 I'm using a base black g9900 and a clear so it is easy to match.
Dakazman

[gideon]

From personal experience and everything I have read about fibreglass repair I would not choose polyester resin for repairs or alterations to existing polyester resin fibreglass. Always epoxy because epoxy sticks to polyester much better than polyester sticks to polyester.  I don't know if this has anything to do with your bubbles, but I think it's worth saying anyway. 

[gideon]

I wanted to dig up a reference to back up my assertion about epoxy being a better choice than polyester resin.  This is from the manufacturers of the most well known brand of epoxy resin in the boat building/repair market.

https://epoxyworks.com/index.php/west-system-epoxy-vs-polyester-for-fiberglass-boat-repair/

I trust what they say.

[dakazman]

That’s all true.

Still sometimes you want the flexibility that the polyester gives . The examples I can only give we’re done 18 years ago , have about 400, 000 miles on it and still no hairline cracks .a full glass nose installed removing the factory neoprene bumper and side skirts molded into the entire lower section and up the forward side of the rear wheelwell. Boats are a different animal and probably need the higher bonding adheasion . These blisters were in an unrepaired area and I see no reason to use a higher cost product for such a small repair .
Dakazman

[gideon]

Actually, epoxy resin is more flexible than polyester - from the west system article. "epoxy offers 3.5% to 4.5% tensile elongation at failure compared to 1% to 2% for typical polyester resins".  Epoxy also shrinks less on curing.

I completely understand that if you already have some polyester resin, and it's a small repair, then you're not going to rush out and spend money on a more expensive product.   And, yes, polyester fibreglass lasts incredibly well.  And, yes cars aren't quite the same as boats.  But that all being said, epoxy is still a better choice than then polyester for fibreglass repairs.  I know from past experience that it is much easier to get a strong mechanical bond with an epoxy resin like west system, than with polyester resin.  The additional cost of the resin is typically small compared to the time and effort involved in making a repair, which is why I use it.  Though, it does help that I already have some in stock for boat repairs .

For small repairs, there is an inexpensive repair kit they sell with resin sachets, fillers and some other useful bits and pieces.  Here's one source

http://www.fawcettboat.com/pc_product_detail.asp?key=DA21D3FB9D4044F4A70CD347F973AD66

I'm only saying this now because I really think it is good advice, supported by a lot of practical experience, and I would like to pass it on.  I'm sure your repairs will be fine, but maybe for somebody else it will pay to use epoxy resin instead .

[dakazman]

Very well stated, Gideon!
You learn something new every day , which I have.
Dakazman

[GavinT]

G’day, dakazman,

I don’t know if you’ve tried it but there’s a commonly available product colloquially known as “kitty hair” . . brilliant stuff for those little annoying repairs.
It consists of fine fibreglass strands mixed with a polyester base with a similar constancy to common polyester body filler and uses the same catalyst paste.

FWIW, the method I’ve used is to dab in the required amount, cover it with cling wrap and give it a quick roll using a wallpaper seam roller.
Wait till it goes cheesy, then, using a sharp blade, slice off anything proud of your masking tape.

Hope that helps, & cheers,
Gavin

[GavinT]

[...] because epoxy sticks to polyester much better than polyester sticks to polyester.[...]

True enough . . . polyester doesn't stick to epoxy brilliantly.

This is probably not a big issue either way, but with say, potential future repairs I wouldn't want to confront sheathing an engine cover (for example) with tissue using polyester resin and find out months later that it's delaminating due to sub-optimal adhesion and being out in the hot sun.

More grist for the mill . .

[dakazman]

Thanks GavinT
Just a little stuck in my car ways a bit but open to new ideas.
The VHS tape may give it away a bit but this is as my bible.
I did like your repair method and use it on repairs not depending on gravity. ( overhead)
Lol. Tape in place , roll ..  and let sit.

[GavinT]

The VHS tape may give it away [...]

It does . . you've lost it.
I'm kidding . . 

Then again, I might confess to using my fathers wood chisels from the 1920's!

[dakazman]

GavinT , it was painful to watch 25 years ago , the worst thing is I transferred them to DVD .
I can send you a personal copy 😀😩.

Btw , how does density of the epoxy mix compare with polyester?

Dakazman 

[dakazman]

This is from fibreglast.com a development company.


Selecting Resin
Resin selection is based on fabric compatibility, service conditions, and the desired characteristics of the finished part. There are two common types of thermosetting resin to choose from: epoxy and polyester. Moldmaking, molding, laminating, and casting operations can be performed with either system. Epoxy is the higher performance and higher priced system. It is used in weight critical, high strength, and dimensionally accurate applications. Polyester resins are less expensive, offer more corrosion resistance, and are more forgiving than epoxies. For this reason, they are the most widely used.

Vinyl ester is a third resin option, often described as a cross between epoxy and polyester resins, as it falls between them in price and handling characteristics. It offers excellent corrosion and abrasion resistance, so it is well suited for applications like chemical storage tanks.

Certain resins are not compatible with all fabrics. For instance, Kevlar® often exhibits adhesion problems, so epoxy or the highest grade polyester should be used. Also, fiberglass mats have a polyester soluble binder. Epoxies can dissolve this, and should never be used with mat. Check material compatibility thoroughly when designing.
 
I believe these cars are polyester base matting . That is also why I chose polyester resin.

Dakazman