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

[GavinT]

G'day dakazman,

Reckon I'll have to stumble along without a VHS tape, but thanks for the thought. 

Not sure what you're driving at re "density of the epoxy mix compare with polyester" ?

The point you make about chopped strand mat is a fair one. They're all lightly pre-impregnated with polyester resin and unsuitable for Epoxy. Also, it's best to avoid woven cloth on surfaces that are going to have a finish painted surface. The cloth weave will print through and become visible under the paint. Ask me how I know. Oooops . .

[dakazman]

Yes the cloth weave is patio furniture quality.

Not to rehash epoxy over polyester ... we agree epoxy is better.
However,
The first patent for epoxy resin brought to market date 1984 .
Our cars are 60-70 ish . How we’re all those cars repaired?
Dakazman

[EuropaTC]

I believe these cars are polyester base matting . That is also why I chose polyester resin.

Yep, I couldn't see them being anything other than polyester resin, and probably cheap ones knowing Lotus 

Personally I'd stick with polyester resin as well. I remember being told that epoxies were "better" in that they had less shrinkage and therefore held out better on repairs, but I'm not totally convinced it's an essential feature.  I don't get much in the way of sinkage on the repairs I've done using plain polyesters.  When you think of the usual stresses on bodywork over mileage and the thermal expansion/contraction you get from +30C to -20C then I think I'd prefer that all the resin has exactly the same properties.

But  if you're building a race car and want to have bodywork 1/16" thick or want to use carbon fibre then yes, I can see the value in selecting a different resin.   

[gideon]

Epoxy dissolves the binder used in chopped strand mat, so you'd have a problem if you tried using epoxy with fresh chopped strand mat.  It's not a problem any more once the original mat is set in resin. 

Two arguments against epoxy for repairs that hold up are 1) price and 2) polyester doesn't stick well to epoxy.  So, if you think you might want to use polyester in the future then avoid epoxy.  Personally, I plan to always use epoxy. 

The comment about corrosion resistance from Fibreglast.com is a little puzzling.  I was not aware of lack of corrosion problems with epoxy, but I guess it depends what chemicals we're talking about.  I found these tables of corrosion resistance, which unfortunately aren't easy to compare

https://www.engineeringtoolbox.com/chemical-resistance-epoxy-d_786.html

https://www.engineeringtoolbox.com/chemical-resistance-polyester-d_784.html

Luckily, and this is important, I have learnt that both epoxy and polyester are resistant to beer.

[gideon]

UV resistance, that's the other thing.  Epoxies need to be protected from UV light.  Polyester resins are much more UV resistant.

[dakazman]

 Beer good😜
Even with we car and rear view camera she still backs into a pole.
More bodywork for me😓😢
Dakazman

[surfguitar58]

More bodywork for me
Dakazman

Practice makes perfect! (Practice on the Honda, save the perfect for the Lotus)

[dakazman]

At this point  yep
At a breaking point . Four daughters are killing me😀lol
All princesses.
Dakazman

[Certified Lotus]

Four Daughters....... you are a saint!

[GavinT]

Two arguments against epoxy for repairs that hold up are 1) price and 2) polyester doesn't stick well to epoxy.  So, if you think you might want to use polyester in the future then avoid epoxy.

Yes, but there's also arguments that are more to do with what's practical.

If epoxy is chosen as the preferred resin, then one is comitted to adopt an epoxy based system thereafter due to the polyester -> epoxy adhesion issues.

For example, one would be precluded from using the commonly available chopped strand mats.
One would also need to use an epoxy based filler to replace the typical polyester based 'Bondo' or the like.
And as mentioned previously, future repairs would likely be problematic.
Unless you know all the epoxy repaired areas going in, it's a crap shoot. You can't visually determine which areas are epoxy and which aren't.

IMHO, it's not so much the narrow question of which resin is "better", but more the wider perspective of what's most suited.
There's a plethora of chopped strand mats, fillers, fine skim fillers and spray polyester fillers all aimed at a polyester based repair for the automotive industry. It's all a well trodden path, and compared to epoxy based systems, far cheaper.

I'd have to see something very compelling to ditch that well worn path, I reckon.

[gideon]

Gavin,

I had experience long ago (I'm talking late '80s) of poor adhesion from polyester resin while repairing a boat.  Likely my technique, preparation, etc. wasn't quite right.  Since then I've used epoxy resins and very rarely had adhesion problems.  You can get a good bond with polyester, but my batting average is higher with epoxy.

I choose woven or knitted cloth over chopped strand mat.  Longer fibres make a stronger composite.

You don't necessarily need a lot of different products. You can mix additives into the epoxy for different purposes.  Microballoons for a lightweight, sandable mix.  Silica thickener for a dense, hard, non-slumping mix.  Milled glass or carbon fibres for tensile strength, etc.

But, to each his own.  I have my preferences, you have yours.  So be it.

[GavinT]

G'day gideon,

My apologies if that last post came across as combative. It wasn't intended to be but can see now that it might be interpreted that way.

And certainly, our own experience tends to guide our thinking . . as well it should, so no harm and no foul as far as I'm concerned.

That said, I'm curious as to the materials you intend to use. My experience with woven cloth (even the really fine stuff) is that the weave pattern just prints through and is visible under the paint.

And for what it's worth, I'll add that adhesion problems are not unknown in an all polyester repair, either. I expect we've all seen them.
It's important to remember that polyester lay-up resin contains wax. During the curing process, that wax floats to the top of the laminate but is essentially invisible.

To put a further layer of polyester resin over that lay-up without abrading the the top layer (to remove the wax) is inviting a de-lamination.

As an aside, I've toyed with the idea of making a windscreen surround to convert the Type 54 into the Type 65 for the purpose of adopting the much neater bonding in of the windscreen.
My intention would be to make the surround using polyester resin as a separate piece and use epoxy to glue it in.
Epoxy would be far more appropriate for the gluing, I reckon.

Cheers,
Gavin

[buzzer]

Quite a busy thread here on resins. Put in my pennyworth from experience.
1) Epoxy is much more difficult to work and hates tight bends, if you don't believe me try before you use.
2) Epoxy is stronger, more expensive, takes longer to go off, and bonds well to polyester
3) Polyester will not bond well to Epoxy, bondo etc are all polyester based so will not bond well to Epoxy.
4) Polyester will bond well enough to existing polyester if properly prepared for repairs so why use Epoxy

On blistering. the top layer of any exterior repair that should be painted should be tissued with resin to provide a top protective layer that seals off any glass fibres, to in effect replace the gel coat. Open fibres will absorb water by capillary action, so keeping the exposed body dry is important.

[dakazman]

Thanks buzzer, that pretty much sums it up!

Now , today marks a milestone that all my tools are under one roof.
40 years in the airline industry are over. Not retired yet but being pushed in that direction.

Dakazman

[surfguitar58]

One more nail in the coffin of this resin business: I have been told, by people who work with fiberglass a lot and at least SOUND like the know what they are talking about, that a polyester/polyester bond is greatly improved by not only mechanically roughing up the mating surfaces (sanding) but also by "reactivating" the polyester by wiping down with styrene solvent, and NOT acetone. (Acetone will weaken the bond, or so I'm told.) https://www.jamestowndistributors.com/userportal/show_product.do?pid=57891

In fact, this company is very knowledgeable about all things fiberglass/composite and has just about every kind of resin, solvent, filler and reinforcement you can imagine (and no, I'm not on their payroll, just found them easy to work with).