A Bit More Progress

[fletcherson]

It's a great thing. The adhesion and gap filling properties are second to none. I'm convinced that it's even better than epoxy for attaching fiberglass, wood or prepped metal. Epoxies can be too hard and brittle while polyurethane body fillers stay more flexible. I've had spills of both where it got on an area it shouldn't be. The epoxy will chisel off, body filler has to be ground off.

Something I do nearly every time I mix body filler is add polyurethane resin. It makes it spread like creamy butter and aids in even better adhesion. Sometimes I leave it thicker, sometimes super runny.

That purple liquid settled at the top of a new can of Bondo is simply polyurethane resin. And the tube of cream hardener is just a paste form of MEKP.

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I keep a squeeze bottle with resin ready to go.

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I do the same.

 

[rubicon]

Thanks Chopp. That's a good thing to know.

 

[guilld]

Chop could you send a link to where you purchase. Also are you mixing two parts. The bottle you show would it not harden up if two parts. (I am a rookie)

 

[choppinczech]

For making these mold plugs I buy the cheapest Bondo brand filler and fiberglass resin from Home Depot. I use a lot of it.



Or there's USC brand Feather-Rite which is cheap. And most local body shop supply places have their own "house" body filler around $13-$16 per gallon.



I know there's lots of specialty body fillers out there like Evercoat Rage, Z-Grip, USC All-Metal and they have their purposes. But it's a lot like tire manufacturers where it's basically the same thing with lots of fancy marketing and packaging. Some of those fillers are $100 a can.

I'm just a novice but I haven't noticed any difference in the cheap stuff and the expensive stuff. Other than pretty can graphics and cool filler colors.

The squeeze bottle with resin is just a more convenient way of pouring it. There's no catalyst in it. I'm just thinning out the body filler from the can to make it spread and stick better.

 

[Indycars]

I'm just a novice but I haven't noticed any .....

If you are a novice, then I would love to see what an expert can do !

 

[choppinczech]

These are the same thing in different forms.


So thin the Bondo with fiberglass resin to your needs and mix in the red hardener as normal. It'll spread much better.

 

[guilld]

Any thoughts on the best way to make a inside radius when mating fiberglass to wood where you would normally have a 90 degree joint

 

[choppinczech]

Sure. Those are called fillets. Donny Ray and I were going over those just a while ago.

For wood ribbing that'll be glassed over, Bondo works great for both gluing it in place and for the fillets. Rounded top corners will save you headaches too.


The more you mask off where you don't want the Bondo, the happier you'll be later. Because it can get messy.

Remove the masking tape when the Bondo is about half set up.


There's lots of ways to get the Bondo into the corner. ZipLock bags with the corner snipped off works well. Like a disposable grout bag. As for the concave shape, anything with a circular end to it. I get the best control from hot gluing a fender washer to a dowel. I can maneuver it the easiest. And clean it off with acetone.

 

[Island Girl]

I see the term polyurethane resin being used for what I expected would have been polyester resin.

Is this just a miss use of the term polyurethane, or is there really polyurethane resin that uses the same hardener, MEKP, as polyester resin and bondo?

 

[choppinczech]

Yes, polyester. Sorry for the mix up.

 

[fletcherson]

Yes, polyester. Sorry for the mix up.

I have used a lot of body putty over the years and there are differences. Basically in how it spreads. Higher priced stuff is usually easier to spread. Personally, I think the cheap stuff is fine but I try to buy it from supply houses that sell a lot of it so it is fresh. It tends to dry out and become less workable and stiff as it ages. Blending resin into it helps.

 

[old round fart]

There is an additive to thin bindi out but I can’t remember what it is. Something like polymer maybe?

 

[choppinczech]

Or, you can thin the whole can if you want.

Thinning Bondo: How it Works | Classic Car Restoration Club

 

[choppinczech]

There is an additive to thin bindi out but I can’t remember what it is. Something like polymer maybe?

Maybe styrene?

But that's already in the fiberglass resin.

 

[DonnyRay]

I just learned something today. Polyester resin as a bondo thinner.

 

[choppinczech]

 

[Flyer]

Bondo is basically a mixture of polyester resin and ground plexiglass (Poly-Methyl-Methacrylate) . If you want to thin the stuff out, add acetone, the solvent for plexiglass. To make it easier to sand, add micro-balloons, available from model airplane type hobby shops or Aircraft Spruce & Specialties. Micro-balloons make bondo stiffer, so add a small amount of acetone to make it easier to spread.

 

[choppinczech]

I finally got these pieces laid up. Prepping the glass is time consuming but makes the lay up much smoother.



They're made up with a surface veil against the gel coat, chopped glass fillets, three layers of 1 1/2 oz. mat, 2mm Coremat, and another three layers of mat. It makes the part lightweight and very stiff.






I'll get them fully trimmed and epoxied in this week. I've got some days off coming up this week.

 

[fletcherson]

Incredibly labor intensive. Nice work.

 

[choppinczech]

I want to send just one cable from my parking brake to rear and run the cables 90° straight down the rear end tubes.

Are any of you aware of an OEM part that will do this?

I could make my own bell crank but I'd like to use something already engineered.