Sanding between layers with Bondo resin?

[vandy21]

So from what I understand, there are two different types of polyester resin. Type A (requires no sanding) and Type B (requires sanding). Is this correct? if so, what is Bondo's resin? I think I read that it is type B, but i'm not sure. I'm trying to avoid sanding. This is the stuff I'm talking about.

Thanks, Vandy

 

[danond]

Re: Sanding between layers with Bondo resin?

Put down two layers while it's still wet. Saves sanding anything altogether and results in a faster cure and better adhesion.

I'm also going to suggest you use Epoxy from US Composites. That bondo stuff isn't fun to work with.

 

[Mark42]

Re: Sanding between layers with Bondo resin?

I just went through a few quarts of Bondo resin working on my hard top window frames. Depending on what you plan on using the resin for, Bondo may or may not be a good choice. Bondo has a short work time, maybe 10 minutes tops, even less if you work from a cup with a brush (pouring it out and spreading gives a little more work time because it doesn't heat up as fast as sitting in a cup). And its thick, so it has good build up, and acetone thins it if you need it thinner. It is also a waxed resin, so it dries without being sticky. And it does need sanding and/or washing with acetone between coats.

So, mall repairs, small projects, Bondo is good. Large areas, and the setup time may be too fast.

If you want more work time (like doing a new deck), buy a laminating resin and hardener that will not set so fast.

 

[vandy21]

Re: Sanding between layers with Bondo resin?

Thanks a lot. I'm be using it for stringers/transom/deck, so it sounds like a laminating resin? I was just wondering about the bondo because I can buy it locally and save on shipping, but I'd rather have the right tool for the job than the more convenient one.

 

[Mark42]

Re: Sanding between layers with Bondo resin?

For what you are doing, you should buy some laminating resin and some wax additive for the last coat so it dries without being sticky. The hotter it is outside, the quicker it will set. Longer time is better than too short.

 

[Truefire]

Re: Sanding between layers with Bondo resin?

For what you are doing, you should buy some laminating resin and some wax additive for the last coat so it dries without being sticky. The hotter it is outside, the quicker it will set. Longer time is better than too short.

IN reference to this "wax additive", what exactly is it per se?

• Does it come in different grades
• Are there differing grades of this wax additive
• Can you typically utilize any grade/brand with laminating resins
• Are there certain laminating resins to steer clear of

I have the same project, i am reworking my stringers in my boat, 17' lengths to be precise, so setup time would certainly be a factor for me as well.

Thanks for any advise - input,
Chris

 

[danond]

Re: Sanding between layers with Bondo resin?

Guys just go to uscomposites.com and buy the thin or "laminating" epoxy resin with a hardener that's appropriate to your temperature. You can't go wrong with the quick hardener if you're living in sub 80 degree temps. It doesn't start setting for about 30 mins in 50 degree temps. Lots of time to work.

If you're doing stringers/sole you're going to need at least 3 gallons to start with, more once you figure out how much you're using and get a feel for what you're going to need.

You can skip the wax thing in the last step if you wish. I would skip it. The "sticky" stuff is just the epoxy doing something called blushing. It gets a film on it that won't take paint very well - you have to wipe it off with acetone or something similar, then sand. No big deal.

 

[erikgreen]

Re: Sanding between layers with Bondo resin?

Hmm.

The Bondo resin is a laminating resin with a wax additive. If the wax wasn't there, it wouldn't harden at all unless covered with plastic or something else to prevent air from getting to it.

It's an ok resin, not great stuff, and in fact not the cheapest out there. The thing is, it's typically pretty high quality poly resin so it has a good shelf life.. the purer the resin the longer it lasts on the shelf. Plus it's available everywhere.

Note that you probably shouldn't use the Bondo body putty on a boat except in limited circumstances because it will not last in any extremely wet use.

It's ordinary poly resin though, so you should either work wet on wet (preferable) or else sand between layers.

The US Composites epoxy 638 is nice stuff though... if you use the medium or slow hardeners they're non blushing, and I typically don't get blushing even with the fast stuff. Plus the work time is, as stated, rather long, much longer than the comparable west system resins.

If you really want poly, US Composites sells that, too, and it'll have a longer working time than the bondo stuff.

Erik

 

[Mark42]

Re: Sanding between layers with Bondo resin?

IN reference to this "wax additive", what exactly is it per se?

• Does it come in different grades
• Are there differing grades of this wax additive
• Can you typically utilize any grade/brand with laminating resins
• Are there certain laminating resins to steer clear of

I have the same project, i am reworking my stringers in my boat, 17' lengths to be precise, so setup time would certainly be a factor for me as well.

Thanks for any advise - input,
Chris

When working with polyester resin, typically laminating resin does not contain wax that makes it cure with a non-tacky surface because you want to add another layer right on top. When all work is done, the last layer you want to dry non-tacky, so a wax additive is added to the mix and it makes the poly dry non-tacky.

Not to be confused with anime blush from epoxy resin, its something totally different.

Any shop that sells laminating polyester resin will sell the wax. I don't think there is much in the way of good and bad grades.

The only polyester resin I read multiple people complain about was Elmers brand (the glue people). That's the stuff sold in Home Depot.

If you don't want to do wax, you can always brush or roll on a layer or two of gel coat or finishing resin. Finishing resin has wax in it. Gel coat would look nice in the bilge.

 

[vandy21]

Re: Sanding between layers with Bondo resin?

so, I was checking out US Composites, and I found what I think I want. 435 Standard Polyester Layup Resin. Does these seem like it will work for my needs? Thanks guys, I appreciate all of this advice. I'm new to all this, but I'm learning.

 

[erikgreen]

Re: Sanding between layers with Bondo resin?

That should work just fine.

FYI, it's unwaxed (you can get surfacing wax at the same place).

Or, the resin will actually harden if covered with plastic or sprayed with PVA (polyvinyl alcohol, a mold release agent) which you can get at the same place.

The wax or whatever just keeps the air off of it.

Erik