Sealing / filling balsa: Spot putty diluted with wood hardener

Hi folks,

I tried something new (to me) today. I took some Minwax Wood Hardener and put into it approximately the same volume of bondo spot putty. Stirred it around until uniform.

Using disposable brush (cheap foam kind) I brushed it onto several projects. Balsa fins, a balsa nose cone and transition, and some previously primed basswood that has since had some bevels sanded into it.

It soaked right in (typical for the hardener) and the high solids content seems to be on track to give me a nice smooth surface. I let it dry a while, put a heated fan on it later (after explosion risk gone), did a rough sand, and now it's drying in my basement before final sanding tomorrow.

I'll post results after I'm done sanding and priming...

Marc

I look forward to your results.I did not know the spot putty would dissolve in the min-wax ,must be a MEK base formula ?


Paul

Yeah, the suspensibility (?) of the putty solids was the big question in my mind. But with a popsicle stick stirring, it dispersed nice and uniformly, despite the 45 degree F weather.

I probably should have let it dry longer before attempting to sand it (about 2 hours total, including plain hanging out in a cold garage and then with warm air blowing on it). Parts of it were still soft then, but I checked it a little while ago (7 hours drying total time) and it's hardened up a bunch. By tomorrow should be fine for final sanding.

Some spots were a bit thin and might need a re-application.

Marc

Yes, I suspect the cooler temp. will slow down evaporation and drying time quite a bit.I find Bondo Spot putty dries almost too fast ,but great for spirals and such and dings in wood.

I use SIG sealer with talc powder (baby powder) and that stuff dries crazy fast.I can do 4 coats on fins in a half hour ,plus sanding between the last coat.

Pretty smelly stuff though ,I wear a respirator for this .I thin with lacquer thinner.

Paul

I finished sanding down the fins and stuff today. Now that the hardener/putty mix was thoroughly dry, it sanded like a dream. Very smooth results. A few spots still show some grain where I was too thin in the original application, but it was good enough to move on to priming.

Today was freakishly warm in Indianapolis (upper 50s) so I sprayed primer on a couple models (using hot water-warmed Rustoleum auto filler primer) and even got bold and sprayed a previously primed model with Rusto white gloss enamel. My garage was probably a couple degrees above outside ambient, but not much since the door had been open and remained partially open to vent fumes.

So far results look great. Will examine tomorrow. Expect extended drying/curing times due to cold weather moving in.

Marc

Do you think the mix would keep if it was stored in an airtight container?

If stored in glass with a suitable top, probably so. I mixed just enough for the job (got lucky!) but do plan to locate some moderate sized glass jars for this purpose.

Marc

Marc_G said:

If stored in glass with a suitable top, probably so. I mixed just enough for the job (got lucky!) but do plan to locate some moderate sized glass jars for this purpose.

Marc

Click to expand...

This is intriguing enough to try out on my current project.

Thanks for the tip.

OK, I brought in the primed articles. Frankly they look awesome to me!



There are a few places where a grain trough shows through, due to light coverage with the mix, but mostly it worked out just fine. Here are some pics:

Here's some Minwax Wood Hardener in a small bowl with some putty in it before mixing. Note, I added a bunch more putty after this shot was taken because my original mix was too thin.



Next, a shot of a scratch Der Big Red Max fin (originally was very grainy balsa) coated with the mix and dried a bit. Drying was out in the garage with a heat fan blowing after the pieces had mostly dried with the door open. You can see where I was a bit thin with the mix coverage.



Here's a shot of a mini version of the Fliskits Praetor that I made with basswood fins (primed with Rustoleum) then beveled. I mostly wanted to make sure the hardener/primer mix was OK with the rusto primer.

Like I said before, I did some rough sanding (220 grit) after a few hours of drying (including some heated air blowing), but at that time there were still some soft spots to gum up the paper.

By the next day, everything had hardened up nice and tight and sanded with the pleasant dusty feel resulting in very smooth surfaces (I used 320 grit, dry). The soft grainy balsa had really hardened up and was now pretty smooth.

Being unseasonably warm yesterday, I heated up some Rustoleum grey Filler Primer and hit my pieces with it. Here are pictures of how they look today:



Close ups of the DRM fins:





A little 320 grit sanding of the grey primer and these will be ready for topcoating.

In summary, I'm very pleased with the Wood Hardener / Putty mix. My usual process has been to spray the whole fin set (before taking out of the balsa panel) with primer, let dry, sand, repeat until smooth. But the wood hardiner/putty mix has some advantages:
-1 application should be enough.
-Hardens the fins more than the plain putty due to penetration by the hardener
-Can be done in the cold

I'd be interested to hear others' experiences with such mixes.

Marc

Marc

I went out today to get the material to try this. I went to Lowes first. They had neither the spot putty nor the wood hardener although they are a Minwax dealer.

Next step was to Advanced Auto parts where I got the putty.

I remembered seeing the Minwax wood hardener at Sunset Ridge Hardware and went there to find them closed for New Year's Day.

I then went to the duplex where I used to have my shop to pick up some supplies and found I had lost my keys to the place. I last remembered seeing them at Lowes.

Back to Lowes and I found nothing but then remembered the Auto Parts place across the hiway. I went over there and they had nothing.

I sadly went back to the duplex I've spent most of the last month fixing up and started trying to remove a door. I got it off the hinges and splintered some wook when my phone rang. It was the auto parts place. Had I lost some keys?

Back to the Auto Zone and I got my keys. I put the door back and used up a lot of my new tube of putty fixing the cracks I had made.

Now I need a nap. This rocketry stuff is exhausting.


BTW, Mark, how did you apply the goop? I thought I had read something about those disposable sponge brushes but looking back I see no mention of them.

Sorry about the run-around you went through today! Wow, that's exhausting. But at least you got your keys back.

I used an el cheapo foam brush to apply it. Applied a "first coat" with a brush very wet with the mix, just slathered it on. It soaked RIGHT in. But the time I was done with my several pieces, the first was "dry" (as in, not wet, but of course not fully dry). I went over the pieces a second time with a less fully loaded brush, trying mostly to smooth things out. I learned as I went, which explains some of the early thin coatings.

About finding the stuff: I got mine at Lowes and have seen the same thing at HD and Menards. However, you have to look REALLY CAREFULLY to find it. It's usually (in all three of my local stores) hidden between two other things that have similar color schemes and camoflauge it. Look for the round can; it's the most distincitive attribute. And it's usually not fully stocked, so you have to look toward the back of the row it's in. Frequently they'll put some other product in front of it to make the shelves look less empty so at times I've had to read tags to find it.

IF you can find the lone wood expert at the store, he (or she!) can help you find it.

Marc

The results look very impressive ,and will have to be tried.I have the putty just need to find the hardener (hope they sell it in Canada)

Bonus tip !!


Paul

Marc_G said:

I used an el cheapo foam brush to apply it.

Click to expand...

Hey, I resemble that remark.

Sorry, didn't mean to step on any trademarks! :wink:

I'll suggest folks use a "cheapie" foam brush instead!

Very well. As a result of your graciously recanted statement, I'll call off the dogs.

I picked up a can of the Minwax wood hardener between services today.

If I can find the energy, I may try it tonight.

I mixed a batch and applied it to my FSI Intrepid. So far I like it and will check things out tomorrow.

I sanded the results today and I must say I like them better than anything I have tried thus far.

I have the leftover sealed in a jar my wife let me have. It has a Korean label on it and I can honestly say that the jar has found the aroma to be a pleasant change for the better.

I am trying to think what I want to call this stuff so I can label it and prevent my wife from trying to serve it.

Marc's elixir?
le goop Marquesse?
Better than Kimchi?
Red Paste of Perfection?
Da Stuff?

BTW, the parts I used it on were basswood. I will be interested to see how much it will harden real balsa.

Glad to hear it seems to do well for you on your first try.

I was pleased with its performance on a fairly grainy balsa fin set. They are definitely harder than "plain balsa with putty smeared on them" but they are not as hard as "plain balsa soaked in CA and allowed to cure fully." Then again, just try sanding the CA soaked fins! That takes work...

For Balsa, I recommend one application, let sit until surface dry (probably just 10 mins or so) then apply another coat on top. Then let fully dry & sand (or let partially dry, rough sand, fully dry, finish sand).

As far as the name, while I'm the first to post (at least recently) this combination, I doubt I invented it. And if I did, it's just because I listened to others here on the forum and put my own twist on it.

I suggest the name: Teamwork Filler
The putty and hardener team up, just like the community here is a team.

Marc

Marc_G said:

Glad to hear it seems to do well for you on your first try.

I was pleased with its performance on a fairly grainy balsa fin set. They are definitely harder than "plain balsa with putty smeared on them" but they are not as hard as "plain balsa soaked in CA and allowed to cure fully." Then again, just try sanding the CA soaked fins! That takes work...

For Balsa, I recommend one application, let sit until surface dry (probably just 10 mins or so) then apply another coat on top. Then let fully dry & sand (or let partially dry, rough sand, fully dry, finish sand).

As far as the name, while I'm the first to post (at least recently) this combination, I doubt I invented it. And if I did, it's just because I listened to others here on the forum and put my own twist on it.

I suggest the name: Teamwork Filler
The putty and hardener team up, just like the community here is a team.

Marc

Click to expand...

Much too modest for your own good.

Teamwork filler it is.

Marc_G said:

Glad to hear it seems to do well for you on your first try.

I was pleased with its performance on a fairly grainy balsa fin set. They are definitely harder than "plain balsa with putty smeared on them" but they are not as hard as "plain balsa soaked in CA and allowed to cure fully." Then again, just try sanding the CA soaked fins! That takes work...

For Balsa, I recommend one application, let sit until surface dry (probably just 10 mins or so) then apply another coat on top. Then let fully dry & sand (or let partially dry, rough sand, fully dry, finish sand).

As far as the name, while I'm the first to post (at least recently) this combination, I doubt I invented it. And if I did, it's just because I listened to others here on the forum and put my own twist on it.

I suggest the name: Teamwork Filler
The putty and hardener team up, just like the community here is a team.

Marc

Click to expand...

Have you thought about applying this to the plain balsa in the sheet (either laser/die cut or just plain sheet)?

How hard would it be to cut with an Xacto?

If you get a chance to test it, let me know.

Thanks.

Cheers,
Jon

I plan to do this on a full sheet next time I open up a kit with a fin sheet. It wouldn't be too hard to cut. "Wood hardener" is a relative term. It doesn't make it very hard.

I might also do a full or partial sheet of stock balsa. I've done this before using the "filler primer" method (spray, sand, spray, sand) with good results. This "teamwork filler" would probably just cut the process down to one application.

Because I'm quite lazy, I usually use a palm vibrating sander when I do full sheets. Makes it easy to get very uniform results.

Marc

This all sounds very good.I shall have to try this on my next Estes project (Alien Invader)

Thanks


paul

The results of my experiment with this stuff can be seen here: https://www.rocketryforum.com/showthread.php?p=158416#post158416

Fabulous to work with. Just tried it today. Thanks for the tip!! :clap: