3M High Strength Small Hole Repair for wood filler

[SolarYellow]

https://www.3m.com/3M/en_US/p/d/cbgnawus1398/

Saw this product recommended on this site some time ago and bought a tub. I used it for the first time last night on a balsa fin. Thinned it some with water to make it brushable. The first side swelled and warped the fin badly. The second side unwarped it a little bit, but not enough. I clamped it between a couple chunks of plywood with a few layers of newsprint over the fin in a bench vise overnight and it seems to have dried nice and straight. But I'd like to not have to do that again.

Is anyone else using this? Do you thin it before brushing it on fins?

I've previously used the DAP Plastic Wood filler and thinned it without significant warping problems:

https://www.homedepot.com/p/DAP-Pla...l-Paintable-Latex-Wood-Filler-00581/206667339

 

[bjphoenix]

I use the Elmers Carpenters Wood Filler, thin it with a few drops of water so I can brush it on, and I put it on both sides of the fin at the same time. I've done it that way on 2 rockets with the fins glued to the tubes already and had no problems with warping. If you do it on a bare fin you run the risk of the fin warping, if you try clamping the fin between 2 flat surfaces then how does the filler dry? Maybe you could clamp the fin between some thin pieces of wood so most of the fin area isn't blocked.

 

[Hobie1dog]

I didn't have very good luck with it and once I thinned it down a little bit, but I opened the tub back up and it had already started to harden, so I quit using it.

 

[bad_idea]

Saw this product recommended on this site some time ago and bought a tub.

Same here.

I used this for the first time today and was very disappointed. It was already pretty dry and only gave the coverage I needed when it was caked on thickly. Hoping it sands as well as people say, because I have tons to remove.

Did anyone ever go back and try thinning it with something other than water?

 

[bad_idea]

I used this for the first time today and was very disappointed.

I should have said "I applied this for the first time." Sanded it for the first time today. Have to admit that it sands beautifully, far easier than the tub of Elmer's Carpenters' Wood Filler I've had for years and have used on many rockets before. Not sure the ease of sanding is worth the mess of applying, and I'm still bothered that I probably won't be able to thin it.

Have yet to try DAP. Based on other reviews here, Timbermate may be the next I try.

 

[SolarYellow]

I picked up a jar of Timbermate. It's sitting on the bench waiting for a future build. Lowest shipped price I could find for an 8-oz jar to try was here:

https://www.rokhardware.com/searchanise/result/?q=timbermate

Once you commit and want the larger container, Amazon is the best deal.

I did use the 3M again on some spirals. Thinned slightly and rubbed it into them with a gloved finger to be sure it was worked into the corners. Sanded off pretty easily. Haven't primed yet, for a long story explaining a chain of dependencies that nobody wants to read.

 

[WizardOfBoz]

Any water-based fillers would seem likely to warp dried wood. Especially balsa, with its porosity.

Is the goal to fill the wood grain, or actually make a structural repair? For filling holes and wood grain and tube spirals I got a suggestion on this site to use red glazing compound. It's like lightweight bondo, but its one part (no mixing) and air cures and is not water based. At first I used the Bondo brand and it worked great, but later I got some 3M Acryl White. The white may be a little harder to sand but it also makes it easier to get a white primer coat to cover. You avoid perhaps one primer coat.

 

[Back_at_it]

Anytime you add any water based products to wood you are risking warping. At the very least, primer over the parts then add your fillers on top of that. If you're looking to repair holes or other damage, you're far better off filling those in with epoxy then sanding and finishing. The epoxy will soak into the surrounding materials making them stronger than they were before the repair.

 

[WizardOfBoz]

... to repair holes or other damage, you're far better off filling those in with epoxy then sanding and finishing. The epoxy will soak into the surrounding materials making them stronger than they were before the repair.

Agree that water based stuff will warp wood, and that epoxy will fill in holes and won't warp, but sanding epoxy is one of my least favorite things. Yeah, it's plastic but its harder than the hubs of hell. That's why I like the glazing compound (red or white). It's specifically designed to fill holes smoothly, and to be sanded and painted over.

But the strength point is well taken. And one could epoxy paper to the fin to give even more strength and stiffness, and this to some extent eliminates having to sand...

 

[SolarYellow]

All fillers and all primers add weight, sometimes a surprising amount. One of my objectives is to minimize weight in LPR rockets. Build with a gram scale, and don't stop gram scaling when you start painting.

 

[tlainhart]

I picked up a jar of Timbermate. It's sitting on the bench waiting for a future build.

Curious as to how it works out for you. I tried it on my last build and think that I prefer CWF. Could be that practice is needed.

 

[neil_w]

Label papering avoids all these issues, and you get some extra strength as a bonus. It's not perfect but I find it *so* much preferable to CWF for fins (I still use CWF for spiral filling, and occasional pieces that are impractical to paper for whatever reason, like dowels, and other balsa pieces like nose cones and transition).

Just sayin'.

 

[bad_idea]

I am using this stuff to fill and fair uneven fiberglass, so I have no concerns about water, and I also sadly can't use label paper. I will try thinning with water next time I use it, especially if it's dried out more by then.

 

[SolarYellow]

I would use phenolic microballoons for that.

 

[WizardOfBoz]

All fillers and all primers add weight, sometimes a surprising amount. One of my objectives is to minimize weight in LPR rockets. Build with a gram scale, and don't stop gram scaling when you start painting.

There's weight and then there's drag. Both are important. But in fact, sometimes a little weight gives you inertia for higher flights. So I like a smooth finish. But if there's one thing about this hobby, its that different people have very different interests and opinions. Uber-light is a design goal and a challenging one. For lightening a fill using epoxy onne can do as you say:

I would use phenolic microballoons for that.

I use colloidal silica to give me better viscosity for fillets. I think silica gives better strength, but balloons are ligher and more easily sanded.

Label papering avoids all these issues, and you get some extra strength as a bonus. It's not perfect but I find it *so* much preferable to CWF for fins (I still use CWF for spiral filling, and occasional pieces that are impractical to paper for whatever reason, like dowels, and other balsa pieces like nose cones and transition).

Just sayin'.

I think that Neil has made a lot of rockets with techniques like using PSA or label paper! I agree, I didn't like CWF when I used it (got too dry, too quick, and didnt sand easily). I much prefer the red and white glazing compounds.

I am using this stuff to fill and fair uneven fiberglass, so I have no concerns about water, and I also sadly can't use label paper. I will try thinning with water next time I use it,

My experience with glazing putties to smooth out rough (due to silica) fillets has been terrific. A revalation for me, at least.

 

[SolarYellow]

Fillets are for looks and structure more than for aerodynamics. Stine looked at the wrong graph in Hoerner.

I’m well aware of optimum mass. Sometimes the rocket needs to be heavier, sometimes the rocket needs to be lighter. Most of the time, if I’m talking about filling grain on balsa fins, lighter is better.

 

[WizardOfBoz]

Fillets are for looks and structure more than for aerodynamics. Stine looked at the wrong graph in Hoerner.

I’m well aware of optimum mass. Sometimes the rocket needs to be heavier, sometimes the rocket needs to be lighter. Most of the time, if I’m talking about filling grain on balsa fins, lighter is better.

Ah, yes, I recall that you are an engineer (in addition to having way more experience in rocketry than I).

There is an interaction between the "hold the fins on" and the "make it aerodynamic" and the "make it look good" approaches.

Drag will involve Area times Cd. Without fillets I think that you'd need a thicker fin at the fuselage/fin root joint. For the same fins, a fillet will increase cross-sectional area. It may decrease the Cd a bit regarding interference drag. But if one is building a rocket and needs to use 1/4 plywood to get a strong enough glue joint without fillets, or 1/8 plywood because fillets give a joint that is strong enough, the fillet might lower area a bit.

I put in fillets to hold the fins on better, and because I think they looks nice.

But some notable rocket authorities apparently did not use fillets.