MBD British WWII "U" class sub Build

[roedj]

Fixing the FUBAR limber holes - Epoxy repair kit plus micro balloons

David,

Don't forget I have the Caswell epoxy repair kit (A & B) plus micro balloons. What if I put some clear tape over the back of the hole to keep the epoxy from just falling out and then put some epoxy repair with micro balloons (thickened like paste) into the hole - wait 24 hours - sand sort of flush - and start over with a brand new hole?

Is that approach better or should I just go the CA + baking soda route?

I really appreciate the time you're taking to keep/bail me out of trouble.

Dan

[Kazzer]

David,

Not sure what you mean by "bow on some baking soda"

I've got some spatulas from my chemistry days or some wooden craft sticks to basically slap some baking soda on the CA. Is that what you meant?

Dan

He meant BLOW! I corrected it.

[He Who Shall Not Be Named]

Sorry about that Dan. Should have proof-read my response to you.

I ment 'blow' on some backing soda. What you do is sprinkle the baking soda onto the work, then blow off the excess, the mass hardens quickly, then you go back and cut out the proper shape of the limber hole. Takes only minutes per 'fix'.

David,

[roedj]

I can't get it hard

David and All,

I wanted to learn about the Caswell epoxy repair kit so I used some of it to fill in the FUBARed limber holes. I mixed it to a specific 2:1 ratio, as specified on the can, and added some Cabosil to thicken it up a bit. I carefully used some heat from a heat gun, keeping the gun about 2 feet away from the work. I tried that for about 1 minute. Set the whole thing aside but checked on the hardening every 12 hours or so. After 3 days it doesn't seem to be rock hard but I don't think it's going to get any harder either. Tried drilling a hole in it just to see how it would look. The drill is entirely gummed up with epoxy repair "stuff".

Did I do something wrong? I tried the CA + baking soda trick on some other holes but wasn't really satisfied with that fix either.

Where do I go from here. Instead of Cabosil maybe I'll try Viagra.

Dan

[Kazzer]

How much did you mix up? Small amounts can easily be easily incorrectly measured out. I didn't like the look of those 1/4 teaspoons, far too little material. At least I would mix up 2 tablespoons of A to one of B. Leave them for 10-15 minutes after mixing to allow the reaction to accelerate. Make sure you scrape all the material off the spoons to ensure volume accuracy.

Your results are a direct result of either insufficient mixing or incorrect mixing ratio.

[roedj]

Mike,

I used the 1/2 and 1/4 tbsp sizes. It was more than enough to fill in the existing bad holes. I thought I mixed it thoroughly but I did not wait the 10 - 15 minutes to allow the reaction to accelerate although I fail to see how that can be a problem. Wouldn't the reaction just take place after I placed the mixture into the hole?

Anyway, I'll try it again being careful about the ratios (although I was very careful the first time, I thought), mix thoroughly, add just enough Cabosil to make it thick, wait 10 to 15 minutes, and then place the mixture into the hole.

But.....

And I should have asked this first, how do I get the existing bad "stuff" out of the hole? In the absence of any Caswell approved solvent or method, I guess I'll just go in with some tool and dig it out. OK?

Thanks for the help,

Dan

[roedj]

Posting the pictures

Mike,

1) I still can't quite figure how the picture attachment process works. I load the pictures in the order I want them to be on the page but the picture loader places them in a completely different order.

2) I name the pictures to describe the contents but the loader cuts off the name after only a few letters.

..............

1) I have no idea on how to get around this.

2) I can handle this. I'll just place the description of the "action" right on the photo.

Dan

[Kazzer]

Mike,

I used the 1/2 and 1/4 tbsp sizes. It was more than enough to fill in the existing bad holes. I thought I mixed it thoroughly but I did not wait the 10 - 15 minutes to allow the reaction to accelerate although I fail to see how that can be a problem. Wouldn't the reaction just take place after I placed the mixture into the hole?

Dan

I think this is your problem - incorrect mix ratio. Those small spoons and the tiny quantities involved are the culprits. Mix up in tablespoon quantities. Warm the resin to 80f before measuring out, it will be much runnier and not stick to the spoons so much. Also, the 80f will kick off the resin. This material is not a fast cure, (it's a high strength epoxy) and so thin cross section, small amounts, and incorrect mix ratio will all add to the problem. Better to waste a bit but get the ratio right. Put the Cabosil in 10 mins after the initial mix.

Of course, you could mix up the Cabosil into each separate component A & B so you have 2 pastes. Then you simply mix 2 parts of A to one of B as and when you need it. Make sure you put the same amount of Cabosil into each resin part.

The one minute of heat gun was probably not enough and the heat in the resin was quickly absorbed into the hull. You really need at least 30 minutes at around 120-140f to kick it off adequately. I use a 40 watt light bulb at about 8-12" distance from the repair area.

[roedj]

Caswell Epoxy repair - the better way

All,

Well, Mike, you were correct. I'm not surprised. Here's what I did to fix the incomplete epoxy cure problem:

1) Epoxy Part B at 66F is OK to measure and pour as its viscosity is low enough.


2) Part A, on the other hand, at 66F ( My Michigan basement) is way too thick to measure or pour.


3) Heat Part A in a water bath to about 106F - measures and pours well.


4) Mix well - heat with lamp for 24 hours.


5) Epoxy is rock hard


Next step is to do it again with Cab-o-sil and fix the FUBAR holes

Dan

[Kazzer]

Yup! Bin Thur! Dun That! Lotsa times!

The cure time under a lamp for could be cut down to a minimum of four hours at approx 150 f (surface temperature of model) and you will achieve what is called a 'post cure'. This means the resins will initially cross link to create a solid state, then a while later, a second cross linking will occur, making the overall repair about 10% stronger and more chemical resistant than a strait room temperature cure. However, full cure in both situations will not occur until about 5-7 days, only approx 90% of full cure occurs in the first 24 hours.

I once had a customer buy some of our gas tank sealer. Cursed me up hill and down dale because it fell out of his freshly painted tank. He was going to shove the tank up my - well you know - and actually visited me with the tank. After a half an hour of listening to his rantings about the crap we sold, I tried to get him to explain exactly what he did. "Followed the instructions exactly!" he snorted!
"Oh! Really! Tell me how you mixed it." (The clue was the resin was rather snotty and gooberish)
"I measured out the part A and poured it in the tank, then I measured out the part B and poured it in the tank, then I sloshed it around in the tank to mix it!" I pointed out the nowhere in the instructions did it say to mix it like that.

My sides still ache for the fits of laughter I couldn't contain as he waddled off down the drive with a very red face, muttering to himself. I gave him a free unit to start over with.

Thankfully Dan has been much more of a gentleman about this, as I wasn't looking forward to the insertion of his 1:36 scale submarine.:wink: