Sink hole refuses to go away!

[bh1701]

I have been trying for over a week to remove 2 "sink holes" on the trunk of a 65 Continental model. These were sink holes that were over the posts that the chassis pins fit into.

I primed the model the other day and I thought I had finally gotten rid of these sink holes. I could not see any evidence of them under magnification. But, after applying the first color coats to the model, one of the sink holes is detectible again. The photo I included shows it within in the red circle; it doesn't look that bad in the photo, but in real life it is very noticeable(at least to me).

I used many different techniques. I started by drilling a hole in the trunk over each sink hole and applied Tamiya white putty into the hole. After this first application dried, I applied one or two more coats of putty to ensure that the hole was filled with enough putty to be higher than the surrounding trunk area. After sanding, the sink hole depressions were still very apparent. After that, other methods were to use Bondo , later some Bondic, and even some more putty. After sanding down each time (using sandpaper grits ranging from 600 to 2000 grit), I could still see sink holes.

Finally, I drilled holes again and inserted plastic rod into the holes. I left the rod protruding a bit higher than the surrounding trunk area. I did not have a drill bit that was exactly the same size as the rod, so I used a smaller bit and slowly enlarged the hole so the rod would fit. I used Plastruct Plastic Weld cement (liberally applied to the rod and to the trunk area around it).  My assumption was that the rod and trunk surface would "melt" together to form a seamless patch that could be sanded down. I did end up with small pinhole gaps in several spots at the places where the rod and trunk met, so I used Super Glue to fill these gaps. After sanding, most of the gaps were gone. I used more Super Glue and sanded, but still could see small pinholes in one or two spots. More super glue, sanding, and eventually some more putty.

All looked good now. after the primer was done..at least until the color coats went on and one sink hole became apparent again. As an FYI - I use Tamiya TS paints (primer, color coats) - in case that has any impact.

I think I have finally admitted defeat and will just live with the one sink hole on this kit.

But, for the future, what am I doing wrong or what is a better method to use?

Thanks,

Bart

 

 

The sink hole is in the circled area. Kind of hard to see in the photo; but, in real life to the naked eye, it is quite noticeable.

 

 

[Tom Geiger]

Been there! Played that “out darn spot!” game!

The only thing I can think of.. how did you putty and sand? Did you concentrate just on the indent? Or putty across the trunk lid and sand with sandpaper on a flat shape?

Edited June 21, 2021 by Tom Geiger

[bh1701]

11 minutes ago, Tom Geiger said:

Been there! Played that “out darn spot!” game!

The only thing I can think of.. how did you putty and sand? Did you concentrate just on the indent? Or putty across the trunk lid and sand with sandpaper on a flat shape?

Tom,

I applied the putty over the sink hole and extended it out at least 1/2" on all sides of the hole. 

When I sanded, I did not use anything like a block to "flat sand" the area. I used a piece of sandpaper that was wider than the puttied area. I did not bend or fold the sandpaper. I wet sanded and used a fairly gentle touch as I sanded the area.

Thanks,

Bart

[niteowl7710]

The thing is liquid plastic cements are a few percentages removed (like 52/48) to straight lacquer thinner, that's why it melts plastic. You can actually glue things with thinner if you had to...using Tamiya TS Paints is constant reactivating the putties (particularly the Tamiya White since it's basically just solidified lacquer thinner). When you used the Bondo was it God's honest two part body filler or just the single part glazing kind? You either need a 2 part epoxy based putty - like sincere Bondo, Tamiya Epoxy, etc. Or put down a primer coat of something like Badger Stynlrez (which is an acrylic polyurethane) to seal in that body work. Otherwise the lacquer thinners in the TS Paints are going to keep chemically reactivating the lacquer solvents in the glue, putty, etc and you'll play Whack-a-Hole with it until there are enough layers of material (primer/paint) on there that the thinner can't go deep enough to effect the fillers.

[Snake45]

I've had good luck filling such holes with putty, block sanding to shape, then hitting the putty with superglue. The superglue soaks into the porous putty and, when it cures, stabilizes and locks it into place. Then I block-sand again. Haven't had a hole come back since I've been doing this. 

[64SS350]

19 minutes ago, Snake45 said:

I've had good luck filling such holes with putty, block sanding to shape, then hitting the putty with superglue. The superglue soaks into the porous putty and, when it cures, stabilizes and locks it into place. Then I block-sand again. Haven't had a hole come back since I've been doing this. 

Ditto on this process!!

[Rick L]

Be careful and patient with your paint. The lacquer is shrinking the filler. Be sure to apply your paint in layers, working up the volume of paint as you go. Be sure each layer is dry and hard. This will give you protection from the next coat to attack and soften its underlying coat. The super glue idea will also work to block the lacquer from eating underneath but you need to sand that smooth before paint. So be careful not to sand that out.

[bh1701]

2 hours ago, niteowl7710 said:

The thing is liquid plastic cements are a few percentages removed (like 52/48) to straight lacquer thinner, that's why it melts plastic. You can actually glue things with thinner if you had to...using Tamiya TS Paints is constant reactivating the putties (particularly the Tamiya White since it's basically just solidified lacquer thinner). When you used the Bondo was it God's honest two part body filler or just the single part glazing kind? You either need a 2 part epoxy based putty - like sincere Bondo, Tamiya Epoxy, etc. Or put down a primer coat of something like Badger Stynlrez (which is an acrylic polyurethane) to seal in that body work. Otherwise the lacquer thinners in the TS Paints are going to keep chemically reactivating the lacquer solvents in the glue, putty, etc and you'll play Whack-a-Hole with it until there are enough layers of material (primer/paint) on there that the thinner can't go deep enough to effect the fillers.

Thanks - I had a feeling that the Tamiya paint might be having some effect on the putty and other things I had used. The Bondo I used was the glazing one-part stuff.

 

2 hours ago, Snake45 said:

I've had good luck filling such holes with putty, block sanding to shape, then hitting the putty with superglue. The superglue soaks into the porous putty and, when it cures, stabilizes and locks it into place. Then I block-sand again. Haven't had a hole come back since I've been doing this. 

What would you use to make a "block sander"? I think someone had mentioned a Pink Pearl eraser (the rectangular kind) to secure some sandpaper to. Are there other suggestions for making a block sander?

There are so many different styles of CA/superglue. What type of superglue would you use?

Thanks,

Bart

[Snake45]

I've grown fond of Duro super glue, purchased in 4-packs at Walmart, but for this particular use, I'd think almost any thin or thin-ish CA would work. You just want it to soak into the porous filler and then cure hard and lock everything up. 

As to a sanding block, any suitably sized FLAT piece of wood, metal, plastic, etc. works fine. The rubber eraser makes a good sanding block for surfaces that aren't perfectly flat. A sanding block ain't exactly rocket surgery. 

[Plowboy]

Tamiya White Putty shrinks terribly! To me, it seems better suited for filling scratches after primer. The Tamiya Gray Putty is much better for filling. I've not had any problems with shrinking since I switched to the gray putty. 

[Michael jones]

Sprue goo can also work very well, but it can be hard to sand. The problem I have is if the filler is not white, it can show through or shadow once the paint is applied (on light colours). Thats what makes the Tamiya white putty appealing. The super glue over tamiya white putty idea is great however!

[Muncie]

All good advice - 

The putty is one of the layers that is shrinking.  Best to use as little putty as possible.  Drilling out the hole to fill it, means more putty, more putty means more shrinking. 

The same thing is happening with the plastic rod and plastic weld - the more plastic weld means longer for the plastic to dry.  I've had that show up months later on parts that I thought were thoroughly dry. Same can happen with sprue goo if it's applied too thick.  After some previous experiences, I avoid sprue goo...  Plastic weld or the Tamiya's super thin is best when used sparingly and give it plenty of time to dry before moving on. 

On the sanding block - no need for anything fancy to hold the sandpaper on the block.  Just a piece of sandpaper big enough to wrap around the block.

Edited June 22, 2021 by Muncie

[Rick L]

I’ve found Evercoat Polyester Glazing putty to be the best in the industry. Very fine, smooth, easy to sand and most importantly minimal shrinkage if any. Expensive but worth the money. 
Another note about polyester resins is to keep it well sealed in the can and thoroughly mix EVERY time you use it.

[TarheelRick]

I have found acrylic nail filler to be a good choice for filling holes, etc.  You can buy a complete kit in the cosmetic section of WalMart or any beauty supply store; it is the same stuff all these fingernail designers use. There is a bit of a learning curve with it and it does not like dehydrators.  It is also quite difficult to sand, but when dried, and it does dry rather quickly, paint does not have any effect on it. There does not seem to be any day-later shrinkage either. You might want to give it a try.

[Pete J.]

2 hours ago, Rick L said:

I’ve found Evercoat Polyester Glazing putty to be the best in the industry. Very fine, smooth, easy to sand and most importantly minimal shrinkage if any. Expensive but worth the money. 
Another note about polyester resins is to keep it well sealed in the can and thoroughly mix EVERY time you use it.

Been using this for years and expensive?  No, not really.  Not cheap to buy, but per ounce, it is far cheaper than any modeling putty on the market.  Just bought a can yesturday and it was $41 but that was less than $1 an ounce.  Tamiya putty is about $6 an ounce.  

I have had one issue with it though.  If you buy the plastic bottle or pouch, the container cracks or leaks after a while.  If I don't buy the can, I transfer it to a glass jar. Also, you need to replace the hardener from time to time.  Same issue.

Edited June 22, 2021 by Pete J.

[Rick L]

I have to agree with you there but you can’t buy it by the ounce. The smallest amount I can find is a 36 oz. can at $36.00, so yes it costs $1.00 an oz. but I’m not repairing 1:1 cars. I’m using it on 1:25 scale models. 36oz. Is more than enough resin I’ll need before it dries out. 

[Pete J.]

18 hours ago, Rick L said:

I have to agree with you there but you can’t buy it by the ounce. The smallest amount I can find is a 36 oz. can at $36.00, so yes it costs $1.00 an oz. but I’m not repairing 1:1 cars. I’m using it on 1:25 scale models. 36oz. Is more than enough resin I’ll need before it dries out. 

I understand, but I would rather spend $36 for a can than the same price of 6 tubes of hobby putty.  The tubes of hobby putty seem to be far worse at dry out long before they are empty.  When I was working on customs, I use to go through a lot of tubes of Tamyia or Squadron putty.  It seemed like when ever I would grab a tube I had opened for prior project,  it was dry and that always seemed to happen at the worst point in the build.  My experience with eurosoft is that it lasts for 8 or 9 years and never had the resin go bad.  I always get a crack in the plastic container long before that.  I seem to have more of an issue with the catalyst tube cracking long before the resin does, but my local supplier will give you another tube of that anytime you ask. 
 

The other huge advantage to eurosoft is that you can sand within 30 minutes and paint within a couple of hours. No waiting overnight for the stuff to harden.  Just a better product all around.  Cheapest way to do it is for one person to buy a can, divide it up into smaller containers like large Tamiya mixing bottles and split the cost with a lot of your fellow modelers. 

[Oldcarfan27]

When I start, I block sand the areas where the dips and divots are located. Many times I can eliminate many sink marks just by leveling it out. No sinking if it's just original plastic. 

If I can't sand enough down to eliminate it, at least I can get it smaller before filling it in.

Also, I never use plastic model cement to attach sprue to fill the holes in the body. I find that it invariably sinks over time. I use super glue with no quickset for a solid fill and block sand to level out. Finally a small skim of filler to perfect the area.

[carrucha]

Another method is using really thin sheet styrene to fill in the "sinkhole".

[alan barton]

I feel your pain, Bart!  I have just been through very similar experiences on two long term projects with major bodywork. 

I have only recently switched to Tamiya products, on account of you can't buy Testor's here anymore, and I have had way more issues than I ever had with Testor's.  I seem to be having a lot of problems with tight concave curves, where no matter how light or heavy I apply primer, I get cavities underneath.  And this was before our winter struck, when I had nice warm days and was leaving things up to a week between applications. I also have been having issues with bodywork raising up through the primer, sometimes several coats down the track.  I will be taking into consideration what people are saying about the potency of Tamiya primer.

There are a lot of good suggestions in this thread but i find it frustrating when techniques I have used for decades are suddenly not working!  I have certainly used superglue in the manner described by Snake but you also have to be careful because it doesn't sand as readily as the bare plastic around it - block sanding is a must here. 

Right now I really need to build a few models without bodywork!

Cheers

Alan

 

[Vince Nemanic]

Put a drop of liquid glue in the sink mark, then top it with a small piece of plastic flash on the glue and let it dry. Put a drop of glue on top of that and let it dry again. Sand and repeat as needed. if the original kit had some flash, the repair will even match the body. Often I don't even need to use putty, or the layer of putty is VERY thin. Yes, there IS a use for the dreaded plastic flash! 

[charlie8575]

On 6/21/2021 at 12:43 PM, Snake45 said:

I've had good luck filling such holes with putty, block sanding to shape, then hitting the putty with superglue. The superglue soaks into the porous putty and, when it cures, stabilizes and locks it into place. Then I block-sand again. Haven't had a hole come back since I've been doing this. 

This is a good idea. I may try this next sink hole.

Charlie Larkin

[EngineerBob]

bh1701, as others have mentioned, there can definitely be a reactivation/softening of the underlying materials when using lacquer paints. A couple of things that have worked for me is to give the putty you use some extra time (days) to dry and then lightly primer and again give the paint extra time to dry before recoating. If the low spot is in a relatively flat area then make sure to block sand with a very firm or even solid block to back the sand paper, no block or a soft block will still be able to contour to the surface and sand out fillers that are typically softer than the surrounding plastic. I have had good success using Evercoat Pro-Grade Glazing Putty for areas requiring major bodywork or where I need a filler which is almost a hard as the plastic. The Evercoat is a two-part catalysed glazing putty (important that it be a glazing putty and two-part, ie you need to add a hardener) that comes in a 3oz tube for $10 at any autoparts store and is enough to do many models. Bondo also has a pro-grade two-part glazing putty in a tube for a similar price.