[:nl]Hoe repareer je een barst in bakeliet?[:en]How to repair a small crack in bakelite[:]


Oh dear a crack in my bakelite!
Oh dear a crack in my bakelite!

An often occurring problem is a small crack in your bakelite telephone (or any other bakelite object). Bakelite is, after all, brittle and this kind of damage can easily occur. In this article I will show how to do a relatively easy repair. It does however take some practice, so please try it out on a test subject first. Please do mind that it works best on black (really black black) bakelite. It works on other plastics too, although other plastics may better be repaired with another type of glue.

The blacker the material, the less visible it will be. We are using superglue. As it is translucent when dry it will take up the colour of the surrounding material. There is no need to colour the glue before applying.

In this case I am repairing the front corner of a Heemaf 1955. A crack in this position is a common occurance. It is at a dangerous position, because here at the business end of the telephone there is a risk of cracking further. So a repair is needed.

Do I really need to repair this? Beware!

The crack is bigger on the inside!
The crack is bigger on the inside!

That is always the question, why should you repair it? Repairing it with this method is irreversible. And this method can be botched up, resulting in the object being worse off.

So there are several aspects you may want to consider, before you start.

Firstly, do you have the skill? Have you practiced this method? Were you happy with the results?

Secondly, how valuable is the object you are going to repair? And how does this relate to the first point, your skill to perform this method?

And thirdly, is it safe to leave it as it is? In the case of the telephone in this article, the crack ran all for quite a distance along the inside. There was a risk of the crack getting bigger, because the telephone in question will actually be used and handled.

And last but not least, after the repair the crack may still be visible, albeit faintly.

In the case of the example in this article the telephone in question was meant to be used on a daily basis and not just a static display. Leaving the crack as it was, would risk further cracking and breaking off. Please note that the crack was even bigger on the inside, than on the outside.

What do we need?

Stuff we need...
Stuff we need…
  • Superglue, the slow drying kind. It will need to stay liquid for a few minutes. Some products dry really quick. Test it first.
  • Sandpaper, 800, 1500 and 2000 grit.
  • Toothpicks
  • Scratch remover, polishing agent, Brasso, displex etc
  • Dremel with polishing wheel and grinding implement

Clean, clean, clean!

First, wash the object and make sure the crack is clean and there is no dirt on it. Also make sure there is no dirt in the crack itself. Brush along the crack with a brush and soapy water. Make sure it is dry for the next phase.

Does it fit?

We are going to put glue in the crack later, so it is important to see if the crack closes properly. Both sides of the crack need to be as flush as possible. When you go with your fingernail across it, you must not feel a ridge. Please mind to go across it both ways! Do you feel a ridge? Make sure the crack is clean and nothing is stuck in it. Also try pressing it closed and see if it fits better that way.

If you cannot get it to close properly, you may want to reconsider repairing it.

Wiggle it!

Wiggle the edges carefully
Wiggle the edges carefully

When we put on the glue later on in the process, we are going to wiggle the edges of the crack. This moving the edges of the crack will cause the glue to permeate fully through the crack. That is also the reason why we need slow setting superglue. Otherwise it will harden before the glue has fully penetrated the whole crack.

Do mind that you do not put too much force on the crack, otherwise it may crack even further or you will break off a piece of bakelite. You only have to wiggle it a little bit.

So do a test wiggle, before gluing it for real.

Sometimes it is not possible to wiggle. Then proceed to gluing, without wiggling.

Put it to the grind stone

The crack ground out
The crack ground out

Sometimes I grind out the crack on the inside of the piece I am repairing. There are a number of reasons why this may be advisable to do so. Firstly, we are going to put the glue on the inside of the housing, squeezing a small line over the crack. Grinding it out makes gluing a lot easier.  The glue can be put in the ground out trench easily.

In this case the crack was longer on the inside than on the outside. To make sure I reached the very end of the crack with the glue, making sure the whole crack is glued. The crack in this is case is in an area that is exposed and we do not want the crack to reappear.

And of course the position of the crack makes it possible to grind it out.

There may be reasons not to grind it out. For example when the area is visible, or in a hard to reach area.

Glue and wiggle and glue again

Putting in the glue
Putting in the glue

So, no we are ready to glue. We are going to start on the inside of the housing. In this case I have put an steady line of glue along the ground out trench. If you have not ground out the crack, just put a nice bead of glue over the crack itself.

After applying the glue, start wiggling the edges of the crack. By the motion of the sides of the crack, the glue will permeate through the hole crack. After a while the glue will start to appear on the other side, in this case the outside of the telephone. Please do not stop at the appearance of the first small drop.  Continue wiggling until all along the outside of the crack drops of glue start to appear. You may want to apply some more glue on the inside and start wiggling again.

The glue is coming out the other side. Some more wiggling to do
The glue is coming out the other side. Some more wiggling to do

Please make sure there are no accidents with the glue. So hold everything carefully, preferably the glued part facing upward, and the crack facing down as much as possible. Also beware of glue running through the inside of the housing. And do not get any on your fingers!

When the first glue is well distributed, leave the glue to set. Make sure the crack is closed properly and the 2 sides are flush. This is a critical moment.  The flusher the sides are, the less visible the crack will be when finished.

Then hold the crack in place until the glue has set enough. You may speed up the setting process by breathing on the wet glue, like you would when fogging glass. Cyanoacrylate (superglue) sets quicker, when it comes into contact with moisture.

Forming a bead of glue
Forming a bead of glue

When the glue is set, take a toothpick and put a line of glue over the crack on the outside of the housing along the whole crack. You may want to repeat that 1 or 2 times. The glue will decrease in volume when setting. This forms a slight trench along the crack. It needs to be completely filled before we can start sanding.

Sand, sand, sand

U shaped sandpaper
U shaped sandpaper

Now we are going to carefully sand away the excess glue with coarse sandpaper. I take a little piece of 800 grit sandpaper and bend it U-shaped. With this bent piece of sandpaper I take care to sand just over the glued part and try to avoid sanding the surrounding area as much as possible. Sand it down until all the excess glue is gone and the surface totally smooth. Then sand it again with finer and finer sandpaper.

Ready for polishing
Ready for polishing

Polish, polish, polish

First I polish the sanded area with Valma scratch remover a couple of times, using a felt polishing wheel on my dremel. Afterwards I polish it by hand with an agent called displex. Displex is a compound for removing scratches from telephone touch screens. It works really well on plastics too.

Show it off to your friends

If all goes well, the crack will be invisible. And you end up with this result, see last picture. Please mind that when the bakelite has faded a bit, the crack will show up black.
But in this case I am very happy with the result.

Where has that crack gone?
Where has that crack gone?

For more on bakelite repair, see also my aricle on repairing chipped bakelite:

How to repair chipped bakelite


4 Reacties

  1. Dear Matilo,

    I have a bakelite receiver which is cracked from an antique wall phone. I don’t know the name of the wall phone but I can send you a picture along with a picture of the damaged receiver. Just hoping the receiver cap can be repaired.

    • Hi Lisa, thanks for your message. Please send me some pictures and we’ll see what can be done.
      You can basically always glue bakelite parts with superglue. But if it will hold, especially on parts that suffer from forces excerted on them, is a different matter.

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