View Full Version : Repairing Broken Slate Clock Case

10-12-2007, 07:14 PM
Hi, I know this has been posted before, but I have issues with the MB's search feature, and I'm not going to spend 2 hours trying to find it.

Does anyone know what was originally used to hold these cases together. It almost looks like plaster of Paris, but it's a bit more gritty, like cement (but not quite).

I recently bought this poor thing for a measly $37.00 (plus shipping), but the case has come apart in two places. It has split right in half at the joint between the top/bottom, and the left panel is splitting from the inner stone core (popping out slightly.

I'd appreciate any help as to what methods I can use to fix this.

I am aware that new products and glues can be used to reglue the two halves, but I'm more interested in what I can do with that left side, so as not to break it.






10-12-2007, 07:16 PM
Also, there's a bog enough chunk broken off the top right corner. Someone had posted about products that can be used to fill-in broken chunks of slate.

Also note that these are the "as received" photos, so it's still all dusty, and covered in small flakes of dry grout.

The clock has beautifully engraved corner decorations, which have a combo of red and gold filling.

10-12-2007, 08:31 PM
I know your correct about the prior thread and the search feature. If my memory serves me correctly(once in a while) I believe it was a morter mix.

Your going to have a very nice looking clock when your done! Very delicate yet substantial looking.


10-12-2007, 09:16 PM
Sooth, do yourself and the next owner a favor: reassemble the slate slabs with epoxy resin. Although the "do no harm" clause in our credo would have you using the original plaster of paris, too many slate case clocks have been dropped on the owner's foot because they lifted the clock by the top slab!

I have a strong suspicion that the black slate clocks were put together on "jigs" to hold the pieces together while the plaster cured.

The chipped corner of the top slab can be filled with J-B Weld, an iron filled epoxy resin that is just about the same color as the slate. First drill a couple of holes in the broken area and insert wire pins as "reinforcing bars" first. Use any kind of plastic pieces as forms for the resin fillet.

When the J-B resin has cured, you can shape the fillet with a coarse file. Follow up by block sanding the surfaces with wet abrasive paper from coarse to very fine and finally with 600 grit or finer.

The dull gray color of the slate can be restored to jet black using either shoe dye or better yet, black "Rub 'N Buff" a liquid paste available at art supply or hobby stores.

The "Rub 'N Buff" is a very hard wax applied as a liquid. (don't ask me how it cures but it does) When dry the wax does not shine; it has to be buffed. The wax is hard but responds very well to a hard brush in the Dremel tool at high speed. The brush heats the surface of the wax such as one does with a shoe shine cloth to get a "spit-shine."

The same "Rub 'N Buff stuff in gold can be rubbed into the incised decoration in the slate after polishing. Remove excess gold color with mineral oil.

My friend Jim Glidewell has developed the above process and shows how to do it at chapter meetings.

10-13-2007, 07:49 PM
Eckmill, I have no problem trying the JB Weld to fix the chip, but I'm pretty sure it's a dull grey (I have some, and I've used it once), and not anywhere near black. Thoughts?

I'm also not worried about the dull looking stone. It's mostly dirt and oils, and with a good cleaning, and marble polish, it will look great.

I managed to carefully work the side panel loose, so that I could refit it in place properly. It was originally held to the interior stone (cement?) blocks using some sort of hard black (and now dry and crumbly) adhesive. Almost looks like tar, but it's hard and dry (not flexible).

Here's how the clock looks currently.




10-13-2007, 08:41 PM
I always wanted one of them slates or heavy iron one. Just feared the shipping cost.


10-13-2007, 08:50 PM
Sooth - I wouldn't overlook the possibility that the clock was already repaired once, but inadequately. Could be the stuff you're trying to identify is not original to the clock. Just a thought :)

10-13-2007, 11:05 PM
Oh the black stuff is definitely original. I can see traces of it in other places where the clock is still intact (inside on the other side, and also in the base).

Plus, I think the side panel was firmly attached and in original condition before the clock was shipped. I can see no evidence anywhere that anything was tampered with, except for the hole in the base of the clock (which also weakened both side support braces - the two metal wires).

RJ, shipping was only about $45 USD. The clock cost me 90$ total in CAD. It was a real bargain (understatement), and I'd strongly encourage you to consider getting yourself a nice French clock (slate or wood) if you get the chance. They are simply exquisite, and a real treat to work on. The movements are masterpieces.

I should also point out that this particular clock was well packed, so this isn't one of my horror stories involving poor packing. It's just old and fragile, and didn't like the trip here.

10-15-2007, 09:47 AM
Sooth, if you do no t want to deal with coloring the grey of a JB weld repair there are now 2 part epoxy's available at building supply stores and others that are jet black and make an almost completely invisible repair on slate clocks. It also is great to reattach loose parts and you don't get a white line between the parts to deal with.

Gordon Andersen
10-15-2007, 05:04 PM
Hello Sooth,
I had a similar problem with a French slate clock case. After much soul searching
and hemming and hawing, I finally decided to try using (of all things)
"GORILLA" glue. It worked beautifully. You just have to be cautious regarding
the amount of glue you use. It expands greatly. I put the glue on close to the inside side so any oozing would be on the inside of the case.
Gordon Andersen
Adams, Wisconsin

10-16-2007, 06:40 AM
I think, good ol hide glue. At least you can undo...!

One of these days Sooth, I gotta checkout the French clocks.

Been on my list for a while now.

When I think French clocks I think tiny brittle pivots. (every body says that here...).


10-16-2007, 08:34 AM
I think that the point that other horologists try to make (when they talk about the pivots) is to simply be careful, and gentle. Though I'm sure the pivots are fragile, and hair thin, I've never broken one, and I've worked on 2 of these clocks.

You just have to take your time, and not force anything (like if the pivot is pinned between both plates, don't force/drag it into it's spot.

As for Gorilla glue, I don't like the idea of an expanding glue at all. If anything, I'd want the opposite.

Hide glue, I dunno. It might work, but I want to be sure. Epoxy sounds like the best option so far, for this type of application.

harold bain
10-16-2007, 09:40 AM
This is one case where you don't want to have the glue joint not hold. I use epoxy for case repairs on these slate clocks, and have never had any problems. Just make sure you have it properly positioned, as you won't get any second chances to correct if it isn't right.

10-16-2007, 08:31 PM
I think, good ol hide glue. At least you can undo...!

One of these days Sooth, I gotta checkout the French clocks.

Been on my list for a while now.

When I think French clocks I think tiny brittle pivots. (every body says that here...).


10-16-2007, 08:37 PM
RJ: Do I have a deal for you. I have a french basket case clock that is piled in the corner of my shop,picked it up in a truck load deal and don't have the time or desire to work on it. Its yours for the shipping. The catch is that you have to take pictures before and during repair so the rest of have some entertainment. I live in WI not sure what the cost would be for shipping but the thing is heavy.

10-16-2007, 10:30 PM
I don't think hide glue would have the strength you'll need for slate. Harolds' epoxy idea is probably best. You definitely don't want the glue to let go and watch the clock fracture into tiny parts when it hits the floor :)

Kevin W.
10-17-2007, 11:19 AM
Sooth very nice clock and for under a 100, cant complain there.That is not oo bad for shipping i guess, considering the weight of this clock.Nice find. :thumb::thumb:

10-17-2007, 09:45 PM
I have repaired several of these type of cases that were broken in similar fashion to yours. I know that there are those who are not in favor of it, but I have found that Gorilla glue is very effective for these repairs. The breaks on these cases are usually very irregular so you need a glue that is going to fill all of those irregularities. Gorilla glue expands as it cures so it addresses this issues very nicely. As mentioned above, though, one does have to be careful not to use too much of it. It is best to practice first. Also the parts must be clamped when the glue is curing.
As for the gray dingy color of the case, there is a solution. I worked for over a year trying several different methods to get back to as near as possible the original condition of the marble(slate) finish of the case. I found more than one method that worked,but most were very labor intensive. I have finally found one that works quite well and is relatively easy. It is this. Rub the case with a rag soaked in acetone. You need to be careful with this stuff. You just rub and rub until you get a nice uniform dull black color. Then after allowing to dry apply thin layer of MinWax paste wax, let dry for 15 minutes, buff with a clean cotton cloth and repeat the wax and buff process several times until you get the depth of appearance you want.

Gordon Andersen
10-18-2007, 07:28 AM
Good morning all,
What are the feelings about using "Rub 'n Buff" on French slate clock cases?
Would it be a feasible application? The use of acetone, as mentioned above,
does sound like it is a good approach to shining up a case such as this, but I am still wondering about the use of Rub 'n Buff.
Thanks for your input,
Gordon Andersen
Adams, Wisconsin

Tony Ambruso
10-18-2007, 09:59 AM
I agree with Ronr. Gorilla Glue would be my choice over epoxy. I find epoxy unnecessarily tedious, and Gorilla Glue is at least as strong. An expanding glue for this type of repair is the way to go.

10-18-2007, 10:19 AM
Hey Analogtime;

Sorry I did not post sooner. Got side tracked.

Sure! I'll write to you (pm) with my address and let me know what shipping is. I'd be glad to do before and after. I like a challenge too..!


10-18-2007, 10:25 AM
Hey Analogtime;

The messageboard won't allow me to pm you. I think you have to change a setting in your user profile.


10-18-2007, 09:01 PM
Ok changes are done

Bill Ward
11-04-2007, 12:57 AM
The gritty plaster-like stuff is indeed plaster. Plaster is made by roasting certain rocks and then crushing and grinding them up. Coarser plaster is cheaper because it isn't ground as much. Also, it's frequently a darker color because the raw materials are less pure.
Back when house walls were real plaster, it was applied in 3 layers. The 1st two (the brown coat and the scratch coat) were of this cheaper, rougher stuff. The texture also permitted the following layer to adhere better.
Today, it's hard to find, unless you have a good masonry supply house- and even then, you'll be buying at least 25 pound bags. But the finer, white plaster of paris sticks just as well.
Generally, in materials selection, it's a good rule of thumb that "Like Goes with Like". So, for instance, it's a poor idea to apply masonry stucco over wood, because the expansion characteristics are so different that it'll soon come unstuck. In the same vein, I'd recommend the original plaster adhesive. It should be fine if the clock doesn't get damp. I suspect that the reason so many of these cases come apart is that they've been stored for years in the shed or basement. Plaster was used to glue marble mantlepieces together, and I can tell you, it's a bugger to get them apart without breaking the marble. Epoxy is certainly a strong, waterproof and permanent adhesive- maybe too much so, unless you think the clock might get wet. It can make a very thin joint, so it's the perfect solution for broken stone slabs. But it's not reversible. It's also difficult to control in that the viscosity varies widely with temperature, and the curing reaction is exothermic (produces heat.) So, you smear on this thick, treacly goo, and a few minutes later it turns to water and runs out all over everything.
No offense intended, but, when I first read this post ( and had no time to reply) the first thing that ran through my head was: anything but Gorilla Glue! Although this has been heavily marketed for everything shy of hair transplants, it has definite limitations.
Most important is that it foams up when curing. The force of this foam being generated will push all but the most securely clamped joints out of alignment. THe force is terrific. For example, I don't think there would be any way to hold a tenon in a blind mortise while this glue sets. Now, this is an advantage when a void has to be filled because the surfaces are rough and don't fit. But there's nothing rustic about French black marble clocks. They're austere, efficient, and perfectly proprtioned. They don't have centimeter-wide joints, so let's not add any!
Secondly, Gorilla glue is activated by moisture. This is OK for wood, but wood always has some moisture in it. If it's kiln dried, the manufacturers recommend spraying a little water on the joint surfaces. But slate is quite impervious to moisture. Most probably, the glue on the exterior of the joint would set and harden (perhaps from atmospheric moisture) while that on the interior would remain liquid. Then, as moisture eventully reached it, it would foam, and the constrained pressure would set up internal stresses which might result in early failure.
Thirdly, I'd lay dollars to donuts that the expansion characteristics of this organic glue are miles away from those of slate or marble.
And, yes, the black coating on the inside is original. It's asphaltum or bitumen. I've heard that it was applied to prevent moisture from migrating through the stone and causing a bloom on the finish, and, alternately, that it was to darken the inside of the case, so the rough surface wouldn't be so easily seen.

11-04-2007, 06:17 AM
Hey Sooth;

Did you make any progress? Wondering which direction you took. I gotta do the same (for Armel)...


11-04-2007, 10:10 PM

11-04-2007, 10:29 PM
I used JB Weld (epoxy) to reassemble the case, then patched up all the inside voids with a custom mix of about 2/3 plaster of paris, and 1/3 white sand.

The repair seems quite solid.

Photos... eventually.

11-06-2007, 05:38 AM

Wondering what you mean by filling the voids. I understand using plaster in the cracks, but can't envision how you fill the voids when you have glued the pieces together with epoxy.

How did you have access to pack the plaster, from inside of case via movement hole or from underneath bottom...?

Also wondering if you scraped off old plaster at epoxy contact points, because I believe if not, the plaster may just crack, not as firm a grip as contact to slate would be.

I'm thinking that I might want to scrape/loosen/moisten to remove old plaster so epoxy or gorilla glue would adhere better.

Or maybe just use plaster, or glue only edge joints and plaster under flat sections.


11-06-2007, 06:55 AM
Hey, Sooth, you got a buy there! My son had a similar one and he decided to give it a bath in the bathtub. Duh! Of course, it came apart! So I will learn from the posts as well how to reassemble the case.

Hope you can get it repaired successfully as it is definitely a nice clock.