Mounting an irregular stone in plaster?

[bugbear]

I finally got round to making a case for my Charnley Forest stone;

car-boot-hone-t105298.html?hilit=charnley

(May last year, doesn't time fly!)

EDIT; link to the other thread, for convenience:
mounting-an-irrgular-hone-t105318.html

I took the last opportunity before casing it to flatten the upper surface. Despite seeing many reports saying CF is a hard Novaculite stone, it was soft, and as easy to flatten as a slate stone.

Onto the case. Following advice from an old book, I traced the outline of the stone, and drilled down to full stone-depth throughout, making no attempt to contour the hole (i.e. the hole had a flat bottom, but was stone shaped).

The end cheeks of the case were around 2/3", and the sides only 1/4"; the remaining timber under the stone was around 1/3" thick.

I mixed up plaster of paris according to information both from the 'net and the pack. I actually did a trial run with a small mix, so that I was sure of the setting rate and behaviour. It's most unlike concrete, in that you can continue to work it as it gradually thickens over about 10 minutes (*).

What could possibly go wrong?

I wasn't sure how to judge the amount of plaster needed, but I guessed and got it right. Fortunately. Success!

Sadly, when I checked a day later, the wooden case had DESTROYED itself. The water from the plaster had caused enough expansion to actually crack and split the wood.

So - has anyone successfully cased an irregular stone, and what did you do that was different to me?

The obvious thing to try would be to seal the hole (varnish or shellac), but there may be other issues to solve that I haven't anticipated.

So I would like to benefit from other people's mistakes and/or successes. All advice and knowledge welcomed.

BugBear

(* It is this property that is the key to setting a bubble vial in a traditional spirit level)

 

[D_W]

I'd say use a water tolerant wood. I've set several stones (western and japanese naturals) in plaster of paris and haven't had any issues other than the odd time when the plaster amount is so much that it shrinks a little and has cracks where you can see (this is a japanese only thing).

I have used apple (which isn't ideal, but it's what I had that I thought would make a pretty box) and cherry.

If the irregularity is relatively simple (thinner at one end than another, etc, contoured boxes are not uncommon. If you want a guaranteed tight fit, a bed of silicone caulk is fine.

Shellac is a good idea if you need a temporary barrier that something will stick stick to.

 

[bugbear]

I'd say use a water tolerant wood. I've set several stones (western and japanese naturals) in plaster of paris and haven't had any issues other than the odd time when the plaster amount is so much that it shrinks a little and has cracks where you can see (this is a japanese only thing).

I have used apple (which isn't ideal, but it's what I had that I thought would make a pretty box) and cherry.

If the irregularity is relatively simple (thinner at one end than another, etc, contoured boxes are not uncommon. If you want a guaranteed tight fit, a bed of silicone caulk is fine.

Shellac is a good idea if you need a temporary barrier that something will stick stick to.

I used beech. I don't understand what you said about the plaster (of Paris!!) cracking being a Japanese only thing.

BugBear

 

[Derek Cohen (Perth Oz)]

Hi BB

I use car body filler for this type of work. It is essentially epoxy and holds up well when wet (with natural waterstones).

Regards from Perth

Derek

 

[D_W]

I'd say use a water tolerant wood. I've set several stones (western and japanese naturals) in plaster of paris and haven't had any issues other than the odd time when the plaster amount is so much that it shrinks a little and has cracks where you can see (this is a japanese only thing).

I have used apple (which isn't ideal, but it's what I had that I thought would make a pretty box) and cherry.

If the irregularity is relatively simple (thinner at one end than another, etc, contoured boxes are not uncommon. If you want a guaranteed tight fit, a bed of silicone caulk is fine.

Shellac is a good idea if you need a temporary barrier that something will stick stick to.

I used beech. I don't understand what you said about the plaster (of Paris!!) cracking being a Japanese only thing.

BugBear

It's not a japanese thing - part of my thought process with that was not typed (it gets to be in great volume). Trying to head off "can i see a picture of the crack".

Some inexpensive japanese natural stones can be so irregular that you just set them in a shallow base or affix them to a piece of cedar without having the whole of the stone perimeter sunk deep enough that there's not exposed "air space" below the surface. That leaves large seams of plaster of paris if the base is sunken but shallow, and larger spans can crack.

Point being, I don't think there will be any issue with the more regular but not perfect western stones.

Beech is completely intolerant of fast changes in moisture. I can have a stick for planes that's been in my garage for two years, and one cold subzero night and it's end checked and side checked the next day, never to be check free again. I'd use something else, even pine. Cedar or something traditionally water tolerant to there would be fine, but I don't think you're going to see the problem that you found again.

The plaster doesn't have to be perfect either - you can mix a more dry batch.

 

[bugbear]

Hi BB

I use car body filler for this type of work. It is essentially epoxy and holds up well when wet (with natural waterstones).

Regards from Perth

Derek

The ultra purist in me thinks that the mounting should be (in principle) reversible. With P of P, you could split away the wood, then simply hack, scrape and finally scrub away the soft plaster.

This is probably absurdly OCD on a 50p stone, but I did say I'm a purist!

BugBear

 

[AndyT]

Now you see what happens if you don't use the proper lead, like I told you to!

mounting-an-irrgular-hone-t105318.html

 

[bugbear]

In case anyone thinks my use of DESTROYED was exaggeration...

Yikes. :shock:

BugBear

 

[AndyT]

Ouch!

I can see that's annoying and disappointing.

It's not trad, but I'd be tempted to use Plumber's Mait. It's a sort of putty, used to set washbasins onto pedestals or seal around basin wastes. Its key virtue is that although it gives a firm seating, it never quite sets, so remains reversible. Widely available from the usual places.

 

[ColeyS1]

Stixall

Sent from my SM-G900F using Tapatalk

 

[bugbear]

One thing I did which might be of interest.

I wanted the upper surface of the stone to be as parallel as possible to the base of the wood.

To achieve this (by wiggling the stone while the plaster was soft) I set the wood on a flat surface. I set a M&W combo square so that the rule was vertical, and set a small 4" bladed engineers square on the stone.

By sighting the blades of the squares against each other, it was rather easy to judge when the stone was level. This process was done lengthways and widthways until all was well.

You could probably use squares with a fair degree of inaccuracy for this process.

BugBear

 

[Sheffield Tony]

It's not trad, but I'd be tempted to use Plumber's Mait. It's a sort of putty, used to set washbasins onto pedestals or seal around basin wastes. Its key virtue is that although it gives a firm seating, it never quite sets, so remains reversible. Widely available from the usual places.

Plumber's Mait smells of linseed oil to me - very like window putty. If so, note the advice in the article you posted :-

"If ordinary tub lead is used, the stone will absorb the linseed oil and be hardened".

 

[D_W]

That won't be a problem on a charnley, but it would be a problem on a stone that was porous.

 

[D_W]

In case anyone thinks my use of DESTROYED was exaggeration...

Yikes. :shock:

BugBear

That looks familiar. I'm probably telling you things you already know, but oil and moisture travel through beech end to end in less than a day in a long distance - it's like a pipeline of very low resistance straws. Adjacent straws collect a little bit and then it leaves as quickly as it arrived.

When I want to add weight to a plane I'm making, I bottle up the mouth of the plane with some kind of plug, pour raw linseed oil into the mortise and it appears on the ends or sides of the plane (wherever the straws go) by the next morning. This occurs on a 24" try plane that is sitting on the level - it is incredible how fast liquid moves through it.

 

[AndyT]

Good point Tony, I will do my best to resist temptation.

(It should be fairly easy as I don't have any gloatable old irregular stones that need mounting!)

 

[Cheshirechappie]

Perhaps it might be worth a small experiment, excavating a small depression in scraps of different woods you have to hand, and filling the depression with fresh plaster of paris mix. That might indicate which woods are prone to the same behaviour as beech, and which seem relatively immune. A simple shallow round depression made by a large centre bit or similar would be fairly quick to do, rather than the full work of excavating a rectangular or stone-shaped hole.

That would then allow the present method to be used, as it seems successful in all regards except the effect on beech.

Another thought is that with the final box on a flat surface, the level of the stone face on fitting could be judged pretty accurately by placing a winding stick on it, longways and crossways, and seeing whether it was parallel to said flat surface. Care on placing stick would minimise chances of disturbing the wet plaster.

 

[bugbear]

Another thought is that with the final box on a flat surface, the level of the stone face on fitting could be judged pretty accurately by placing a winding stick on it, longways and crossways, and seeing whether it was parallel to said flat surface. Care on placing stick would minimise chances of disturbing the wet plaster.

Yes - winding sticks would provide a pair of horizontals to match, my way gave me verticals to match. Same principle.

I think the winding sticks would be a little harder to use, because they normally sit on the same surface; in this instance the stone surface is an inch or so high than the reference surface.

BugBear

 

[StraightOffTheArk]

I would end up using the stone as is, of course every time I used it, it would irritate me a bit more until I finally felt compelled to do something about it, I should think the whole process could be over in as little as say, 10 years!

Cheers,

Carl

 

[Saer Llongau]

I've mounted several stones on Teak with Sikaflex marine adhesive. This was about 10 years ago and the Teak is still split free and straight and it's impossible to get the stone off without ruining it. I've found this to be the best method.

 

[Trafalgar]

Use glue size and then the plaster. Let the size dry thoroughly.