Joining soft sandstone - with wiggle room

[David]

I have a bird bath of sentimental value, where the stone support has broken in two.

It does fit back together, and an earlier attempt to stick it with PVA lasted for a short while, but I need a permanent fix.

One obvious route is to drill a hole down the centre of each piece, insert a post of some kind (metal rod?) and fix the whole thing together.

Past experience indicates that I am unlikely to be precise enough in marking up and drilling to get a snug and accurate fix where the two bits just fit together on the post.

So my plan is to make the holes a bit bigger for a "sloppy fit", fix the metal post into one with some kind of cement/glue, then fix offer it up to the other half with more cement/glue.

Big question - what would be a suitable fixative? Secondary question - what to use for the post?

Stone upright is about 160mm in diameter.

Cheers

Dave R

[The Natural Philosopher]

Epoxy is the obvious choice.

Milliput is good for terracotta, and there are ones that look like stone as well.

I question the need to drill and peg it with epoxy too.

PVA is a simply terrible solution

Try and get it all off before you use epoxy or it will never bond properly.

Soak it in water for a few days and wire brush it

[The Natural Philosopher]

Also see

[Tim Watts]

PVA??? That's good for wood and paper and not much else.

Araldite would probably have worked, or a car body filler type glue.

But less so now, unless you can scrub the PVA residue off.

if you give it a good scrub with water, a little detergent and a wire bush over the faces to be glued, you should be able to get a very good bond with the correct adhesive.

[Malcolm Race]

Big question - what would be a suitable fixative? Polyester resin as used to fix stids in brickwork. For rixing studs the hol;e should inly be 2mm or so bigger than the stud but in your case I would think that tha tolerance could be greater

Galvanised studding or possibly aluminium rod. Whaterver you use it must not rust as sandstone is porous and the stud will be damp

Malcolm

[David]

Kudos for the pun :-)

PVA is, however, much used in building for bonding stuff, like fresh screed over an older concrete floor, and the plastic bottle says that it will bond concrete, brick, plasterboard etc.

So it seemed like a good option.

Cheers

Dave R

[David]

As I just mentioned to TNP, PVA is much used as a bonding agent by builders. Comes in large plastic containers.

One thing I forgot to mention - the sandstone is very soft, so I am not confident that bonding two fairly weak and crumbly surfaces will do more than encourage the plinth to break again, leaving behind a thin strip of expensive sand paper.

This is why I was contemplating strengthening it with an internal rod.

Cheers

Dave R

[Tim Watts]

If using stud, use stainless...

[Tim Watts]

You believed that?

It is used to prep old surfaces for new plaster and it does that well.

For almost every other claimed application, there's something better.

PVA is not waterproof and it has bugger all gap filling properties - you need both.

[Tim Watts]

That's good logic - I'm trying to recall how weak sandstone is...

In that case, some screwfix no nonsense anchor resin (which is a vinylester IIRC) should work quite well and be inexpensive.

Blow all dust out of the holes you drill, pump full of resin, insert stainless stud into one, apply other piece, clamp.

[David]

Sounds like a plan.

All I need now is a suitable clamp.

Although given the weight it should stay in place one fitted together standing upright - the break is almost straight across.

At most it should need some support to stop an unplanned wobble.

Cheers

Dave R

[harry]

Stainless steel for the joining rod. And just plain sand & cement for the filler. Stone is very weak in tension, no point in some super strong glue.

[Bill]

In message , harry writes

Many years ago I was working in Liverpool Anglican Cathedral. A building surveyor was there supervising repairs so I asked him what they were using. He just said epoxy. I know no more.

But, my understanding of the virtues of epoxy includes the concept that epoxy molecules are small and so it freely wets and runs into what it is bonding, unlike the common "fibreglass resin".

The Cathedral is, of course, a sandstone structure.

[Brian Gaff]

This may seem stupid at first glance but many years ago a Neighbour had a sun dial with this problem and he used a length of stainless steel studding and an epoxy of some kind. The fact that it was studding made it actually less likely to move when the first part was cured. Always leave the resin in the hole below the level of the break or when you come to try to line up the bits it will leave a gap all around. Not a job to be hurried he told me.

Brian