Repair green river slab

[Pixpaleosky]

I broke a large green river slab with fishes.

Fortunately there are no small pieces.

Which glue do you suggest to make it one piece again ?

[Randyw]

Do you have any pictures of the damage?  I normally use either of these ca glues. The rapid fuse is thick but grabs really fast. The other is very thin that is good for letting seep into tight cracks but takes longer to grab. Some people also use a paraloid mix. It’s important to get any loose material out first. If the edges fit really tightly I will put them together on a PROTECTED surface and let the thin seep into the crack. If its a bigger gap I will use the thick and press them together

Edited February 26 by Randyw

[FossilNerd]

@Ptychodus04 @RJB

[Ptychodus04]

Pics of the slab would help a lot. You can use any cyanoacrylate to glue them back together but it may not be stable, depending on the size of the plate. You may need to back it with plywood to keep it from breaking again if it is largeish.

[jdp]

I would not use cyanoacrylate (superglue). Paraloid or polyvinyl acetate won't deteriorate the way cyanoacrylate does, and won't damage the rock. If this is a particularly large slab or a slab you plan to display by hanging on the wall, I would agree with ptychodus that you might want to build a wood frame/backing to support it as none of the glues are going to be strong enough to hold the rock together while under strong tension.

[jpc]

2 hours ago, Ptychodus04 said:

Pics of the slab would help a lot. You can use any cyanoacrylate to glue them back together but it may not be stable, depending on the size of the plate. You may need to back it with plywood to keep it from breaking again if it is largeish.

...and to take it further... what glue to you use to bond the plywood to the slab?  

[Ptychodus04]

1 hour ago, jpc said:

...and to take it further... what glue to you use to bond the plywood to the slab?  

 

I've used many different glues for backing applications with good results. I have one client that requires slow setting marine epoxy. It's very strong, stable for long term use but messy. It's probably the best option for large (>24"x24") or thick (>1") slabs due to its ability to hold significant weight.

 

Medium or thinner slabs respond well to slightly weaker but easier to use adhesives. For this I have used silicone, non-expanding Gorilla Glue, and even high viscosity Paraloid. The catch with these glues is that the weight of the slab itself is often not great enough to achieve a strong bond. I typically lay a piece of 3/4" plywood on top of the glued slab and pile on a bunch of weight to provide "clamping" pressure. If you're backing a prepared specimen, a thin layer of closed cell foam is added between the prepared surface and the plywood pressure board to keep from damaging the specimen. The weight required depends on the size of the slab being glued but I typically use 50-100 pounds evenly distributed over the surface. Extremely thin or fragile slabs need special care not to break them during the process.

[jpc]

Thanks for this info, Kris

 

[hadrosauridae]

1 hour ago, Ptychodus04 said:

 

I've used many different glues for backing applications with good results. I have one client that requires slow setting marine epoxy. It's very strong, stable for long term use but messy. It's probably the best option for large (>24"x24") or thick (>1") slabs due to its ability to hold significant weight.

 

Medium or thinner slabs respond well to slightly weaker but easier to use adhesives. For this I have used silicone, non-expanding Gorilla Glue, and even high viscosity Paraloid. The catch with these glues is that the weight of the slab itself is often not great enough to achieve a strong bond. I typically lay a piece of 3/4" plywood on top of the glued slab and pile on a bunch of weight to provide "clamping" pressure. If you're backing a prepared specimen, a thin layer of closed cell foam is added between the prepared surface and the plywood pressure board to keep from damaging the specimen. The weight required depends on the size of the slab being glued but I typically use 50-100 pounds evenly distributed over the surface. Extremely thin or fragile slabs need special care not to break them during the process.

 

To follow up the topic ( I hope the OP doesnt mind expanding the original question), Do you use any adhesives to seal the edges of larger slabs?  I have seen some my slabs that are waiting prep to develop a spontaneous delamination.  Its not completely through the slab (yet), but my fear would be to hang it, then have the front half fall off at some point.  This is also from the split-fish or sandwich layers.

[SPrice]

I have over a hundred pounds of GRF slabs and plates. Some ended up getting split quite thin ( less than a quarter inch )and have that spontaneous delam. issue.  I mounted some on masonite with white glue and weighted during the glue cure so as to not let the masonite curl. Works for me. They got glued around the perimeter as well with the white clue. I even did one fish with a diluted formula of 50/50 glue and water to coat the entire surface with a thin coat. It came out like you think it would. Wet looking, darker matrix but certainly not flaking apart. Only did one as a test on a less articulated specimen.  When held side by side one would like one or the other. Separate, I would almost choose the coated one every time. And, yes, these are the split fish layers, not the 18 inch layer fossils.  just my experience.

[Ptychodus04]

31 minutes ago, hadrosauridae said:

 

To follow up the topic ( I hope the OP doesnt mind expanding the original question), Do you use any adhesives to seal the edges of larger slabs?  I have seen some my slabs that are waiting prep to develop a spontaneous delamination.  Its not completely through the slab (yet), but my fear would be to hang it, then have the front half fall off at some point.  This is also from the split-fish or sandwich layers.

If the slabs start to delaminate, I drop a liberal amount of thin cyanoacrylate into the delamination to stop it and then will use Apoxie Sculpt to fill in the crack. The delamination is caused by the rapid drying of the rock around the edges. That stuff is WET in the quarry, unless it's been sitting dug out a long time. I've been working on a pad in the middle of July and had water seeping out of the rock while I'm working. It's really comfortable to use as a resting spot during a midday break.

 

I've never had one split completely in half on its own. The drying is so slow in the middle of a slab that the rock tends to hold together. I've moved around 5 tons of GRF material in and out of my lab over the last 5 years and I'd say 10% will develop a significant delamination but it's always stoppable with glue. Glue it as soon as you see it starting to keep the delamination to a minimum. The longer you let it go, the wider it will get until it stops drying quickly.

 

 

14 minutes ago, SPrice said:

I have over a hundred pounds of GRF slabs and plates. Some ended up getting split quite thin ( less than a quarter inch )and have that spontaneous delam. issue.  I mounted some on masonite with white glue and weighted during the glue cure so as to not let the masonite curl. Works for me. They got glued around the perimeter as well with the white clue. I even did one fish with a diluted formula of 50/50 glue and water to coat the entire surface with a thin coat. It came out like you think it would. Wet looking, darker matrix but certainly not flaking apart. Only did one as a test on a less articulated specimen.  When held side by side one would like one or the other. Separate, I would almost choose the coated one every time. And, yes, these are the split fish layers, not the 18 inch layer fossils.  just my experience.

 

You will eventually regret using white glue if you put it on a specimen you want to keep forever. It yellows terribly over long time storage. Ant it will eventually crosslink. It's a polyvinyl alcohol solution and it is not recommended for long term curation. If you want to coat a specimen, use Paraloid or Butvar. You'll get the same slightly wet look but it is stable and reversible forever.

[SPrice]

Thanks, Kris. One disarticulated fish coated in Elmo's gloop isn't going to be the end of the world for me. It was a test for entertainment purposes only. I coat the fish only with Paraloid after prepping them out and CA along the way  where needed. Most of my slabs were from August collecting timeframe. Still dry and warm in Kemmerer. I did see some folks at the quarries trying to split fresh plates.  Whoa! Stop! it will not split that wet....said the quarry assistant who had brought them from the wall to the splitting piles. Enthusiasm got the best of them.

 

Would the cross-link in the polymer chain of the PVA mixing with the calcium ions from the calcium carbonate matrix result in a gel coat..like a sticky mess? Or would it become extremely stiff, brittle and cracking all to pieces?

[Ptychodus04]

1 hour ago, SPrice said:

Thanks, Kris. One disarticulated fish coated in Elmo's gloop isn't going to be the end of the world for me. It was a test for entertainment purposes only. I coat the fish only with Paraloid after prepping them out and CA along the way  where needed. Most of my slabs were from August collecting timeframe. Still dry and warm in Kemmerer. I did see some folks at the quarries trying to split fresh plates.  Whoa! Stop! it will not split that wet....said the quarry assistant who had brought them from the wall to the splitting piles. Enthusiasm got the best of them.

 

Would the cross-link in the polymer chain of the PVA mixing with the calcium ions from the calcium carbonate matrix result in a gel coat..like a sticky mess? Or would it become extremely stiff, brittle and cracking all to pieces?

I’ve never used it personally, but I’ve spent a lot of time dealing with old fossils that were treated with it. I don’t know that you’d see much pick up of molecules from the matrix but anything is possible over time. The pieces that I’ve worked on had the 2nd result bar none. All were super hard, badly cracked, and yellowed. There’s no easy way to remove it either. Acetone will soften it but not dissolve it completely, leaving you with a sticky booger-like material that has to be removed mechanically.

 

I’ve dealt with some really nasty stuff over the last 3 decades. 

 

Back to the OP’s topic… @Pixpaleosky shoot us a picture when you can.

[Pixpaleosky]

Here is the picture.

Thank you for your answers. 

All i have is either white glue or strong glue with trimethoxyvinylsilane ?

Do i have to glue in vertical or horizontal position ?

[Ptychodus04]

That's a good candidate for cyanoacrylate and looks thick enough to not need a backing. Glue all the little pieces back on first, then glue the main break. Make sure to put a light coat of glue on all the surfaces and clamp them together if possible. This will make for a much stronger bond.

 

You want to lay it flat so it doesn't have the opportunity to fall over.

[jpc]

And I will add, put a layer of plastic wrap or something between the fossil and the tabletop so any extra glue squeezing out the bottom does not glue the fish to the table.  

[Pixpaleosky]

Great I will try and keep you posted !

[Pixpaleosky]

Here is the result but I am unhappy with the crack. How can I fill it ?

 

[Randyw]

Scrape some matrix from the backside as a fine powder, fill crack, sprinkle matrix dust over repair while it’s still wet so it sticks…

[Jaybot]

Don't use superglue for the crack, as in my experience it darkened the powdered matrix and left me with a darkened filled crack.

[Pixpaleosky]

I'lk try thank you !

[Ptychodus04]

I use Apoxie Sculpt. You can mix in dry pigments to match any color of rock. The filling with matrix route is ok but I much prefer the epoxy clay.