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cracks in pulp

#1 2010-12-13 17:40:34

laura.wacha
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Registered: 2010-12-13
Posts: 11

cracks in pulp

I am using a fiberglass globe as an armature, and I keep getting cracks in my pulp as it dries. I am only getting cracks on the portion of the sculpture where the fiberglass is. But then, it's that sphere shape...
I'm thinking it's one of 3 things.
1. A temperature thing(?), with the fiberglass expanding as my studio gets warm (it's winter here now). I actually watched and heard the cracks appear last night as my studio warmed up.
2. Or could it be the pulp shrinking and pulling from all directions? But, I've never had this problem with cardboard globes.
3.Also, my new batch of Celluclay seems lumpier than usual. Could it be defective?
Does anyone have experience with this? Any solution? Wait until spring?

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#2 2010-12-13 17:45:43

dopapier
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From: UK
Registered: 2004-12-04
Posts: 754

Re: cracks in pulp

Yes, pulp shrinks as it dries.  Think of all the water that helps make up the volume and then evaporates.
Solutions?  Why use pulp?  If you want a nice bonded surface with strength, try laminating, alternating bond paper and kraft.  How many layers?  It depends what strength it needs and how big it is.  Normally six layers would be strong but you might want to go up to a dozen.  Don't use flour paste and let it dry at least every two layers.  If you want to model pulp on top (for contours, shapes etc.) paint your laminate with PVA first which will help resist water soaking into the under layer.
Don't worry about Spring.  Central heating is great for drying.
DavidO


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#3 2010-12-13 20:10:49

laura.wacha
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Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

I always start with strips, but I've never tried to put on a coat of PVA before pulp. What about a coat of gesso? Of course, I've never had any trouble with pulp cracking before. I like pulp because of the somewhat bumpy texture, but haven't made my own for years! I would never use flour-too many rodents here! I'm still not sure how to fix this one sculpture that I'm working on without ripping off his head and starting again! Maybe I'll repair the cracks with strips before I repulp...?

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#4 2010-12-14 09:30:42

dopapier
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From: UK
Registered: 2004-12-04
Posts: 754

Re: cracks in pulp

Yes, and use PVA to create a really strong bond.  Also keep your pulp layer fairly thin.  If you take a lump, put it between two plastic sheets and roll it thin, you can apply it more easily, using a plastic knife or similar.
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#5 2010-12-16 04:41:37

CatPerson
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From: Washington State, U.S.A.
Registered: 2006-01-09
Posts: 1314

Re: cracks in pulp

You don't have a light on inside that sphere, do you? 

Did the cracking happen in the final stages of drying, or early on?

If you like the texture of the pulp, maybe laminating strips first, as the base, and when that is dry, add pulp to the surface.

You also didn't indicate how thick your cracking pulp was...

But with the texture of the pulp, it might be more simple just to let the sphere dry and crack, then fill in the cracks with more pulp.

Sue

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#6 2010-12-16 18:50:03

laura.wacha
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Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

Yeah, I always do strips first. I like to then use the pulp to get a bumpy texture. I think the issue here was that I usually start with a cardboard globe (absorbent) and not the fiberglass one that I have used this time. I think the cracks are fixed; i put some tiny strips to bridge the gaps and a thin layer of pulp. It needs more layers of pulp, but I should be able to refill any little cracks as (if!) they form. Thanks for the tips!

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#7 2011-02-08 19:26:01

laura.wacha
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Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

Okay. I finished the piece over 3 weeks ago (Pieman) and we had a cold snap. I'm talking minus 15 degrees farenheit. I don't know how cold it was in the unheated studio, but I had further cracking. I have incorporated the cracks into the design (can't always fight nature) but I will never use a fiberglass globe as an armature again...

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#8 2011-02-08 20:10:14

mavigogun
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From: Istanbul
Registered: 2009-04-22
Posts: 106

Re: cracks in pulp

How dry was your pulp when the glue was added?   Less water = less shrinkage.   Do you squeeze out every last drop?   I put my pulp in a pillow case and wring out as much as I can, then press out the remainder by rolling my fists over it while they support my weight.   Do you know your pulp to binder ratio?

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#9 2011-02-08 22:10:46

laura.wacha
Member
Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

I use Celluclay (I like the ease and after painting on canvas for years the price seems waaaay cheap!). I also live in the desert, so drying has never been an issue. I've made a few spherical pieces, but this is the only one that has this cracking issue and I can only think it's the fiberglass globe underneath that is shrinking and expanding. I always put on strips of newsprint first and I use Elemer's Art Paste for that. Poor Pieman. He has been attacked by the birds that he has baked in the pie...

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#10 2011-02-09 23:00:37

skwirl
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From: Oklahoma City, OK
Registered: 2008-11-12
Posts: 34

Re: cracks in pulp

Maybe the problem is that the fiber glass DOESN'T expand or shrink? Maybe the cardboard globe (by the way, where in the heck do you get a cardboard globe? I've never seen one and would love to use one!) gets wet with the pulp and expands and then shrinks back right along with the pulp,when the fiberglass doesn't?

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#11 2011-02-10 04:31:19

CatPerson
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From: Washington State, U.S.A.
Registered: 2006-01-09
Posts: 1314

Re: cracks in pulp

Desert... you didn't happen to dry this piece in the sun, did you?

I don't know about fiberglass, but if rubber/plastic spheres are placed in the sun with PM or concrete on them, the sun heats the air inside the sphere and expands it, and splits or cracks the PM or concrete.  You should see what it does to concrete... it's awful after all that work!

If you don't want the cracks, why not just fill them in with more Celluclay?  Or does it emphasize the cracks even when thoroughly dry?

And Mavigogun is right about the moisture.

Sue

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#12 2011-02-10 17:23:00

laura.wacha
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Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

No not in the sun, it's winter and very cold! The cracks happened after it was all dry and painted. I have contemplated concrete as a material, but that cracking of which you speak would definitely happen with our extremes of temp here. It is my plan to learn to weld! Shouldn't be any issues then?

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#13 2011-02-10 17:25:24

laura.wacha
Member
Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

Oh and card board globes... Most are cardboard, I got a couple from a school library that I suppose were intended to be handled more roughly and one was plastic and one fiberglass. I won't be using them again!

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#14 2011-02-11 02:18:22

CatPerson
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From: Washington State, U.S.A.
Registered: 2006-01-09
Posts: 1314

Re: cracks in pulp

The cracking with the concrete doesn't happen as long as you use the minimum amount of water and don't set the sphere in the sun, and then keep them moisture (under plastic) for at least a couple of weeks.  They look quite gorgeous, actually!  I've done most of mine on plastic balls.

I guess the only thing you have to worry about with the welding is rust!

Sue

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#15 2011-02-11 15:57:39

laura.wacha
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Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

You get a lot of rain up there, don't you? We have the opposite problems here in New Mexico. Dry dry dry and sometimes a vast temprature difference from day to night. I'm not too familiar with cement/concrete, but I'm interested. I've been wanting to build a bottle wall, but wasn't sure of the mixture to use, to get pre-mixed, add sand and gravel, etc. Do you wear gloves? Maybe this summer I will just give it a go and see what happens...

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#16 2011-02-16 07:56:15

CatPerson
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From: Washington State, U.S.A.
Registered: 2006-01-09
Posts: 1314

Re: cracks in pulp

A premixed Type N masonry cement would probably do fine for that use.  You don't want gravel with mortar work, too lumpy.

Always use gloves with cement (thin latex is great for finish work, but not really durable), and a mask with dry cement (you can remove it when the cement is thoroughly dampened). When that stuff gets into your lungs, it stays there.  Eye protection is good, too.  Cement is pretty caustic, esp to mucous membranes.

You would have to make small batches at a time.  The bag should tell you what the set-up time is, and however much you mix needs to be used up within that time.  And no matter what some guy tells you, you CANNOT add water to it when it starts setting up, to keep it moist! NO, NO, NO!  It will weaken it and your hard work will crack.

Add half the estimated amount of water and moisten all thoroughly, then slowly add small amounts of water to reach the right consistency.  And it's dead EASY to PASS the right consistency!  Practice is the only way to learn.  Pack some in a cheap plastic cup and then unmold it immediately.  If it slumps too badly, it's got too much water.  If it seems dry and doesn't stick together well, it's too dry.

Due to your dry climate, you would have to keep misting the section you're working on so it doesn't dry out too fast.  Cement curing is a CHEMICAL CURE, not a drying cure.  It takes 28 days to cure, period.  The longer you can keep it moist, the stronger the bond will be.  Mist and cover with plastic when soft, hose it down and cover with the plastic after setting (initial hardening).

If you have to stop and start again the next day, thoroughly wet the first section before you start the second one.  Wet cement will not stick to dry cement.  Guess how I know that?

Keep your cement dry, preferably in 5-gallon plastic buckets with lids.  If it has hard lumps in it, take it to the dump or dig a hole in an out of the way spot and bury it.  It's history.

Okay, I guess we've digressed far enough from papier mache...

Sue

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#17 2011-02-16 15:44:02

laura.wacha
Member
Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

Thanks for the info! I will give it a go. I dread toxic stuff and masks, but I'm also drawn to fiberglass...
Meanwhile, my Pieman has continued to crack! And this is weeks after the fact, but still with fluctuating temps. I am going to patch some more and give it more time. If he still cracks, I will sadly have to remove his head and give him a new one. Sigh. I have an exhibit in May and I was planning to include him. We shall see...

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#18 2011-02-19 03:15:08

CatPerson
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From: Washington State, U.S.A.
Registered: 2006-01-09
Posts: 1314

Re: cracks in pulp

Laura, is there any chance that the cracking part may not have been completely dry before you painted it, even in your climate?

It just sounds... wrong.  Esp the continued cracking.  It's like a mystery where the answer is obvious, but I'm missing it.

Sue

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#19 2011-02-22 19:06:29

laura.wacha
Member
Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

Yeah, I'd love to figure this out! But no, the head was done first and it was all plenty dry before it was painted. I'm pretty sure it's just the spherical shape combined with the obscenely cold temps and the paper on the outside contracting differently than the fiberglass on the inside. I have several other round headed PM sculptures in the same space and they all survived the -15 degrees just fine.
You can imagine the tension on a shrinking sphere coming from all directions; something's gotta give...

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#20 2011-02-23 05:24:59

mavigogun
Member
From: Istanbul
Registered: 2009-04-22
Posts: 106

Re: cracks in pulp

A Google search for "Celluclay" and "shrinkage" returns over 8 thousand hits- and almost all of the first page of returns mention cracking.    Many reduce/eliminate significant shrinkage by adding a plastic medium- PVA glue or acrylic.   One such poster used 30% PVA, while another also added flooring acrylic.   Others uniformly textured the bonding surface.   If your shell bonded to the substrate in a single place, stresses wouldn't be distributed evenly.

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#21 2011-02-23 15:42:59

laura.wacha
Member
Registered: 2010-12-13
Posts: 11

Re: cracks in pulp

I used several layers of paper strips under the celluclay, but I'm looking for an alternative to the celluclay because I don't like how sticky it is. I want some texture as a top layer. Any suggestions? I'm not into making my own pulp, but I remember seeing pre-pulped paper at a pet store (for rodent bedding?). I was thinking of mixing it with Elmer's art paste, which I love. I like to be as simple as possible with my recipes!

Can you clarify? Is PVA just regular old white glue?

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#22 2011-02-24 07:07:09

mavigogun
Member
From: Istanbul
Registered: 2009-04-22
Posts: 106

Re: cracks in pulp

PVA = Polyvinyl acetate; it is most likely what you referred to as "white glue", commonly used as a wood adhesive.   If you're striving for simplicity, cooked wheat glue might appeal, as it is purported to be more hardy at low temperatures.   Cooking activates the gluten, transforming the wheat substantially; it's hardiness is well documented.   Rodents are no more attracted to gluten bonded paper pulp than a piece of wood.

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#23 2011-02-24 10:24:52

dopapier
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From: UK
Registered: 2004-12-04
Posts: 754

Re: cracks in pulp

There have been many experiences related in past correspondence in this Forum which says that rodents are definitely attracted to gluten bonded paper.  The difference from wood is that it is easier to gnaw and sometimes makes a lovely home.


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#24 2011-02-24 11:20:17

Jackie
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From: England
Registered: 2002-09-14
Posts: 389
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Re: cracks in pulp

PVA (white glue) comes in differing qualities. Avoid the cheaper, thinner white glues sold for children's crafts as they won't be strong enough.

I buy my pva from builder's merchants. You can get a really big tub at a reasonable price and its strong. The glue sold in craft shops is so much more expensive. OK if you only want to do one small project, but not if you are becoming a papier mache addict!


Jackie

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#25 2011-02-24 12:31:26

mavigogun
Member
From: Istanbul
Registered: 2009-04-22
Posts: 106

Re: cracks in pulp

dopapier wrote:

There have been many experiences related in past correspondence in this Forum which says that rodents are definitely attracted to gluten bonded paper.  The difference from wood is that it is easier to gnaw and sometimes makes a lovely home.

A reading of a number of posts support the contention that flour glue is the equivalent of Mouse Crack -which this author was, apparently, smoking when comparing the relative attractiveness where rodents are concerned.   No mice were polled when confabulating the assertion.   My affiliation with Houses for Mouses was not a factor, I swear...

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