Yes, most (if not all) of the food-based adhesives (wheat flour, rice flour, potato flour) will mold if not dried completely and sealed well.  All of those materials are hygroscopic, meaning they will re-absorb moisture out of the air even after being well-dried if they aren't sealed immediately, inside and out.  If they are dried and decorated with most water-based paints (such as watercolors and tempera), they will absorb more water from the paints and must be re-dried.  If sealed without drying, or if simply not sealed at all, you're going to get mold.   

And putting papier mache in a damp environment is just begging for mold.

Jackie (this website owner) did some pretty thorough testing of sealants under wet outdoor conditions and posted them under Articles:  http://www.papiermache.co.uk/articles/w … ier-mache/ and she did find success... eventually. 

You probably won't need to use The Ultimate Sealer on indoor projects, a regular sealant like varnish should do fine.

Even so, please realize that you must seal the entire piece on every side that will be exposed to air.  If your project is intended as an outdoor piece, especially, you'll have to be absolutely certain that you cover the entire surface.  One tiny uncovered spot smaller than the head of a pin will allow moisture to enter, and all your work will be spoiled. 

If you are making hollow forms with any kind of opening, you must seal the interior, too.

Please follow David's advice, as there are mostly-non-organic adhesives that won't FEED mold, but all of them do need to be sealed.  Paper molds -- it's a law of some kind.

And welcome to the forum!  Check out the Articles and Tutorial sections (bar near the top) and feel free to post your own discoveries... and photos of your work.

Sue

The only non-toxic sealant that I'm aware of is real, natural shellac, which is made from shellac flakes dissolved in denatured alcohol.  The alcohol is toxic to ingest, but when the shellac dries the alcohol has evaporated.  Shellac is often used on toys and is safe for use around animals.

The alcohol in the liquid shellac is very flammable, but I'm reasonably sure the dried shellac is not.

You can buy it in flake form and mix it with the alcohol yourself, or buy it already mixed, which lasts about one year.  Real shellac is usually dated with the mixing date.

Bulls Eye is a well-known brand in the U.S. 

Synthetic plastic lacquers are not the same as real shellac, and may be flammable.

Sue

Bugaloo, I haven't found anything that is both non-toxic and a #1 sealer.

All the best sealers are dependent on carriers that have toxic ingredients.  The alternatives aren't as long-lasting or as dependable with their water-resistance.

Most of the polyurethanes seem to be suitable for indoor sealing, but as far as I've found, they aren't very sunlight (ultraviolet) resistant.  The ones I've used first cloud, then crack, then peel.

It would be nice to find something that is all things to all people, but I'm not going to hold my breath.

Sue

It depends. 

If I want a more matte surface, and I'm working indoors in winter, I use shellac, due to it's lower toxicity

If I want a glossier finish, and if I can apply the sealer outdoors, in good weather (not raining or humid or very hot and no wind) I usually use regular varnish.  If I need a seamless finish, I'll use the spray type, and apply several thin coats so it doesn't make run marks.

I've used the polyurethane sealants, and for indoor purposes they seem to be okay, but for some reason I tend to gravitate back to shellac and varnish.  I think it's a personal mental aberration more than something that is rational.  8-)

But if your project is destined for outdoor use (even just in good weather), make sure your sealant contains UVLS (UltraViolet Light Stabilizers), or at least specifically says that it is suitable for outdoor use.  I've had such damage from UV sunlight on sealed materials that some projects have ended up in the burn barrel.

If anyone lives in the deserts of the U.S. Southwest, do yourself a favor and keep your finished works out of that strong sunlight.

Sue

I had a bad mod-podge experience early on (stayed tacky) and haven't used it since, so I can't comment on that. 

But I do use a sealer that is nontoxic and I feel is a pretty good compromise between good sealer and low/non toxicity.  I am usually finishing pieces indoors, so it's important to me to be able to do this in a way that won't harm me or my animals.  (I can use a respirator, but they can't!) ...

It's called Shields-All, and there's a longer-lasting, higher solids one called Super Seal. 

http://www.hytechsales.com/prod50.html  Shields-all
http://www.hytechsales.com/prod52.html  Super-seal

I have not yet done a real stick-it-outdoors-and-let-it-pour/freeze, etc. but this is designed to seal wood decks and outdoor things.  (I found it from a reference on a plaster sculpture discussion board conversation -- the outdoor plaster sculpture company used it to finish their outdoor plaster sculptures.   They now seal their sculptures with Aqua Resin instead.  This level of sealer is good for me tho.)

I make papier mache horns (for marching in a parade) and I needed them to be able to handle getting a little rained on without dissolving.  That was my goal -- not an outdoor semi-permanent sculpture -- tho I have those ideas as well.

I'll try Super Seal next, but a gallon of Shields-All goes a long way.

(You can also add it to regular latex paint to improve flow and weatherability ... : ) ).

They only sell it as a gallon, and it's a bit pricey to ship, but when I priced it out it was comparable to a gallon of the super toxic spar varnish -- which I wasn't going to be able to use indoors -- so I gave it a shot.  It's all I use now.

It's glossy -- so if you want a matte finish, you'd need to spray it with a matte spray as the final coat. 

Also -- you can paint over it (unlike many finishes) ...  so you could actually seal a piece first, then paint it, then seal the paint.  (Might help with things like cracking paint causing a prop to get waterlogged.) ...

They have some interesting information about how deck sealants work (which is pretty much how papier mache works as well -- from the sealant perspective) ...

http://hytechsales.com/howtopaint/wood_decks1.html

-- b