Shelf life of plaster

[Dan_Musicant]

A book I have (Renovating Old Houses by George Nash) noted as an aside in one sentence that plaster will only stay usable for around a year. I just bought 100 lb. of plaster (50 lb. USG Struct-o-lite and 50 lb. USG Diamond Veneer Finish plaster) and wonder if it will last longer if I store it in air-tight containers and store in a cool location. When I bought these last week I had no idea it wouldn't keep indefinitely. I have a lot of plaster work to do, but may well not get around to 95% of it for a year or longer. Anyone have experience with these things? Thanks for any info.

Dan

[Richard J Kinch]

Plaster will strike in the bag due to infiltration of humidity. It will still be a powder that mixes up OK, but given enough storage time and humidity before use it will have a final strength of a Ritz cracker.

I would think the cost of proper containers would approach the cost of the plaster.

Most cost effective would be 5-gallon paint buckets with the O-ring lids, with a sock full of calcium chloride as a dessicant.

Easy enough to do your own "lab" testing later to verify setting quality. Make some cylindrical samples (cast in a pill bottle) now and when you plan to use it. See if you find any difference in strength or setting time. Better than wasting a lot of labor on material that turns out to be flawed.

Steady non-condensing relative humidity is more important than cool. Warmer may make your RH lower.

[Doug Miller]

Yes, absolutely. In an air-tight container, it will stay fresh for a long time (at least two years, in my experience, and I live in an area with fairly humid summers).

Temperature doesn't really matter that much. What's important is keeping it dry.

It's better to use your plaster as soon as possible after opening the bag, but the stuff will keep a long time as long as you keep it dry.

[Goedjn]

It will keep longer in an airtight container with dessicant, but still not forever. Plaster is cheap. Give the excess to your kids to play with.

[Dan_Musicant]

:Dan_Musicant writes: : :> wonder if it will last longer if I :> store it in air-tight containers and store in a cool location. : :Plaster will strike in the bag due to infiltration of humidity. It will :still be a powder that mixes up OK, but given enough storage time and :humidity before use it will have a final strength of a Ritz cracker. : :I would think the cost of proper containers would approach the cost of the :plaster. : :Most cost effective would be 5-gallon paint buckets with the O-ring lids, :with a sock full of calcium chloride as a dessicant. : :Easy enough to do your own "lab" testing later to verify setting quality. :Make some cylindrical samples (cast in a pill bottle) now and when you plan :to use it. See if you find any difference in strength or setting time. :Better than wasting a lot of labor on material that turns out to be flawed. : :Steady non-condensing relative humidity is more important than cool. :Warmer may make your RH lower.

Thanks for the post. I cut open the bags last week and put the plasters in plastic bags, fairly thick ones mostly. But I got the idea shortly thereafter to use some plastic buckets I have. These aren't 5 gallon buckets but food service buckets I got from a fast food place. They gave them to me free. They had 10 lb. potato salad in them and I got them with the tops. I have 13 of them now, and can get an unlimited supply in the future for free (I made an arrangement with another source.

I presume they will be air tight, but I think your admonisions are advisable - dessicant and testing. I would never have thought of the dessicant, and I wouldn't have done the testing without your suggestion. However, like you say, it's really important that I not invest time and materials into repairs that turn out to be crap.

Great ideas with the old pill bottles. I have a bunch of them, been saving them for some good use, and this is sure one. Thanks again.

Dan

PS: Anyone know where I can get calcium chloride in quantity economically? Thanks!

[Keith Williams]

Nice. I buy them at the BORG. Free is better. ;-)

Not to mention the work to tear out crap.

It is a good idea. I may have a little grout and thinset to do this with.

The better sidewalk/driveway ice melter is calcium chloride (read the container, NaCl isn't a desicant). You should be able to find it for $12is for a 50lb bag at the BORG or a bit more at a hardware store. It's also available (for a lot more $$) at grocery stores in the winter (too soon now :-( ).

[Richard J Kinch]

Polyethylene bags are poor vapor barriers.

Swimming pool store.

[Dan_Musicant]

:Dan_Musicant writes: : :> I cut open the bags last week and put the plasters :> in plastic bags, fairly thick ones mostly. : :Polyethylene bags are poor vapor barriers.

Thanks. : :> Anyone know where I can get calcium chloride in quantity :> economically? : :Swimming pool store.

Thank you. It doesn't snow here, so swimming pool water conditioner is easier had than snow melter.

[Dan_Musicant]

:Most cost effective would be 5-gallon paint buckets with the O-ring lids, :with a sock full of calcium chloride as a dessicant. A pool supply place I'm talking to doesn't have it but they stock calcium hypochlorite, which he says is a "pool shocker" or some such thing. Is that a dessicant (i.e. OK) or do I want calcium chloride? TIA

Dan

[Doug Miller]

No.

In my experience, an air-tight container is sufficient. No need for a dessicant.

[Richard J Kinch]

No. Calcium hypochlorite is an elemental chlorine source. You don't want that near anything or even inside the house.

You want calcium chloride. Any pool supply place will have that. Perhaps they're too typically ignorant to know the chemical name. They might only know it as some variation of the words "calcium hardness increaser." Look on the bag or tub for a chemical ingredient.

[Dan_Musicant]

:Dan_Musicant writes: : :> A pool supply place I'm talking to doesn't have it but they stock :> calcium hypochlorite, which he says is a "pool shocker" or some such :> thing. Is that a dessicant (i.e. OK) ... : :No. Calcium hypochlorite is an elemental chlorine source. You don't want :that near anything or even inside the house. : :You want calcium chloride. Any pool supply place will have that. Perhaps :they're too typically ignorant to know the chemical name. They might only :know it as some variation of the words "calcium hardness increaser." Look :on the bag or tub for a chemical ingredient. The guy I had on the phone was far from knowledgable. Sounded like a kid. He said to call tomorrow (which is today) and ask for his boss, which I'm going to do right now...

I talk to him and he says they don't supply it. It's a place called HD Pool and Patio Supply. I ask him for recommendations near me and he gives me the name of a place that's around 15 miles from me. I think I'll try looking up wholesale chemicals warehouses. I bought some chemical some years ago from such a place and thought it reasonable.

[Dan_Musicant]

:In article , Dan_Musicant wrote: :>On Mon, 28 Aug 2006 21:53:19 -0500, Richard J Kinch :>wrote: :>

:>:Most cost effective would be 5-gallon paint buckets with the O-ring lids, :>:with a sock full of calcium chloride as a dessicant. :>A pool supply place I'm talking to doesn't have it but they stock :>calcium hypochlorite, which he says is a "pool shocker" or some such :>thing. Is that a dessicant (i.e. OK) : :No. : :> or do I want calcium chloride? TIA : :In my experience, an air-tight container is sufficient. No need for a :dessicant.

The problem is that I'm uncertain if these containers will indeed be air tight or not. I think they may be absolutely air tight, but I'd hate to find out they aren't by having my plaster go bad, especially if I've gone ahead and used it. I'll try to find a cheap source of calcium chloride.

[Doug Miller]

Why bother, Dan? You _don't_need_it_. An airtight container is all you need.

[Doug Miller]

Haven't you been reading my posts? I've said at least twice that in my own experience, putting it in an airtight container is enough. How hard is it to find an airtight container? All I'm using is a five-gallon bucket and lid that I bought at Lowe's for about $8, and it works _just_fine_. No dessicants. No driers. Just a tight lid.

[Richard J Kinch]

Putting a dessicant in a leaky or permeable container just lengthens the time the interior stays dry. Eventually the dessicant saturates and becomes inert. In the case of a deliquescent like calcium chloride, it turns into a nasty, corrosive goo. Thus the advantages to silica gel or molecular sieves.

[Dan_Musicant]

:Dan_Musicant writes: : :> The problem is that I'm uncertain if these containers will indeed be air :> tight or not. : :Putting a dessicant in a leaky or permeable container just lengthens the :time the interior stays dry. Eventually the dessicant saturates and :becomes inert. In the case of a deliquescent like calcium chloride, it :turns into a nasty, corrosive goo. Thus the advantages to silica gel or :molecular sieves.

I've spent an hour or two trying to locate CaCl2 hereabouts, but not done well. The pool supply places say they don't carry it and most are a ways from me, anyway.

Chemical supply places are too expensive. I did find one that will sell me 50 lb. for around $55 including tax, so that's a possibility. But 50 lb. seems like a lot and I'll have to store IT somehow so it stays dry!! Pretty funny, in a way. I found some on eBay, 5 lb. for around $22 shipped. Maybe I'll do that. The CaCl2 is $10, the shipping $12. Or 10 lb. for around $32. I guess if I can keep it dry, it might be a good investment.

[Dan_Musicant]

:>The problem is that I'm uncertain if these containers will indeed be air :>tight or not. I think they may be absolutely air tight, but I'd hate to :>find out they aren't by having my plaster go bad, especially if I've :>gone ahead and used it. I'll try to find a cheap source of calcium :>chloride. :>

:Haven't you been reading my posts? I've said at least twice that in my own :experience, putting it in an airtight container is enough. How hard is it to :find an airtight container? All I'm using is a five-gallon bucket and lid that :I bought at Lowe's for about $8, and it works _just_fine_. No dessicants. :No driers. Just a tight lid.

It's hard for me to be certain that my containers are tight. I better do something soon, though, because I have the plaster in my garage and the rainy season is around the corner. On top of that, my garage needs a new roof! I'm gonna be a busy guy.

[Dan_Musicant]

:Why bother, Dan? You _don't_need_it_. An airtight container is all you need. I can and may well just try that. I can test my plaster if I'm nervous. Thanks.

[Richard J Kinch]

That's odd. It is a necessary ingredient to protect any plaster pool surface from soft-water etching. Maybe the pool supply places are in the replastering business, too.

Another source is concrete suppliers, where it is used as an accelerant.

I would also ask at an Agway feed store type place.

Or just the 42 oz DampRid refill at Home Depot.