Plaster of Paris is used to put casts in fracture patients.Although Plaster of Paris only depends on one simple chemical reaction for its setting, it is possible to vary the features of the process according to different requirements.
Temperature
If a bandage is immersed in cold water the initial set will be delayed and thus “working time” lengthened. However, if a very rapid set is required soaking the bandage in warm water will accelerate the rate of reaction. However over 50 degree C the setting rte slows and at 100 degree C no set occurs.
Strength
The final strength of the cast depends on the crystal structure. If the cast is manipulated after the “initial set” or prevented from drying out, it will be weak. Drying out will be delayed in cold or moist conditions and accelerated in a warm and dry environment.
Obviously, the cast strength is dependent upon the thickness of plaster and the shape of the cast which follows the contours of the affected limb. However, excess plaster will also increase weight and bulk and heat product. Therefore these different factors must be weighed against each other.
Padding
Padding is used under a plaster cast to mechanically protect skin, soft tissue and bony prominences from pressure and abrasion and cast removal. Also to protect the skin from thermal injury because of the exothermic generated during setting. Poorly applied padding may produce sores. Over padding will reduce the closeness of the fit of the cast, and possibly permit excess movement at the fracture site resulting in impaired healing. Thus skill in padding is as essential as plaster moulding in the production of a therapeutic cast.
Incorporation
Because plaster of paris is infinitely mouldable in the wet state it can be set around cast brace hinges and walking heels with ease. However for maximum strength, the plaster should dry out first and the walking attachment affixed with a fresh plaster of Paris bandage.
Absorption
The property of Plaster of Paris to absorb moisture has meant that casts have been used as wound dressings. However, too much moisture from inside or out will reduce the strength of the cast and make it liable to breakdown.
Time
The strength of Plaster Paris builds up over a period of time in 3 stages and so load may be gradually increased. Excessive premature loading will produce a breakdown of the cast and patients need to be advised how much load they can apply and at what time.
Can Plaster of Paris is usable once used?
Hi Vardhman,
If plaster of Paris has been used once, it cannot be used again.
There are changes in its structure and material properties which render it non usable.
What is hemihydrate? And Dihydrate?
Hemihydrate is when half molecule of water is attached. It is depicted as 1/2 H2O the equation.
2H2O is dihydrate.
Hello sir,
i our area we are geting gypsum. so i am intrested in manufacture plaster of paris. kindly inform me the manufactruer proces mainly the heating proces and what digre? i am plan to manufacture School chalk also.
Kindly help me giving above projects
Authi,
We do not know and do no offer that kind of advice. We are concerned with medical use of plaster rather than manufacturing point of view.
Arun Pal Singh
1. which kind of bandage is used in manufacturing POP? howmany squares per inch in a bandage is there?
2. what is the maximum temperature in exothermic reaction in POP?
my question,
is it suitable if POP and aluminum as a material to make an implant..i'm doing my research about that
Khairil,
I am not sure if I understand that question. Plus I do not know much about implant manufacturing.
Sir,
we want to build a particular structure with plater of paris as the mould i need to know the variations of the material in or order to use it and different qualities available so pls send me some links where i can get to know about it
Aun,
I am sorry I do not possess that knowledge. I think you would be better helped by searching from Google.
Does plaster of paris have any allergic reactions? Especially when removed with hot water.
Truly speaking one can be allergic to anything even water. But it is not a common phenomenon to find people allergic to plaster.
What is the exact problem?
Hello sir,
I want to make a little model of bridge with plaster of paris.and my model's volume is approximately 0,025 m^3 and i have 6 kg plaster of paris.My question is this 6 kg plater will be enought for filling my model??f it is possible can u send me the density of plaster of paris to my e-mail pls?
thank you wish ur success continue
@bora karagenç,
My knowledge about plaster of Paris is very little and relates to what is required to know for its use in medical field.
i am sorry i am unable to answer your query.
Hello dr Singh,
I'm doing research for comparing a new hybrid cast-brace to replace conventional casting. I now that the padding will loose thickness with time and compression, plus the plaster will shrink with time and drying.
That situation permit the joint or fracture to have some movement, and theoratically extend the time of healing or risk of non union.
do you know who would have info on those subjetc: shrinking of cast, reduction of thickness of padding and amount of mouvement in cast in time.
Thank you
@Serge-Eric Blais,
Looks like an interesting concept and could be used where rigid cast is not desirable.
Unfortunately I do not have the information that you have asked for.
I think a little search could help you, if there is available info.
Good day Dr Singh,
I'm researching information to the effectiveness off cast immobilization during the 6 weeks of wear.
I'm part of a team that develop a cast-brace hybrid that can replace regular casting. Since our product is moulded directly to the patient and can be remould many times over, our product would perfect for that new approach in rehab that calls for a faster passive mobilization of a joint to reduce complication due to immobilization.
But to be able to compare both approaches, I need to know if (to your knowledge) there are some studies that exist on the effectiveness of casting.
Thank you in advance
@Serge-Eric Blais,
Sorry again! I do not have that info.
Thank you for the reply.
I haven't stop the search, and already came up with a few info.
When I have enough info, I will post my finding on your blog if you'd like.
SEB
@Serge-Eric Blais,
Sure! We can work on that
Im not sure if Im on the right site ..
august 30 2009 I was in a motorcycle accident and suffered a spiral mid shaft humerus fracture …A clam-shell was used to stable my fracture .. Its been 5 months and Im still very uncomfortable..
@Kathy,
Yes! you are right.
It is probably wrong page to talk about fracture.
Plus you would need to elaborate your query.
Find a page on humeral fracture or fracture in general and post your query in detail
which chemical increasing hardness of plaster of paris. what are the process chalk stick making. what is effect of mesh size of pop on chalk stick.
@Dinesh Chandra,
I am not aware about these things. Sorry.
To answer your question, the plaster use in the casting material is a gypsum base powder. The mesh is there to augment the structural integrity of the final product. To cast does not become harder or softer, but rather more or less porous. To have a cast that is more porous, you would use more water. As the water dries, it create micro pores. It’s very important to remove as much water from the cast rolls as possible to make a solid and more durable cast.
As for chalk stick, google it.
Thanks Serge-Eric! That was really nice of you to answer that question.
how to control (slow) setting time without loss strength.
@Dinesh Chandra,
Using water at lesser temperature might help.
1.does pop reflects lights effectively?
2.does pop absorbs moisture consistently & help reducing humidity?
its urgent
@ramnath,
I do not think your queries are related to health field. I am not sure if I could answer that.
Dr Pal Singh, do you know if there is any study of the pourcentage of mobility allowed in cast, and/or the the amount of mobilty acquired by the patient in is cast as the cast dries and contracted and as the inner protective materials get compacted with time.
If not, I was on the verge on preparing a x-ray study of casted patient from day 1 to the end of treatement with x-rays taken every to weeks. Would you be interested?
@Serge-Eric Blais,
The literature does mention the approximation of the immobilization provided.
But I do not think there iare enough studies providing quantification of immobilization.
Let me know the idea and We would see if it can be worked out.
I was wondering if you have any tips for getting POP to set well in the tropics. I work in a hospital in PNG where we have very high humidity. A lot of our POP will not set. We have tried heat, doing it in theatre with the airconditioner on to reduce humidity… any ideas??
@Daniel Priest,
Did you try water at higher temperature?
Your problem is related to the evaporation of water in your cast. I would suggest removing as much water from your cast roll before making your cast. You could also use a fan to force the evaporation of water. When POP sets, the excess water that remains in will make your cast more porous. Hotter water will accelerate the chemical reaction but not the evaporation, the danger in using hotter water is the risk of burning your patient. You could also use salt in your water to accelerate the reaction, but again be careful the heat produced by the reaction.
Fibercast or other synthetic material would be a better choice for your environment, because water facilitates the reaction.
plz guide me…….
which has quick setting property (get dry quickly) among these…….? either plaster of paris or chalk powder………..
@vignesh,
I have no idea about chalk powder.
Plaster of Paris is under what type of material? it is ceramic or concrete…k
@azrin,
I think it does not fall into either. Somebody with this knowledge is welcome to comment on the topic.
dear Doc how long gonna stay in cast a patient with hip spica? Wish u all the best!
@Tsegaye,
Depends on age of patient and indic.ation for spica
Need the help for the manufacturing of the POP BANDAGES in my final year of Pharm-D
Sir I am a student of Pharmacy and my project is to make the POP Bandages with high setting time do you guide me or help me out to determine the whole ways procedures involving in the manufacturing and how get fast setting time pop
@Zubair Ishtiaq,
I am sorry. I do not have any idea about POP manufacturing. You would need to consult someone from industry.
in how many stages does plaster of pARIS set ???and what are those stages ???
@asif,
You would need to consult a resource with knowledge in the field. I am not aware about chemical properties of plaster beyond use in medical field.