hello there and here we are on frequently asked questions this is frequently asked questions
number three and today we're going to talk about plaster of paris casting and other plasters
also but mainly plaster of paris casting and how to avoid air bubbles in your mix
which appear on the cast when the plaster of paris is cured and also how to avoid cracks
in your plaster of paris and other plasters also
so this question has been asked quite a few times since the channel started and we'll address it
here now so we've got an array of items here an array of casts this is a plaster of paris cast
i've sprayed this with car primer paint automotive primer paint as you can see you see like
in these uh touching up again here it's been lying about for a long time i wanted to use this as a
paint effects cast paint job in one of the videos but never got around to doing it but we were at
some point and also as you can see this cast has turned out pretty much perfect and no air bubbles
or minimal air bubbles in this mix this is from the same mold i just filled it up part way in
view of make turning this into kind of a plaque thing and this cast also turned out very well
with hardly any air bubbles at all in the mix this has actually been mixed in with
nylon strands to reinforce the plaster so a later date this will be turned into a
plaque we've got pine cone here which has actually been featured in a few recent videos but anyway
the main cast here has turned that great very crisp perfect cast on the top if i turn it
upside down you'll see a few holes around the base there around the underneath of the
actual pine cone the reason the air got trapped here is because the mold envelopes that part of
the cast so you need some extra shaking and tapping to get the air out of the plaster
if you're having problems with your plaster the things to check first of all make sure you follow
the directions that will come with the plaster that you're using so with plaster in paris you've
got like a 50 50 mix of water to the plaster and what you want to do is you want to mix the plaster
to the water so you put your water in a container and then put your plaster in another container and
gently put that plaster into the water so sprinkle that in so that's going to reduce any possible air
that's going to get into the water plus when you're stirring be mindful of not to introduce
any more air let that settle beforehand before you stir let the plaster settle into the water before
you stir but stir quite carefully but deliberately to get the plaster nicely mixed in with the water
and then get that to a nice consistent mix and then you can pour that into your mold so
what i mean by consistent mix is is to get all the lumps out
so it's all uniform a nice uniform mix which you can then pour into your mold and then also
tap any air unwanted air out from the mold so when you've got your mold you can tap
on a surface to get that unwanted air out of your mold if there's any air in there
also what you can do is what i often do and sometimes forget um is to spray in some
diluted washing up liquid or dish soap into your mold and that'll line your mold you don't want to
saturate it you just want to spray around if there's too much water in there or just get rid
of the excess by tipping it out and that should kind of lubricate the outside of the mold and help
the plaster find its way around the mold a lot easier so um with a more detailed
molds that would come in handy so this you might class this as a more detailed mold
so if we look closely we can see some air bubbles that were trapped underneath the rim of the
helmet there this is actually actually crystal coat r to make up these stormtrooper buddhas
there's a lot of detail around the hands in some places it's come out great
but other places you might see there there's a little air bubble that's been trapped
actually this is on the whole this has turned out pretty well but this was a kind of rejected cast
because of the some of the imperfections there's a few there there's a little bit on the sleeve there
now in this case it might be a little bit more difficult to get rid of the air
bubbles so you might want to think about using different materials so
when i've casted these in the future i used um a resin so i think this is a polyurethane resin
and i can't remember the name of the resin on this particular cast and that's eliminated pretty much
all of the air bubbles so you want to think about what materials you're using for um the models that
you will be molding i mean this needs tightening up and still got some flashing that needs to be
tidy up and all that sort of thing we'll um perhaps do that in a later video tidying up
these pieces and um getting them ready for paint painting and do some paint jobs on them as well
so i think i covered everything there so first of all make sure you look at
the directions which will come with your plaster whether that be plaster of paris
crystal cali orthodontic plaster or whatever so make sure you look at that because the ratios
uh with the water mixes might be slightly different you can't go wrong with plaster of paris
because it's 50 50 but some other plasters they might have a different ratio for instance with the
um crystal cow r um you need less water which might cause problems with your pouring because
the consistency is a lot thicker so um you need to see how your materials behave your plasters
behave to be appropriate for whatever project you're using the plaster for
i mean in the past i've used the crystal calar and add a little bit more water to make it more fluid
um but it probably loses a little bit of strength which now we come on to um cracks in your plaster
so if you get any cracks in your plaster this is something i don't really experience very often
but um if you get any cracks in your plaster you're probably mixing
the plaster wrong you probably put too much water in with your plaster so avoid that
so like i say um look at your directions make sure you're getting the ratios right
um so number one is to look at your look at your directions number two maybe line your moulds out
with a diluted soapy water mixture which isn't going to interfere with your molds and your
plaster so you can use um very liquid for that or washing up liquid dish soap for that just water it
down just to help it flow around the mold when you mix up the plaster introduce the plaster to
the water not the other way around and take your time mix your plaster to a uniform consistency
pour that into the mold carefully oh another thing when you're pouring your plaster into the mold
is look for some areas pour against the side or some little ridges where you're not gonna
introduce any unwanted air don't pour it so haphazardly and straight down the middle to
the bottom and things like that like in this mode maybe you can pour it onto the side here the top
edge get a nice sort of stream going so you're not getting any air um into the mix and just be
patient with that filling up around the whole mold there's some videos on the channel already
so that should come handy for anybody that's uh wants to see in more detail
and when your mode is full like i said before tap that take your time tapping obviously you need to
fit this into your time frame before it starts to cure and most plasters do start curing relatively
quickly but you'll see the curing times on the instructions and directions with whatever plaster
you're using but like i say make sure you tap tap your mould to get any unwanted air out of your
cast mixture so there we are i think that's pretty much it covered um if anybody else is watching
this and they've got any more advice to add then please let us know in the comments below and let
us know what you think in the comments below with any projects that you're working on and if you
want to share anything with anybody else and there we are so anyway more videos coming up soon with
this and that paint jobs perhaps we'll get into some casting shortly as well hope everybody's
doing well and we'll see you soon thanks for watching and over and out for now hope everybody's
doing well thanks for watching i hope this video has helped see you soon and over and out for now
you