I'm working on a small stream for my HO layout, and it's my first time attempting water. I have some Envirotex Lite for the resin. This is on extruded foam board. Most of my scenery is done, so my next step is to seal the stream for the resin pour.
I attempted using WS lightweight Hydrocal this week, but I had opened the container last summer (2019). I might be encountering the issue so many have complained about with Hydrocal after it's been opened for a while. I can run my finger across the stream, and white powder covers my finger. If I attempt to add some paint, the "rock" falls apart.
Since it should be dry by now, is it likely the Hydrocal is no longer usable? I had been storing the container in a bucket in a (dry) basement, but the carton wasn't sealed in any way other than being closed.
If I need to toss it, is there a good way to clean it out of the stream bed? Maybe if I sprayed some water on it I could scoop it out?
A friend had suggested using WS Flex Paste as a sealant. I tried the Hydrocal first since I already had it, but I think I'll try the paste if I'm able to successfully clean out the Hydrocal.
Before you try to put your mixed hydrocal down WET the stream bed with water so it is wet. Then add your mixed hydracal to the stream bed.
Rob Spangler mentioned he used drywall mud for his stream bed. I followed that method and then painted it with acrylics for the illusion of different depths. That work very well. No hydrocal needed.
Rio Grande. The Action Road - Focus 1977-1983
I don’t buy Hobby Hydrocal, too much $$$. I’ve been using Hydrocal Dental Plaster for over 20 years and it works better than great at a fraction of the cost of Hobby products.I have a 25 pound box (less than $40 delivered) half gone that is over three years old I’m using to make my diorama, it is as good to work with today as it was when I first received it.https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=dental+plaster+hydrocal&_sacat=0&LH_TitleDesc=0&_sop=15&_odkw=dental+plaster&_osacat=0 Works great for molding rocks. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
woodone Before you try to put your mixed hydrocal down WET the stream bed with water so it is wet. Then add your mixed hydracal to the stream bed.
I don't use Hydrocal for stream beds. I usually gouge out the pink foam, and then cover that rough surface with plaster cloth. As it dries, I use my fingers to add more water to seal the cloth. I think I've used white glue to help seal it, too. Then I paint and finally add the Envirotex. Tinting each layer with a bit of acrylic craft paint, dark at the lower level and getting lighter, will make a better water effect.
I had one container of Hydrocal go bad after a couple of years. I think some moisture got in. Castings just crumbled.
It takes an iron man to play with a toy iron horse.
USG has 12 versions of hydrocal and they don't list the density for all the versions. They also have other versions of artistic plasters.
It is hard to believe they would let WS rebrand one of their art plasters as Hydocal. In the 80's I was able to source a big 80# ? bag of it. I'm guessing it was between $25-$50. I'm sure I used it over a longer period of time than 6 months. I never experienced the chalkiness you describe. It came in a paper bag, that I kept in the basement using about half of it. It eventually turned into a solid block of plaster.I looked at a dental supply website. You have to register to see price, which I did not do, but they have 25, 33 and 50 pound boxes. They have various brands, but they all probably come from USG. It could be a cheaper alternative to WS.
Henry
COB Potomac & Northern
Shenandoah Valley
611,
Most likely the plaster is bad. You can test it by mixing up a batch and letting it harden at the work bench. It should get warm to the touch and set solid as a rock. If it doesn't, toss it out and start over.
You should be able to clean the plaster off of the roadbed with some water and elbow grease. I recommend buying new plaster at a plaster and lathe supply company. They will have hydrocal and dental paster both of which work quite well.
Guy
see stuff at: the Willoughby Line Site
Just as a note: the secret trace ingredient in Hydrocal hydrates at a different rate from the plaster of Paris that is its main constituent. Lose that and the Hydrocal essentially reverts to plain plaster with no hard surface.
In a pinch you should be able to use Hydrocal that hasn't wholly slaked by adding a small amount of calcium oxide silicate mortar (no more than a couple percent by weight thoroughly mixed). But I have not tried this firsthand, so YMMV.
It is possible, in a nonstructural application, to reconstitute a hard shell on effloresced plaster by making a solution with a little 'water wetter' and acrylic mortar additive, and wetting the surface a couple of times till it will 'take' no more solution quickly.
If hydrocal is properly stored you can use it over a long period of time. I have used 10 year old stuff with no problems. Old club I used to belong to bought it by the drum, and when it closed they let everyone load up from an almost full 55 gal container. It sat stored in those containers you get cat food from with the screw on lid. Just used regular plaster I bought 5 years ago and no problems, again properly sealed.
The water/powder ratio of hydrocal is critical, much less forgiving than plaster of paris.
I mix mine by weight using a very precise scale. The instructions on the USG site give the mixing ratios by weight.
It sounds like your mix ratio was incorrect.
-Kevin
Living the dream.
Glad to see you back, Kevin
One other point I may add is that in most (if not all) cases I was taught to add the plaster to the cold water. Most people seem to have the tendency to do the opposite.
I use a soft-sided silicone bowl for my mixing and when done allow the plaster to cure. Then it is easy to turn out the set plaster into the trash (actually I add it to the compost pile) and the bowl is ready for the next use.
Good Luck, Ed
gmpullmanOne other point I may add is that in most (if not all) cases I was taught to add the plaster to the cold water. Most people seem to have the tendency to do the opposite.
I learned about plaster in the ER. Hot water will heat a plaster cast up enough to burn the patient. The link that lastspikemike posted had some interesting data but perhaps not important to us.
Setting time become less with higher temps, to a point, then it lengthens. That's a surprise, but who wants to work with 140 degree plaster?
Mixing time increase strength but decreases setting time.
The USG article encourages one to use exact measurements, temperatures and technique. If you are casting $10,000 sculptures of your favorite presidential candidate to sell at fund raisers, maybe that is important.
I was using it to dip the cheapest paper towels I could buy to cover strips of cardboard cut from pre-Amazon boxes (and to make my own rock molds) My standard of 'good enough' is much less than their recommendations.
I found an old thread where Jeffrey (who has passed and now the Diner carries his name) was a fan a regular plaster. He said it chipped easily if you did not "seal" it, before painting. He used shellac.
Above graphs from https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/plaster-mixing-procedures-application-en-IG503.pdf
FWIW, I have found W/S hydrocal to be hit 'n miss. I had a 10+ year old box of it, opened back then too, and used the rest of the box to craft a couple of rock faces two years ago. It was fine, hard and durable. The newly purchased box made cruddy crumbly rocks that I discarded. Soooooo......take that for what it's worth.
I've never bought hobby plaster products, as they're usually over-priced. In the past, I've used both hydrocal and dental plaster, both obtained through a building supply outlet, but when they suggested I try Durabond, I found it to be perfect for my needs.
Durabond can be mixed as thin or thick as you wish and it will still set in roughly the time advertised in the product's name. In addition to using it for all my on-layout water scenes, it also works over aluminum window screen to create the landforms which keep derailed trains from falling to the concrete floor of the layout room. It also works well in rock moulds.
Wayne
I was always told to mix hydrocal to a peanut butter consistency. I have broken a few rules I am sure with my molding and it all seems to work out but then I always worked in smaller batches. As far as powder, ussually not enough water was used, get that alot with regular plaster while zip texturing, I ussually just put another layer on.
LastspikemikeConcrete on the other hand, or mortar for brickwork for that matter, is usually done the other way around: add water to the cement. Not sure why.
Because of the way a mixing drum on the delivery truck works. It has nothing to do with the chemical reaction.
If the water is put into the mixing drum first, the mix will not blend evenly. Usually aggregate is added first, then cement, then water. I have seen some cement plants where aggregate and cement are mixed before being added to the truck drum.
If mixing a small batch of concrete at home in a large tub, I do not think it makes any difference in reality.
Grout and thin set both instruct to add water to the powder, but I do it opposite because it makes less of a mess with my paddle mixer on the 3/4" drill. Never a problem.
rrebellI was always told to mix hydrocal to a peanut butter consistency.
Peter-Pan or Skippy?
I have never mixed plaster as "Smooth as a fresh jar of Skippy."
Best video of Uptown Funk at 1:50:
The original:
Lastspikemike Shelf life is 6 months according to US Gypsum. Presumably only in an air tight container stored in dry conditions. https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/usg-hydrocal-B-11-gypsum-cement-southard-submittal-en-IG1391.pdf
Shelf life is 6 months according to US Gypsum. Presumably only in an air tight container stored in dry conditions.
https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/usg-hydrocal-B-11-gypsum-cement-southard-submittal-en-IG1391.pdf
The shelf life of Hydrocal is highly dependent on exposure to moisture/humidity. I bought a large paper bag of Hydrocal from a hobby shop in the mid-1990s when I was working on my HO scale layout, which I tranferred into a large Ziploc freezer bag with the air squeezed out every time I sealed it.Would you know, that same bag of Hydrocal is still in use today, over 25 years later, for making rock mold castings for my N scale layout! The hobby shop I bought it from closed almost 20 years ago...
Lastspikemike There is a reason you should add the water to the cement. It does make a difference. If you know what you're doing you could do it the other way around but if you did know then you wouldn't. With plaster of Paris or hydrocal you add the powder to the water. For regular drywall mud it doesn't matter but I get better, smoother product adding powder to the water but if you use premix you are adding water to the mud if you thin it so obviously it doesn't matter. Drywall mud is just mud, no chemistry. For those setting type muds you should follow the instructions. I'd be surprised if those include adding water to the powder. This is literally not rocket science.
There is a reason you should add the water to the cement. It does make a difference. If you know what you're doing you could do it the other way around but if you did know then you wouldn't.
With plaster of Paris or hydrocal you add the powder to the water.
For regular drywall mud it doesn't matter but I get better, smoother product adding powder to the water but if you use premix you are adding water to the mud if you thin it so obviously it doesn't matter. Drywall mud is just mud, no chemistry.
For those setting type muds you should follow the instructions. I'd be surprised if those include adding water to the powder.
This is literally not rocket science.
And so it goes...
SeeYou190And so it goes...
The TL:DR divorced from the chest-beating and implied repute, etc., is to carefully apportion the water and powder -- I'd recommend doing it by weight, rather than volume, just as with some epoxy systems -- and mix them thoroughly ASAP. (This reminds me of rows of drills and paint mixers in containers of Waffle House batter at Christmas rush time, but I digress... ).
Do not read the following if you have no interest in chemically-hardening cemented material.
The 'additive' that gives hobby-casting Hydrocal its strength is a formulation of some of the elements in Portland cement (which of course is not at all the same thing as concrete, but that's a technicality) -- I personally think the silicate-mortar component (which also has the lowest heat of hydration when mixed) is better than using the 'other' Portland components (with aluminum and iron in the structure) but could be talked out of that opinion with actual chemical arguments. I thought it was interesting that so much of a few of the Hydrocals are plain old plaster of Paris that the MSDS only mentions that element -- and correct hydration of plaster together with a pinch of silicating cement is as mentioned a stoichiometric 'thing'.
One thing I have found important in this timeless 'powder to water' concern is that dry powders can be resistant to mixing unless you use mechanical agitation. "Sieving" powder to water overcomes some of the natural tendency of powders to aggregate (and form 'lumps' of dry material that resist proper mixing). The concern isn't there for 'cement mixing' because the action of combining the aggregate and binders with the cement naturally accomplishes this within a few mixer turns, long within the 'retarding' period before chemical setup begins. Products with more prompt initiation would benefit from 'sifted' introduction...
I speak mostly from a shotcrete perspective, where there are very different concerns with mixing, transportation, placement and rebound, etc. than with even typical pumped-to-place mixes. Most of the aggregate used in my applications was comparatively fine, and could be mechanically mixed before truck roll; as some of the constituents of 'reinforcement' need to be wetted too for proper internal adhesion, early assured mixing to spec would be preferable to introducing water to powder in my opinion for this specific type of application.
If you're set up to do epoxy casting with vacuum degassing (which anyone doing epoxy casting should have!) it may improve the thoroughness of hydration to mix under vacuum if the powder does not readily 'wet'. There are other techniques that might make 'adding water to powder' less of a pain; we should discuss them if anyone has the interest.
Things you might want to consider:
You don't have to put the plaster in the water first - it makes no difference that I can find, and is a huge hassle to slowly add plaster to the water. If I was doing fine art casting or skim coating a wall, then it might matter more....
1. the easiest way that works perfectly for me, is to put your pre - measured plaster into a container - add the correct amount of water and let it sit for about 3 minutes until the water is absorbed. Don't touch it until then or you will get lumps. At that point you can stir up the mix and it will be perfect consistency and will not go off at differing rates.
2. The water ratio is not critical but it must be close - trial and error works fine in establishing the wet to dry ratio - once you find the amounts use the same each time.
3. Hydrocal and dental plaster have a wide range of tolerances but they all go off with some heat and very decisively. If you are wondering if the batch is setting up - its not. You have either a grossly out whack proportions to the mix (rare) or a batch of plaster that has absorbed water while sitting and has gone bad.
4. Always do a small test with plaster that has been sitting for awhile.
BTW: Don't buy the WS light hydrocal - it is expensive and spotty quality.
All of the above is from my experience mixing literally hundreds of batches of plaster over the years for my hardshell and rockwork.
Opinions will vary,
trainnut1250BTW: Don't buy the WS light hydrocal - it is expensive and spotty quality.
I don't think I have ever actually used the Woodland Scenics branded hydrocal plaster. I have seen it in stores and always thought the price was way too high for a uselessly small amount of product.
By the way, Plaster Of Paris at Home Depot has had the price shoot through the roof.
SeeYou190By the way, Plaster Of Paris at Home Depot has had the price shoot through the roof.
I bought a 25 lb. bag two years ago for $12. Today it is $15.40. Not unreasonable. Perhaps there is a shortage in Florida?
Cheers, Ed
gmpullmanI bought a 25 lb. bag two years ago for $12. Today it is $15.40. Not unreasonable. Perhaps there is a shortage in Florida?
My Home Depot only stocks Plaster Of Paris in what looks like 1/2 gallon milk jugs. They do not have it in 25 pound bags. It is about $8.00 for 4 pounds.
I have thought about trying the 45 minute set time drywall joint compound on the layout. It is not very expensive.
KevinMy local HD has the 25 pound bag of Plaster of Paris in stock at $18.31.
Just checked Lowe's, in stock same price. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
RR_MelJust checked Lowe's, in stock same price.
Incidentally the price listed for the moulding plaster is $12.81.
Lastspikemike rrebell Lastspikemike There is a reason you should add the water to the cement. It does make a difference. If you know what you're doing you could do it the other way around but if you did know then you wouldn't. With plaster of Paris or hydrocal you add the powder to the water. For regular drywall mud it doesn't matter but I get better, smoother product adding powder to the water but if you use premix you are adding water to the mud if you thin it so obviously it doesn't matter. Drywall mud is just mud, no chemistry. For those setting type muds you should follow the instructions. I'd be surprised if those include adding water to the powder. This is literally not rocket science. Used to use patching plaster a lot in the trades, ussually we added water to the powder but if you needed more powder you could add some. You could also add a bit of water to stuff that was just starting to be less workable but there were limits. Depends what was in the "patching plaster". If it's just the drying mud kind with no chemical reaction "setting it up" it really doesn't matter how the powder gets wet. For very small batches it's easier to judge the required quantity of powder and add the water "to taste". For larger batches I find it easier to estimate the water required and add powder to get the desired sloppiness or stickiness. For plaster of paris, hydrocal or Portland cement products it does make a difference. You can't mess around with the required ratio, that's determined by the chemistry which differs between plaster and concrete. Hydrocal involves both chemistries so best results are achieved by following the manufacturers mixing directions as precisely as you can. Hydrocal is far stronger than we need so as long as the stuff you mix works then fine. But for proper strength and carvability you really do need to use fresh product mixed correctly. Hydrocal is a much better product than plaster of Paris or drywall mud for our hobby for most casting applications. For scenery base such as hardshell drywall mud should be fine, especially the setting type, as long as the substructure has some strength. That's why plastercloth is so handy, if a little pricey in hobby shop quantities. It comes with a tried and true substructure already included.
rrebell Lastspikemike There is a reason you should add the water to the cement. It does make a difference. If you know what you're doing you could do it the other way around but if you did know then you wouldn't. With plaster of Paris or hydrocal you add the powder to the water. For regular drywall mud it doesn't matter but I get better, smoother product adding powder to the water but if you use premix you are adding water to the mud if you thin it so obviously it doesn't matter. Drywall mud is just mud, no chemistry. For those setting type muds you should follow the instructions. I'd be surprised if those include adding water to the powder. This is literally not rocket science. Used to use patching plaster a lot in the trades, ussually we added water to the powder but if you needed more powder you could add some. You could also add a bit of water to stuff that was just starting to be less workable but there were limits.
Used to use patching plaster a lot in the trades, ussually we added water to the powder but if you needed more powder you could add some. You could also add a bit of water to stuff that was just starting to be less workable but there were limits.
Depends what was in the "patching plaster". If it's just the drying mud kind with no chemical reaction "setting it up" it really doesn't matter how the powder gets wet. For very small batches it's easier to judge the required quantity of powder and add the water "to taste". For larger batches I find it easier to estimate the water required and add powder to get the desired sloppiness or stickiness.
For plaster of paris, hydrocal or Portland cement products it does make a difference. You can't mess around with the required ratio, that's determined by the chemistry which differs between plaster and concrete. Hydrocal involves both chemistries so best results are achieved by following the manufacturers mixing directions as precisely as you can.
Hydrocal is far stronger than we need so as long as the stuff you mix works then fine. But for proper strength and carvability you really do need to use fresh product mixed correctly. Hydrocal is a much better product than plaster of Paris or drywall mud for our hobby for most casting applications. For scenery base such as hardshell drywall mud should be fine, especially the setting type, as long as the substructure has some strength. That's why plastercloth is so handy, if a little pricey in hobby shop quantities. It comes with a tried and true substructure already included.
rrebellno, patching plasdter, sets rock hard in 15min or less.
doctorwayneI used Durabond patching plaster for all of my water scenes, and thoroughly wet all of the plywood riverbeds before apply the Durabond. Durabond comes in a variety of setting times, and I prefer Durabond 90, which sets in roughly 90 minutes, so there's lots of time not only for application, but also for forming eddies, ripples, and waves. Its advantage over drywall mud is that it sets-up very hard, so it will stand-up well not only to cleaning, but also to the many cameras which have been set in the rivers for photos of trains crossing the bridges.
Durabond patching plaster is not fussy as far as mixing goes.... you can make a fairly stiff mixture, or one similar to the texture of peanut butter, or one that can pretty-well be poured out of the mixing container. It will set in roughly the time noted on the package, and it will be strong and hard once set.My Durabond-on-aluminum window screen terrain will support my full upperbody weight if I'm standing on a stepstool, extending myself and supporting myself with either one or two hands. I doubt that it would support my full body weight were I to stand on it, but how many times would a modeller need to walk on their layout?
In my opinion, drywall mud is pretty-well useless for layout scenery: I made roads using it, but the material gouges easily, whether it's a camera sitting on it or an HO scale vehicle.I've used hydrocal and dental plaster, and both are fine for making castings, but they set-up too quickly to be useful for making scenery.
doctorwayneIn my opinion, drywall mud is pretty-well useless for layout scenery:
I completely agree. The only thing Joint Compound (AKA "Mud") is really good for is river beds that will have a clear coat added.