I agree with Henry. Throw out what you have a get some fresh plaster.
Guy
see stuff at: the Willoughby Line Site
20 years ago I bought a big bag, #50?, and unlike what others have posted, I added water to the hydrocal, not hydrocal to water. I used enough water to get a creamy mix, maybe like brownie mix.
After that my memory is vague on how long it took to set up, but when I could pick up a mold an put it on curved cardboard lacing, without any running out of the mold, I did. I'm certain the mold was removed within an hour of mixing.
It was never ever crumbly. I suspect your hydrocal has interacted with the humidity in the air. Instead of little bits of plaster, reacting with water to form a solid, think of it as micro bits that have already reacted with humidity and are not inclined to bond to each other.
It wouldn't hurt to try more hydrocal, but if it is crumbly, I would throw it away rather than trying to coat it with something.
Henry
COB Potomac & Northern
Shenandoah Valley
Arto After quite few cracked/broken castings I finally settled on 4 parts Hydrocal (lightweight) to 1 part water. This hardens enough so the the curved (inverse mold) tunnel portals don't crack when being removed. This is quite a bit more Hydrocal than the 2.5 to 1 ratio Woodland Scenics recommends. For a wetting agent I'm spraying the cast with full strength Finish JetDry dishwasher rinse instead of the usual water & dishwashing liquid soap solution.
After quite few cracked/broken castings I finally settled on 4 parts Hydrocal (lightweight) to 1 part water. This hardens enough so the the curved (inverse mold) tunnel portals don't crack when being removed. This is quite a bit more Hydrocal than the 2.5 to 1 ratio Woodland Scenics recommends.
For a wetting agent I'm spraying the cast with full strength Finish JetDry dishwasher rinse instead of the usual water & dishwashing liquid soap solution.
I know this is an old thread but I'm having the same crumbling problem as Arto.
The other day I mixed 2 small batches of Woodland Scenics light hydrocal ( the box was unopened but a few years old) and poured them into 8 rubber molds with wet water as the mold release. After almost 2 days of setting up they still came out crumbly.
Would it held if I added alot more hydrocal like Arto did for the next batch so that I can use up the boxes I have, or do you guys think it will be a waste of time?
Also, is there something I can coat the few rocks that did come with so that they don't disappear to dust?
Thanks, Alan
Is the dye/pigment you use from Lowe's intended to color concrete?
.
-Kevin
Living the dream.
If you are using rock molds spray a light coat of water, with a few drops of dish detergent mixed in, then pour the hydrocal and the rocks will come out easier. Also you can use Concrete color, Lowes has it in 4 colors, in hydrocal so if a rock gets chipped it still has color all the way through. I use the charcoal mostly and it is very strong so a drop in a cup of water will give you light gray colored rocks.
You don't really need a good balance for mixing plaster but I need mine for mixing coloring pigments in the plaster top coat to get a certain shade. I model the high desert sand and if you don't get the proportions exactly right it the color difference between two applications really stands out . I used the balance to measure the density of of a small sample of Hydrocal that I put in a container that I tapped on the bench to make it settle. Every time I mix a batch I tap the container to get the same density and since we know the density of water I get the correct 45/100 ratio. I want the strongest Hydrocal possible for my hardshell so I want the correct ratio. When I put on the colored plaster over it I am not too concerned about mixing ratios.
A beam balance? I did not know.
Nor did I know that you had the hydrocal to the water. Maybe that is the way to go, I will try when I start that phase.
I built a whole layout the other way round. If I didn't add enough water there were still bits of dry plaster. Add more water and mix. I never managed to add too much water but I concede it is possible.
1/2 hour to thicken is way too long. The hydrocal is bad.
If you are dipping paper towels to lay over cardboard you want your mix on the thin side. If it's way too watery that will be instantly obvious. Using molds it can be a thicker.
It's like baking bread, you have flexible.
45 parts water to 100 parts Hydrocal- BY WEIGHT ! When you measure by volume the mix will vary depending on how dense the Hydrocal is that you are using. To do it right you should invest in a good beam balance- it's useful for a lot of things.
Thanks for the info James, didn't know that.
As far as I know, Finish Jet Dry is not a detergent. It is a rinsing agent. Either way the setting time isn't too critical in this situation. I have 4 tunnel liner molds and that's about all I have time for each day. They sit overnight before taking the cast out. Hydrocal sets really fast compared to the regular plaster of paris I had been using many years ago.
Arto, full-strength detergent as a wetting agent is apt to materially impact setting of Hydrocal. Hydrocal is susceptible to rehydration if not tightly sealed in original packaging. Once it hydrates even partially its strength will be deminished. I have worked with Portland cement, an other gypsum based hydro set, and organic admixes materially impacted setting time. I suspect using a detergent for mold release would also impact overall setting time by as much as 3 to 4 x normal setting time.
Mixing plaster is fun once you get the feel of it.
Once you understand this chart, mixing any type of plaster is easy. I won't go into how to read this chart, I'll let others do that. But its a chart to have and keep. I'll offer other tips that I have learned through the years.. but I just wanted to post this chart and see if that helps.
Take care Keith
Thnx.
I just bought the Hydrocal. Maybe it's been sitting in the store for a long time. I'll try buying some from another store and see what happens.
I also just made a third batch. It took a very long time to thicken up. Some of the water would separate for a long time. It took maybe 1/2 hour to thicken enough to stay in the tunnel liner mold (sort of an inverse of the usual mold - put the plaster on the outside - no "cup-like" to hold the plaster). The Hydrocal was put in the mold much thicker this time. If it still comes out brittle & soft I guess it's definetly "old" Hydrocal.
ArtoThe Hydrocal is so brittle and soft enough that I can turn it into back dust with a tooth brush!
After 24 hours the Hydrocal casting should be very hard. Your experience is the same as mine when I tried to use very old Hydrocal, even though it had been in a sealed container. I bought a new container and it worked fine.
It takes an iron man to play with a toy iron horse.
Well, my last casts have cured for almost 24 hours. The Hydrocal is so brittle and soft enough that I can turn it into back dust with a tooth brush!
I tried gluing the broken tunnel liners back together but that is impossible since it just breaks very easily somewhere else.
Clearly something is wrong.
My bag of DAP casting plaster calls for an initial ratio of 2 parts plaster added to 1 part COLD water (40°F to 50°F) Stir to smooth consistency. Do not mix more material than can be used in 6 to 10 minutes.
I have heard that you can add vinegar to slow setting time but I never do.
I like to use the soft sided silicone mixing bowls and as stated above allow the plaster to set and shake it out when set.
Ed
Hydrocal will last a long time if stored properly. I used very large cat food plastic containers with a screw on lid, got the stuff ten years before and who knows how long the club had it as they had bought a 55 gal. drum of it.
The Hydrocal I use is the "lightweight" variety.
1/4 inch should make a solid casting, but I don't think 1/8 inch will be very strong.
Did you use a "wetting agent" on the molds? I put a few drops of dish soap in a spray bottle, and spray the mold before adding the Hydrocal. This helps the casting release from the mold more easily.
When I had problems with old Hydrocal, the castings were crumbly and soft, not hard and brittle.
I just started (trying to) use Hydrocal. In the past I've used plaster over window screen covered with paper mache' with great results.
In the current project I decided to try Hydrocal for making some tunnel liners using Woodland Scenic tunnel liner molds. I've gone though several batches of Hydrocal and I must say I'm really disappointed in the results. The casts are really weak and break apart very easily when trying to remove them from the mold. I was under the impression that Hydrocal was supposed to produce an extremely strong cast even when very thin. The casts I'm making are 1/8" to 1/4" thick and basically worthless (so far). I've followed the directions and formula for mixing that are on the carton. I've also watched several YouTube videos including one by Dave Frary. However I'm not getting the same results.
What am I doing wrong?
EDIT: I took another look at the carton for a possible "freshness" date since I've read old hydrocal can lose it's strength - didn't see a date - but noticed I bought "Lightweight" Hydrocal (C 1201). Maybe this is the wrong product for what I'm doing?
I pour the plaster into the water while stirring. The guys who plastered the walls in my house did the same thing.
Dave
Lackawanna Route of the Phoebe Snow
gandydancer19 Dave Frary, in his scenery book, recommends one cup of plaster to one cup of water. Pour the water into the dry plaster.
Dave Frary, in his scenery book, recommends one cup of plaster to one cup of water. Pour the water into the dry plaster.
I guess when it comes to mixing plaster, it's kind of like, "who makes the best ketchup (or catsup)". You'll get different answers to the same question. Most of the people that use plaster products say to pour the water in first, then add the plaster. I don't know about ratio for Hydrocal, but for casting plaster, they recommend a 2:1 mixture of water:plaster. If you need to lengthen the working time, I add a capful of white vinegar to the mixture; and it works!
My first post said a "cup of vingear". Heck, it may NEVER set up if you added THAT much vinegar to it.
Marlon
See pictures of the Clinton-Golden Valley RR
Thank you all for your ideas & insights. I ended up at roughly 2:1 Hydrocal:water, added Hydrocal to the water gradually while stirring. Worked well with heavy paper shop rags. Messy but fun!
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
Yes, plaster is great fun. It was one of the first things I started doing, scenery-wise, when I got back into the hobby. I discovered that I got a lot of satisfaction out of hydrocal castings.
I also put the water into the container, and then add the plaster. I think it mixes better that way, simply because you don't end up with plaster stuck on the bottom. I use yogurt containers, which my wife and daughter provide in great abundance. I wash and re-use them to be green, but I don't mind when I throw them out, either.
Take the mold you will be using, fill it with water, and dump the water into a yogurt cup. Mark the outside of the cup at the top of the water line with a Sharpie. This will give you a good idea of how much plaster mix you will need for that mold.
Don't pour excess plaster down the sink. Let it harden, squeeze the sides of the yogurt cup and it will crack and fall out.
I buy the 10-pound jar of Hydrocal from my LHS. It's not the most cost-effective way to purchase Hydrocal, but it comes in a convenient, re-sealable container. When my last jar got down to the bottom, I discovered that, even in a closed jar, it has a shelf life of a year or two. So, while it may be cheaper to buy a huge bag, you may find that you throw part of it away. Old Hydrocal makes weak castings that crumble, so if you have that problem, try getting fresh material.
Quick comments to what has already been mentioned..
Don't set the bag of plaster directly on a concrete floor - It will absorb water from the floor very quickly - Use the 5 gallon bucket storage method.
When mixing the plaster and water use a measuring cup and carefully check the ratio of water to plaster until you get the consistency that you like. Use the same formula each time (very easy) If you let the plaster sit in the water for two minutes before stirring, you won't have lumps regardless of which ingredient was added to which...
Enjoy. Plaster is great fun..
Hydrocal, like any other of the gypsom products will vary slightly from batch to batch as far as the amount of water needed for mixing. A good starting point is described above. The actual mixed consistancy can be varied depending on it's use. The above ratio is good for mixing for pouring molds, thinner if doing soaked paper towel. Thicker batches (will set quicker) can be used for direct application to bond hardened or semihardened castings or for fill-in scenery.
Storage of an opened bag is rather important. Once the product is opened it will absorb moisture and start to affect the properties of the drying and curing. This is especially true if storing for extended periods. We buy Hydrocal in 99# bags and once opened will repackage to smaller baggies for individual projects as needed. The baggies of plaster are stored in a sealed 5 gal pail.
Another note for coloring, I perfer to color w/ powered masonry dyes, these have no affect on the curing time or the final cured produvt. Paints and liquid colors tend to only color lightly and require a considerable amount to darken.
Hydrocal always mixes far better when plaster is added to water, less lumps and no dried product stuct to sides of container. You just have to get the feel of the water amount for the batch size you need. Another hint, have additional molds handy or figure a use for extra plaster before mixing. This way if you end up w/ a considerable amout extra, you can use it instead of tossing it out. Remember, after about 5 minutes the plaster will be setting and dry in the mixing container. Many like to use a very flexable bowl/ cut in half rubber ball etc as once dried you just flex the container and dump out the crumbs and wash out the remains. DON'T dump any of this into you sink or toilet! even excess powder can settle in drain pipes and traps and harden under water like concrete.
Modeling B&O- Chessie Bob K. www.ssmrc.org
If it helps you any:
I have the boxes of Woodland Scenics Lightweight Hydrocal C1201. Here is what the instructions say:
Use Clean bowl and utensils. DO NOT wash product down the drain.
1) Shake box thoroughly for 30 seconds.
2}slowly add 1 1/4 cups Hydrocal to 1/2 cup water, mix.
3}immediately pour into molds or brush on terrain surface.
Working time: 5 minutes.
Setting time 40 minutes.Overnight for complete cure.
{And a warning not to use internally, keep away from children and to not use for human body casting as the heat will cause burns}
I also recommend you keep it in air and moisture tight container{s} so as not to become a 40 pound bag of plaster lump!
-G .
Just my thoughts, ideas, opinions and experiences. Others may vary.
HO and N Scale.
After long and careful thought, they have convinced me. I have come to the conclusion that they are right. The aliens did it.
I've never used any formula.......
Put a cup of two of powder in a bowl and add water. If you are doing something vertical then thicker is better. If you want to pour full the spaces between tracks for example on a level surface, then add more water. It's really rather forgiving.
You will discover that unlike plaster of paris, when it starts to kick off it really goes.
Warning on multiple batches. Don't mix a new batch over an old in a bowl without thoroughly washing out the bowl. Any remaining plaster that is trying to kick will accelerate the new batch and you will hardly have time to work with it.
Similarly, if it starts to kick don't add water to thin and attempt to slow it down...... It's going regardless.
After that....play with it.......... it is a really fun medium to work with.
see ya
Bob
What is the proper ratio of Hydrocal to water for scenery construction? I just bought a 40 lb bag on eBay and it has no mixing instructions at all.