plaster cloth and hydrocal not sticking to blue foam

Discussion in 'HO Scale Model Trains' started by Edavillenut, Jan 19, 2007.

  1. Edavillenut

    Edavillenut Member

    ok i am having a big problem the plaster cloth and hydrocal i am using to build my hardshell is not sticking to blue foam that i am using as a base. and ideas why
  2. ep1taph

    ep1taph New Member

    I am working on one of my first projects that involves using plaster and styrofoam. I had a similar problem when I was running tests and learning the basic technique. What I have done now is lay the styrofoam out as the basic supports and shape, then covered it all (and formed hills somewhat) with a very fine, sturdy wiremesh. I don't know exactly what it's called, but there's probably only a few millimeters between each wire square.

    After that, I can easily attach plaster cloth or paper towels wetted with it. I'm new to this, but that solved my problem. I am just glad I ran some tests first!
  3. ezdays

    ezdays Out AZ way

    One suggestion might be to add some white glue to the water, or paint some glue on the foam before applying the plaster cloth.

    I don't use either plaster cloth or hydorcal, but I have used paper towels dipped in plaster of paris and I've used joint compound, both directly on the blue foam and have not had any separation problems. I've alos bee able to glue two pieces of blue foam together just using white glue, so that's why I'm suggesting to mix some in with the water.
  4. MasonJar

    MasonJar It's not rocket surgery

    Have you painted the foam or are you trying to stick the plaster directly to it?

  5. Edavillenut

    Edavillenut Member

    so i guess i will bw painting it tonightsign1
  6. yellowlynn

    yellowlynn Member

    I assume you are aware that the foam has a plastic sheet on it. I had lots of problems until I found this out. Flick a fingernail at a corner until you see the film seperate. It is a very thin film, but tough, and will peel easily once it is started. I found this out by accident when I painted the foam, glued some stuff to it, then tried lifting the stuff. The paint and film started peeling off.

  7. Edavillenut

    Edavillenut Member

    the foam i am using has no plastic on it
  8. yellowlynn

    yellowlynn Member

    foam film

    It may vary in different parts of the country, but every new piece I have ever bought has had this film on it. You can't tell by looking as it is virtually invisible. The reason is that this foam is for insulation and the film keeps the moisture out. If you ever see a damaged sheet, you will find it. I won't swear that this is what is causing the problem you're having, but I make sure I peel every sheet before I use it. Both sides.

  9. Edavillenut

    Edavillenut Member

    just checked a couple peices i have and when i try to peel anthing upp all i get is foam no film
  10. Skammer

    Skammer Member

    Before going through the effort of painting it all, you might want to just give it a quick going over with some rough sandpaper. Don't apply much pressure, just lightly go over it to break the sheen and make it slightly rougher. A wire brush would also work but sandpaper is probably easier.

    Also -- this can never be said often enough - whenever you paint styrofoam, make sure you are using acrylic or water-based paint. Don't use enamel or oil-pased paints - they'll eat right through it. I once found that out the hard way!
  11. yellowlynn

    yellowlynn Member

    foam film

    It sounds like yours doesn't have that plastic film. Well, that shoots a good suggestion in the head. I tried.

  12. Edavillenut

    Edavillenut Member


    thanks for telling me about the plastic at least i now know to look for it
  13. Jim Krause

    Jim Krause Active Member

    I haven't had that problem, but I've only used plaster cloth at the joints between two sections of scenery. (I had to build the scenery at home and then take it to the club layout for installation).The foam was built up and contoured before I applied the plaster cloth, so the surface was ruoghed up.
  14. IAIS 604

    IAIS 604 Member

    The Woodland Scenics "Scenery Manual" says that "Lightweight Hydrocal (which I think is the basis for their plaster cloth) will not readily adhere to cellular styrofoam".

    They suggest that the surface be roughed up using a rasp.

    Maybe TomPM could chime in ???

    He doesn't seem to have any problems with a styrofoam base - maybe regular POP sticks better ????

    As I am about to start this, I want to know the answer, too !!!
  15. 60103

    60103 Pooh Bah

    One of the original intents with hardshell scenery was that it would be self-supporting. The first hardshell was usually put over crumpled newspapers and such which was removed after the plaster cured. I haven't used plaster on foam but I think it would probably not stick unless there was a mechanical join like a rough surface.
  16. DixonRobertson

    DixonRobertson New Member

    I found the plastic film only on the 1/2" thicknesses from Lowe's; the 1" and 2" sheets did not have the film. Like Jim Krause, my foam was at least a little roughed up before I applied the plaster cloth. I used a rasp--but boy o boy you better be good with a vacuum cleaner.
  17. Russ Bellinis

    Russ Bellinis Active Member

    Anything you want to apply plaster to needs to be soaking wet before you apply the plaster. If the foam or whatever is dry, it will suck the moisture right out of the plaster and keep you from getting a bond.
  18. Amrap1

    Amrap1 Member

    Had the same problem today. I bought 2 rolls of Woodland's plaster cloth and it had much less plaster than the last rolls I bought. It didn't stick very well to anything. I used warm water and then dipped it in a tray with watered down joint compound. It stuck and made it much easier to work with.

  19. jwils1

    jwils1 New Member

    The blue foam at Lowes in the Denver area has no film and plaster cloth adheres just fine.

  20. Jim Krause

    Jim Krause Active Member

    I noticed a recent ad in a model railroad publication by Woodland Scenics, touting their "improved plaster cloth" with more plaster. Maybe they realized that they had a problem? Now we have to wait until all of the old stuff is off the shelf.

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