How best to cover rigid foamboard & expantable foam on an incline

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videobruce

Tower Operator
I have a long area that consists of 1/2" rigid foamboard smooth & 'shaved' with expandable foam (also shaved down) on an incline that I'm not sure how to treat.
Go over it with hydrocal or brush full strength PVA glue and sprinkle with medium Talus.

See the photos. (The 2nd pic, note the much darker 'gray' when I painted the expandable foam)
 

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Selector

Well-Known Member
Spackle, or plaster cloth, drywall mud (it will crack in places but you can add a second skim coat, or just cover the cracks with ground foam and bushes), Woodland Scenics filler products (I forget the newest versions, but they're there)....
 

videobruce

Tower Operator
I had a recent bad experience with WS plaster cloth (which I was warned about, but I wanted to try it). It's too thin and wraps back around itself. It also wound up not sticking after setup time. I thought about hydrocal, but I was concerned about the inherent 'mess'. :(
 

logandsawman

Well-Known Member
I had a recent bad experience with WS plaster cloth (which I was warned about, but I wanted to try it). It's too thin and wraps back around itself. It also wound up not sticking after setup time. I thought about hydrocal, but I was concerned about the inherent 'mess'. :(
Not sure what mess you are experiencing with the hydrocal? Unless it is the fine dust when you measure it, however once it gets in the mixing bowl you should be good to go.

I think it is great stuff, given a bit of patience and maybe practice. I spread mine with a rubber kitchen scraper, or if the consistency is right will use my fingers in the later stages.

May be easiest to go with the glue. However, I used some of the expandable foam on one of my layouts and say a year later noticed some shrink/swell with the foam product. If you use the hydrocal over it, you could nip that potential disaster in the bud.

Dave LASM
 

videobruce

Tower Operator
Drips and globs of material dropping for example.
Any issue with painting the foam 1st to see the effect, then applying hydrocal over that?
 

logandsawman

Well-Known Member
This technique works really well, I use paper towels dampened over my framework:

IMG_2068.JPG


Just plain paper towels, I use an eyedropper to get it damp or wet

IMG_2070.JPG


I don't use anything fancy, just an old scraper and cool whip container

After mixing, I usually wait a while before applying, I let it thicken a little but NOT TOO MUCH. Towards the end, it can be smoothed with the fingers to get the best surface. It pays to plan ahead and work quickly at this stage.


IMG_2096.JPG


No mess here, this is everything I use. A little residual dried hydrocal in the mixing bowl doesn't hurt anything

IMG_2095.JPG


I use these exact measures. I do not add more than what you see in the cups. First pour in the water, then GRADUALLY sprinkle in the powder, adding more as it sinks in the bowl

At the very end, the last 1/8 or so, I stir a little to get it dissolved. The only mess is the powder

This takes a while, as soon as some dissolves I add some more. Then, after the powder is all added, I will stir some and usually wait a minute or five for it to stiffen up a bit

Then pour or apply with rubber scraper to whatever

This is how it looks now, the area on the left was just painted, the rest pretty much done

IMG_2223.JPG


I think the most important part is mixing. Sprinkling it on the water and waiting for it to sink then sprinkling more is the key, I think. The bowl could be swirled too. I don't recommend any stirring unless it absolutely will not absorb water on its own, the less stirring the better.

hope this helps!!!!!!
 

Snowman

Active Member
I have a long area that consists of 1/2" rigid foamboard smooth & 'shaved' with expandable foam (also shaved down) on an incline that I'm not sure how to treat.
Go over it with hydrocal or brush full strength PVA glue and sprinkle with medium Talus.

See the photos. (The 2nd pic, note the much darker 'gray' when I painted the expandable foam)
Hydrocal won't adhere to foam, but this will:


Get it at any building center, and also pick up a roll of metal window screen material while you are there. Metal screen...usually aluminum these days...will fold, bend and crumple and hold it's shape, while the plastic screen won't.

Apply the adhesive along the edges (top and bottom) in a bead...and maybe the ends too if needed. Polka dot globs for other large areas. Stick the screen right down on top--edges oversize, trim them later--so that the screen pretty much lies flat on the foam...or perhaps slightly off the foam surface. Smooth out adhesive that squeezes through the mesh with a finger (or glove...or baggie over your finger, etc) so it's smooth on top--it cleans up with warm water.

After it dries and you trim it out, apply thick body latex paint until the mesh disappears--one or more layers--and your chosen ground cover on top. I suppose you could try a plaster coat too, but I would be cautious about too much too thick. If it's too heavy a coat it might pull the screen mesh off.

You could also use it to fasten rock castings directly atop the foam without the screen at all...I think. Haven't tried it myself though.

Re: The edge beads. After you trim the screen, you can also apply another bead or two and smooth that out with a wet finger as well, until it meets your own "scenery edging standards." Then paint, and paint again as needed.
 

videobruce

Tower Operator
Are you talking about expantable foam or rigid foamboard?? Smooth surface or 'scraped' (formed) with a scrapper tool?
 

logandsawman

Well-Known Member
Hydrocal won't adhere to foam, but this will:


Get it at any building center, and also pick up a roll of metal window screen material while you are there. Metal screen...usually aluminum these days...will fold, bend and crumple and hold it's shape, while the plastic screen won't.

Apply the adhesive along the edges (top and bottom) in a bead...and maybe the ends too if needed. Polka dot globs for other large areas. Stick the screen right down on top--edges oversize, trim them later--so that the screen pretty much lies flat on the foam...or perhaps slightly off the foam surface. Smooth out adhesive that squeezes through the mesh with a finger (or glove...or baggie over your finger, etc) so it's smooth on top--it cleans up with warm water.

After it dries and you trim it out, apply thick body latex paint until the mesh disappears--one or more layers--and your chosen ground cover on top. I suppose you could try a plaster coat too, but I would be cautious about too much too thick. If it's too heavy a coat it might pull the screen mesh off.

You could also use it to fasten rock castings directly atop the foam without the screen at all...I think. Haven't tried it myself though.

Re: The edge beads. After you trim the screen, you can also apply another bead or two and smooth that out with a wet finger as well, until it meets your own "scenery edging standards." Then paint, and paint again as needed.
Sounds like the same technique above, the screen is under the paper towels.
 

Snowman

Active Member
Sounds like the same technique above, the screen is under the paper towels.
Not much different, no. I kinda boiled the question down to "what sticks to foam," or "how can I make things stick to foam, and not come off."
Or..."how can I fasten things mechanically to foam so they don't come off."

I have fiddled around in the past will small mockups of modules or layout ideas (for scenery purposes), sometimes using plasticine clay.* "You can't paint plasticine clay," it's often said--it's clay with a wax/oil additive--"and you particularly can't paint it with water-based paints." Generally true. You certainly won't have success painting it with watercolors anyway, but you CAN paint it with a thick paint that forms a skin if your paint is mechanically keyed to the clay surface. Add enough closely spaced indentations to the surface and a latex paint skin will stay in place.

[* You probably know, but if not: it's the craft clay kids play with in school. Doesn't harden. You can rework it years later.
Also used to make moveable clay figures for "claymation" videos like SNL's "Mister Bill. "Oh NOOOoooooooooooooo...". :D]

Screen is just another form of keying the surface, and it's much easier and faster than poking holes would be over large areas.
 
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regme

Member
Hi

Just a bit off topic, when you say incline are you referring to the grade of the track or the batter?

If it's the grade of the track how did you cut the foam to the grade you wanted?

Happy to create a new thread for this.

Cheers
 

videobruce

Tower Operator
Grade of the scenery,not the track.
See these pics of the new area that I am tackling. This was done with outdated Sculptamold that turned out looking like cottage cheese.
eek.png
The 'rocks' were too 3D for the size of the area. The area towards the bottom is rigid foamboard filled in with expanding foam that pushed out the foamboard at the base when it expanded.
 

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videobruce

Tower Operator
This is with Hydrocal applied and some initial detailing (thou not much);
 

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