Hi, I was wanting to make a base for a 1:18 scale mortar pit and since i had so much drywall compound laying around the house that was my main material. I cut out a cardboard template and started adding about 5 thick layers of compound until I had a base that was 2.5cm high. I left it to dry for a few days and it started to crack. I'm still new to the hobby and this was going to be my first base. Is there any tip or trick i left out? Was I completely wrong to use drywall compound? Is there anything I could to do fix it to make it hard? I kinda expected it to become rock hard since its been a full week. Thanks for any help

Drywall compound shrinks significantly when it dries even if you're using it to fill joints in your walls ! The amount of cracking seems to be proportional to how thick you lay it on, so the scenario you described sounds like a perfect storm to produce some major cracking. If you ever get a chance to work with a really good drywall guy you will see they lay the stuff on in thin layers and use non-shrinking compund when they can.

You can use drywall compund for thin layers of groundwork, and the stuff is cheap, but there are far better solutions available. For uneven ground, a good solution (that is still pretty cheap) is to make the basic shape from scraps of styrofoam or other packing material, or even scrap pieces of wood. Once you have the basic shape, adding a thin layer of actual ground cover can be done with celluclay, durham's water putty, plaster of paris, or even a mix of ordinary dirt and white glue.

My favorite method for a thin cover of dirt (not for grassy areas of course) is a soupy mix of white glue, cheap brown tempera paint, chopped up roots, static grass, chopped up basil (bought in bulk or it'll be very expensive) all slathered on the base. If you want it to look a bit damp or muddy, add a bunch of future floor polish. If you want it dry and dusty, add a bunch of pastels or pigments once it is dry.

For a grassy area, a very thin layer of almost any plaster wil do, followed by static grass, all airbrushed to whatever shades you need and then drybrushed.

I just completed a diorama with very high sloped terrain - up to 8-10 inches of vertical drop - and built up almost all of it using chunks of styrofoam. The layer of ground cover on top of that is probably less than a half-inch in the thickest places.

Hope this helps.

Danny Egan
AMPS
http://www.amps-armor.org

I usually mix drywall compound with cell-u-clay and try to keep it to about 1/2" thick at the thickest points. I build the rough base out of styrofoam or foamboard and cover that with the drywall compound / cell-u-clay mix. Alone the cell-u-clay tends to peel back at the edges but the drywall paste cures that and it drys like a rock but can be cut, drilled and carved easily. I texture it before it drys with a scotch pad.
Cheers,
Charles

I have mixed sawdust with white glue thinned with water before and had decent results. The using real dirt in the mix part sounds interesting.

All my bases are styrofoam cut to shape and covered with plaster of paris. Other additives are added depending on what type of ground you are trying to achive.

I went out and got plaster of paris. amazing stuff and it dried in 20 mins. Beaufitul. Thanks

I'll use styrafoam or wood for the foundation and then build and texture it with the taper's mud that has sand and acrylic or water color added. As above,I try to keep the thickness of the layers down to prevent cracking. The sand also helps on this note.
Sometimes the cracking is desirable if you are trying for the dry wash or creekbed look.
Cheers!

I reckon so. Rick! I have visions of doing a LRDG/SAS diorama with a jeep or truck on a dry creekbed created this way...
Brad

Once it's cracked is there anything you can to do fix it? Should I add smaller layers to fill the cracks?

Well, if the cracks don't go all the way through,then you can probably fill them in with more of the same. If you have a few that are through and through, then I would start over and not have any doubts.
Cheers!

Great. I checked my base and theres mold growing all over it! I used plaster of paris and for colouring I used cayman pepper, water and orange paint. I assume the mold is from the pepper but could it be from the plaster? Any other dirt cheap ways of colouring? I preferred the pepper over the paint as it made the plaster thicker and not watery.

As for coloring your ground work I use cheap acrylic paints I buy at the local art store. I usually wait till they have a clearance sale twice a year and pick up a whole bunch of colors of folkart or accent in 2 oz. bottles real cheap. browns, black, white and gray. I mix in enough with the plaster to get the color I want, squirt in some white glue ( helps streagnthen the plaster and dish soap, helps it spread real easy,) any walla, got your self looking like mother nature to a point. Remember that as it dries the colors will fade to a degree but, you wont have any white plaster showing where you don't want it. Your mold is probably from the pepper. Haven't had that problem with plaster even while working in my basement which was so damp I needed to run a dehuidifier.

Bob is right about the color fix-cheap acrylics mixed in.
Adding some sand will thicken the mix and give it some strength. Talc,in the form of either baby or foot powder will also do the trick but costs more and you may need more to do the job.
Cheers!

When you say dish soap, do you mean the liquid or the dry soap flakes? Thanks for the tips both of you. Making another attempt today

liqued dish soap. It helps break the surface tension and spreads easier.

Same project different topic haha. I needed to make a base to lay my groundwork on and I went out and bought some architect's board (pretty much styrofoam sandwiched between two thin boards). I plastered it but the plaster is cracking. Do I need to scuff up the board so the plaster sticks to it better? I had no problem originally with cardboard but I decided not to use cardboard since it's not as strong and if it moved it would crack my base. Is there anything else I should do with the architect board? Thanks.

If it were me, I'd just use some thin (1/4" maybe?) oak sheeting, or luan, handy board, etc. Easily found at home depot.

However, I usually make my bases with some sort of decorative edge. Sometimes you can use an old picture frame for this.

Here's some articles with info on bases.
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Oh, and for coloring the groundwork, I usually just build everything and then paint it up with acrylic craft paints afterwards. Buy do whatever works best for you.