What do you guys use as a gap filler for the corners(plastic buildings) that sometimes just don't meet up the way there suppose to?

Mark

First choice - to get the corners to line up square in the first place. And since that isn't always possible considering casting defects, warped pieces, etc, my second choice would be to glue in little slivers of styrene into the gaps using solvent cement (or laquer thinner) then cut and file to shape. Thin cracks I use a tube of auto body spot filler. The problem with the body filler is that if the gap is too wide, it's both hard to blend so that it is not noticeable, and it tends to fall out of the gap over time.

Which building kit is it?

Depending on the kit, if its brick, it will be hard to hide the seams. A couple of the Lunde Studios kits I have recommend making a "right angle jig" for getting the wall alignments right, but then these kits have flat surfaces that don't interlock.

Depending on the size of the gap, and if you're painting over it all later too (recommended), you can also use CA type glues.
Gel versions fill gaps really nicely, and what's more, it doesn't suffer from shrinkage such as 'liquid plastic' fillers do.
It is also possible to sand it afterwards.

Koos

Squadron green putty, or mix your own "goop" by melting plastic sprues in solvent cement or lacquer thinner. The latter method was recommended by the late biL Marsland (P5e Camelback) in a number of his threads.

Andrew

I prefer to sand the bevelled mating surfaces to a sharper angle so that only the visible portions contact one another. The next step is to align the mating surfaces so that they're square to one another and use solvent-type cement to affix a strip of square .100" or .125" styrene to either one of the wall sections - push it tight into the corner thus formed, but cement it to only one of the walls. Next, coat the angled faces of both walls with solvent cement, along with mating surface of the reinforcing strip. Wait a few seconds while the plastic softens, then recoat all mating surfaces and assemble the parts, clamping or otherwise supporting them so that they're square. Let the joints harden fully - at least a couple of hours, but preferably overnight.
The exterior of the corner can then be cleaned-up. Scrape off any oozed-out plastic, and re-scribe mortar lines where necessary, then lightly sand to even out the surface. There should be no need for any filler, and the joint will be strong and permanent.
This was the method used for the corners on this structure, and also for the vertical butt joint at the midpoint of the long wall.



Wayne