I want to use Envirotex on the river portion of my layout, the problem is that most of the river goes off the layout and exposed in a cross section. What would be the best way to seal the Envirotex to prevent leaked and make it estheticly appealing?
Thanks
If you wish, and Joe Fugate did this on at least one spot quite effectively, you can make as smooth an “end” as possible so that you get an aquarium-like view of the sub-surface of the river…complete with little foil fish, painted scummy rocks, submerged logs, etc. Otherwise, if going to all that detail puts you off, just paint the end a colour of your choice using acrylic paint. Flat black would be great, but so would the colour of your fascia…if you have it…, or any colour that blends with the surroundings. Not sky blue, though.
thanks, but how do I keep the water in the river, and not flow off the table?
If you want the effect of seeing the edge after the pour, place a temperary dam w/ waxed paper to the inside. If you need to just stop the flow, either use the temp or place the facia and shape accordingly, seal the riverbed with plaster, caulking, large fills done with Great Stuff foam, etc, paint and scenic if desired then pour.
Bob K.
Sorry, I was suspicious of my interpretation of your first iteration, but Robert seems to have guessed your meaning.
As he so correctly stated, you must seal the entire area, vertical and horizontal surfaces, and anything in between, that the mixture will contact. It is best to use a cheap caulking for the river bed sealant, spread thin but not broken anywhere, or use a putty. You can buy dry powdered wood putty and spread a 1/16" thick layer over the flat parts, and run some of it about 1/2" up the banks, or higher if you intend to have a deep river. Plaster would also work. Paint it all when it is dry, and use painter’s or masking tape pressed firmly against the open edges of your table. You might have to file the edge smooth and sand it, and then apply the tape to ensure a good seal. The way I did it was to place two lengths of tape facing each other and press them together so that one had about 3/4" of the sticky side exposed, and so that when in place the non-sticky surface would come in contact with anything poured. Once you are sure that the edge is sealed, place a pan or several layers of paper under the open edge to catch any oopses. Mix your batch, pour it, let it dry for about a day, and then add layers as you need it…only about 1/8" at a time if you can help it.
A hint is to cover the whole thing with a dust and lint-free rigid item so that no dust and hairs, cats, etc can marr the surface while it is still sticky. Let it breath to dry, of course, but try to cover it from anything blowing or that might fall into it.
Thanks to you both, thats exactly what I was looking for, when its done, I’ll post some pictures!
I ran the facia across the the end of my stream, before pouring.
Nick
I built a temporary dam from cardboard covered with KY jelly held in place with map pins. The KY sealed it and them came right off when I was done. And yes, I know the other uses for it. 
Fred
I did the same thing, but used Vaselene!
Bob Boudreau
I did mine in true Redneck fashion…I made my dam out of duct tape!!![;)]
A little fine sandpaper and fascia paint when I was done to fini***he end.
Oh, by the way, if you happen to get scratches in Envirotex (over time, it happens), you can recoat it with glossy water based polyurethane. Gently stir the can prior to appluing with a soft brush, DO NOT SHAKE the can. Otherwise you get so many bubbles that it becomes unusable.
great tips! Thanks everyone!