woah.... finally got to the last post!
I can understand why people want to be lazy and not read such a long thread end to end, but for a project like this, it becomes critical when there are so many variations of methods and proportioning being tried.
For instance, way back there is a link to an article which makes known the 3:1 ratio for mineral spirits and gives the reason why, and stressed the importance of correct measure. Later, a post was made referencing the use of naptha which used the ratio 5:1. Since then everyone following has been using every mixture in between, some even eyeballing it, probably because they missed that post from not reading...reading is fundamental....
so for the benefit of others after this post here is what I've gleaned so far just from reading:
USE Personal Protection Equipment! Mineral spirits and other chemicals will destroy those cheap disposable gloves, exposing your skin to absorbtion. I have those big thick green gloves that go to the elbow, not sure where to get them because I got mine from work and haven't had to replace them yet. I also prefer a full face shield over goggles, it has better visibility and I don't feel so claustrophobic. Damage to your eyes is forever and so is exposure to some chemicals, always read the MSDS sheets. (I was doing preventative maintenance on a processor one day and a pressman comes in and dips his bare finger into the developer asking "this isn't corrosive is it?" "um yeah... it's corrosive 8... the highest the scale goes, go wash your hands in soap and COLD, COLD, water." Mind you, I'm wearing a chemical resistent apron, full face shield, and elbow length chemical gloves)
Mix: 3 parts mineral spirits to 1 part exterior silicone or bath and shower (do not use waterbased interior/exterior or painters because it will dissolve in water after it cures) NOTE: air bubbles from mixing and application are the enemy!
Soaking the fabric seems to ensure better penetration into the fabric so long as you work the fabric enough to remove air bubbles
brushing or sponging using a back-brushing technique (paint 3 rows at a time, each time starting one row below your previous first row to ensure overlapping coverage) can also be adequate but there's a greater chance of missed spots and introducing air bubbles. just like when painting, always try to stay ahead of the drying, maintaining a "wet edge" and don't overwork the sil during application (going back over it after it's begun to dry) or it won't bond properly.
set up your project as you would if you were using it for sil application and drying. This will ensure that the stresses of real-life use are actively in place and all threads are exposed that would normally be during use. High-stress points are along the ridge-line and at any tie-outs. If you apply the sil and then stress it you'll be opening up voids that were not there when you soaked it.
Pre-treat any reinforcement fabric that will add an extra layer to ensure that it gets penetrated on both sides.
from the look of things I'd say the best practice would be to soak it first, then hang it as for use, then brush over it again while it's still wet, paying strict attention to the stress points.
Squeegee: I could be wrong but I doubt a squeegee would really be very effective for this. screen printing inks are very thick and has to be forced through the threads in comparison to this dilution of sil and I saw many posts where people said they had no problem sponging it on.
rollers: I used to work in prepress dept for RR Donnelley and the processors we used for film and printing plates pushed the sheet beneath a spraybar, through a chemical bath, squeegeed it off on the other side, rinsed under another spray bar, followed by a heated blower that dried it. the difference is that film and printing plates are fairly rigid compared to fabric, so to make this work you'd have to come up with a way to splice on a sheet aluminum leader to your fabric. the other issue is that it's only 3 feet wide which is definitely not going to accomodate a full tarp. I'm not sure how many printing companies are still using film these days, so if you watch for when they go out of business you might be able to pick up a Kodak Polychrome film or plate processor for pretty cheap. Likewise for vacuum tables and parts for them such as the pumps. When my local plant closed I came home with a vacuum pump, desk, and a light-table for a total cost of $15.
I haven't personally tried any of this stuff I've been reading yet, in fact I've only just joined, having found my way here via a youtube video from one of you about making a hammock. I've been camping and hiking my whole life, but only with my North Face Cumulus tent which is wearing out and heavy, and never for any extended trips, only ever day hikes and canoe camping where you find a site and explore the surrounding area. For the last year though I've been cycling in preparation for some cross-country trips I want to do, and I've been commuting to work by bicycle for the last 7 months. I'm looking to reduce my pack weight in essentials so and so I thought maybe a hammock or a bivy, and from what I've seen on here, I'm swaying heavily towards the hammock.