"Are you sure you mean 30:1 ratio of mineral spirits to clear silicone caulk?
I'd say even 15:1 may be too thin. 10:1 is the thinnest I would likely go for a canopy coating. 5:1 worked very well on my TT Moment."
Yeah, well calks can vary in consistency. 5:1 is OK for seam sealing. Working in an outside area, the mineral spirits will evaporate off in about 5 minutes. If applied to a canopy, though, after a year or two of use, it will pull loose, leaving some peel. A thin coating won't do that. If it still leaks after a 30:1 coating inside and out, you can do it again without high weight penalties. Note that the tarp or tent needs to be fairly clean.
Generally 30:1 or 40:1 will do older silnylon, stretched silnylon, or untreated spinnaker. (I prefer my packs to have high water resistance, so, I did this with an old g5 spinnaker also.) High qualty calks require thin dilutions...the point is not to cover the thread and leave tiny "puddles" on the surface, but to fill in between, penetrating any streatched fibers and pores. Any coating on the threads does nothing for water proofness, the thread should be water proof. Too thin, 60:1-70:1 say, may not leave ANY coating outside if it is worked in properly. There is a minimum film thickness that will bond to other things and itself. Calks vary, between 20:1-50:1 is about what I have run into. You can apply this to a small piece of glass to check it. If it spreads evenly, it is good. If it beads up as it dries, it is too thin.
Yes. You can do it with 10:1 but it is real messy. It will require more work to apply evenly, forcing a thinner/stiffer brush, more spreading, and slow going. It gets a bit stickey after a few minutes so this is difficult to use on large areas, like a tarp. 5:1 is nearly impossible to get a fairly even coat without a double roller squeezing excess out...a factory process. 5:1 Mineral Spirits/GE clear silicone calk is about what I use for seam sealing (in a small tube, or, injector.) Thinner and it won't stay in the tube too well. Thinner does nothing to the actual calk. It simply spreads the calk out, then evaporates off leaving the calk to cure.
I have done 5-6 tents and 7-8 tarps with 30:1 (or there about...) For close weaved fabric with some silicone coating (or worn out tarps and tents starting to leak) it just needs to fill in between the tiny pores between threads. A coat outside, worked in with a brush will do that and remove most excess *on* the threads. As it dries it gets stiffer but it may "pop" the filled pores leaving a small open pore. Working it in and doing the other side fills the pores, again, with the brush wiping off most of the excess. The resulting coating is very light, about .3-.4oz per yard. It has filled the pores, insuring no misting, no leaks. It will also bond the fibers in the threads, and, the threads in the weave, making the fabric more durable, generally improving quality. But it will add .3-.4oz per yard weight. For the SpinnTwin, about 60 sqft means ~2oz, This is about what the factory should be adding to fabrics as a siliconized coating. So, the overall weight correctly matches the factory "coating weight." But this means about 30:1 for the mix ratio applied to both sides of untreated fabric, or, old silnylon. Untreated fabric *might* require another coat. Again, the goal is to fill any pores, not coat the surface of the fabric. For untreated fabric, I often go a bit thicker on the mix, but it doesn't really require it. I could add a third coat, but I am lazy and am trying to avoid the third coat.
Ripstop has a larger thread every 1/4" or so. This is a bit more difficult, since the larger thread creats a small build up or "puddle". This means that it has to be applied diagonally(left and right) and worked in a bit more.
For spinnaker it is smooth. A cheap throw away brush (bristle, not foam) about 3" wide works well. Work until it stops bleeding onto the fabric surface. Overlap strokes about 20% or so. Doing both sides will allow the mix to bond with itself through any pores, too. A LIGHT coat can be too light, but doing both sides will insure it seals the fabric. Again, IFF needed, you *can* add a third coat.
Small patches can be applied for burn holes, over small fray holes. To do the patch and the fabric, lay the patch on wet with 100% calk, then carfully brush it down. It must lay flat. Brush off any excess on the other side. About 1"x1" patches can be applied. Do this before coating the tarp. They stay on fairly well, but, they can be peeled off.
I use slightly thicker for floors, again, both sides. Abrasion can wear it off after a couple years or puncture it. UV damaged fabric is still damaged, of course. But, an old tarp coated with WHITE calk will bond it together, and, slow further UV damage. Most white calks are made with titanium white filler/pigment. It blocks some UV. But, it does show. Floors don't need a UV coating, of course. Bonding damaged threads can help with durability.
Usually, tarps treated like this do not stick together after 24 hours of drying time. If it sticks together, the coating was applied too heavily. But, a light dusting of plain talc works to prevent sticking. Unscented, plain old talk...no corn starch.
I tend to err on the side of caution, meaning two, three or four coats of thin mix will do the job, but, not add additional unnecessary weight. Again, if needed, it can simply be recoated with only some lost time. Applying the coating too thick can cause peeling because the bond between the fabric and calk is not as good as the bond in the calk, ie, if the bond was weaker in the calk, it would never peel. Peeling, of course, ruins that area; it could start leaking or misting again. Overall, it is safer to simply thin it out more(30:1) and apply a third coat IFF the first two still mist/leak.
Also, the calk layer is very hydrophobic in comparison to the nylon. Often, most tarps only leak in stress areas (from stretching) or from damage (fraying.) A thin coat will add water repellancy to these areas, without actually filling the pores. More like a very durable water resistance, than a water proof layer.