DIY silicone seam sealer
Better mixing of DIY silicone seam sealer is described to give it a longer pot-life and more relaxed time to do a good job.
Introduction
I have dabbled a lot with this silicone rubber for my work and for my hobbies and have posted on the many uses that it has for DIY backpacking tinkering. Bulk acetic cure builders RTV silicone rubber is very cheap and is my favourite for all projects. As a retired chemist, I trust the acetic solvent in this product most of all (compared with many other nasty solvents) because it might smell nasty and take your breath away, but acetic acid is already made in us and is just a part of life. “Sorry about the chemistry lecture, but I thought you should know why.”
Many of my tinkering uses of this thick silicone rubber work best when I make a DIY silicone seam sealer with a solvent such as clean mineral-based turpentine. The thinned liquid rubber can be used to water seal sewn seams on compatible fabric and or make compatible stitching threads waterproof or water repellant and to prime and impregnate compatible fabrics to prepare them for silicone coating, glueing and lamination.
Depending on the application various dilutions of the rubber are required or simply preferred. Experience quickly guides you to what is required to make the end product easy to make. “For what it’s worth I use thinner mixes than most others, typically 1g:4g of thick silicone liquid to clean turps (accuracy is not critical). On a large item such as a tent, it will eventually add less weight. Thinner sealant works-in better and faster, so fast that it will often come out the back of the fabric. Of course, more rubber can easily be applied if a thicker or smoother finish is required.
Now to the DIY silicone seam sealer mixing fun bit or is it a mistake?
The thick pasty silicone is reluctant to quickly dissolve in the thin runny turpentine. I, like many others, have resorted to mixing the two liquids together with a tiny ‘whipper-snipper’ style whisk that in my case was run in a high speed, Dremel Tool.
This method is temptingly quick. But these carefully crafted tools are now redundant for my DIY silicone seam sealer mixing. This is because the whisk also incorporates a lot of air bubbles into the mix and these bubbles carry atmospheric moisture into the mix. This RTV (Room Temperature Vulcanising) silicone rubber naturally uses water to catalyse the polymerization, vulcanisation, setting or curing of the soft silicone into the finished solidified polymer.
This speedy mixing method makes the thinned silicone liquid have a very short ‘pot-life’ and it is likely to turn thick and goopy before it is used up. Consequently, I found that simple, calmer and more anaerobic mixing methods could be used to give a long pot life for jobs like sealing many meters of tent seams.
In laboratories, a device called a stomacher blender is used for anaerobic mixing where the samples in sealed plastic bags are gently massaged by rollers or paddles to effect thorough mixing.
A ziplock bag could be used in a similar way with most of the air removed and then massaging could be done with fingers or a soft plastic foam brush or similar. I seldom need a great quantity of thinned silicone to justify using this method.
Now I regularly use a small smooth ceramic bowl and the application brush to calmly and gently mix the two liquids together. At first, it seems slow, but the two liquids are quite willingly soluble in each other, it just takes a little time. “Much less than the cleaning time of any formal mixing device!
Sometimes I complete the mixing as I start applying the mix. If I find little blobs of the thick mix. The brushing action will also complete the mixing. Also, the brushing action will incorporate air and the curing will start quickly enough on the work face.
As an example, the shirt cotton fabric below was first impregnated with 1:4 thinned silicone rubber. In this case, I used a straight-sided artist’s spatula to first mix the liquids and then squeegee the liquid thoroughly through the fabric until it oozed out onto a plastic backing sheet.
When the liquid cured the warp and weft of the fabric could be seen as a matt finish through the sealing, but it was totally waterproof and the threads were immune from any fraying. Because I wished to make the cotton heat resistant to 300C to make a tent stove jack, I coated the impregnated cotton with a layer of thick silicone rubber on both sides to give the generous shinny coating shown in the photo below. “This coated fabric is still very easy to sew on a regular sewing machine or by hand stitching, in fact, it is easier than the parent material!”
Conclusion
Only mix small amounts of thinned RTV silicone rubber appropriate to the task ahead. Mix the liquids together gently with the application brush or spatula, smearing it around the mixing bowl so as to incorporate the least amount of air in the mix for a long pot life.
Tim
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