RTV Silicone rubber uses for backpacking gear

This post is about various ways in which I use RTV silicone rubber to make innovative ultralight gear for backpacking.

RTV silicone rubber is a wonderful technological gift from science. I hope this post will help you to make use of it for your tinkering.

It’s bonding, low cost, flexibility, moldability, penetrability, high-temperature tolerance, chemical resistance, versatility and long service life make it an exceptional addition to our tinkerers toolkit.

If used carefully it is much safer than many other alternative adhesives.

Note: This post is a work in progress and may never be completed because of the exponential growth of possibilities that flow from the success (and importantly the failures) of each glueing experiment or project.

The post is already far too long (according to SEO analysis). However, reading the whole post may provide you with a better understanding of the potential (and pitfalls) of this wonderful adhesive.

Eventually, I will make a list of links to my individual post that use RTV silicone rubber.

However, you may wish to come back to this long article to understand it in context, as each little subject usually relates to several others.

Reading the long article will be at the risk of hearing me ‘bang-on’ about:

• The wonders of the element silicon,
• Its oxide silica,
• The many useful derivative silicone polymers and
• That they are abundant and can be made from sand.

Understanding these issues can vastly expand a tinkerer’s toolkits.

The list of related individual posts that use RTV silicone rubber

DIY stove jack- Glue-on and sew-on for hot tents

A load bearing hem for the apex of pyramid tents

Silnylon glueing

Introduction RTV silicone rubber

Technical stuff

RTV silicone rubber love-affair

I have always had a fascination with RTV (Room-Temperature-Vulcanizing) silicone rubber. I have mostly used ‘acetic cure’ or ‘acetoxy cure’ RTVs that use moisture from air as the catalytic agent that causes RTV silicone rubber liquids to polymerise (vulcanize, go solid, cure or set).

From my early days working in a research laboratory, implantable surgical silicone rubber was very new and expensive. Dow Corning also had these little metal tubes of liquid RTV silicone rubber that were equally expensive.

Anyway, I was told the two were incompatible and could not be bonded together by mere mortals like me. Examples of this can still be found. Even in those early days, I was showing a stubborn characteristic of not taking no for an answer.

I tried glueing the two together. The tubing was neutral/clear and the liquid was jet-black. Nevertheless, the rather ugly device held together strongly and lasted forever while I expectantly waited for it to fail.

Many years later, this little success still inspires my RTV silicone rubber tinkering investigations. This wonderful RTV silicone rubber is now abundantly available if you know what you’re looking for and is cheap if you know where to look.

Heat-cured silicone rubber- another love-affair

Much later I fell in love with another silicone rubber. It was a heat-vulcanizing silicone rubber for moulding items for making my own prototype gismos for all sorts of wonderful research tools and parts including tiny pneumatically operated elastomeric valves for dairy research.

These gizmos made my research possible and made my devices look more like commercial devices that funding organizations might back.

Differences between natural rubber and silicone rubber

Natural rubber (from rubber tree sap) has an interesting and essential chemical reactivity in its unsaturated carbon-carbon bond structure. This allows it to polymerise (make long linked chains of the parent molecules) to make solids or flexible soft rubber for condoms, rubber bands, tyres or even hard bakelite (a forerunner to modern plastics). It revolutionised industrial technology and our parent’s lives.

However, this same reactivity that is residual in the softer polymers is also it’s Achilles-heal. Put simply, sooner or later it perishes. This is my segway to my obligatory ode:

Old stories of the rubber mountaineers I cherished,
With gear primitive by the elements punished,
Names of renown but no oxygen or super-down,
And some rubber mountaineers went up and perished.

Natural soft rubber will, in time, perish when exposed to oxygen. If the rubber is stretched, as it is often required to do, it accelerates the perishing.

As another example, if bulk rubber bands are stored in a sealed airtight jam jar they will ‘last forever’. Collectively, they will mop-up the oxygen from the head-space gas and slow the perishing process. In contrast, if one of those bands is stretched out around the same jar, it will perish quickly.

For me, this makes a simple test to see if my precious purchased premium rubber bands are silicone rubber or other natural rubber.

For my mountain adventure activities perish free rubber bands are good. One of my skiing nicknames at Mt Baw Baw was ‘rubber man in the blue knitted suit’. This was not on account of my rubber fetish or mountain perishing, although I did once experience frostbite. It was on account of my odd skiing style and my unique and my beloved blue onesie ski suit that was knitted by my dear Mum.”

I also have an exceptionally brief related post on DIY perish free rubber bands if you should be interested. “Yes, ‘$ free’, perish-free, guilt-free and any size'”

Permeability and stretch- not all rubbers are equal

As the saying goes, it’s ‘horses for courses’. While you will hear me extol the qualities of RTV silicone rubber, when compared with natural rubber, it has limited stretch and high permeability to gases and organic compounds.

As an example, my prior research was in the dairy industry and I often ‘married silicone rubber experimental things with other black or red rubber things. Slowly, the red or the black pigment would migrate into the otherwise neutral/clear silicone.

Similarly, fat from milk in milking machine teat cup liners would slowly migrate through the silicone rubber and appear on the other side that never contacts milk.

As another example of permeability, my Lay flat kettle allows a tiny leakage of smoke flavour through the silicone rubber and into the boiling water when cooking with wood. “It is not particularly unpleasant and is an expected extra in my tea when adventuring and using use wood for fuel.”

Lastly, we know that natural rubber balloons slowly go flat. I made pneumatic balloon valves from silicone rubber they worked well when pulse on and off very often. However, they would not ‘hold gas’ as it leaked through this membrane, like a sieve! “So don’t try to make a long-life silicone rubber balloon.”

Wonders of the ways of chemistry

I apologise for this final ‘bang-on’. This flexible RTV silicone rubber is essentially a polymer that can be made from quartzite sand (SiO2). “Sounds unlikely?” My most popular post is also about Sodium silicate for making rock-like DIY refractories at home from various cheap mineral powders and soil. Guess what? It too is made from sand and is another polymer or glass that binds the mineral particles, but has only slightly flexible.

One last shout-out for silicates

Although a little off the track, I could not leave this secret-silicate-trick off the list. Sodium silicate, when added to common Portland cement mix, makes it set-up quickly just when you want that to happen. If you are interested, please see my post Cement accelerant.

Silicon an infinite resource

Not surprisingly for an ‘iron planet’, iron (Fe) is our Earth’s most abundant element. Australia has it in spades (Exported iron-ore (iron oxide) & imported spades (iron metal). However, oxygen (O) and silicon (Si) are the second and third most abundant elements at ~30% and 15% respectively according to Wikipedia. How lucky are we to have this infinite resource available for our creations?

It is fascinating to think that such rubbery or glass-like properties can be exhibited by the same combination of these abundant elements and I have a passion for both as should be evident from my posts.

“I wonder if space explorers will one day find a life form based on silicon? It has many of the chemical characteristics of carbon which is our-stuff-of-life and the source of our most problematic pollution.”

Yet another silicone?

Yes, if you have not nodded off by now before we get to the fun bit, there’s more. Yes, it is worth knowing the difference, and especially the potential RTV silicone bonding problems that tiny traces of silicone oil (or any other oil) may induce.

Silicone oils are yet another polymer of this magic stuff derived from sand. They are formed from chains of O and Si atoms linked in an alternating pattern. Then they can have pairs of various organic side branches (often methyl groups) bonded to the tetravalent (capable of forming 4 bonds) Si atoms. “A sort of inorganic/organic molecule that only a human could make.”

They too have endless uses including lubrication, anti-foam agent, water repellency and a moulding release agent for heat vulcanizing silicone rubber.

If, as I later discuss, fabric has been treated for water repellency (DWR) with one of these compounds then it will probably put an end to bonding with RTV silicone rubber in my experience.

Back to ultralight tinkering

Having retired, I no longer have those laboratory resources and toys at my disposal to play with. However, both you and I have cheap and abundant RTV silicone rubber available to make wondrous gizmos, if you know what to find, where to find it, and how to use it.

“It can do so much for our tinkering. So, my silicone rubber love affair continues and I share my ideas with you and would like to hear about your tricks to add to my list.”

Methods- my list of a tinkerer’s tricks and tips for using RTV silicone rubber

Background information

I have a post on Silnylon glueing and sealing of tent fabric with RTV silicone as ‘neat’ liquid or in a diluted form using clean mineral turpentine and some tricks for quick mixing. This is probably good background reading.

In that post, I describe how some silnylons bond well for load-bearing purposes and some only bond for water sealing without much peel strength. Unfortunately, I have no way of predicting these properties before purchasing fabric for a project.

Anyway, I thought it was time to investigate if other fabrics and materials can be bonded with RTV silicone rubber. This would include water-repelling, impregnating, sealing, sticking/glueing/joining and bonding. I will also include related RTV issues in the post including compensation for lack of peel strength.

I will add to this list of successes and failures and would welcome contributions from others through the comments section below or using my contact form (On the right of the top menu bar).

The rest of this section is all about general tips about the RTV silicone rubber and below that is the list of particular uses for the rubber.

What type of RTV silicone rubber?

This seemed to me to be a good starting point. I like to use acetic cure RTV silicone rubber. Other alternative rubber solvents probably can perform well. As a chemist, I know the concentrated acetic acid solvent is breathtakingly nasty and corrosive.

However, acetic acid is much safer and uniquely more trustworthy than any other synthetic solvents that are often used.

To explain, in general, I always will use a chemical that is part of life. Acetic acid is part of life and when diluted you might even put it on as vinegar onto your fish and chips.

Some researchers indicate that acetic acid or acetate is a tonic for us when it is produced in our colon when eating a High fibre diet. Anyway, it is a much better risk than some synthetic chemical that has not been with us over millions of years of evolution.

I have no proof, but I think the acid also acts as an etching and cleaning agent on many surfaces such as metals and helps to make a good bond.

A good source of cheap RTV silicone rubber

Aldi periodically has cheap 300g tubes of acetic cure silicone on sale. There also is a vast array of 300g silicone rubbers at Bunnings and many have become quite expensive ($20-30).

Even the best storage tubes leak solvent and the content will polymerise with time and so much liquid silicone is ‘sort-of’ wasted in this way.

Consequently, a cheap source makes this inevitable decay for the tinkerer much easier to accept. Even so, the solid cylinder of polymerised rubber that is left has uses that I will describe later.

I have found that Bunnings has a very cheap acetic cure RTV. You may need to search through the shelves of many alternatives to find this cheap acetic cure product.

The word ‘acetic acid’ is well hidden in the ‘fine print’ of the tube that I purchased, hence the long search. However, I note that the image shown in the link below has the extra ‘acetic cure’ written in black bars on the front of the tube. “For a while, I thought I was going mad, and maybe I still am.”

In the web information on, Parafix window and glass, the ‘acetic cure’ is more obvious in the descriptor and the image of the product. That information helped me find it on my third visit while waiting for the Aldi special. “This is also why I delayed making this post. Well, this is my excuse anyway.”

Reducing spoilage of an opened tube

I usually use a tube of RTV silicone rubber for many projects over a long time. Consequently, preserving the quality of the remaining rubber (stopping spontaneous polymerisation) after cutting off the plastic tube seal is paramount.

Water initiates curing

The above type of RTV silicone is cured with contact with moisture, normally from the air. An exposed rubber surface can have accelerated cure (as well as smoothing) by smearing with a generous film of water (preferably soapy).

Preventing premature curing

Any leakage of air (with moisture in it) into the stored RTV silicone rubber will start to solidify the rubber in the storage tube.

Most sealant tubes of the above design use a screw-on conical nozzle to deliver the product. It is tempting to simply put a nail in the hole in and hope that the air will not get in and the solvent will not leak out. For the acetic cure product, this does not work well. “Hard rubbish is littered with such failures.”

I normally do not use the nozzle for delivery. Instead, I use the nozzle in its uncut form as a screw-on lid. I put a square of thick polythene sheet over the threaded end of the tube and screw the cone on (As shown in the above photo). This forms a much better seal than a nail.

Even so, when the tube is next opened sometime later, there will be a little plug of polymerised rubber in the opening and some gelled liquid behind that. “This is easy to clear out before getting to the good stuff.”

Ultralight sachets of RTV silicone rubber

On my ultralight walking or skiing trips, I like to have a comprehensive ultralight repair kit. A tiny quantity of liquid RTV rubber is a useful addition to such a kit for mending holes, binding and whipping etc.

In my previous research career, I made and used form-fill-seal machines that used heat sealing of metalised polymer laminates to form a gas-tight sachet. So in my retirement it was irresistible for me to investigate sealing small portions of RTV silicone in gastight sachets for my field repair kit.

The sachet contents stayed liquid for a period of about 12 months.

[Add a photo of sachets of RTV silicone rubber]

Thinning the thick RTV silicone rubber

Thining RTV silicone rubber with mineral turpentine (not turpentine derived from trees) is quite tricky. Although they are infinitely soluble in one another, they do not naturally mix.

Consequently, there will naturally tendency to whisk the mix to speed the mixing. This incorporates air bubbles. This adds atmospheric moisture into the mix. This will greatly shorten the ‘pot-life’ of the mix as it will quickly start polymerising and become ‘gooopy’ and unusable.

Note. There will be more on avoiding this mixing problem and even on avoiding the thinning step later.

DIY impregnation of fabrics with RTV silicone rubber

For all fabrics discussed in this post, I used this application method using a strong black polythene backing sheet. I use a small sheet of plastic and brush on a bench for little things.

However, for large things like tents, I use a large brush and an old fold up ironing board. “From the curbside hard rubbish, of course.”

On this, I place a board or plank (as long as the wall of the tent). The plank is wrapped tightly in the black polythene sheet and taped together at the back of the plank.

“I have a lifetime supply of used polythene silage cover that conveniently is ultra-black on one side and ultra-white on the other. The black finish is excellent for observing the extent of wetting and black on white is just great for ‘see-through-contrast in some critical situations where precision masking is required.”

The thinned rubber can be brushed in on the top of the fabric and thorough penetration is indicated by the black plastic surface becoming ‘wetted’ by the thinned silicone rubber.

More fabric can be moved onto the wetted area and the process can be repeated with thorough impregnation and this way there is little wastage.

The brushing action will add more ‘air moisture’ to the mix and accelerate the polymerisation. Working fast and systematically with a suitably large brush is important.

Eventually, the fluid will go gelatinous and no longer penetrate the fabric and a new batch that is of a more appropriate size can be prepared. The surface gell swarth that forms near the end of the ‘pot-life’ can be easily rubbed off later.

Note: I have not yet found a use for the waste gel, but I am sure that I will. Don’t attempt to burn it in a fire as it makes a ghastly soft fluffy white residue that floats on the slightest of breeze. I suspect that it is silica (SIO₂) and could be very dangerous for causing deadly Silicosis.

As an aside, I find it is interesting to think that, in this white form, that it has returned once more silica, but in a much more deadly form than beach sand from which it was made. “That was a long background, so now for the fun bit!”

The list of RTV silicone rubber bonding uses

This list will include bonding, moulding and sealing of fabrics, metals and plastics in various combinations. It will be assembled in a somewhat chaotic order over time as projects progress and time beyond Covid 19 permits. The ideas will be presented as real gizmos or as simple test pieces.

Cotton and canvas impregnation and glueing

I have been curious to know what fabrics other than silnylon can be sealed and glued with RTV silicone rubber. So like some of my other threads, I think this may be the start of a long journey? Some day it may reveal why some silnylons don’t bond well?

I was looking for a waterproof glueing method for Trevor’s truck camper. For his wood burning tent stove, he wanted to fit a heavy version of my heat resistant Ultralight flue gland or stove jack to his roll-up canvas awning.

Right or wrong I have always assumed that the success with bonding to some silnylons would have been due to the manufacturer impregnating all the fine fibres of the fabric with silicone rubber during manufacture.

In effect, every single fibre of the fabric is perfectly primed with silicone rubber. Then the additional RTV rubber can vulcanise onto the rubber rather than to the nylon polymer of the actual fabric.

However, remember, I mentioned above that some silnylons don’t bond so well. I don’t know why this should be so? Consequently, it was without high expectations that I started to test cotton canvas. I also tried some simple woven (not knitted) cotton shirt fabric that was leftover from Covid 19 mask making (It may even be a cotton polyester blend, but it does not make sweat stinking clothing.

This ‘cotton’ burns with a clean self-sustaining flame with no melting or shrinkage away from the heat source. So it is probably cotton or some other cellulose-rich fabric (Fabric identification). “This is the trouble when one purchases wonderful discounted bulk fabric at only$2/m. There is a lifetime supply, but you don’t quite know what it is without setting fire to it!”

This is my segway to my obligatory ode:

$2/m fabric  from darncheapfabrics,  for this little buyer, 
I’ll have the small roll from this kind supplier,
For a Covid19 mask was it cotton, fit for the task?
To be absolutely sure would I have to set it on fire?

Both the canvas and cotton easily ‘wetted’ with the thinned RTV silicone rubber and came out onto the backing sheet.

When cured and ‘dried’ the rubber was stable and not easy to rub off.

Next, using only the impregnated portions, a thin film of thick RTV silicone rubber was spread onto all surfaces that were to be bonded. Gentle pressure was applied to the bonding areas and they were left to cure in the sun.

“Being impatient, the drying was hastened by placing the test strips in a redundant solar food drier. Even so, it still had the smell of residual turpentine many hours latter”

The bonding appears to be quite strong and I thought it was only fair to allow more curing time before testing bond strength.

Glueing and sewing

After allowing the above test joints time to fully cure, I tested the peel resistance and I felt that it was inadequate for load-bearing purposes. Consequently, I oversewed the joints and rubbed in silicone rubber into the stitches. It looks as though it will form a very strong tensile (sheer loading) load-bearing bond or joint that would also be water-resistant.

Sewing through RTV glued fabric

I have elsewhere declared that I am an ambitious but crap-sewer. So it was with some trepidation that I started to sew through the bonded fabrics. I was quite ready for failure. Then I would have hand sewn the joints. I even thought of using detergent and water as a lubricant. However, the sewing was easy and hey, I didn’t need to use pins or tacking stitches!”

Now it’s time for another ode;

I searched for a noun for a male who crudely sews,
Not the obvious word sewer associated with poohs,
Meaning might twist if I correctly used sewist?
Or should I settle for a 'crap-sewer', who knows?  

Water repellency and anti-wicking

I have found that some fabrics and sewing threads may not be glue-able with RTV silicone. However, many fibres can ‘take-up’ enough rubber to become permanently water repellent when impregnated with the thinned rubber. “I suppose for the tent canopy, being water repellant and the sewing threads non-wicking is the next best thing to being waterproof.”

Polyester bonding with RTV silicone rubber

I have tried to treat polyester tent fabric with thinned RTV silicone. From my limited experimentation, the liquid rubber penetrated the fabric well, much like my best bonding silnylon. However, when cured, quite a lot of the cured rubber rubbed off. It was water repellant but it did not impart the property of preparing the fabric to be able to form a strong bond using thick RTV silicone rubber.

These polyester fabrics were of ill-defined origin. They were recovered from discarded tents. They may have been treated with silicone oil water repellent and this may be the cause of the failure to bond well as discussed earlier.

Pedigree polyester bonding with RTV silicone rubber

I purchased some polyester with a pedigree and it was sold as an untreated woven polyester. It has a reflective silver finish on one side and is meant to be a ‘water vapour breathing’ fabric.

I primed test strips of this fabric with diluted RTV silicone rubber and then applied thick RTV silicone rubber to glue test pieces together as described above.

Both bonds had quite a good shear strength that was much better than the ‘second-hand polyester tent fabric. The silver coating surprisingly did not seem to influence the quality of the bonding. However, by my assessment, the peel strength was inadequate for outdoor load-bearing purposes. Consequently, over-stitching would be required to supplement the bonding.

My assumption about water-repelling treatment causing the previous bonding problems with polyester fabric now must be questioned. Alternatively, my new polyester fabric may have been water repellent treated? This information may have been mixed-up during English/Chinese translation? I will need to find another source of pure polyester to test this further.

Ripstop nylon spinnaker fabric bonding with RTV silicone rubber

This fabric has a pedigree even if the documentation is now lost. I purchased a roll of this (then) high-tech fabric many years ago. It was for making my own down adventure quilts. The fabric was the first to be made in Australia for the America Cup challenge (In the days when such boats did not fly above the water).

“Our boats had, at last, become a little competitive and the US pulled out the rule book and insisted that even the sail fabric must be made in the country of the challenger. So that was my luck. My quilts are the same red colour as the challenger’s spinnaker.

[Add a photo of one of my adventure quilts]

“This nylon fabric has an odd shiny look and stiff feel that I think was to reduce air leakage through it (I have just discovered the likely word for this extra process is, post weaving, heated rolling that leaves it ‘Calendered’.). Anyway, neither the thinned nor thick RTV rubber bonded well with it.

Shirt cotton bonded to shirt cotton with RTV silicone rubber

In the above shirt-cotton to cotton-canvas test, I suggested that suboptimal bonding may have been due to a silicone oil type water repellent treatment on the canvas. If so, the shirt-cotton may successfully bond well to itself.

I also thought that contaminants from the thinning solvent may have compromised the bonding. Consequently, I did the next bonding test with shirt-cotton without thinning.

In a single process, I quickly primed both sides with neat RTV by squeegeeing it in with an artists flat ‘painting’ spatula. It penetrated after some effort and then I ‘buttered’ both sides lightly with thick RTV silicone rubber and pressed them together until the glue squeezed out a little around the perimeter.

The bonding was strong and had good peel strength.

“This to me means that the canvas or canvas water repellency treatment was probably the bogeyman in the problematic canvas bonding.”

It was remotely possible that the thinning solvent was compromising the bonding. However, later bonding with priming with thinned rubber worked well.

“So my lifetime-supply roll of stripey shirt-cotton may never become a shirt. However, it may become the new hi-tech ultralight fabric of the future, that is if it does not get used up making masks for the next pandemic.”

An Instagram video demonstration shows the bonded cotton supporting 6kg of groceries.

Good cotton bonding after priming with thinned RTV silicone rubber

The following bonding test was done after priming with thinned RTV silicone rubber. For this test, to load the groceries, I used a strong fibre shopping bag. This meant that I could bounce the load and it still held securely.

Easy and good RTV silicone rubber priming

The test showed that the priming with silicone that was thinned with solvent did not spoil the bonding strength. It also made the priming quicker, more uniform and easier.

“I suppose the cotton-on-canvas or canvas-on-canvas suboptimal bonding with poorer peel strength was due to the properties of the canvas. Prior canvas waterproofing treatment is still a likely bogyman.”

Embedding of shirt cotton in thick RTV silicone rubber for thermal protection

Using cotton fabric that is impregnated and then embedded in RTV silicone rubber could make an excellent material to make an ultralight stove jack for a hot tent.

The maximum flue pipe temperature at the silicone contact point could be 150C indefinitely without causing significant damage. Even at 200C it will last for 10,000h (Shin-Etsu silicone). Interestingly, they say that: “If the rubber is brought close to the flame, it will not ignite easily: but once ignited it will continue burning.”

Anyway, it bodes well for the possible appropriate safe use of silicone rubber on flue pipe exit holes. More discussion of thermal resistance protective properties of RTVsilicone rubber is in my post on DIY ultralight stove jacks. It shows that RTV silicone rubber can withstand sustained temperatures of 300C.

If such embedding works well, it may protect the cotton well enough without the need of the metal gland or fibreglass/silicone rubber sheet. This would make a cheap and simple fixed-in-place tent flue gland option. “No excuses needed for leaving this one behind when going camping.”

The sheet of embedded shirt cotton below was impregnated with dilute RTV silicone rubber and then was coated with the thick rubber on both sides.

Please see how the embedded cotton survived thermal testing my related stove jack post.

Soft cotton DIY tool handles

“For DIY hand tools, a good handle maketh a tool.”- Mothy the elder.

A generous wrap with a long strip of cotton shirt fabric that is held in place with RTV can make a cheap and very comfortable handle.

Cotton flue gland pocket

I have developed a hot tent stove jack system for ultralight hot tenting. I call it a tent flue gland and it used an inverted water-shedding pocket made of silnylon that is glued to the tent canopy that is also made of silnylon. The pocket can hold a removable metal foil gland that can protect the tent fabric from the heat of the flue pipe. Also, a thin plastic acetate sheet can be substituted as a window ‘for viewing the sky from bed’ when the stove is not deployed.

Glueing with supplementary stitching

The glueing with RTV silicone rubber can also be supplemented with sewing if peel strength of the bond with the tent fabric is not perfect.

As an example a flue gland pocket arrangement (shown below) can be glued and sewn onto a tent canopy. It then will allows a heat resistant metal gland to be easily fitted and removed so that the tent packing can be very compact. It also can allow different sized pipes to be used.

A caution about auto-vulcanization

I mentioned above that soft natural latex rubber stays reactive to air oxidation (perishing) and that silicone rubber is wonderfully free of this property. However, I found that RTV silicone rubber is not entirely free of reactivity after its initial curing (polymerization and vulcanization).

I found that the above pocket vulcanized to itself after it had been cured for some days. This happened twice while making some small modifications to the above pocket. This happened once with extreme provocation when the pocket was held under a plastic foam pad in between two compression boards. The boards were weighed down with 20kg of rocks in a bucket. “Possibly overkill!”

The next time it happened with just the gentle weight of the fabric pressing the layers together while preparing it for postal delivery.

This means that the pocket will need to have a plastic insert placed in it to prevent it from auto-vulcanizing. The good news is that it means that the surfaces are is in good condition for bonding more RTV silicone rubber if required

Bonding other materials

I have started to investigate other fabrics and materials that can be impregnated and or bonded with RTV silicone rubber.

Cotton is a cellulose fibre and forms strong bonds with RTV silicone rubber. Consequently, I now would expect that other natural fibres of cellulose or even protein (wool and silk) may also bond well, particularly if they are untreated. Even synthetic fibres (nylon, polyester, glass, carbon and carbon/kevlar) if left untreated may bond well. “Endless testing to do and more to come…….”

Bonding pure nylon

Early in the section titled ‘General information’, I have reported that some silnyon fabrics bond very well with RTV silicone rubber and the bond has good peel strength. “I have not yet had the courage to make a stitchless tent with such silnylon, but it should be possible.” Unfortunately, other silnylons form seals, but do not have adequate peel strength for load-bearing bonds.

I thought that the success was due to the thorough impregnation of the fibres with silicone rubber during manufacturing. Finding silnylons that don’t bond so well makes me question this theory. Additionally, my ever-growing list of fabricks that form load-bearing bonds without factory impregnation was challenging my long-held theory. So here is a little ode to human frailty about our precious theories:

Long-held precious theories morph into facts,
But an outstanding exception reveals the cracks,
Out with the old, a new theory to behold,
Truth is a little closer but beware exceptions and the axe.

Consequently, I thought that it was time to smash (or confirm) this theory with a glueing test of pure simple (untreated) nylon. I had pure nylon in abundance in the form of stockings or more correctly factory reject pantyhose legs that were not even dyed.

I reference this versatile fabric is in my whole citrus jungle juice recipe. “They have many uses from water filtration, soft plant ties to sand-filled ultralight diving weights. I draw the line at bank robberies.”

I found that the pure nylon glued easily and formed strong load-bearing bonds with itself.

Nylon bricklayers line

You will see me using this cheap, fine, light, strong and durable bricklayers cord on many of my projects. I presume it is untreated and I found that I could easily impregnate the cord with thinned RTV silicone.

I just stirred it around in my mixing pot that was a ‘motel single-serve thick glass marmalade jar’. When the diluted mix cured the cord has a waxy feel and a bowline knot can be securely tied in it, but the slipperiness makes a reef knot slip undone.

It makes a nice feeling waterproof cord for camping. It may also increase the cord’s resistance to high temperatures if it is well coated. The yellow cord that is shown in the above photo was treated in this way.

Silicone rubber USB electrical connectors

Previously I have described my primitive but effective fang fitting that can be used to supply USB power to blower stove fans. It used natural rubber contact adhesive to separate, waterproof, stiffen, insulate and bind fine copper conductor components beside each other to connect robustly with tiny 1.5mm pitch PCB sockets. “It is a crude but very effective custom fitting that is designed for rough treatment while camping.”

While the adhesive used was effective, the toluene solvent in the adhesive is given off while using it. It is quite a noticeable nasty toxic chemical. “A laboratory would these days be shut down if staff were exposed to toluene vapour at such noticeable level.”

Consequently, I thought that RTV silicone rubber would make a simple, cheap and safer alternative adhesive with relatively benign acetic acid solvent.

[Add photo of RTV silicone rubber bonded fang fitting]

Stainless steel to stainless steel bonding with RTV silicone rubber

The custom cooking pot for my KISS Stove is very light and thin and has no protruding lip around the rim. These factors make secure gripping with standard pot lifters difficult and somewhat hazardous.

Consequently, I thicken a tiny portion of the pot rim with RTV silicone rubber and a shim of stainless steel. This makes the use of standard pot lifters secure and does not interfere with the efficient packing of the stove in the pot or other larger pot on the outside of the primary pot.

I sand the surfaces to be glued together, just before applying the glue. “I think the acetic acid in the acetic cure RTV silicone rubber also helps to clean the surface and make a strong bond.”

High temperature whipping

The black cover on the original sensor tip on my new thermocouple melted. I think it was only made of thermal shrink tube (Not quite appropriate for a device that can measure 1,300C!) Consequently, the glass fibre sheath below it started to unravel.

Consequently, my success with RTV silicone whipping of the above USB connector inspired me to use it for the repair for this high temperature situation.

I used RTV silicone rubber and cotton thread for whipping to re-form the terminus of the thermocouple wires. Inside the whipping, I place a fine splint of cane beside the fine thermocouple wires and up into the fibreglass braided sheath. It gives the sensor more rigidity. It also allowed me to form a taper toward the sensing tip so that it can easily be threaded through small holes. The silicone bonded well to the fibreglass sheath.

So far the the new tip has worked well up to 320C without any signs of damage.

Bonding aluminium to silicone rubber

I was searching for a quick, tolerant and simple means of whipping a stove mounting clasp to a bush pole to form legs. I required this to support an ultralight tent stove up above the snow surface. I found that whipping with nylon cord was a bit tedious and it may not maintain tension if the wood should shink with drying.

Whipping with many layers of stretched silicone rubber ribbon could do the job. I just needed to make simple clips that could hold the ends of the ribbon together after the stretched whipping was done.

Aluminium foil from soft drink cans is one of my favourite free, versatile and ultralight microengineering material. I also knew that it could be glued well with acetic cure RTV silicone rubber if the polymer coating on the aluminium surface was first cleaned off with sand paper. The bent foil clips were folded so that a tongue was formed on end and a slightly wider pocket to receive the tongue was formed on the other end.

The silicone rubber ribbon bonded well to the stainless steel clasp and the aluminium foil end clips. The stretchy ribbon attachment method is a great improvement on the whipping with cord. It is fiddle free, compact and very secur. “I am sure that when I am out skiing next, that the clasp will stay secure as the wooden pole dries out and shrinks.”

Please see ultralight stove mounting for more details of how these clasps, bent mounting wires and legs are used.

Bonding stainless steel to aluminium

I was using handles made of strong and stiff stainless steel on my ultralight aluminium foil pot lids for backpacking. The handles can tear the soft aluminium foil lid.

I found that a small disk of scrap stainless steel foil with a slit in it can be bonded to the foil lid with RTV silicone rubber to make a very strong mounting pint for the handle. It can be bonded with RTV silicone rubber and clamped together while the rubber cures.

No-see-um netting glueing

Ultralight ‘single-skin’ backpacking tents often have condensation problems that can be improved by providing insect-proof ventilation.

The strength of the bonding of the No-see-um netting to the tent will depend on the properties of the tent fabric and any waterproofing that has been applied to that fabric. This means that some bonding will be excellent while some will be mediocre with respect to peel strength.

Even in a mediocre glueing situation, the glueing can be used successfully if supplemented with hand or machine stitching. “This stitching is made very easy, for a mug sewer like me, after the silicone glue has cured. For me, the glueing is easier than pinning, tack stitching and then formal sewing!”

Tyvek glueing

Tyvek is a wonder fabric that is used by many for outdoor adventure gear. Tie-outs and strengthened anchor point can make the fabric more versatile. Consequently, I thought it was time to see if I could glue tie-outs to Tyvek by glueing with acetic cure RTV silicone rubber.

I started by priming the surfaces with silicone rubber that has been diluted at about 1:5 with clean mineral turpentine.

The best bonding requires gently compression while the thick silicone rubber cures. Consequently, while the primer was curing, the clamping boards, non-stick polythene sheets, and the spring clamp were prepared. This was so that they could be applied quickly when the tie-out was ‘buttered’ a thin layer of the thick silicone rubber and put in place, as the rubber cures quickly once exposed to moisture from the air.

Whether I am sewing or glueing, I like to affix tie-outs onto both sides of the sheet. I think it applies the load more evenly. “Who knows, I am sure it pleases the god and I think it looks good.” The small piece of polythene sheet was put into the area where there should be space for a rope or peg to prevent bonding.

As usual, I tested the bond strength in tension and it was quite good. However, I could easily tell that it had poor peel strength. So, as for my other bonding that had this characteristic, I sewed the tie-out.

The machine sewing, after the glueing, was surprisingly easy and it also should be so if hand stitching was necessary.

I washed the above groundsheet to test the glue survival. The tie-out survived OK. However, the washing of the building tyvek (as shown above), changed it from having a smooth and shiny surface to a much softer, wrinkly and ‘hairy’ surface. I will do more test on the glueing of the new surface in this changed condition to see if the bonding is any better.

Silicone rubber impregnation of cane

I use pieces of cane skewers to make all sorts of lightweight things and impregnation with thinned silicone rubber makes the cane waterproof and easy to glue. The RTV silicone rubber can be diluted ~1:4 with clean turpentine in a plastic freezer bag. Then the cane sticks can be soaked in the mixture with in the bag.

Tim

More silicone rubber bonding to come……

Tim

Idea list

 Simple woven fabric of pure: nylon, polyester, acrylic and polyolefin

Knitted stretch fabric of pure: nylon, polyester, acrylic and polyolefin

Natural cellulose and protein fibres

Super stretch Lycra fabric, Polyether-polyurea copolymer

Insect mesh (No-see-um)

Cotton/ polyester sewing thread

Polypropylene

Polyester guy lines

Tyvek

Copper foil

Stainless steel foil

Titanium foil

Aluminium foil

Glass fibre

Carbon and carbon/Kevlar fibre

Silicone/fabric hinges

Waste RTV silicone rubber

Rubber cutting lubricants

You may also be interested in my post about other unusual but useful mouldable rubbers Ooogoo, Sugru and Kintsuglue.

Tim