RTV silicone rubber, Oogoo, Sugru, Kintsuglue and Tommy Tape comparison

This post compares RTV silicone rubber with Sugru, Kintsugle, Tommy Tape and DIY Oogoo in the context of DIY tinkering.

Introduction

RTV silicone rubber- a geeks perspective

I am particularly interested in the use of RTV silicone rubber to create DIY gear for backpacking, walking and skiing.

Of course, other less noble things such as repairing holes in rainwater gutters are also OK. The photos below show examples of a couple of my many mad creations that use silicone rubber. “Usually fire and heat are not far away (RTV stands for room temperature vulcanizing or curing).

.

Note: Large trade tubes of RTV silicone rubber are very cheap. However, after opening, the tube must be sealed well to prevent the rubber from solidifying in the tube. “A nail in the nozzle is just not good enough for this product!” I find that a small square of thick plastic sheet makes an excellent seal when pressed over the threaded port that has been ‘clean-cut’. An ‘uncut’ nozzle can be gently screwed on to form a plastic cap that will prevent air and moisture entry and loss of acetic acid solvent.

A big tick for Acetic cure RTV silicone rubber.

RTV silicone rubber is a wonderful gift from science for us backyard tinkerers. The acetic cure type is my choice because it is cheap, abundantly available and most importantly the acetic acid solvent used in it is the safest solvent.

Acetic acid, the dominant chemical in vinegar, is part of life and we even make it in our bodies as a ‘tonic’ when we have a healthy diet. Most other liquid rubbers glues are made with nasty and toxic solvents such as toluene……just don’t smell them…..unfortunately they are the only other solvents that provide adequate solubility——enough said.

Mothy The Elder

Oogoo, Sugru, Kintsuglue and TommyTape

I am assuming that all of these adhesives are based on silicone rubber. I have used RTV silicone rubber in many of my projects and was curious to find out about a moldable adhesive called Sugru. It was out of stock and then I discovered a similar product by Loctite called Kintsuglue.

The trail led on until I found a very interesting Instructables post on DIY Oogoo. This post indicates that Oogoo can, in many cases, be used as a cheap substitute for the rather expensive commercial moldable adhesives.

Oogoo is a DIY moldable adhesive for DIY tinkering as described in an Instructables Workshop post titled How to make your own Sugru substitute. It seems to be a very versatile and inexpensive substitute for other commercial mouldable/shapeable adhesives. Sugru claims to be the original and Loctite Kintsuglue has a similar sound within its name.

I was also happy to see that the Oogoo post also encouraged the use of acetic cure RTV silicone rubber to make Oogoo and this accords with my safety message above.

Oogoo is made simply by mixing corn starch with RTV silicone rubber and optional colouring agents. According to the post, Oogoo cures uniformly and quickly in thick molded items. This is much quicker than would be the case when using RTV silicone rubber alone (as I have done for so long).

The post explains that a trace of water within the dispersed starch acts as the vulcanizing (or curing) activator throughout the entire RTV silicone rubber item. Without the water from the starch, it will cure more slowly as it then depends on the slow migration of atmospheric moisture into the depths of the rubber to slowly activate the curing.

“Now, just in case you are thinking how can water move through a waterproof material? The answer is that silicone rubber is waterproof to liquid water but quite permeable to water vapour. This quote from Versaperm captures the idea:

It (silicone rubber) is an excellent barrier against liquids, but many vapours – such as oxygen, water vapour and hydrogen can pass through most types of silicone almost as if it was not there.

Versaperm

DIY Oogoo can be used in similar applications as Sugru, but importantly, it also can be customized to have a much wider range of consistencies or viscosities, curing speeds, colours, electrical conductivity and opacity for visible light transmission. This should have great appeal to innovative DIY tinkerers.

The RTV silicone rubber in the Oogoo can be made to cure more or less quickly (according to the proportion of starch (with moisture) in the mix). “I have yet to try that trick, but it does make perfect sense to me.”

My take on the water activation of RTV silicone rubber

I have made a post about the ever-growing list of RTV silicone rubber DIY uses that I have discovered. These include molding, impregnating, sealing, bonding, waterproofing and heat protection to 300C using this wonderful adhesive in combination with a host of unlikely fabrics, cords, threads and metals. “The list just keeps growing.”

I certainly have experienced slow curing of large molded objects.”They become firm on the outside while they stay soft and squishy, like breast implants, on the inside. So far I have been happy enough to just wait patiently for the inevitable cure while I dream up the next project.

I agree entirely with the Oogoo idea of the water in starch activating the vulcanizing of the RTV silicone rubber throughout a thick molding. However, I think that there are other simple ways that will provide the dispersed water activator and it could be as free as the air we breathe.

At first, I thought that the Kintsuglue might have a different chemical activator. However, the instructions on the packet indicate that it should be kneaded for about 10 seconds after removal from the gas-tight sachet. Maybe this is just mixing in a trace of water from the air or skin to act as an activator?

I have used RTV silicone rubber that is diluted with clean mineral turpentine for impregnating and priming porous surfaces in preparation for RTV silicone rubber coating, bonding and sealing tent seams etc. I needed to quickly mix the two liquids that were stubbornly slow to mix. So, somewhat mistakenly, I used a Dremel Tool and a miniature DIY ‘whipper-snipper’ thing to ‘whisk the crap out of the mix’ to just quickly get on with the real work.

The more I whisked the more the pot life of the sealer shortened. This is pure speculation, but I think the incorporation of a lot of fine air bubbles into the mix also introduces moisture that is dissolved in the air. The incorporated water from the air is enough to activate the vulcanization of the RTV silicone rubber. “Just like the Oogoo starch moisture does and the kneading of the kintsugle probably does.” A pot load of rubber could turn into partially polymerized slime before much of it could be used.

I no longer mix this way, but use a calm method that largely prevents air incorporation. However, combining this lesson with the information from the Oogoo post, I am confident to say that the simple and abundant incorporation of moist air or water mist into RTV silicone rubber will greatly accelerate the vulcanizing process in the thickest of moldings. Smearing soapy water over the outside of a molding certainly accelerates the cure and helps the smoothing.

My first try at Oogoo

I immediately raided my pantry and made my first Oogoo (approximately 1:1 weight ratio of RTV silicone rubber to corn flour). “For fun, I thought I might try my DIY wholemeal flour as the activator. It would be good alongside the peas and carrots in a synthetic silicone rubber vomit!”

The photo of my first Oogoo below shows that the process worked and resulted in a neat test puck that looks and feels like the same puck that would have resulted from my normal use of pure RTV silicone rubber.

The mixing of the flour into the silicone was a bit slow, but the expected fast and even cure resulted and I was able to cleanly strip off the polythene plastic cover strip after an hour or two Rather than a day or two as would have been the case when not adding the flour. “Three cheers for Oogoo!”

The Oogoo was just as sticky and hard to handle as the original RTV silicone rubber that I have often used, so don’t expect Oogoo to solve this sticky situation when molding it.

Sugru and Kintsuglue on the other hand solved the sticky problem with their formulations. However, they are relatively expensive for such tiny quantities if the user wishes to tinker with making many large and small things as I do. So if you are prepared to fiddle a little, please see my comments below about dealing with the dreaded stickiness when molding with Oogoo or straight RTV silicone rubber.

DIY cable repairs with silicone rubber-based adhesives

Oogoo, Sugru and Kintsuglue all seem to be promoted as suitable for repairing those pesky but necessary USB cables and plugs that get damaged despite our good intentions. The photo of the Kintsuglue packet shows such an image.

I have not yet had the opportunity to repair such a cable, with Oogoo or alike so I can’t comment on its effectiveness. However, my experience with making and repairing cables with neat RTV silicone rubber may be of interest.

Making DIY low voltage cable plugs

As well as repairing USB power cables, for some years with RTV silicone rubber, I have also created them from scratch. I make them compatible with 1.5mm pitched PCB socket that I use for the devices that I take backcountry. It involves simple whipping with fibre thread and RTV silicone rubber. In the core of the device, I insert a portion of a cane meat skewer to act as a stiff spine that runs from a pointed end that protrudes into the insulation sheath and up to the space between the copper conductor pins that have been soldered to the wires. They can be made so light and tough that they will never need to be repaired! Consequently, I was curious to see if my direct use of silicone rubber was in any way inferior to the use of Oogoo or like products.

I conclude that my method was on par and I know that it makes the plug/connector mechanically so strong that it can be stepped on by a hairy-legged bushwalker’s boot and work just fine, even if the pins might need a little realignment. “It is also the way that I will repair other broken cables so that they will be better than new, regardless of the glue that I use.”

Managing the stickiness of silicone rubber when moulding with it

Oogoo or liquid RTV silicone rubber are both sticky to mold with, but the creative rewards will be worth it. They can be made less sticky by smearing with soapy water.

On round objects, such as electrical cables and plugs, I often use stickiness to my advantage. I cover the item with RTV silicone rubber and then bind it with whipping threads that become impregnated and glued in place as a silicone/fibre composite.

I have found that threads made from natural fibres (cotton, wool, etc) all work well and some synthetic fibres such as raw nylon also impregnate and bond well with the rubber. “It just takes a little trial and error.” Smoothing with a spatula and covering with cling wrap as shown below will leave the item with a smooth glossy finish, especially if you use your fingertips to massage the silicone through the wrap.

A special wrap for pantyhose whipping wrap

Another fabulous fibre that is very compatible with RTV silicone rubber is nylon stocking or pantyhose fabric. I cut it into strips (calamari ring style is easy) that have amazing two-dimensional stretch. I use them to bind and manipulate the freshly placed blob of silicone rubber within it. It eventually forms an impregnated skin over the bulk of the rubber and allows it to be easily shaped beneath with very little stickiness for your finers. The fabric will impregnate with the rubber with a little massaging. A mist of water to activate the vulcanization and another layer of silicone rubber and more pantyhose can be added to add to the shaping. “A bit like making a plaster cast for a broken arm.”

If coated with a cosmetic layer of silicone and smoothed with a temporary cling-wrap plastic cover it will cure with a good finish, great flexible reinforced strength from the invisible pantyhose. Cables connections and other whipped silicone things can be smoothly finished and shaped this way and it forms excellent handles.

Small quantity moldable adhesives for repair kits

I love to take a small repair kit on all my backcountry adventures (Multitool, wire, nails, sewing kit, with fabric for patches, assorted threads and glues including superglue and epoxy resin that now come in cheap miniature tubes.

I have experimented with carrying small DIY metalized sachets (gas tight) of RTV silicone rubber in this kit. Disappointingly, the rubber has kept satisfactorily un-vulcanized for a little over a year.

[Add a photo of my sachets of silicone rubber]

I think it is nearly impossible to avoid moisture contamination during the transfer process. Consequently, I felt a bit better about my failure when I found that the commercial Kintsuglue is only good for 18 months. “Maybe they have a tiny trace of water contamination too?” This is not the end of the possibility of a long life silicone repair adhesive for tiny repair kits.

Other self-bonding or fusing products with an infinite shelf life

Other self-fusing, bonding, vulcanizing products can do similar excellent cable repairs where the application involves a tight stretching and wrapping many times around something like a cable, plug, pipe or stick.

My first encounter was with a small sample of Bear Brand self-bonding rubber tape. “Given to me by a friendly workplace electrician.” It was only a little bit and was rolled up like a black wrinkly liquorice strap in a ribbon of nonstick plastic. It lasted seemingly forever doing repairs on electric fences, pipes etc around the home and farm.

I can’t trace the product now, but it predated the current plethora of silicone rubber products. So I presume that it was a self-vulcanizing butyl rubber or possibly a modified natural rubber. It pulled out like stiff and stale chewing gum and could be wrapped thinly and tightly as a fine ribbon around something, and it stuck to itself, never to come apart, while still holding tension. “The electrician assured me that it worked on 240V wiring that was on a submerged pump motor that was many meters down a well.”

Much more recently, I stumbled across an Aldi repair tape that I think is silicone-based and it is clear and has a similar stretch and self-bonding properties. A little portion of it could be safely carried in a small backcountry repair kit. “It is funny that just when I think I have found that special solution to a particular problem, I start finding alternatives everywhere.” Here are just a few from a very limited search:

Tommy tape is similar to the Aldi tape described above. It is silicone rubber-based, only activates after stretching and wrapping, and is good up to 200C.

HellermannTyton self amalgamating tape (synthetic rubber with mastic adhesive, non-silicone)

Bondall Repair wrap (Fibre-reinforced, water activated, cures hard)

A repair with Tommy Tape

After the stickiness of RTV silicone rubber and Oogoo, I was quite surprised by how un-sticky, on the hands, the Tommy Tape was in the long strips that I cut from the roll (as shown in the video below). Magically, it was very sticky towards itself and it formed a bond that would not easily be broken. Here is a little video of the stickup and stretch.

I did a repair to an old USB cable with it. I first stretched tape and wrapped the plug in it. On top of this, I put a piece of a toothpick and continued to stretch and wrap the pick to the cable to form a protective splint. “It worked just as well as my silicone rubber whipping and would be good for a bush repair.”

Conclusion

RTV silicone rubber is an indispensable foundational thing to have in your backyard tinkerers’ tool kit. And remember, for your health and safety, look for the word ‘acetic cure, acetic acid or similar’ in the fine print on the label”. It will be essential for making Oogoo if you are particularly into molding. Also, if you seal the tube well (as described above) there will be little waste.

Oogoo should add another versatile variant for the tool kit. It should be especially good for projects requiring fast curing where RTV silicone rubber alone may be too slow to cure in large moldings. It also allows the user to vary the properties of the rubber as described in the Oogoo post (This also applies equally to straight RTV silicone rubber).

Sugru and Kintsuglue products, on the other hand, may have special niche applications for one-off repairs involving wrapping/glueing and molding. They could be used in a small repair kit while away from home, but the 18month kit life is not good.

Tommy Tape, in contrast, is exclusively for wrapping repair applications and probably will not work in cavity molds. So for wrapping repairs it greatly surpassed the other commercial wrapping/glueing products (except for the Aldi equivalent) with regard to:

• Price,
• Quantity (a life time supply unless you are disater prone),
• Portability, (safe to carry a small piece anywhere)
• Divisibility (can be cut up for use in multiple repair kits at home and while away adventuring) and,
• Infinite shelf life that avoids waste.

“It could save the day in some remote area and restore your communications and leave you looking like a heroic Mr/Ms-fix-it.”

To finish with, I feel like an ode to the wonderful polymers of silicone that are made from sand. They can be as soft as oil or hard as rocks and everywhere in between:

To rant about polymers of SiO2 , am I mentally fit?
Finding silicone rubber glues that will be a hit,
Choosing water, air or starch as a catalyst fast?
Or just a strategic squeeze, to make your repair kit indefinitely last?
Of silicone are you sick or just ready to stick it?  

More posts on RTV silicone rubber tinkering

DIY RTV silicone rubber general tinkering uses

Shock cord whipping with silicone rubber

DIY silicone rubber seam sealer

Glueing noseeum netting with silicone rubber

Silicone rubber glue tacking tent tabs

Silicone glueing tent seams instead of pinning

DIY silicone stove jacks for hot tents

Silicone rubber temperature resistance for tent stove jacks

Silnylon glueing with silicone rubber

Silicone rubber lay flat kettle

Addendum 1- A silicone rubber toothpase transfer tube

I thought that this post would just be words if I did not give a concrete example of the comparison of the performance of different silicone rubber wrapping adhesives. So I made a device for transferring toothpaste from a big tube into a small tube (for backpacking, camping and travel etc) from various silicones.

Silicone rubber tubing. If you are lucky enough to have some ‘left over’ silicone rubber tube from a laboratory (or similar) the transfer tube can be as simple as a slice of the tube as that shown in the photo below.

Tommy Tape. I next made the tube from Tommy Tape by stretching and forming it around a rod that was coated in cling-wrap. It worked, but I found that it was soft and could easily be squashed and if that happened it would stick to itself. I think this might just be a property of this tape, that stays ‘reactive’ and it is forever ready to vulcanize onto itself or a similar rubber. I think this is best for fixed in place wrapping repairs only.

RTV silicone rubber. This transfer tube was made from my beloved bathroom silicone rubber that was simply smeared onto a rod that was coated with cling-wrap. After the first coat, I added a ribbon of nylon mesh that I had cut (calamari ring style) from a pantyhose leg. I stretched this around the growing tube and shaped the silicone below the mesh without any stickiness. Slowly the silicone came through the mesh. Then I smeared it with some soapy water and added more silicone that was smoothed with soapy water to give the final finish. The soapy water helps the rubber cure quickly and also make it less sticky for smoothing.

All silicone rubber solutions worked, but I think the RTV silicone rubber was the simplest and most effective and it can be used for so much more.