Sciencemadness Discussion Board - Why does caulk smell like acetic acid ?

Why does caulk smell like acetic acid ?

metalresearcher - 10-1-2011 at 12:23

When sing a caulking gun for sealing Ismell a strong acetic acid smell. It is special sanitary caulk used for sealing toiletpots, etc.
Why ? Is it for the curing process ?

not_important - 10-1-2011 at 12:37

Many silicone based caulks have the the prepolymer chains in them capped with acetate. When exposed to water, including the moisture in normal air, the acetate groups hydrolyse to give acetic acid while the short chain silicones link up to give longer polymers - hardening of the caulk.

RDI - 23-1-2011 at 16:39

It is worth noting that if your silicone based caulk smells of acetic acid, do not use it to seal metals as it can lead to corrosion. Go out and buy some neutral cure caulk.

peach - 24-1-2011 at 13:54

I always loved the smell of acetoxy caulk. Until I got round to fitting a new sink in the bathroom and was squirting half a tube out in a small room to do the taps, drain, edges of tiles, pvc frame of the double glazing and so on. The stench of it starts turning into brain ache if you sit around for long.

Both not_important and RDI are correct.

You can also get polysulphide and polyurethane sealant.

There is another incompatibility issue with the solvent in cartridge adhesives, which will mess up some plastics and foams; this is why you see the 'solvent free!' versions next to the manly solvent tubes.

Mentioning that you use a coin to round off beads of silicone to a plumber will get you lots of

and

in the replies, because small amounts of the copper will end up in the bead and it'll go green.

If you have a movement joint, like a door / window frame or panel, you may want to pick a low modulus silicone.

When you see HMA or LMA on the cartridge, that's high / low modulus acetoxy cure.

Getting a perfect line with caulk has to be one of the trickiest things about decorating. Yet it also makes a huge difference when all those eye catching cracks, gaps and shadows disappear.

Not forgetting you also have acrylic caulk, which is a lot easier to deal with but not water repelling- e.g. it'll stain if brightly coloured food gets left on it. But, unlike silicone, you can easily paint over it with emulsion and a tube of it is about 70p when bought by the box.

I bought 24 of them and have been wandering round the house doing all the skirting boards and so on. Much easier than using fillers, which will crack on movement joints anyway; whereas the acrylic has a lot of flex.

So, for instance, you wouldn't want to use acrylic to seal up the bathroom or an external window edge. But it is far better for internal door frames, skirting, surrounds and the likes.

SIROFLEX sell practically everything you'll ever need to glue someone to a ceiling or wall them up

Alternatively, go nuclear on it with epoxy

Epoxies are fun, fun stuff in litre quantities. There are quite a few sites in the UK offering seriously knocked down epoxy systems (paints, resins, putties, mortars, injectable cartridges, anchor kits, screeds and so on), because they don't have any branding on the containers.

I was over the moon when I discovered cartridges of it at B&Q that were part of their stock clearance. Clearly no one new what they were for, so they had a shelf of them going for 50p a piece. I raked the last of them off the shelf and into the basket with my arm, netting around £100's worth with change out of a fiver.

{edit}Don't call it caulk. It's silicone caulk.

Caulk is anything used to pack a gap. Tar and rope are used to caulk boat decks. Using caulk alone can lead to many great headslap moments of misunderstanding.

[Edited on 24-1-2011 by peach]

HHammerHeadD - 27-3-2011 at 05:11

my guess is cloro fluro solvents that you smell

[Edited on 27-3-2011 by HHammerHeadD]

HHammerHeadD - 27-3-2011 at 05:12

http://www.osipro.com/msds/quad_voc_white_msds.pdf

or perhaps titanium oxide

[Edited on 27-3-2011 by HHammerHeadD]

condennnsa - 29-7-2011 at 02:30

Does anyone know what would be a suitable thinner for clear silicone caulk, the one that smells like acetic acid when curing?

MeSynth - 31-7-2011 at 00:26

caulk....

condennnsa - 31-7-2011 at 06:16

what do you mean, i'm looking for something to thin silicone caulk, to allow it to be applied in thin films using a brush, like paint. I tried acetone, ethanol and white spirit with no success

peach - 31-7-2011 at 07:49

Interesting question. I went digging around the tubes and discovered;

This <--- link

Quote:

Though it is probably not necessary, I like to give my newly made molds overnight to finish curing before I start casting in them.

If you feel you need to thin silicone caulking, xylene is the solvent of choice, but work outdoors and protect yourself from the vapors, they can cause health problems, so read the label. Mineral spirits will also work, but weaken the material and leave it with a greasy feel. Mineral spirits will also slow the cure from hours to possibly days.
Also, volatile solvents will result in shrinkage of the finished mold in proportion to the amount of solvent added to the silicone.

Adding things or applying thick layers will make the cure slower. I would leave it a day or three before putting it to use or tossing it. Silicone will not stick to it's self once a layer has cured, make sure you get it all done in one hit or the second layer will delaminate. Also make sure there's nothing already on the surface that might help the first one come back off (a lot of dust will mean the silicone will stick to that rather than to the surface below). If you're producing a mechnically important seal, 'scrub' it into the surface to make sure it gets a good grip and then go back over, quickly, to tidy it up.

If you have something particularly special in mind, there are pourable silicones sold for the mould making industry. Quite a few places sell the materials and kits for moulding things, including body parts; although I think direct to skin moulding is done with alginate instead (the thing dentists use to make moulds of teeth in 30s), silicone might not be a good idea if that's what you have in mind. These kits are used extensively in jewellery making, where a prototype (master) is made, a silicone negative copy produced from that, the negative is used to produce wax positives, the positives grouped together on a 'tree' where the branches are ring blanks, the tree is then used to produce a plaster negative, the wax is melted out with steam, then the traces burnt out in a furnace, then the gold / platinum / silver goes into the plaster negative to produce the precious metal positives, which get chopped off, tidied up and then dumped into vibratory polishers to make them sparkly before the gems go in.

Quote:

Silicone Thinner is a clear silicone fluid that can be added to reduce the viscosity of Silicone RTV. Ideal for creating a bubble free skin coat prior to adding a thick coat. Use no more than 10 parts of thinner to 100 parts of silicone by weight. The thinner will increase working time and decrease final hardness and tear strength. Sold separately.

AND, a video, all for the price of one post;
<iframe sandbox width="640" height="510" src="http://www.youtube.com/embed/M400dj19nUs" frameborder="0" allowfullscreen></iframe>
<iframe sandbox width="640" height="510" src="http://www.youtube.com/embed/NVvGc7VDFvc" frameborder="0" allowfullscreen></iframe>

[Edited on 31-7-2011 by peach]

condennnsa - 1-8-2011 at 01:43

Thanks peach
I looked up and found that silicone thinner and found its MSDS

http://www.smooth-on.com/msds/files/Silicone_Thinner.pdf

which says it's 100% dimethylsiloxane. How is dimethylsiloxane prepared commercially?

watson.fawkes - 1-8-2011 at 04:00

Quote: Originally posted by condennnsa

which says it's 100% dimethylsiloxane. How is dimethylsiloxane prepared commercially?

The MSDS lists CAS 63148-62-9, which with a little search reveals itself to be polydimethylsiloxane, a polymer, not the monomer dimethylsiloxane.