FS: Dow Corning 795 silicone

[marinebetta]

I have 12 tubes of black DC 795 silicone for sale at $14.50 per tube. Expiry in May 2004. DC 795 silicone is widely recommended for large tanks on many forums and a few of us here in SRC have tanks made with it.

Excess from my tank project - had to buy a case as they did not sell loose and am selling at cost (contractor pricing, and actually less than cost as I had to pay GST!).

These are the foil pack (like bologna sausage) 591 ml packing which is almost double the normal plastic applicator tube. A special applicator is required but I will lend it to you if you are not taking the lot (who needs that much anyway ); if you want it all, then I will throw it in for free (an $80 value).

Note of warning: This sealant is a slow-cure silicone and will take at least 6 days before it will be safe to move the tank. However, once cured, it is solid! If your tank maker has no experience with it, you will need to warn them.

[Achilles Tang]

Actually the cure time should be extended to 10 days or 12 to be extra safe.

Be generous with the spreading so that it will 'grip' more surface area as it can be rather soft when thin.

[Terryz_]

black silicon is better than white silicon huh...

[Achilles Tang]

Generally, yes.

[SpiderOne]

ANyone heard of that black silicone by Megastrong industries and another white one by US brand. was told by tank maker they dont use dow corning as there is quality problems . instead they use these 2 (presumably better)

[marinebetta]

Actually the cure time should be extended to 10 days or 12 to be extra safe.

Be generous with the spreading so that it will 'grip' more surface area as it can be rather soft when thin.

True....cure time on spec sheet is actually something like 21 days. 6 days is minimum before attemping to move the tank! Anything before that and it's liable not just come apart!

[marinebetta]

ANyone heard of that black silicone by Megastrong industries and another white one by US brand. was told by tank maker they dont use dow corning as there is quality problems . instead they use these 2 (presumably better)

I doubt that QC is a problem with DC. Most likely deterioration dt poor storage (needs to be stored <30C)improper usage, or not knowing how to use it - most likely the latter.

My tank maker was a little worried - he called me after 3 hrs to tell me that it doesn't stick! Luckily he was smart and tried it out on a small piece of glass first. If he was a little worried, I was even more worried - those small pieces still didn't stick after 3 days!! (maybe because we had already seperated them earlier?) Fortunately with leaving it for 6 days, the tank stuck and is solid as a rock now.....phew!

I think most tank makers cannot afford the time to let the tank take up space for 6 days before moving!

[Octo]

black silicon is better than white silicon huh...

There are many cheap brands of black silicon available in the market too. (China and Malaysia made), likewise the expensive ones such as Dow Coning 795. You have to understand whats the main core business these glass suppliers are doing besides making fish tanks alone, well unlike AquaTechnic as they are expensive too use and not to forget these silicons have a limited shelve life whether you use them or not.

For extra strength industrial applications such as glass walls at California Fitness, appliers dont use 100% 795 straight from the tube or cans, but a mixture of black and white from a mixing tank. However the cure time is much much shorter as compared to using 100% 795, about a week.

Theres also a beige colored silicon from Dow Coning, the 791s. Would be a good match with cabinet stands that are wooden or maple in color.

[tank_maker]

It is not advisable to mix different silicon before applied. The approach tank maker used is applied first round of white silicon on primary joint; and subsequently applied the black silicon on fillet & bracing (including the vertical & bottom) which will ensure fast curing of structure. And transfer the entire tank to storage location for full curing.

I think it is not recommended by DC to use DC795 on surfaces that are continuous immersed in water. to use DC 795.

according to their usage ( http://www.dowcorning.com/DataFiles/090007b5801797db.pdf ), Under Limitation, DC stated that the DC 795 is not to be used on surfaces that are continuous immersed in water. So for fish tank that has this silicon used must not have water in it, I guess

good night

[tank_maker]

A bit of experience to share.

Has seen several tanks with black silicon peeled off (after 2 weeks of curing) before water was in; but so far not in clear silicon.

Modulus expansion of silicon is around range of 30~50%; I would agree black DC 795 is best in term of it (50%) but it is meant to be used in building; especially effective in glass with gaps/tapered joined.

[Wei]

It is not advisable to mix different silicon before applied. The approach tank maker used is applied first round of white silicon on primary joint; and subsequently applied the black silicon on fillet & bracing (including the vertical & bottom) which will ensure fast curing of structure. And transfer the entire tank to storage location for full curing.

I think it is not recommended by DC to use DC795 on surfaces that are continuous immersed in water. to use DC 795.

according to their usage ( http://www.dowcorning.com/DataFiles/090007b5801797db.pdf ), Under Limitation, DC stated that the DC 795 is not to be used on surfaces that are continuous immersed in water. So for fish tank that has this silicon used must not have water in it, I guess

good night

Hmmmmm....

Guess we better head down to AquaTechnic and warn them!! FAST!! Haha.

Wei

[tank_maker]

Hope not to cause any alarm.

I guess the main conerned in fish tank is water resistant; so long the silicon is both water and weather resistant and is 100% silicon is safe.

DC specify that DC 795 is of very strong weathersealing (which is very important to building). I don't thick they claim that DC795 is water resistant.

Many silicon are both water/weather resistant; so in general they are safe for fish tank making.

[Wei]

Hi Tank Maker,

I believe DC 795 can be used for tank. AquaTechnic 10ft and lots of other tank uses the DC 795. AT & Alvy tank also use DC 795. If it is not meant for tanks, I think AquaTechnic will get sued long time.

Best thing is, it smells herbal!! *high liao!

Wei

[Reenee]

can i buy 2 tube from u?

i need it for my new tank.

rdgs-reenee

[Achilles Tang]

To clear all doubts, here is an extract of an email from the Dow Corning manufacturer to me a few years ago!

--------------------------------------------------------------------

We do not warrant applications where sealant will be immersed in the water long term. Nevertheless, sealant has been used successfully in the aquarium for many years so customers must understand that they do so at their own risks.

When fully cured, DC795 will not react with saltwater, it is also resistant to ozone and UV radiation. What I would be more concerned with is the size and the design of your tank (eg. water pressure, any supporting brackets) and whether you are using the sealant to support the glass only. You would also need to allow sealant to cure fully (full adhesion build up) before using the tank.

---------------------------------------------------------------------

I read the datasheet as follows:

PHYSICAL AND CHEMICAL PROPERTIES

Physical Form: Paste

Color: Black

Odor: Slight odor

Specific Gravity @ 25°C: 1.52

Viscosity: Not determined.

Freezing/Melting Point: Not determined.

Boiling Point: Not determined.

Vapor Pressure @ 25°C: Not determined.

Vapor Density: Not determined.

Solubility in Water: Not determined.

pH: Not determined.

Volatile Content:

Not determined.

10. STABILITY AND REACTIVITY

Chemical Stability: Stable.

DOW CORNING® 795 SILICONE BUILDING SEALANT, BLACK

Hazardous Polymerization:

Hazardous polymerization will not occur.

Conditions to Avoid:

None.

.....and there's a line in there regarding

Materials to Avoid: Oxidizing material can cause a reaction. Water, moisture, or humid air can cause

hazardous vapors to form as described in Section 8.

It may be just for the curing stage... which needs about 5 to 10 days for maximum strength (depending on amount used).

[Achilles Tang]

Here's the full email transcript.... names have been removed to protect the innocent!

---------------------------------------

If you are allowing curing on both sides, then it is most likely

enough.

Regards

Hor Cheong Tong

DC Singapore

Tel : 65-63593307 Fax : 65-62536070 Mobile : 65-97578795

Email : cheong.tong.hor@dowcorning.com

-----Original Message-----

From: 'me, mua, myself'

Sent: Thursday, August 22, 2002 12:30 PM

To: cheong.tong.hor@dowcorning.com

Subject: RE: Ask a Product Question - SINGAPORE

Hi Cheong,

I agree on the safety aspects. This tank I want to

construct is not too tall... but its wide... the

dimensions are in feet 5L x 3B x 2H. The top of the

tank will have euro-bracing (all along edge, there are

horizontal panes) as well as a centre brace.

The glass will be 12mm thick and we intend to let the

tank cure for 7 days before we move it. In our

humidity, do you see a problem?

Thanks!

Conrad

--- cheong.tong.hor@dowcorning.com wrote:

> There is a difference in water pressure if you have

> a high and narrow tank

> (eg. 2m high and 1mx1m tank) vs a wide tank that is

> not high (eg. 1m high

> and 2mx2m). For the high tank, the glass will be

> subjected to very high

> water pressure. the other tank would be much lower

> pressure.

>

> Sealant is subjected to tensile and shear stress so

> you have to be very

> careful when designing the tank. Another observation

> which I made is that

> some tank makers think that sealant is some kind of

> super glue, ie. you

> glaze and after a short while, it dries up and the

> tank can be used. In such

> cases, if the pressure is too high, and if the

> sealant has not built up full

> adhesion on the glass, the tank will just collapse.

>

>

> Regards

> Hor Cheong Tong

> DC Singapore

>

> Tel : 65-63593307 Fax : 65-62536070 Mobile :

> 65-97578795

> Email : cheong.tong.hor@dowcorning.com

>

>

> -----Original Message-----

> From: 'me, mua, myself'

> Sent: Thursday, August 22, 2002 12:04 PM

> To: cheong.tong.hor@dowcorning.com

> Subject: RE: Ask a Product Question - SINGAPORE

>

>

> Hi there,

>

> Thank you for replying.

>

> You expressed concerns using only the sealant to

> hold

> the tank together. Can you elaborate?

>

> Conrad

>

>

> --- cheong.tong.hor@dowcorning.com wrote:

> > Conrad,

> >

> > We do not warrant applications where sealant will

> be

> > immersed in the water

> > long term. Nevertheless, sealant has been used

> > successfully in the aquarium

> > for many years so customers must understand that

> > they do so at their own

> > risks.

> >

> > When fully cured, DC795 will not react with

> > saltwater, it is also resistant

> > to ozone and UV radiation. What I would be more

> > concerned with is the size

> > and the design of your tank (eg. water pressure,

> any

> > supporting brackets)

> > and whether you are using the sealant to support

> the

> > glass only. You would

> > also need to allow sealant to cure fully (full

> > adhesion build up) before

> > using the tank.

> >

> > Regards

> > Hor Cheong Tong

> > DC Singapore

> >

> > Tel : 65-63593307 Fax : 65-62536070 Mobile

> :

> > 65-97578795

> > Email : cheong.tong.hor@dowcorning.com

> >

> > From:

> > 'me, mua, myself'

> > Sent: Monday, August 19, 2002 2:45:35 AM

> > To: product.inquiry@dowcorning.com

> > Subject: Ask a Product Question - SINGAPORE

> > Auto forwarded by a Rule

> >

> > Email: conradchua@yahoo.com

> >

> > Please enter your question. Include the material

> > name and other information

> > that will help us with your inquiry

> > If I were to build a glass tank for marine

> livestock

> > with Dow Corning® 795

> > Silicone Building Sealant Black, is it safe in

> terms

> > of chemical leaching

> > from the silicone? Does it react with saltwater?

> > What is it's ozone or UV

> > resistance like? Pls advise urgently! Thank you!

> > Conrad

> >

> >

> >

> >

>