Mastic sealant toxic?

[jacquelynn]

I just talked to a well-recommended HVAC company who told me he NEVER would use mastic sealant on sheet metal or duct connections inside an attic or house, since it's made of tar and is carcinogenic.

Has anyone else heard this?

[billva]

never.

[drk]

oil based will off gas! Stick with the water based! TAR WHAT THE WHATA

[amickracing]

Maybe something they used 50 (or more) years ago was bad for you (ohhhhh, say asbestos for example). But everything today is 100% safe. With all of the people being as concerned about indoor air quality now-a-days, there's no way duct sealer would be bad for you.

What is bad for you is unsealed ducts. It brings in contaminated and usually unfiltered air and you breath that.

[billva]

sounds to me as though he just does not want to take the time to do the job correctly.

have you recieved any other estimates?

[mark beiser]

Modern water based latex duct sealing mastics are safer than the latex paint covering your walls.

[jacob perkins]

I peel a few avacados and make guacamole with it.No problem

[HVAC Pro]

Find yourself another "well recommended" company.

[jacquelynn]

Thanks, everyone for your emphatic responses!

billva, I was just asking him a few questions over the phone before I scheduled an estimate. I figured I could weed out the companies I didn't want that way. I'm not even sure if he was an installer himself.

And yes, I've received other estimates. The difference between the highest and lowest bids seems to depend on whether or not they do a manual J; whether or not they use mastic sealant versus duct tape; whether or not they connect to existing vent pipe or install a new one; and whether the job takes one day or five. Since the most expensive companies use as a selling point the fact that they use mastic sealant -- I was surprised to get this guy's strong reaction to "run away" from anyone who uses it! BTW, this guy's ballpark estimate over the phone was way more than the highest I'd received so far. I'll need asbestos abatement as well, and the abatement company they recommend charges almost three times as much as the other companies do. Does that mean none of the others would do as thorough a job on the asbestos?!!

drk, amickracing, mark beiser, and jacob --thank you for your reassurance.

HVAC Pro, I'll keep looking. This company has a AAA rating with the BBB, no consumer complaints, and they've been in business since 1970. It's no wonder I thought they'd be good.

[curiousgirl]

Why mastic? why not silicone, or permatex gasket stuff or liquid nails or even some type of glue. Why mastic specifically?

[condenseddave]

The tar comment from this "contractor" comes from the fact that the word "mastic" has many meanings. In hvac, we use the rubberized mastic. No petroleum base, but the auto industry used a petroleum based "mastic" to secure windshields for many years.

HVAC mastic is brushable, and remains flexible after many years of drastic temp changes, fills voids, and (the water-based stuff, at least,) is relatively non-toxic.

In comparison, silicone breaks down after many years and has a foul odor until it cures, which could take days if it is cold out. It is also expensive compared to mastic. It is not brushable, either.

Liquid nails is an adhesive, not a sealant.

Permatex is a company that makes many different products, but the RTV gasket maker is simply a more expensive, higher temp silicone. Again, expensive, not brushable.

You can buy a gallon of mastic for the same price as 2 10 oz tubes of a decent silicone sealer, and be able to wash your hands when you're done brushing it. Silicone makes a hell of a nasty mess, and must be applied with a cualking gun.

Glue is, again, like Liquid Nails, an adhesive, not a sealant.

Pick a contractor that is willing to seal your ducts. in addition to the rest of the installation being in line with contemporary professional standards. You could give that tar guy the url to this website, and if he is willing to learn the truth about the industry, we'll be more than happy to assist him.

[Edited by condenseddave on 11-09-2005 at 02:33 AM]

[cem-bsee]

why do you think you need asbestos abatement? -- leave it alone if possible -- or cover it with alum foil & mastic

[jacquelynn]

cem-bsee: Several contractors have told me the ducts have asbestos. By California law, an asbestos abatement co. has to come in and remove it (or encapsulate it where it's not practical to remove) before a new heater can be installed.

condenseddave:
I would rather pay extra for the safest sealant, as long as it's effective. The fact that mastic is "relatively non-toxic" scares me, as I prefer that all building materials in my house be as environmentally safe as possible.

Approximately how many more years will mastic last compared to silicone? And if the silicone breaks down, can it be replaced without needing to replace the ducts too?

Thanks so much for your information.

[mhafley]

jacquelyn - I just looked at the MSDS sheets for a couple of the mastics available through Johnstone's and there is nothing in them to be terribly concerned about. I say this as a research chemist, not an HVAC pro. Unfortunately in today's society you can not claim anyhting to be completely non-toxic, as even water can kill you and someone will take you to court. The duct mastics use latex to hold together fillers such as clay and calcium carbonate. These are all non-toxic. I would certainly prefer to have a system that is properly sealed, just my opinion though.

[chocfull-o-nuts]

I pulled up the Material Safety Data sheet for Mastic.. I think its about as safe as anything else in a house. I painted this stuff on myself in my old house and never smelt anything from it. Very nice product.

http://rcdcorp.com/pdf/msds6.pdf

Certainly less toxic than heated up silicone.

[tinner73]

we use this stuff
http://www.mcgillairseal.com/textDoc...Ductsealer.htm
about $40+/gal. works well and is oil-based. stinks until it dries. i'd imagine it's in most of the big buildings you go in and you'd never even know it.

[amickracing]

While I wouldn't reccomend eating mastic, I'd bet it's a lot better for you than a fast food restraunts food (might taste about the same too lol).

I don't recall what kinda we use, it's in a white pail with blue lettering (real observant aren't I?).

Just make sure it's sealed and you'll be a happy homeowner

[dec]

Let me ask this one , I had a inspector wanting me to mastic the inside of the sleeve that goes from inside the blower compartment to the ducwork on a coleman mobile home furnace. This was quite a while back but I really was not for the idea of putting mastic in the air stream. I guess I would like to hear your opinions on that. Does anyone here put mastic in the air stream to seal off leaks and have they seen any problems with it staying in place over the years? I asked one of the mastic manufactures if I had to have a certain type to put in the air stream......they just didnt see why anyone would want it in the air stream. On a mobile home a lot of times you cant get to the outside of that sleeve. what your opinions ?

[jacob perkins]

Originally posted by amickracing
While I wouldn't reccomend eating mastic...

To each his own.

When I get a nasty cut from sheet metal and it wont stop bleeding,then I smear it on the wound.It stops the bleeding and fights infection

[Mr Bill]

Originally posted by jacquelynn
By California law
I prefer that all building materials in my house be as environmentally safe as possible.

That mastic is safe even safe enough to use as a shield to hug a tree with so you don't get a splinter, while hugging.