@#12
I got called over to open the kid's place (townhome, 1st floor flooded during Harvey) so that the mold remediation guys could service the A/C unit in the 4th floor mech closet. They found mold - not surprising since the closet has always felt like a sauna - and cleaned it but shook their head that the A/C unit was not properly 'sealed'. Sure enough, cold air from all the joints and I suspect leakage at the return air side as well. They indicated we should have it sealed - they could do it for $349 or not as we desired - but said that the moist air blowing out from the unit was one cause of the mold problems in the closet. Made sense to me, too.

That said, some disagreement on the idea that mold enters where air blows out.. ? Don't know about that but if it's not sealed on the return air side, it would make sense. What say you?

So how do you 'seal' all of the joints on the unit? They showed me a pic of one that looked like the joints were wrapped with some 'material-impregenated' duct tape. Made sense to me.

Unit is about 5 years old. Noticeable air exiting along joints.

So what do we wrap the joints with? Surely not duct tape - that's for everything else Is there some magic that warrants $349? Pix attached of the joint between blower/furnace unit and evaporator and side-to-top panel of main unit. Thanks for any help. I know you guys are digging out, too.

 

The magic word is, "mastic". You buy a gallon bucket of it and smear it on the joints. (Acrylic base) hardens like water based paint. Stopping air leaks is a good thing, regardless of anything growing in the closet.

Fabric based "duct" tape is illegal. Only aluminum tape with purple lettering on it. Spray adhesive makes the tape stick to old ductwork.

 

The magic word is, "mastic". You buy a gallon bucket of it and smear it on the joints. (Acrylic base) hardens like water based paint. Stopping air leaks is a good thing, regardless of anything growing in the closet.

Fabric based "duct" tape is illegal. Only aluminum tape with purple lettering on it. Spray adhesive makes the tape stick to old ductwork.

Awesome! Thanks so much. Didn't know that about 'duct tape'.

'preciate it.

 

In and out in 13 minutes.
That's what you get for dealing with a pro.

 

In and out in 13 minutes.
That's what you get for dealing with a pro.

Presumably a good wire-brushing to remove the flakes then smear it on?
And I do appreciate dealing with a pro!

 

Presumably a good wire-brushing to remove the flakes then smear it on?

Flakes? I don't see any flakes.
I see mastic, badly done.
Try a diluted Clorox wash to kill and remove the mold. Wait for "dry". Apply mastic.
Any way you can. With a cheap, disposable paint brush is the usual. With your hand, with a rag, a trowel, whatever it takes. Mastic is stupid low tech, but it works like magic.

You get the spray adhesive in the A/C aisle of Home Despot or whatever...3M number 99?
Can't remember because it doesn't matter. I've never heard of a spray adhesive that doesn't work.
You don't need adhesive to overcoat with mastic, only if you try to stick tape to mastic or old ductwork. Aluminum tape doesn't stick to either.

 

Flakes? I don't see any flakes.
I see mastic, badly done.
Try a diluted Clorox wash to kill and remove the mold. Wait for "dry". Apply mastic.
Any way you can. With a cheap, disposable paint brush is the usual. With your hand, with a rag, a trowel, whatever it takes. Mastic is stupid low tech, but it works like magic.

You get the spray adhesive in the A/C aisle of Home Despot or whatever...3M number 99?
Can't remember because it doesn't matter. I've never heard of a spray adhesive that doesn't work.
You don't need adhesive to overcoat with mastic, only if you try to stick tape to mastic or old ductwork. Aluminum tape doesn't stick to either.

Thanks. I'll check it out tomorrow and let you know what I find. 'Nite

 

Try a diluted Clorox wash to kill and remove the mold.

I'd go the other way and use a concentrated bleach product to go after a serious mold problem. I've been taking advantage of the good weather to get my pressure washing out of the way. I've finally found a good product that wipes out the green algae and the black mildew spots that grow on the north side of my house. The product contains a phenol that supposedly helps retard future growth, if you don't wash it all away (which I do).


The product is used by diluting into water and is mixed with bleach. I use this product, which is much stronger than laundry bleach:

Inside the house I've had very good luck with this product, which is also more powerful than laundry bleach. Be careful, it can take the color out of wall paint:
http://www.homearmor.com/product/instant-mold-mildew-stain-remover

These are all available at Home Despot

 

Update: I got the mastic smeared on all the joints, tracking down misc. air leaks as I went. My son-in-law thought he found a little one left over so I'll go back to check that. Will apply the Al. tape this weekend.

All in all, it was worth it and all the good advice much appreciated! I have a renewed respect for @#12 and the guys who do this for a living. Messy, dirty and back-crunching crawling in and around joists, ducts, and other junk, slopping the sealant on, moving lights etc.

Many thanks.

 

I'd go the other way and use a concentrated bleach product

What I have found is that the difference is time. All solutions go toward 100% solute as the water evaporates and weaker chlorine bleach just takes longer. Your choice. Personally, I can get quite a snoot full with regular laundry bleach and do not wish to be trapped in a closet with anything stronger than that.

Messy, dirty and back-crunching crawling in and around joists, ducts, and other junk, slopping the sealant on, moving lights etc.

Sucks to be me, but that kind of exercise/discomfort will keep you young.
Ever try working at a car wash as the interior wiper? That is a full body work out!

Will apply the Al. tape this weekend.

I don't know why you want to do that. Mastic is the last step. There is no reason to tape over mastic.
There is probably something here that I am missing.

Let me tell you a story. Forty years ago, the leakage goal was, "less than 10%". I would go in the attic and hold my sweaty face near the ducts until I felt the cool air blowing on me and slap some more tape on. With mastic, the goal is less than 1%. I can't find the leaks with my sweaty face any more!

 

I don't know why you want to do that. Mastic is the last step. There is no reason to tape over mastic. There is probably something here that I am missing.

No worries. I think I misunderstood when you indicated that I would need spray adhesive to get the Al tape to stick to the mastic. You meant over the OLD mastic? I wondered about that and I should have asked for clarification. No tape was used originally. Nonetheless, it is pretty tight, I laid it on pretty thick I'll take the tape and 3M 77 back along with the spare tub of goop and the total outlay will be <$25. Nice!

Thanks again.

 

You meant over the OLD mastic?

Right.

No tape was used originally.

You don't need any aluminum tape if the joints hold still until the mastic dries, but they usually are not that cooperative. We tape new ducts to make them hold still then paint mastic over the tape, + some overlap.

I laid it on pretty thick

That isn't necessary. A basically good joint with a bit of air leak will seal up if you just put a layer on with a cheap, disposable paint brush. The mastic actually likes to go in the holes and a very thin layer will seal against typically...0.15 inches of water column...0.006 PSI. You're not fighting a monster here.

 

I have no idea why every time I use Mastic no matter how I try always get some on my pants, hands, shirt, shoes

kv

 

It will wash out if you get at it before it dries. After it dries, it's as bad a silicone caulk. It's never coming out.
Lose much hair off your arms?
Of course you wore raggedy clothes and $10 tennies? And planned on a garden hose shower as soon as you got out of the closet?
No? Noobie mistakes.

If you did this all the time, you'd have a jump suit that looks like it belongs to a house painter and a ghetto style head rag. Until then, you wear the cheapest, most despicable dregs that you threw away over the years. I have such a basket. It's called the destructo basket. Everything in there is willing to give its life to save me from the worst things I might roll in. The pants don't fit, the shirts have been under many a car, and the towels are worthy of cleaning up oil spills. I recommend a destructo basket for all DIY people.

 

What I have found is that the difference is time. All solutions go toward 100% solute as the water evaporates and weaker chlorine bleach just takes longer.

I'm virtually certain that the hypochlorite breaks down faster than the water evaporates. The effectiveness of any bleach solution is highest at time zero and fades quickly.

Nevertheless, I agree that diluted laundry bleach is probably best for indoor applications, except maybe for spot treatment of mildew.

 

I'm virtually certain that the hypochlorite breaks down faster than the water evaporates.

Let's ask @GopherT

 

Let's ask @GopherT

Let me over-explain...

The “reactants” Cl2 (chlorine gas) and strong base, sodium hydroxide (NaOH) are mixed to produce the “product”, sodium hypochlorite (chlorine bleach). It is more of an equilibrium than an energetic reaction so it is easily reversible. To push the equilibrium towards sodium hypochlorite (product) and essentially trapping all of the chlorine as sodium hypochlorite product, a bit of extra sodium hydroxide is added to the mix. This practice of adding one extra raw material (reactant) push the reaction to completion (product) can be explained with the “Le Chatelier Principle”.

Now, washing down a surface with sodium hypochlorite means the whole mixture is exposed to air and nothing holds the chlorine gas in the mix if the equilibrium does shift back to raw materials.

With that background, there is about 400 ppm carbon dioxide in air. Carbon dioxide dissolve in water readily and becomes carbonic acid, a weak acid but strong enough acid to (1) consume the excess sodium hydroxide, and (2) push the chlorine off of the sodium hydroxide and react with that NaOH too. Once the chlorine is pushed off when the mixture is in open air, the chlorine gas boils out of the mixture. Once the chlorine is gone, it’s gone (non-reversible).

To finally answer the question, it all depends on the air circulation (how much total carbon dioxide reaches the wet surface) and the dew-point of the air (how fast the water solvent evaporates). I’m sure there are some old chemical datatables out there in the old literature but, I’m not motivated enough to look for various scenarios.

Note: bleach is slippery on your fingers because the excess NaOH is turning your skin oil into soap. It will also damage your eyes instantly - denature the proteins and turn them white like an egg. Try putting an egg in bleach (to parody an old public service announcement, “this is your eye, this is your eye on bleach”).

My opinion as both chemist and biologist, a concentration of 1/4 cup Chlorox per gallon of water will kill anything if you get the whole mass wet and allow to air dry. Some mold is hydrophobic and will resist getting wet down to the surface so multiple coats may be required.

1/4 cup per gallon is a reasonable balance between safe and effective.

 

@GopherT , you forgot the main reaction: NaClO -> NaCl + 1/2O2
This is the redox reaction that actually does the bleaching. The peroxygen is reduced to oxygen and released as gas while the reducing agent - the poor bastard getting bleached - loses electrons (gets oxidized). The main residue left as bleach evaporates is a salt haze. As you noted, the small amount of caustic is titrated by CO2 in the air, leaving a small amount of sodium carbonate in with the salt.

 

@GopherT , you forgot the main reaction: NaClO -> NaCl + 1/2O2
This is the redox reaction that actually does the bleaching. The peroxygen is reduced to oxygen and released as gas while the reducing agent - the poor bastard getting bleached - loses electrons (gets oxidized). The main residue left as bleach evaporates is a salt haze. As you noted, the small amount of caustic is titrated by CO2 in the air, leaving a small amount of sodium carbonate in with the salt.

Also true. i had a section on that but the new iPad iOS 11 has a stupid UNDO button when you select the number pad (vs the alphabet). It is placed on the right half of the space bar. I hit that and "poof" a whole paragraph on bleaching power vanished.

Your equation is right for caustic solutions when the chlorine is bound as part of hypochlorite. If slightly acid, the Cl2 becomes the oxidizing agent.

NOTE: I think Oxygen Free radical is a better description than peroxygen. Peroxygen is a di-anion (O-O)2- and more likely found in non-chlorine bleaches (per-borate &, more recently, percarbonate) like OxyClean.

 

NOTE: I think Oxygen Free radical is a better description than peroxygen. Peroxygen is a di-anion (O-O)2- and more likely found in non-chlorine bleaches (per-borate &, more recently, percarbonate) like OxyClean.

We're getting far into the weeds here, but the only reason I used that term is I recall it being used by a guy that had experience with P&G and he was claiming it was the actual molecule doing the bleaching with either bleach or peroxide. Funny how even simple things can become more complex than you imagine once you start digging into the details.