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Moldy shower caulk... fixed!

Dirty bathrooms are a huge turnoff for home buyers. Mold is another huge turnoff. Combine the two and the 'yuck' factor multiplies. I think everyone has seen moldy bathroom caulk before, and if you've tried cleaning this stuff, you know it's impossible.

Moldy caulk in shower Moldy caulk in shower close-up

I was reminded of this topic while blogging about the top 5 places to find mold in your home last week, so I'm doing a re-blog on this topic, along with a video.

Back in 2011, I moved into a somewhat distressed property that needed some TLC. Among the list of neglected items was some nasty-looking caulk in the master bathroom shower. Yep, that's my shower pictured above. I figured I would need to remove all of the moldy caulking and re-caulk my shower walls to get them looking good again, but after doing some online research, I found a cleaning method that worked surprisingly well and wasn't much work. I was so happy with the results that I had to share the process.

How to do it

Gather supplies. You'll need a small mixing bowl, bleach, baking soda, a brush, a roll of plastic wrap, a spray bottle, and a respirator. The plastic wrap (green handle, clear plastic) shown in the photo below is the stuff you use to wrap things together, but you can also use the same plastic wrap you keep in your kitchen. Also known as Saran Wrap. Also, wear old clothes that you wouldn't mind spilling bleach on. It will happen.

moldy caulk cleaning supplies

Mix up your cleaning solution. The cleaning solution consists of a bleach and baking soda paste. You make it by mixing bleach and baking soda in a bowl until it's about the consistency of pancake batter. The baking soda doesn't do any cleaning; it's just a cheap powder that will help make the bleach pasty. Don't skimp on the cleaning solution here; go ahead and make way more than you think you'll need. Bleach and baking soda are both inexpensive. Be sure to wear your respirator while doing this.

Apply the cleaning solution to the moldy caulk. Use your brush to apply the bleach paste onto the moldy caulk. Again, don't skimp here; it's cheap, so cake it on. If you happen to use a disposable paintbrush, I suggest working quickly. The bleach might disintegrate the bristles on your brush.

disintegrated bristled on brush

Cover the cleaning solution with plastic and wait. Covering the cleaning solution with plastic will help to keep the bleach from drying out. Now you wait. If you have a white porcelain kitchen sink or white porcelain whatever-else, spread the extra cleaning paste on it. You can just let the paste sit for about 10 minutes, and then your sink will look brand new when you rinse the bleach off. No scrubbing required.

Check on it. After the bleach has been sitting for an hour, it will probably have dried out, despite the plastic covering. At this point, if the caulking looks as good as new, great! You're done.  If you still have moldy caulk, put some bleach in a spray bottle and wet the walls down right above the plastic wrap. The bleach will run down underneath the plastic and re-saturate the paste. You can do this as many times as it takes, but even with my super-nasty caulk, I only needed to re-apply the bleach one time.

Now clean up. At this point, your caulk should look brand new and bleachy fresh, or at least pretty close to it. Now you can clean up the mess with water. Click on the before and after photos below for a larger version to see how well this worked. If I were a better photographer, all of the whites would have looked the same, but oh well... I think you get the point.

moldy caulk before and after

moldy caulk before and after

I was amazed by how well this worked. The entire project probably involved about 20 minutes of work and required no elbow grease whatsoever.

And now, a word of caution: do this project at your own risk. Bleach is powerful stuff. Read the warning label on the bleach. It says to use in a well-ventilated area, don't let it touch your skin, don't breathe the vapors, etc. Bleach can also cause pits in metal. I used it on the metal trim ring for my shower faucet and no pitting occurred, but other people might not be so lucky. Also, I'm not kidding about wearing a respirator.

Author: Reuben SaltzmanStructure Tech Home Inspections

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The top five places to find mold in your home

We recently did a couple of home inspection podcasts with local mold expert Vickie Swenson, and we asked her about the top five places to find mold in the home. Before giving her a chance to answer this question, we also told her this would turn into a blog post ;-). I had already put together my own list, and our lists were nearly identical.

As a home inspector, I don't specifically look for mold (see Mold or Suspected Organic Microbial Growth), but when I find stuff that looks like mold, I report it as such. A mold issue is a moisture issue. If I wanted a wordy, stuffy-sounding title, I might call this blog post "The top five places to find suspected organic microbial growth."

Finished Basements

Wet tack strips in basement

It's a challenge to finish off a basement in Minnesota and to never have a water intrusion problem. That's not to say it can't be done, however. I live in a 2002-built home with a finished basement, and I'm pretty sure I've never had water in my basement... but there's always tomorrow, right?

Basement carpet is a prime location to find mold growth in finished basements. When basement carpet gets wet, it frequently stays wet for a long time before being discovered. Sometimes, the underside of basement carpet can get damp without anyone even noticing.

We frequently pull back carpet in the corners of basement rooms where we suspect water issues. A less objective method for finding mold, but surely just as reliable, is to simply get down and smell your carpeting. If it smells moldy, it probably is.

Unfinished walls at walkout basements

Mold in fiberglass batts Mold in fiberglass batts 2

When a new-ish home is built with an unfinished walkout basement, there's a good chance that the home will have a mold problem inside the walls. It happens over and over again with these homes.

The problem is that basements suck; through stack effect, air comes in at the basement level and leaves at the top of the home. When humid summer air is sucked into a relatively cool basement, you end up with a bunch of condensation on the insulation side of the poly, and it eventually causes mold growth.

How do you prevent this from happening? I have no idea. I think the way we build houses with fiberglass batts and a poly vapor barrier on the conditioned side of the insulation is stupid, especially when the poly is left exposed.

Prove me wrong.

My last home had this problem, and I solved it by replacing the fiberglass batts with closed-cell spray foam.


moldy caulk

Bathrooms are humid places, and you end up with a lot of moldy-looking stuff. We find it behind caulk in showers, on tile grout, on walls, on ceilings... everywhere.

The best way to help prevent this type of mold growth in bathrooms is to keep humidity levels low. If you don't have a bathroom exhaust fan, fix that. Also, be sure to operate your bath fan for a long time after taking a shower; typically 30 - 60 minutes. To make it easier to do that, I recommend replacing traditional switches with a timer or a humidity sensor with a built-in timer.


Mold in attic

We find a ton of moldy attics. Sometimes the staining in an attic isn't mold, but from a home inspection perspective, we report it the same way. It's a telltale sign that there's a moisture problem in the attic. Moisture problems in attics lead to frost accumulation, mold, stained ceilings, delaminated roof sheathing, and ruined insulation.

Attic bypasses, aka attic air leaks, are at the root of all attic moisture problems here in Minnesota. Check out my blog post on frost in attics for ways to help prevent this.

Behind stored items on outside walls

Hoarder house 2

This one is building science 101. If you have a closet located at an outside wall and you pile a bunch of stuff against the wall, you're moving the dew point. Or to put it another way, that stuff you're piling against the wall is acting as insulation. You're preventing the heat in your home from reaching the outside wall, so the wall stays colder, and you end up with condensation on the wall. That leads to mold growth.

The solution? Don't store stuff against exterior walls. If you have a newer home with 2x6 construction, you'll probably be ok. An insulated 2x4 wall will probably be ok too, but uninsulated walls are the ones that can really have problems.

Author: Reuben SaltzmanStructure Tech Home Inspections

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