Elmers wood glue
Old cleaning method is lint-free cloth saturated in isopropyl alcohol. If they’re really dirty, add small amounts of white vinegar and/or dish soap.
Fixing dumb...Can’t be done.
I used to be an Album Rock DJ in the day. The only time we needed to clean LP’s was when someone got food on them. And that happened a lot. When it would be a while before we could get a replacement from the record company, we used warm liquid dish detergent & cleaned gently with a tooth brush following the directions of the grooves. Then lightly rinse & gently dry.
Of course, for collectors you just have to keep the center label dry.
It hardly ever failed & didn’t scratch the LP.
We didnt clean them till they skipped from crud in the grooves.
mayonnaise
Modern record cleaning is uses either water-based cleaning solutions with a vacuum record-cleaning machine, or an ultrasonic machine with distilled water. There are many record-cleaning machines offered - you can go look at what’s available from vendors like Music Direct and Acoustic Sounds.
If you have limited needs, you might be able to find a record store that cleans records for a fee using an expensive machine, such as the $4000 Audio Desk ultrasonic cleaner.
First thoughts: You have several problems. The album covers, the record labels, and the records themselves. There is a turntable/vacuum system that will clean the record and extract dirt from the grooves. These systems work very well. The other two areas involve paper conservation. The first step in that leg is a quantity of desiccant material or blotters to remove the moisture. It’s likely they are beyond redemption but whatever you can salvage or even digitize is useful.
I can’t speak to the value or rarity as I don’t know what albums are under discussion.
Put a nickel on top of the tone arm.
Rubbing of any kind, dry or wet, will ruin them by grinding grit into the soft surface and scratching the vinyl ridges which produce the sounds. Don't do that!.
If the album cover is not salvageable, they’re essentially trash.
The album covers are a loss but the records can be easily cleaned with soap and water.
I didn't search but I'll bet there are different methods, some good some bad.
Read the comments to see who had success.
I too have a large collection of LPs, something between 2500 and 3000. A general rule of thumb is to store media in an environment comfortable to humans. While I would be heartbroken at the thought of loosing them all, the situation here would force me to make difficult choices.
Time is money and any restoration project is going to require an enormous amount of time on your friend’s part. Unless he has a Beetles butcher cover or something equally rare the records are probably worth much less than his time.
The mold is the very first thing that must be dressed and there are methods that range from enzyme solutions to Clorox, mild dish soap or 90% isopropyl alcohol rinses along with the use of very soft brushes or microfiber cloths and lots of distilled water rinsing between steps.
The PVA glue trick is based on a commercial protect sold for a few years in the late 1970’s by the Empire Phono Cartage company called Disco-Film. It worked, and from what I’ve heard the glue trick does, too. I would think that one should probably do a pre-cleaning first but experiment and see what works best.
May I suggest that your friend should first make a database of what is in his collection and see if the music is available online. Youtube, Spotify and Archive.com should have most popular music published in the last 60 or 70 years. There are ways to download the music to your hard-drive or just log the URL for when you want to listen to the song. Concentrate on salvaging the disks that are not available online as that is an indicator of rarity.
Yes, an LP is going to sound better than an mp3 but not a damaged LP and I’ve found that by up-sampling an mp3 file and saving as a .wav file the music can sound as good as a CD and you loose those annoying Rice Krispies.
groovewasher.com
If he wants to save them for listening, then get an expensive ultrasonic cleaner (or two) and be prepared to spend some time with the collection.
Or hire a kid and teach the kid about the history of audio.
Hose them down then let them dry out in the sun.
The music will be interesting to listen to afterward.