Whenever I make potato salad the potatoes end up mushy to some extent.
When I buy commercial potato salad there is never the slightest hint of mushiness. It’s actually quite crisp, but not unpleasantly so.
What’s the secret to getting crisp but properly cooked potato salad?
In my experience - the correct potatoes are essential. We have different ones over here but I am sure someone more local can advise you.
Both acid and calcium firm up pectins in vegetables like potatoes. A tablespoon of distilled vinegar/lemon juice when boiling the potatoes will leave them firm.
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Moving thread from General Questions to Cafe Society.
Another thing to try, to get the potatoes firmer, is to boil until not quite done then turn off the heat and let sit in the water until just right. It slows down the final cooking phase and makes it much easier to get them just the way you’d like. Give it a try!
Starting with the right potatoes. Around here they come in waxy (suitable for boiling and salads) and floury (best for roasting and chipping). Boiling them whole helps reduce the amount of water they absorb which can help them stay more firm too.
Here’s Martha Stewart’s Potatoes 101 for varieties.
Potato, pototo, let’s call the whole thing off.
If you live in the States, what is sold simply as “red potatoes” in any supermarkets will be a good potato for this type of use. Anywhere where you want the potatoes to hold their shape (like in a stew or a salad), that’s a good choice.
How about how to make Solid Potato Salad? 
(Link to 1940’s video featuring triplets singing a song with that name and doing some pretty amazing contortionist moves - featured here on the SDMB a few times…)
Agree with red potatoes; russets can get too soggy too easily. I usually cut mine up to the appropriate bite-size and then steam them rather than boil them. Yukons might also be a good choice.
You have to start with cold water. If you put very hot water in the pot with the potatoes and then boil them, the outside gets cooked before the inside. Then the outside is mushy by the time the inside is done. Use a sharp knife to check for doneness, when the knife will just go in with a little pressure, they’re done.
Also, make sure you’re using a thin skinned boiling potato. Reds are the best.
The outside always gets done before the center, but waxy spuds like reds can stand up to it better than starchy varieties.
I’ve never thought of doing it that way. That’s a great idea and I’m trying it next time I make it.
I’ve never had any luck with Yukon Golds, they always mush out on me. But I echo the endorsement of the red potato.
When the potatoes are done enough pour them out in a colander and spray cold water over them to stop the cooking process.
Also agree with reds.
Deep fry the potatoes first.
Yeah, I was going to edit that out, but got distracted by something shiny. Yukons work fine for mash, however.
And almost edited them into my post. 
I would have thought Yukons should work okay, but I’ve never tried them, so left them out.
Assuming you are in Australia, Desiree and Ruby Lou are good potatoes for salads. Cook them for less, and dunk them in cold water when they are done.
Yukons are definitely great for mashed. Very creamy, not as gritty as potatoes can sometimes be.