I've got a basement project where I'm attaching 3in studs over 1 inch foam to a block wall (built ~1952). I was planning on using Tapcons, but the threads are not holding. The 1/4 green Spax lags look like they would do the trick, but my concern is - will they will rust out over time?

 

What size tapcons are you using?

 

the tapcons I was using are 1/4 x 5 inch.

 

CMU is soft... so you likely need to drill your holes with a 5/32 bit in cmu... slightly smaller than what is normally used. Also you cannot blast the hole into the block because you will blow out the inner half of the block. Drill your holes carefully, quit pushing the drill hard once you are halfway through. Predrilling a 3/16" or 7/32" hole in the stud will help too. Only the head needs to hold the stud tight... not the threads. You shouldn't torque the screws down as tight as possible with an impact because they will strip out... the cmu is too soft and too thin. If you use an impact, stop once it's snug. If it spins even a little you're done and need a new hole.

No, green spax will not work, they are not for concrete.

You could also try hitting the mortar... you might have better luck in the mortar than the block.

 

ok - thanks I appreciate your time.