Building muscle mass (hypertrophy) can be done with all the basic cali movements, push up's, dips, pull ups etc etc. Taking the target muscles close to, or to actual failure will give the best stimulus to actually build mass. Once you get into the 10-15+rep range you can look at adding weight, if you can do so without breaking form.

Add weight to the free hand, this will improve your forearm/grip strength. Keep the shoulder active rather than passive when you do this, to avoid rotation and build shoulder/ scapula strength. 3 sets of 8-15sec holds every other day would be fine for a start.

@Pau Sorribas Thanks man! It's great in the summer time, fire up the BBQ and get some reps in between the burgers.

@Pau Sorribas No room for a pool unfortunately, but Loch Ness is just a few miles away. 🦕

Another fan of super sets here, keeps your workouts flowing rather than stop start. Get way more done in the session this way.

A deload is sound advice, I usually half my reps but maintain intensity (weight) during this time. (Train a 6 week block, then deload on week 7.) Changing up your routine up a little can help you break through plateau's too. Try warming up with bodyweight paused reps, holding the top position for 1-2 secs, Then dead-hang (passive, straight arms) at the bottom 1-2 secs. Really focus on the squeeze at the top to build strength there, this is usually the weakest part of the movement as people are barely there during normal reps. Repeat for 10-15 reps... Another great exercise I've learned from the climbing world is called "Frenchies" Pull up from passive hang as high above the bar as you can, lock off and hold for 5secs Lower body so arms form 90deg at elbow, hold 5secs Lower again to 120deg hold for 5 secs Lower to passive hang, hold for 5 secs. Repeat for reps. This builds strength throughout the range and gives a crazy amount of time under tension! For your strength work (weighted) try upping the weight a little and dropping the reps, say 15kg for 5 or 6 and repeat for 3-5 sets. Once this gets easy, up the weight again.