Garbage Santa will reward you for learning this skill.
He'll put all kinds of nice inflatable stuff out at the curb for you.
Step 1: Inflate
Big airmattresses often have a big deflation cap and a smaller inflation valve. I usually use the big cap.
One handy trick to know is the mattress inflates a lot faster if you blow the air AT the big intake instead of IN the intake. That's because the air jet from your blower entrains a bunch of surrounding air and sucks it into the mattress along with it.
Step 2: Cap It
Because the air mattress has so much surface area only a few psi are needed to inflate it properly (or pop it). (pounds per square inch * square inches = many pounds)
Next we'll find the leak. One way is to paint soapy water all over it and look for big soap bubbles. It's a sunny day so I'm going to take it swimming and look for bubbles in the water.
Step 3: Go Swimming and Find the Leaks
This is the first sunny day after a lot of rain so the sun's glare is blinding me.
Also my nordic cave-fish ancestors never got exposed to direct sunlight and evolved away their tolerance for it.
People who can be exposed to sunlight without getting sick don't need to make up stories about being the "master race".
Step 4: Leaks Found!
I wiped an area near each leak sort of dry and drew arrows pointing at the leaks. A sharpie marker is good for this because it can mark a surface that's slightly damp. Enough for a couple of arrows anyway.
Now I'm ready to patch. I hung the mattress in the sun to dry out and got my mask out.
It's got a fresh organic vapor cartridge in it so I won't have to breathe or smell any of the braindamage fumes from the glue.
I cut a couple of patches from another air mattress that was slashed beyond repair by a store that threw it away.
Step 5: Rough Up and Cut Out Patches
If your patch comes from a shower curtain it will be greasy and you'll have to de-grease it first.
If the mattress or patch are new you'll also need to degrease them by scrubbing with detergent. Plastic things come coated with some kind of oily stuff to keep them from sticking together in transit.
You've de-greased it enough if water sheets out on it. If the water beads up, degrease it some more. You can also do that by wiping it off with alcohol or the nasty greaseless solvent of your choice. Not Gasoline. It's oily.
SOURCES OF PATCH MATERIAL
My patches came from a totally shot air mattress.
In the past I've cut patches from shower curtains and a raincoat.
Any thin flexible sheet of PVC will be fine.
PVC won't stick to urethane and vice versa. In the U.S. most flexible plastic things are PVC.
That may be different in Europe due to health regulations.
SHAPE AND TAPER
Rounded patches are easier to stick down. If a patch has corners they tend to peel up.
In the past I've tried sanding the edges thin so they would taper down and stretch with the surrounding material better. That's worked well but usually isn't necessary.
Step 6: Rough Up Around the Leaks
I didn't need to de-grease because this thing is old enough that the manufacturing oil has worn off already. Water sheeted out on it when I had it in the lagoon looking for bubbles.
Step 7: PVC Cement
If you're shopping for new glue, you can't beat this "HH-66" stuff for PVC. It's made for truck tarps and ilk. The directions are much different though than using pipe cement. You let it dry first, then re-activate your patch with heat.
Follow the instructions on the PVC cement you have. Some types recommend wiping with MEK or other solvent first. The solvent helps by making the plastic get soft and expand a little.
The cement has a brush attached to the underside of the lid, which always makes me happy.
Don't breathe any of these fumes. If you smell them your brain just died a little. Use your mask.
Wear gloves and keep it off your skin.
Step 8: Apply Glue
By the way, these methods and materials are not good for patching bicycle innertubes.
Get a proper bicycle patch kit for that. They only cost $2 or so.
Step 9: Apply Patch While Wet
Here I'm using my knuckle and the face of a hammer to rub and squish.
Step 10: Clamp It
After an hour or so I took the clamps off and put the thing in the sun to drive off the braindamage solvents.
And that's it! It holds air and works fine!
If your patch leaks you can heat it up with an iron or hot air gun and squish it down. The melting point of the cement should be slightly lower than that of the sheet materials.
If that doesn't work, you can either peel it off and start over, or patch the patch.