We have a good set of chairs which upholstery had seen better days and their padding are almost gone.
So, we both some leather cloth and foam online for a small diy project. 
Little did I know that removing the staples from the old upholstery would be a PITA!
Then I thought that we could just add the new on top of the old one! 
I’m not sure if there are any drawbacks in doing that, so I come to check with the Forumosa’s collective pool of knowledge! 
Thoughts?
I did this once. Why not?
I’m wondering if the new one would slide and move on top of the old one and just crumple in one corner
That wouldn’t be good.
I didn’t have any problems
Is the one on top loose?
Not too much, but not as tight as the day we bought it
When you put the new one on, can you stretch and restaple the old one? Fix as you go?
They should be fine as long as you can pull them tight, you could also add a thin layer of foam to help pad it out and give it a little more tension.
The new one doesn’t need staple. It has an addesive side which makes it easier to install.
On the other hand, it makes it less stretchy too. 
I’ll add foam for sure, as the original padding is practically gone.
Then it will be ok you want a little movement for when you sit down., make sure you can get a good grip on the fabric to tension it.
I once bought burlap pillow covers from Ikea to “upholster” a fake-leather computer chair with the black paint peeling. I used safety pins to make everything stay put. I am sitting in the chair now. Nothing moves around.
Job done!
It was a bit harder than I thought, cutting the foam the right size is not easy and pulling the leather to the right fit can be tiresome, especially on the corners.
Yet, it’s satisfying to see it done, and my butt appreciate the extra cushion! 
I never really tried upholstering stuff or redoing them, but I do notice larger chairs, sofas, etc. tends to have stitches in the middle or thereabouts to keep the leather from sliding around. I’d definitely not leave the old stuff hanging under the new stuff just because that’s just going to slide around.
I do not know if any glue or adhesive is used to keep the foam stuck to the skin either, but that doesn’t sound like a bad idea.
Looks comfy. Let us know how it holds up
I heard once that you can put it in the freezer for a while and it becomes much easier to carve into shape. I have no idea whether that’s true though!
The accepted way to cut foam, at least styrofoam, is with hot wire. You have a thin nichrome wire, you pass electricity through it, and it gets hot, then using a wooden form as a guide the wire melts through the foam like hot knife through butter.
I don’t know about upholstery foam though. My concern with urethane based foam is that using hot wire may release toxic gases.
I think scooter seat is done by sucking down upholstery into a form, and then expanding foam is poured into it, then the inner form is inserted while the foam is setting, which forms the seat cushion. I’ve never seen it but from what I can glean, they do it this way.
The leather we bought is addesive so it sticks to the foam quite well.
I guess there’ll be no movement under it.
Thanks, it is!
But I noticed that it may be risky to rely on the addesive side of the leather to keep everything in place. I’ll go buy a stapler tomorrow to secure it better.
I’m torn between “shoe goo” adhesive vs plastic floor adhesive.
Shoe goo is kinda strong, but it stinks and takes forever to set up, and you have to brush it on both surfaces and wait for it to dry before attempting to bond, and it will bond instantly.
Plastic floor adhesive is very stick and remains tacky even dried, but then you can stick whatever right on.
I had a job where I needed to make a custom case for someone out of a large keyboard case. The guitar is too large to fit any standard case. What I did was a lot of expanding foam, and followed by gluing felt cloth to the inside of it.
I think, or hope I did a good job at it. At least the guitar is somewhat protected and not flopping around.
I’ll try it if I have to do it again.
I imagine it won’t smell nice, and the fumes may be toxic, so it doesn’t sound a good idea.
I used large scissors and a stationery knife to cut the foam. The problem is that it’s not firm enough to cut it clean, so it doesn’t look nice and round on the corners.
But, in the end, it doesn’t really matter, as the imperfections are hidden under the upholstery.
