Why do I need to remove old glue from the rubber's sponge?

[Fnub]

Just curious

 

[Dominikk85]

Just curious

You don't. Only remove when there are like clumps who would make the rubber uneven

 

[Tony's Table Tennis]

because it is just a layer of plastic with no more bounce
Fresh glue can aid the sponge, old glue will make it dead

 

[Scarfed Garchomp]

Its also weight, legal thickness aside, having more than 4 or 5 layers of glue compared to 2-3 on the rubber can make a noticeable difference in the weight in the head of your racket.

 

[turbozed]

An uneven playing surface is an unpredictable and inconsistent playing surface.

With fresh uncured glue, you can clamp or stack some books on the rubber/blade while drying and it'll slowly but surely even out.

With old glue, you're going to get some unevenness after you've pulled the rubber from the blade. Even with a sealed surface and DHS No. 15 glue (the best I've found for not leaving any glue on the blade), there have been only 1 or 2 times where I've peeled the rubber off, examined the rubber, and found the glue layer acceptably smooth.

There's an argument the fresh glue will fill in the gaps left by the old glue, but my experience is that I see more bumpiness through the topsheet when I've reglued without removing the old glue.

 

[Scarfed Garchomp]

An uneven playing surface is an unpredictable and inconsistent playing surface.

Rubber and glue are elastic and deformable materials. If we were talking about a hard surface that did not deform then a bumpy and rough surface would certainly be more noticeable, but the fact that rubbers deform around the ball, the ball also deforms during contact, and the glue layer itself is very thin, I just don't see how a slightly bumpy glue job would even be noticeable during play unless it was intentionally made to be terrible or somehow facilitated sub optimal adhesion.

 

[Fedex78]

I have a fellow player who has terrible glued rubbers, very uneven everywhere: He plays like a razor edge, very precise in each shots, never unpredictable shots...I think the only reason to remove an old layer before regluing is the added weight