Alloy seat post removal using caustic soda


Retro Guru
I have had this Raleigh Thunder Road 531 frame for a long time now (7 years maybe) and the seat post was stuck, stuck, stuck. The use of force was not shifting it and i didn't want to bend the frame especially around the welds at the top of the seat tube and the seat stays, so I decided to give the caustic soda a go.
I cut off the top off the seat tube to give access then I taped up the frame by using cellotape on the decals on the down tube as I wanted to preserve these, then I taped up the frame using two rolls of electrical tape.
I blocked up the bottom of the seat tube using a cut off cork and blu tack. Sealed it further with daughter's homemade playdough in a rubber glove each side in the cups. I tested the seal by filling up the seat tube with water.
I measured out how much water would fill the tube (approx 200ml) and marked off the plastic milk container I was going to use to mix the soda and water. After getting on the marigolds, face mask and googles plus making sure sleeves were not rolled up, I added the soda to the water of 2 parts water to 1 part soda, gave it a shake making sure the lid was slightly off to allow the gas to escape and using a funnel, then poured the liquid in.
It took a few minutes for the liquid to start to work and I left it for approx 20mins. I poured out the liquid into an old roasting tray and started again. After the third time, things were cooking and a lot of bubbling and white gas was being given off.
In all, the process took a while and I did it over a few days, leaving it overnight on the second day into the third to get rid of the stubborn bits left near the top.
The paint was damaged near the top and on the seat tube as it did overflow with the reaction. In all I am pleased with the out come. In all the process took approx 6 to 8 hrs and I used two bottles of 500ml of concentrated caustic soda. Here are some pics.


  • DSC_6305.jpg
    1.2 MB · Views: 381
  • DSC_6306.jpg
    1.1 MB · Views: 381
  • DSC_6307.jpg
    852.1 KB · Views: 380
  • DSC_6314.jpg
    3.3 MB · Views: 380
  • DSC_6324.jpg
    1.4 MB · Views: 379
  • DSC_6325.jpg
    1.8 MB · Views: 379
  • DSC_6330.jpg
    147.8 KB · Views: 379
  • DSC_6333.jpg
    401.5 KB · Views: 381


Saracen Fan
Haha. I did this with a Saracen Tufftrax frame but my mix only took and hour to dissolve the post remnant. I think I got my mix a bit wrong/strong!! At one point the frame was too hot to touch so furious was the reaction.