pier concrete observatory floor concrete isolation foam, what to use?

[muletopia]

Hello,
When the floor for an observatory was cast the around the pier concrete (Beginners pier complete thread) it was surrounded by 20 mm thick boards. These boards have been removed leaving a 20 mm wide slot as deep as the depth of the floor casting,

My question is, would spray in expanding foam in the slot be too rigid when it sets? If so, what density of foam should be used?
Cheers
Chris

[spinnaker]

I used Sika expanding foam to seal the gap between my pier and the surrounding flooring. After trimming away the excess, it forms a very neat finish which keeps out unwanted draughts and creepy-crawlies. I have not been able to detect any transfer to vibration to the pier through the foam, despite my best efforts to do so (like jumping up and down on the floor!).

[The_bluester]

Otherwise you might be able to use something like Sikaflex windscreen adhesive. It is a rubber which cures firm but not hard. There might be a softer curing version too compared to the windscreen stuff, but Sikaflex I used to bond in a window in my race car is still pliable after nearly ten years.

When my long planned obs goes ahead that was what I was thinking of using to fill the gap between pier and floor.

[ChrisM]

I went to Clark Rubber and got some medium density foam to fill the 12 mm gap around the pier. It's easily removable.

Chris

[Dealy]

I'd leave the gap. Get a small piece of carpet, cut a hole to suit the pier and don't fix it to the floor.

That will stop drafts and crawlies and you'll have no worries about vibrations.

[Shiraz]

I made the the formwork out of CCA and left it in place when pouring the surrounding floor - everything shrank a little, leaving slight gaps and this seems to isolate vibration quite effectively. since wood works ok, I doubt that expanding foam would be strong enough to transfer vibration.