Floplast mini (300mm) inspection chamber resizing

[tpb1975]

Anybody had to resize a Floplast inspection chamber. The builder fitted a couple of these when putting in an extension. Both are about 40-50mm higher than damp proof/final patio height (when I get around to laying it). He just said cut it down to resize it. Didn't really think much of it at the time until I've looked at it.

Anybody done this, looks like the 300mm chamber only has 100mm and 200mm risers. So getting a 100mm riser is probably not going to help. To me it looks like I'd need to cut the top of the last riser and then the same amount off the lid. Probably ensuring there is plenty of a weakish concrete mix under the corners of the lid holder to prevent it moving around.

 

[wrathkeg]

I recently needed to cut a 450 mm Clark Drain inspection chamber down. I cut the riser to height (and angle) then concreted round it. Seems fine. I used a combination of a handsaw and jigsaw to cut it down which worked fine. I'm not sure what you mean about cutting anything off the lid. If you're not sure then I'd suggest getting the builder back to cut it for you.

 

[tpb1975]

Thanks for the reply. Just given Floplast a call. They said there is a cut down point on the 100mm riser and possibly 2 cut down points on the 200mm riser. Sounds like you can cut down by about 40mm. Need to dig it out and have a look.

Sounds like the sealing rings are quite important if you cut it down but can't find them. So he said he'd post a few out for me. Nice chap

 

[r896neo]

You can cut the riser in situ with a small grinder if your careful. The cover then simply slides down inside the riser and seals via the rubber/foam ring.

You shouldnt have to adjust the cover unless the chamber is very shallow. The riser is essentially just a large pipe and the frame piece slides inside it.

Put a generous bed of strong 3:1 ish mortar under the frame edges

 

[tpb1975]

The fitting inside the lid has a diameter about 10-15mm greater than the riser and sits in the top. So with the Floplast doesn't look like you can just trim a bit off the top and the lid will sit in. But... I dug one of the risers out and you can see that the diameter of each section means it will sit in the section below. It does look like you loose the supporting ring in the process but like you said, put a good concrete mix under the corners and I guess some MOT under that.

Found a clip on YouTube

, it's for the 450mm rather than 300mm but similar (round lid rather than the square as well). About 1min 35 when he talks about how to cut it down.

He does mention a metal tray for putting your flags in, rather than the plastic. Might have a look into that. Shame to have a couple of plastic lids in the middle of the patio.

 

[r896neo]

recessed covers are great but are very deep compared to a normal cover. They are usually 90mm or therabouts