That old chestnut again.
From an earlier post I was left feeling comfortable that I should first lay the blocks around the new recessed manhole position and then level the manhole on mortar. However, this could only work if the surrounding blocks had been fully wacked down before starting on the manhole. Is this correct? My plan is as follows:-
1) Build-up height of manhole to approximately 15mm below estimated finished level. Keep haunching to minimum and bevelled.
2) Screed whole area (including up to sides of 'loose' manhole frame) and lay full blocks over whole area, keeping blocks approximately 25cm away from manhole in all directions. Cut and insert part blocks around edges of blocked area.
3) Wack whole area to finished level. THEN return to manhole! Level manhole to 3mm below ACTUAL finished level in all directions on a bed of mortar (max 15mm). Allow 48 hours to set before cutting-in part blocks around manhole. Wack new part blocks to finished level.
4) In-fill recessed manhole cover with blocks on a bed of dry-mix mortar.
Is this approach about right?
Thanks
De1b0y
Not the way I do it. Others here may differ, but the first thing I suss on any job is the finished level and falls for the paving as that governs everything else you do. On that basis, you should be able to set the IC cover as soon as the sub-base is prepared. Then I screed and lay, and then do the cuts into and around the tray - these I do on as firm a hand screed as possible, and then I consolidate them in with a mallet, once all is in place it's ready for the wacker.
Tony advises laying to 250mm beforehand - but no compaction until the muck has gone off. The only thing I'd take issue with is that sometimes all you can get is the metal tray but with the plastic frame. You can't set the frame without the tray in it because it's flexible. The chances are that if you set the frame on it's own, when you come to put the tray in it won't sit in square.
Thanks for responses.
Just as I feared.
My first posting on the subject some months ago got the consensus reply of "tray after blocks"; the website topic also states the same "surround tray location to within 250mm with blocks and then set tray". This does not seem quite as easy as it sounds, as these blocks would need to be wacked to finished level before starting on the manhole.
I would prefer setting the tray first to the finished level (which is what is done with the border course!) and then screeding and blocking around the tray along with the main body of paving. Why would this approach be so problematic?
Many thanks
De1b0y
Further to Rich H,s point.
Even with all metal trays and frames, it is best to have tray in frame when bedding in as you can get distortion on the frames.
Del boy re question 3.......when you wack blocks like that you need to be at least a metre from the leading edge. just do as it says on the index and you will be ok m8.
De1b0y wrote:Thanks for responses.
Just as I feared.
My first posting on the subject some months ago got the consensus reply of "tray after blocks"; the website topic also states the same "surround tray location to within 250mm with blocks and then set tray". This does not seem quite as easy as it sounds, as these blocks would need to be wacked to finished level before starting on the manhole.
I would prefer setting the tray first to the finished level (which is what is done with the border course!) and then screeding and blocking around the tray along with the main body of paving. Why would this approach be so problematic?
Many thanks
De1b0y
believe me del ,i have tried it this way and you only have to foul it up slightly an the tray is 20mm proud or 20mm shallow
its fairly simple blocking close to it ,then installing the tray about 12mm below finish,even if wacking takes the drive down 5 mm your tray is still recessed,i find it better to remove the tray prior to final wack removing and KD sand then greasing it and re-installing ir prior to the last wack
cheers LLL
Thanks for all your helpful advice.
I will block around unfixed recessed tray first. Do initial compaction of blocks and then fix tray before final compaction.
Not sure what seanandruby meant by only compacting to 1 metre of leading edge; not seen this mentioned before. Does this mean you should not get too close to the front of the loose-placed blocks with the compactor as this might shake them away from the leading edge?
This raises the question, I suppose, of how large an area of loose-placed blocks should be laid before starting the compaction? Too small and you will always be too close to the leading edge, too large and...what? My main area (out of 3 sections) is 22m2. Is this too large to loose-lay before starting the compaction?
Big Day starts tomorrow!!
Best regards
De1b0y
Sorry for the confusion , "leading edge" is a term we use when erecting a deck. i meant keep a metre away from the end of your unfinished blockwork, or else they will move. hope this clarifies it.
"Leading edge" is a recognised block laying term, Sean.
Some good advice given above but the one fact not mentioned is that all ironwork, and that includes recess tray, should be set to a level 6mm below finished paving level. You can leave the blocks slightly proud in the tray, if you wish, but set the frame 6mm low.
Why? Well because you can always guarantee that flexibly-laid paving will settle slightly. No matter how long you spent compacting the sub-base and the blocks, time and gravity and traffic will result in slight settlement. meanwhile, your ironwork is rigidly-laid, bedded on bricks and mortar and therefore incapable of settlement. the result is that, in the medium-to-long term, the ironwork ends up being proud of the paving - we've all seen this!
When said ironwork is a recess tray cover, it's not the end of the world, but when it's a gully grating, the result is often a drainage point that is actually higher than the paving, and, try as we might, we can't get water to flow uphill!
its an old bete noire of mine the recessed tray that looks like a small hump in the drive,because the sand has no where to go in the tray these blocks stay at the original level,but the rest of the drive drops 5 mm over a period of time
and as we all know the trays are a sod to get out
if they made nicer looking road covers i would go back to these,functionality all the way!!
LLL
lutonlagerlout wrote:if they made nicer looking road covers i would go back to these,functionality all the way!!
LLL
Nice idea Tony! What about getting some 600*450 trojan covers and sticking a layer of block-paving vinyl over the top to match the blocks! Instant winner!
RW Gale Ltd - Civils & Surfacing Contractors based in Somerset
