Manhole Cover & Shaft Brick Moulds: How to Order a Complete Chamber

Buyers usually enquire about "manhole moulds" as if it were one product. It is two. The cover and its frame close the top of the chamber; the shaft below is built course by course out of bricks. They are quoted separately, they are measured differently, and the mistakes that cause re-orders are different in each case.

This guide covers both: manhole cover and well frame moulds and shaft ring brick and well wall brick moulds. Every dimension quoted below is read off our own workshop photographs, not taken from a catalogue.

1. Cover only, cover plus frame, or frame only?

This single question causes more re-quoting than any other in the category. A cover slab cast on its own will not sit flush unless the seat it drops into was dimensioned to match it. There are three legitimate answers:

• Cover only — the site already has steel frames or existing concrete seats. Measure the seat opening before ordering, because the cover has to be sized to that opening, not to a nominal figure.
• Cover plus frame, as a matched set — two moulds designed together so the clearance is built in. The 50 × 50 cm square set is an example: cover plate and slotted frame, dimensioned against each other.
• Frame only — you are re-seating an existing cover, or capping a shaft. Here the number that matters is the clear opening. Our round frame mould is Ø 68 cm on the outside but gives a Ø 61 cm opening, and it is the 61 that has to match your shaft and your cover.

Getting this wrong is expensive in a way that is easy to underestimate: the concrete is already cast before anyone discovers the cover rocks in its seat.

2. Round covers: diameter first, thickness second — and holes are voids, not pitch

Round sewer covers are quoted as diameter × thickness. Ø 80 × 5.5 cm means an 80 cm circle, 5.5 cm deep. Two things follow from that.

First, 5.5 cm is a light-duty section. It suits pedestrian areas, yards and utility access. It is not a roadway cover unless your own concrete design and reinforcement make it one — and that is your engineering decision, not a property of the mould.

Second, when a cover has cast-in drainage holes, the hole dimensions describe the void, not the spacing. On the five-hole Ø 80 cm cover the openings are Ø 22 × 4 and Ø 20 × 3 — those are the sizes of the holes themselves. Buyers occasionally read such figures as a hole pitch and then find the pattern does not match their local standard. If a standard fixes your hole layout, send the drawing: hole geometry is the cheapest thing in the world to change before tooling is cut, and among the most expensive afterwards.

3. Shaft ring bricks: one mould equals one diameter

Circular manhole shafts are built from curved bricks. Each mould is cut to a single arc, and that arc is what makes a course close into a true circle. The consequence catches people out: the number of bricks per course is not a choice.

A Ø 90 cm mould cannot build a Ø 110 cm shaft. The bricks will not meet, and there is no site remedy short of cutting every unit. Projects that mix diameters need one mould per diameter — which is entirely normal, and mixed-SKU shipments are standard for us.

The upside is leverage. One mould is reusable for hundreds of pours, and casting bricks locally removes the freight cost of shipping finished concrete rings, which is where most of the money goes on imported precast chambers.

4. The half-metre mistake: inner diameter is not excavation width

Every diameter above is the inner diameter — the clear bore a worker climbs down. Outer diameter is the bore plus twice the wall:

• Ø 110 cm bore + 2 × 24 cm walls ≈ 158 cm outer
• Ø 70 cm bore + 2 × 17.5 cm walls ≈ 105 cm outer

Trench width, shoring and lifting clearance all come off the outer figure. Size the excavation from the bore instead and you are short by nearly half a metre on the large diameters — discovered, invariably, with the digger already on site. Always state which figure your drawing uses.

5. Rectangular chambers: straight and corner wall bricks

Not every chamber is round. Valve pits, meter boxes and larger junction chambers are often rectangular, and those are built from straight wall bricks with corner units to turn the corners.

• 30 × 15 × 17.3 cm interlocking brick — tongue 11.5 × 4.5 cm, groove 10.3 × 3.3 cm, so courses key into each other instead of relying on mortar alone for alignment.
• 32 × 18 × 17.3 cm corner brick — turns the corner at the same 17.3 cm course height as the straight unit, so courses stay level around the chamber.
• 40 × 30 × 19 cm brick — a heavier unit for larger chambers and thicker walls.

Keep course heights consistent within one chamber. Mixing a 17.3 cm brick with a 19 cm brick in the same wall forces a packing course somewhere, and that joint becomes the leak path.

6. What to send for a quote

Six figures, all from the same drawing, are enough to confirm whether a catalogue mould fits or whether an arc has to be cut new:

• Shaft inner diameter — or chamber length × width if rectangular
• Wall thickness (brick width) your design calls for
• Course height — 20 cm is standard for ring bricks
• Cover size and thickness, and whether the frame is cast too
• Drainage-hole count, size and layout if a standard fixes them
• Number of chambers, destination country, and whether diameters are mixed

A clear photo of the brick or cover you want to reproduce, with dimensions written beside it, is worth more than a paragraph of description.

Frequently asked questions

Do I need a frame mould as well as a cover mould?

Only if the frame is being cast in concrete. Where the site already has steel frames or existing concrete seats, the cover mould alone is enough, but the seat opening must be measured first so the cover is dimensioned to drop in. When both parts are cast, order them as a matched set so seat clearance is designed in rather than ground off afterwards.

How many shaft ring bricks are needed per course?

The mould decides, not the site. A Ø 70 cm shaft takes 7 bricks per course, Ø 80 cm takes 8, Ø 90 cm takes 9 and Ø 110 cm takes 11. Each mould is cut to one arc, so the pieces only close into a true circle at their own diameter.

Is the quoted diameter the inner or the outer diameter?

Inner — the clear bore of the finished shaft. Outer diameter is the bore plus twice the brick width, so a Ø 110 cm shaft with 24 cm bricks measures about 158 cm outside. Excavation and shoring are sized from the outer figure.

What load class do concrete covers cast in these moulds achieve?

Load class is a property of the finished concrete, not of the plastic mould. It comes from mix design, reinforcement and slab thickness. A 5.5 or 6 cm cover section is typical for pedestrian and light-utility duty; trafficked covers need a thicker reinforced section designed by the buyer.

Can ring brick moulds be made for a diameter that is not stocked?

Yes. Supply the inner diameter, wall thickness and course height from one drawing, and the arc and piece count are set so the ring closes exactly. Odd diameters are routine; mismatched figures from different drawings are the only real problem.

Related pages

• Manhole cover, sewer cover and well frame moulds — square 50 × 50 × 6 cm, rectangular 60 × 40 × 6 cm, round five-hole Ø 80 × 5.5 cm, cover + frame set, Ø 68 cm frame
• Shaft ring brick and well wall brick moulds — Ø 70 to Ø 150 cm ring bricks, straight and corner wall bricks
• Drainage channel moulds — the pipe runs that connect the chambers
• Cable trench moulds — utility trenching in the same networks

Need moulds for a manhole project? Send the shaft drawing or a photo with dimensions on WhatsApp or through the enquiry form. We will confirm the arc, piece count and demoulding before quoting.