The Marnham Building, Mill Hill School

The Marnham Building at Mill Hill School was refurbished as part of a major project being carried out at the school by Mansell. The basement of the building had damp problems with the floor slab, the previously painted brick walls and the concrete filler joist soffit below an external pedestrian walkway. The refurbishment of the area was planned to provide a future teaching facility.

Following opening up of the soffit and investigation we were awarded a design and build contract for the repair and strengthening of the defective filler joist steels and concrete surround. Steel joists were grit blasted and 55m of weber.tec force carbon fibre reinforced plates were bonded to the underside with their EP structural adhesive.

Repairs were completed with weber.cem hand applied polymer modified repair mortars. The external walkway above was treated with a Tor coating to provide a waterproof non-slip membrane.

Grit blasting techniques were used to remove defective coatings from the basement walls, to etch the glazed brickwork beneath and to also prepare the floor slab prior to the application of a waterproof membrane.
In addition a chemical dpc was injected to the internal walls using Remmers Aida Injection Cream and defective pointing made good with a polymer modified repair mortar to provide a suitable background for the waterproof render treatment.

15,000kg of Weber Motex Dry-rend waterproof render, consisting of bonding coat and 2 further coats to a total of 12mm, were applied to the prepared surfaces with a fillet and mastic detail at the floor junction.

Finally the prepared floor was treated with 2 coats of RIW Toughseal and a self-levelling screed to protect the membrane.

The Main Contractor’s finishing trades then completed the conversion to classroom conditions with new blockwork and plaster walls and joinery works.

The Main Contractor’s finishing trades then completed the conversion to classroom conditions with new blockwork and plaster walls and joinery works.

A31 Bridges

We initially carried out site investigation, testing and laboratory analysis of concrete samples to 3 bridges carrying the A31 over a bridleway and 2 sections of the River Wey at Farnham for Surrey County Council. Following this a Specification and Bill of Quantities was prepared for the Client.

The conclusion of the investigation work was that all 3 bridges required concrete repair and protective coatings and strengthening was required to one of them to meet the 40 tonne vehicle loading standards.

The following year we were awarded the contract, through the client’s term contractor Ringway Highway Services, to carry out the full proposals that included design & installation of carbon fibre composite plate bonding strengthening.

A full birdcage scaffold was used to access the soffits and walls of the bridleway bridge whilst maintaining access below for pedestrians and horses.

Concrete repairs were carried out using polymer-modified hand placed repair mortars and flowable concrete supplied by Sika Ltd. Coatings ranging from a clear anticarbonation to a siloxane water repellent impregnation were applied where appropriate.

The second bridge had limited headroom and scaffold was not appropriate. Here the work was carried out by operatives wearing waders and using small scaffold storage platforms to keep plant and materials clear of the water.

Strengthening to the third bridge was carried out on the soffits using Sika CarboDur plates. Tony Gee & Partners carried out design on our behalf working to the Client’s brief.

The concrete soffit was prepared by light scabbling and over 300m CarboDur S1012 plates were cut to length by guillotine. Epoxy resin was applied to both the prepared concrete surfaces and to the plates by drawing them through a gauge box. The plates were then offered up by hand to the soffit and finished by a light roller extruding excess resin.

This method of strengthening permitted traffic to continue to use the dual carriageway above giving minimal disruption to the traffic.

60 Charlotte Street

60 Charlotte Street

The 60 Charlotte Street project in west London consisted of the refurbishment of the existing reinforced concrete framed two-storey podium block and seven-storey tower block.

The main contract works involved a full strip out of the existing finishes and plant, construction of additional floors at podium and roof levels, structural alterations to the building, new cladding and glazing, roofing, M & E works and finally fitting out.

We were awarded the structural alterations package by Galliford Try which included: –

  • Strengthening of existing slab edges
  • Filling of redundant voids to the floors
  • Concrete repairs to the structure
  • Forming new service risers with associated structural steelwork
  • Forming new openings in walls

Consideration was given to the use of composites; however, this method was proven not to be appropriate in this situation.

In order to progress early procurement of the steelwork we removed the existing finishes to establish the structural dimensions.  Then whilst our sub-contractor detailed and fabricated the steelwork we carried out repairs to redundant service holes, structural investigation sampling and demolished areas were carried out using polymer modified mortars and a flowable micro concrete.

The need for new steelwork was twofold. Firstly slabs were strengthened and dry packed with shrink compensating grout prior to removal of walls and upstands by Galliford Try. This in turn allowed them to proceed with the extension to the podium block and demolition of walls and slab edge upstands.

Secondly new risers were required for the full height of the tower.  Prior to cutting the holes new trimmer steel was erected and subsequently dry packed.  We employed scaffolding and diamond drilling subcontractors for crash decks and for forming the holes.  Cut edges to the slab were repaired using a polymer-modified mortar.

Over 40 tonnes of steelwork were erected with 25 tonnes of grout, concrete and mortar used over a 20-week programme.