clay tile moulds and samples, borrowed for research

29.02.15 | material samples

Project Lacey Green

In a couple of week’s time, the RCA architecture department’s annual ‘Work in Progress’ show is opening, a chance to present each design studio’s research half way through the year. ADS6 use this an opportunity to spend some time at the Farm fabricating ideas at a 1:1 scale… perfect timing for the project, as this is exactly what I need to do to start refining the design details. At the start of this week I had a meeting with Jim, the third generation director of G H Matthews brickworks in Chesham. I visited them back in November as part of general research into local industry manufacturing, but now wanted to speak to him specifically about red clay tiles, which are a local vernacular roofing material, and what I’ll be using on the pavilion.  I would like to develop a slightly modified design, prototype the mould at the Farm, and then put them into production at H G Matthews.  Jim explained that roof tiles are not something that the company made traditionally; he started experimenting with them about 10 years ago, in response to the closure of many hand-made tile companies in the UK. He hasn’t done an analysis on the locally used tiles to find out if they were ever made in the area, but in his experience the clay from the surrounding pits is not dense or impermeable enough: tiles made with it crack easily and don’t resist water well. He therefore procured the Wealden clay required from the now defunct Swallow Tiles site in Surrey; Swallow was established in 1860, closed in 2008, and is now being redeveloped for residential use (apparently a common pattern due to the ease in gaining planning permission on brownfield sites).

There have been two or three attempts to put tiles into production at H G Matthews over the past 10 years, and they’ve managed to produce around 200,000…but the process has been difficult, with as many as five tiles wasted for each successful one, so they’ve currently halted production. Essentially it’s a lost art in Buckinghamshire, which he hasn’t been able to perfect, but really wants to – and so seemed very excited about a new commission, especially if it’s approached collaboratively as a shared process of learning. For the size of the pavilion, which has a surface area of about 90 m2, he estimates we would need about 5000 tiles, which is feasible. However, because the production line isn’t already up and running they wouldn’t be able to produce them by April; he thinks May / June is more likely but warned that it could take longer. He suggested completing the roof up to the battens, so it’s ready for the tiles to be laid, and making it water-tight until they’re installed. From my point of view, I think it’s more important to embrace the opportunity to collaborate with him (prototype a bespoke mould at the farm and get them to put it into production) than making sure the tiles are up as soon as possible. However, Jim also proposed an alternative option, which would be to procure them from Aldershaw Tiles in Sussex. In the meantime, I collected some samples of H G Matthews’ tiles, as well as a bunch of old moulds that they salvaged from the Swallows site,  and told him I’d come back with 2-3 prototypes made with the clay that’s already at the farm after the WIP show.

The second area of design development, which is slightly more urgent in terms of time-scale, is the timber frame – the material for which is very generously being donated by Hooke Park as part of the long-term partnership with the AA and the Visiting School program. Yesterday morning Callum (who runs the workshop at the Farm) and I headed down to Dorset to meet up with Matin Self (the Director) and Jez Ralph (the Estate Manager & Developer) to organise the procurement of the lumber, and talk through the fabrication process of the lattice frame structure. They had prepared some sample pieces of Norwegian Spruce and Red Western Cedar, based on the rough dimensions I’d discussed with Steve, the structural engineer. While Red Western Cedar is very durable, it’s not very strong (Jez described it as feeling ‘fluffy’ on the saw mill) – and is typically used for cladding, a good example being the recently completed student lodges at Hooke Park, where the exposed pieces have weathered to a beautiful silvery-grey. Spruce is more commonly used in construction, but would need to be treated with Boron to protect it from decay; something with could do as a spray treatment once the structure has been erected. We worked out we’d need around 400 running meters of material, which is 6 m3 of timber – assuming 50% loss through the milling process, that’s a total of 12 m3 of trees, equating to around 12 whole trees. Jez explained that the cost for spruce at the moment is about £70-80 per m3, but that cost (based on it’s ‘standing’ value) doubles once it’s felled (‘roadside’ value) and doubles again once it’s cut (‘saw-mill’ value). Although, like many other things for this project, it’s being given in-kind, I’m trying to keep track of all the costs to be able to understand the true value of the building.

Timber generally takes about a year to ‘season’ or dry out; the best conditions for this are a covered open-air space with plenty of air movement. The electric kiln is used after timber has partially seasoned – but only for interior joinery (if you kiln the wood until it’s dryer that the outside air humidity, and then use it in an exposed part of the building, it will just re-absorb the moisture). Given construction is due to start in about two months, we’ll be using wet or ‘green’ timber, so the joints will have to accommodate shrinkage over time as the wood dries out. However, the dryer it is the better (as it will be much lighter to lift, and easier to cut) so as soon as Steve and I have resolved the design, decided on the species and figured out the dimensions of the planks we need – we can give Hooke the go-ahead to appoint the felling contractors. In the meantime I need to make some 1:1 mock-ups of the joints to smooth out any design and fabrication glitches… if you’re interested in seeing how they turn out – please come along to the WIP show! (12th – 15th February at the RCA’s Kensington campus)