Article - Timber-Resin Splice (TRS)

Development - 1995 to 2013

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Article - How the Timber Resin Splice has been developed since its invention


When faced with a decayed structural timber in a building Architects and Engineers tend to specify complete replacement with steel, or in a few cases they may opt for an epoxy resin repair, cast in-situ, as a solid block.

The Timber-Resin Splice (TRS) was invented in the early 1990's with the intention of reducing the volume of expensive, petrochemical based resin required to repair large timbers in buildings and to offer an economically viable alternative to complete replacement with steel. It is an economic method of repairing structural timber beams in buildings without large scale opening up or destruction of sound building materials.

The concept of the TRS is simple - replace the rotted end or midsection of a structural timber beam with a renewable resource - timber - and use as little resin and steel as possible, both in the manufacture and the installation of the repair unit.

As the sole UK Manufacture since its inception, Property Repair Systems has taken its responsibility to develop the product seriously.

In common with most forward thinking Manufacturers it has a Policy of Continuous Product Development, aiming to fulfil three criteria;

1. Minimise the consumption of non-renewable materials - resins, composites, steel, pre-glued timbers

2. Reduce the Heath and Safety risks - in production, installation and disposal

3. Reduce the whole life cycle costs of timber repair - labour, resins, composites and steel

To meet these criteria Property Repair Systems has undertaken a program of technical improvement, backed by testing, to try to eliminate the problems of using bulk epoxy resin as a repair material;

1. Minimise the consumption of non-renewable materials - resins, composites, steel, pre-glued reconstituted timbers.

A. Timber components - the smaller the timber section that we start manufacturing from, the more machining, laminating and resin that is required. By sourcing the largest kiln dried timbers available and machining with greater precision, we have been able to considerably reduce laminating energy and resin consumption. What little sawdust waste that is created is recycled as animal bedding.

B. Resin components - epoxy resins were originally used in laminating, bonding-in the steel connectors and in the on-site connection process carried out by the Client's Technicians. We firstly eliminated the epoxy from the laminating process, using a less expensive high strength, waterproof single pack glue, and then from the rod bonding process. Epoxy remains the resin of choice for on-site connection, but we minimise its use through computer-based design of the connecting slots and hope to find a more ecologically friendly material in the near future.

C. Composites - originally the TRS and most other site resin repairs incorporated small diameter (5mm) composite Epoxy-Glass Bars, in bundles, for connection purposes. This is wasteful, but it was also discovered that full wetting out of multiple bars in a hole or slot could not be guaranteed, leading to weakness in the repair. We therefore substituted larger diameter Epoxy Coated Steel Rebar, one per hole. However, the epoxy coating was expensive and not reliable, so a further move was made to Zinc Plated High Tensile Allthread. This has proved to be reliable and economic, but with the rising cost of metals we must again move forward and a number of 'greener' materials are in prospect.

D. Pre-glued Timbers - we have experimented with a variety of reconstituted timbers, but the energy equation for renewable virgin timber is still considered to be more favourable and because of the stock sizes we found that these man-made timbers required either more expensive lamination or more waste in cutting than locally available stock kiln dried lumber.

2. Reduce the Heath and Safety risks - in production, installation and disposal

A. Manufacturing environment - despite rigid adherence to the manufacturer's safety instructions all our workshop staff have eventually become highly sensitised to epoxy and cannot even stay in a room with an opened pot. They have worked with epoxy in well ventilated spaces, wearing long arm gloves, plastic aprons and masks, but have still been affected by the vapour, eventually becoming physically sick, dizzy and suffering from skin rashes and blisters. We therefore had to remove all epoxy from our manufacturing processes and since then there have been no new outbreaks of illness. We cannot emphasise too much the need for great care in handling epoxies - I am one of the affected ones and I can vouch for the effects.

B. On Site environment - we strive to minimise the use of epoxies in the installation process. The use of paddle mixed products keeps the Technician further away from the vapour than when using small pack, hand mixed products and Technicians generally have short, intermittent exposure compared with Manufacturing Staff. Nevertheless, we continue to seek alternative formulations so that one day we can further reduce the health risks.

C. Disposal - we had great difficulty in storing and disposing of uncured epoxy residues in pots left over from hand mixing. In the Workshop we have eliminated this process and the products. To reduce this problem on Sites during the TRS installation we mainly specify a paddle mixed, bulk resin product, so that only cured resin remains in the bulk pot. Small residues of liquid epoxies still remain in the component liquid containers - until we can eliminate the epoxy from the TRS Kits this remains as a waste disposal problem.

3. Reduce the whole life cycle costs of timber repair - labour, resins, composites, steel, disposal

A. Labour - minimum machining, minimum lamination, simplified bar bonding

B. Resins - eliminate epoxies wherever possible, minimise their use where essential

C. Composites - eliminate if possible

D. Steel - minimise for now, seek to eliminate in the future

E. Disposal - eliminate the liquid epoxy residues

Obviously, 'whole life costing' is a complicated business and we need to balance our consumption of a small amount of epoxy and steel against the vast amount of labour, energy, steel and other building materials that are routinely thrown away when building timbers are scrapped. There is still a substantial amount of Research and Development to carry out in order to reach our goal - zero scrapping of structural timbers. We have already made a considerable investment over the last 12 years and we hope to continue to develop this excellent concept.

David Moore

Partner, Property Repair Systems



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Site written by: David Moore

David Moore, B.A. (Hons.), C.T.I.S., C.R.D.S. Technical Author