Property Repair Systems

Repairing structural timber joists

This project is sponsored by Property Repair Systems

Summary: Repairing and treating floor timbers - joists, wall plates and carrier beams.

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If you need any help with any type of floor repair or timber treatment, Property Repair Systems expert staff will be pleased to give you completely free, no obligation advice on 01626 336180. The information you need may be in the project below. If not, call them.

Damage To Timber Floors

There are three main types of damage, but they are all caused by one problem – damp. Timber will start to decay at above 18% moisture content (in average softwood species, like an ordinary Pine), so elimination of dampness is our main concern.

  • Wet rot – does not spread beyond the area of wetness, localised damage to timber
  • Dry rot – can spread well beyond the area of wetness and cause serious damage to timber
  • Insect attack – mostly in damp areas, can spread beyond, but mostly slow acting
Damaged timber Joist caused by damp

Damaged timber Joist caused by damp

Damage to brick caused by damp

Damage to brick caused by damp

Repairing Joist Ends

Joist ends become damp because they rest inside or close to the support walls and easily absorb water from damp soil, humid air or water leaks. Any repair or treatment must include attention to the Air Bricks (See our project covering air bricks and vents).

The easiest way to repair joist ends is to fit joist repair plates. These come as a pair of L shaped, metal plates complete with screws and instructions. They have the advantage that joists are extended back into or onto the original bearing, whereas repairs with bolted-on pieces of wood mean that you need a new bearing area, or a more complex solution using three pieces of wood.

Joist repair plate

Joist repair plate

Fixing joist repair plate on to joist

Fixing joist repair plate on to joist

Treating Joist Ends

The end grain ‘cut’ and the support area should be thoroughly treated with Boron Ultra Gel and a piece of damp proof material, like DPC plastic, placed underneath, to prevent damp from being transferred. Use pre-treated timber if possible. Clean out the Air Bricks and fit additional to allow about one brick per 2.25 metres of outside wall. This will only work effectively if the external ground level is well below the air bricks – built-up soil, tarmac or pathways can easily prevent air flow.

Repairing Carrier Beams

These are usually larger section timbers than the joists and may not be suitable for the Joist Repair Plate system. If larger than 10 inch x 2 inch (250mm x 50mm) then you will need to use the Timber-Resin Splice system instead. This provides a new piece of timber, with bars pre-bonded into one end, ready for you to fit using the resins provided in the kit.

During the repair to the ends of your joists it may have been necessary to cut off a section of the joist. When it comes to putting the joist back it may now be a fair bit shorter than it was meaning that you are unable to reach the wall plate or mounting point of the beam. If this is the case you can use joist splice plates to extend the joist to the wall plate and mount it back in position.

Treating Carrier Beams And Wall Plates

In order to repair damaged wall plates or carrier beams they will need trating with with Boron Ultra Gel or similar product. They will need to be injected with a Boron Ultra Paste or similar via 10mm diameter holes that will need to be drilled.

If permanently damp, like some embedded wall plates, such timbers may justify the insertion of Boron Rods, as well as Paste, both placed in the same holes to work together. These Boron based materials dissolve inside the wood and create a reservoir of Borate, which kills and prevents any further rot or insect attack.

If you need any further help with any type of floor repair or timber treatment, Property Repair Systems expert staff will be pleased to give you completely free, no obligation advice on 01626 336180.

Don't fancy doing this project yourself? We work with Checkatrade to ensure that we recommend only reliable and trustworthy tradesmen.

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