Some years ago I built a temperature-controlled cabinet to cure resins and glued objects as well as to dry painted and varnished items. This is a simple but practical alternative, proven in the unheated workshop and boatyard.

Small repairs to glass-fibre or wood structures need to be made all year round. Epoxy resin has excellent wetting characteristics, cures to a harder solid than polyester and shrinkage is significantly less; generally 1% compared to 6%. In addition it is water and chemical resistant.

Devcon market a 50ml syringe cartridge pack known as 2 Ton Epoxy which can be used as an adhesive or as a filler using added colloidal silica. The twin cartridge pack ensures accurate dispensing of resin and hardener, the first step towards a correct cure. This product has a pot life of 8-12 minutes and a setting time of 2 hours at 23º C.

Chamber temperature relative to air temperature over time

That is a problem in our local climate, especially if working in temperatures of 10 degrees or less. At these temperatures the resin has high viscosity and low wetting ability. In addition the chemical string to forming a solid is impaired. A constant temperature of around 20º C is needed to achieve a satisfactory cure. Heat guns and hairdryers can be used but there is a danger of damaging surrounding materials and cooking the epoxy, creating an exothermic state and destroying its performance. An alternative is to use a good old-fashioned hot water bottle…yes, really. It warms the prepared area and the resin during mixing, and maintains a constant temperature during curing (see chart).

Here is a shopping list for a good cure, with suggested suppliers:

  • 1 pack of Devcon adhesive (model shop / Amazon)
  • 1 small pack of colloidal silica (chandlery / Amazon)
  • 1 jacketed 2-litre hot water bottle (Wilkinson / Argos)
  • 1 small tub of putty and 2 pieces of 3mm window glass each 120 x 200 mm - one is a spare (Roman Glass should oblige)
  • 1 roll of insulation tape or similar
  • 1 pack of wooden lolly or mixing sticks (Lakeland / Amazon)
  • 1 old bath towel or fleece jacket

Prepare the area to be repaired or bonded by sanding, filing or scraping making sure broken fibres and loose material are removed. Degrease the area with acetone or MitreFast accelerator.

Edge the glass with insulation tape to prevent injury or puncturing your nice new hot water bottle (HWB). Pour ½ litre of cold water into the HWB. Boil a kettle and add ½ litre of hot water to the HWB. Expel the air and screw the cap firmly in place and briefly shake the bottle. This mixture will achieve a temperature of about 30º C. Place a piece of absorbent kitchen paper over the prepared area and place the HWB on top. Slip one piece of glass and the Devcon cartridges under the flap of the HWB jacket, place the towel loosely over the top, refill the kettle, make some tea and sip leisurely for 20 minutes or so. By now the resin and glass plate will have warmed sufficiently for efficient mixing. Squeeze an appropriate amount of resin and hardener on to the centre of the glass plate. Mix thoroughly then part off about 10% to one side. This is to wet out the repair or bonding area. Add colloidal silica to the larger resin quantity to create a thick homogenous paste, mix thoroughly.



Air temperature at start


HWB temperature at start


Epoxy mixed on glass plate

Remove the HWB and paper from the prepared area. With the sharpened end of the mixing stick, wet out the prepared area with a small amount of the reserved resin. Add the thickened paste carefully until it is flush with the surface.

Now for the cunning part. Form sufficient putty into a snake about 2 cm thick and long enough to make a rectangular ring on the glass outer edge and on the same side as the mixed resin. Turn upside down and press lightly over the active area. Place the hot water bottle on the glass and again cover with the bath towel. The temperature inside the chamber will be about 20º C. Leave to cure completely.



Putty creating curing chamber


Chamber temperature at start


Chamber temperature at end

Congratulations. You have just built a working, re-usable temperature-stable endothermic curing chamber for about £10.00.

Quick tips:

  • Wood dust can replace the silica as a filler; mix in a sheltered area.
  • Pigments can be added to the epoxy.
  • Keep the epoxy cartridge in a sealable (sandwich) bag to avoid leaks.
  • Remove putty stains with white spirit or Mitre Fast accelerator.
  • If it is very windy, tape a cardboard box over the HWB to reduce heat loss.
  • Devcon data sheet:


Coming next… finishing small area repairs