Boss UltraPoxy 1ltr pack

$53.95 excl GST

  • Permanently flexible – Withstands expansion, contraction, and seasonal movement of timber weatherboards.
  • Compatible with any substrate – Recommended for timber, fibre cement, concrete, and metals.
  • 100% moisture proof – Solves common problems with cracking, splitting, and moisture ingress.

Download PDS and SDS Part A and SDS Part B

59 in stock

SKU: BOSS16501 Categories: , Tags: , , , ,


Boss UltraPoxy is a high-performance epoxy filler specifically formulated for filling of nail holes in timber weatherboards where seasonal expansion, contraction, and moisture ingress may be present.

Quick facts:

Boss UltraPoxy is a superior 100% solids epoxy fairing & filling compound with exceptional bond strength to timber, fibre cement, metals & plastics. Measure out equal parts of resin & hardener by volume onto a broad-knife and mix slowly until colour is uniform. Allow 4 hours cure at a substrate temperature of 20°. Curing time is reduced with extra mixing. Do not use below 6°. Ensure full cure before sanding. No spot priming required.

Product Features:
  • Pre-gelled – easy to mix and apply.
  • Permanently flexible – withstands natural seasonal movement of timber.
  • Handy 1 litre kit size, consists of 500ml hardener & 500ml resin. Mixing ratio 1:1.
  • Will not shrink – expands slightly as it cures.
  • No spot priming required prior to topcoats.
  • 100% moisture proof.
  • High impact resistance.
  • Easy sanding.

Boss UltraPoxy has been specifically designed for filling nail holes on timber weatherboards and other exterior timber profiles. Also useful in larger cavities, for example where rotten timber or knots have been removed, or where cracks & joints have opened. Can be used on a variety of other substrates including fibre cement, plastics, fibreglass, and metals. Check for any warranty issues with the substrate manufacturer before use. May not be suitable for use in cavities less than 3-4mm in width or depth. See Limitations below.


The Boss UltraPoxy system does not behave similarly to polyester fillers like standard builders’ bog. It requires a minimum volume, temperature, and time period to reach full cure before sanding. See limitations below.

  • Timber, Particleboard & MDF: Ensure holes are clean and dry. Pre-priming inside the holes with an oil-based primer neither enhances nor inhibits the performance of Epoxy Filler in any way, but where efficacy of timber treatments is a concern pre-priming inside nail holes with an oil-based wood primer offers increased protection against timber decay and can be very advantageous in humid environments.
  • Metals: Degrease surfaces if necessary. Use an abrasive cleaning method such as blasting, sanding, grinding, wire brushing, etching etc to provide a clean bright surface.
  • Fibreglass & GRP: Degrease and cross hatch sand with 60-100 grit paper. Polyester must be fully cured. Take special care to remove any surface wax. Remove sanding dust.
  • Fibre cement boards & panels: Ensure holes are clean and dry. Take extra care to remove dust so that the filler can adhere to solid substrate. Where cohesion of the substrate is a concern pre-priming the nail holes with a specialized fibre cement sealer is recommended.
    Measure out equal quantities by volume onto a board-knife and mix carefully and slowly until colours are uniformly blended. Do not overmix or undermix. Altering the mixing ratio will result in a slower cure and lower physical strengths. Apply immediately to the clean, prepared substrate. Wait for full cure before sanding. Apply 2 topcoats of quality acrylic at a minimum dry film build of 25 microns per coat.
Recommended Primers and Undercoats:
Limitations and Recommendations:
  • May not reach full cure in holes smaller than 3-4mm in diameter and depth. A minimum mass is required to self-generate enough heat to complete the chemical curing process within a reasonable time. As a basic rule, a standard jolt head nail punched to a depth of 4mm will have a high enough volume to reach full cure at normal temperatures within a 4-hour time frame. Hotter days and higher volumes reduce cure time, colder days and lower volumes extend cure time. Application under 6 degrees is not recommended.
  • Substrate temperature must be considered. Even when the atmosphere is warm, the substrate may remain cold, particularly in shaded areas. Cold substrates will extend cure time or may halt it altogether.
  • Over-mixing or under-mixing will affect performance. Over-mixing will cause the filler to cure prematurely leaving insufficient time for application. Under-mixing will extend the cure time, or possibly prevent cure altogether. Mixing should be done slowly and deliberately until the two colours are uniformly blended. Hurried haphazard mixing should be avoided.
  • Mixing ratio must be accurate. A ratio of 50/50 is optimal. Inaccurate ratios will result in imperfect curing.
  • Some expansion may occur after sanding if full cure has not been achieved. Sanding prematurely is to be avoided. If the curing process is interrupted by a drop in temperature, it will restart when the temperature rises. Sanding generates heat and will restart the curing process resulting in further expansion of the product and requiring additional sanding to achieve a level surface. Wait until the temperature rises and do not sand until full cure has been achieved. Careful use of a heat gun may be helpful in slow-to-cure areas.
  • May not be suitable for use with paint colours darker than LRV45%. Check the substrate manufacturers specification before deciding on colours. As a rule, colours darker than LRV45% are not recommended on timber substrates. Substrates painted with colours darker than the substrate’s recommended LRV limit may warp or expand, causing greater distortion and swelling of the filler than is aesthetically acceptable. Use of epoxy filler is not recommended in such circumstances. If in doubt, testing of a few holes with the desired colour is recommended prior to commencement of work to ensure aesthetic expectations are met.
  • Do not store in direct sunlight or near other sources of heat.
  • Epoxy resins and their curing agents can cause skin irritation. Use disposable plastic gloves to avoid skin contamination. Epoxy solvent should never be used to wash hands.
  • Ensure adequate ventilation and use a respirator and safety glasses when sanding. Do not breath sanding dust. Rinse eyes with water and wash skin with soap and water.


Download PDS and SDS Part A and SDS Part B

UltraPoxy and the Boss Fillers range is available from the following stockists:

Additional information

Weight 1.6 kg
Dimensions 11 × 11 × 18 cm