F Ball - Stopgap 300 HD (25kg) Heavy-Duty Floor Smoothing Underlayment

Bulk Buy Discount
In stock
  • 10 items +    £38.88
  • 25 items +    £37.68
  • Available for Next Day Delivery
  • FREE Delivery when you spend over £125

F Ball - Stopgap 300 HD (25kg) Heavy-Duty Floor Smoothing Underlayment

STOPGAP 300 is a fast drying self-levelling smoothing underlayment suitable for use in light to heavy-duty areas for preparing sound absorbent and non-absorbent subfloors prior to the installation of new floorcoverings. 

STOPGAP 300 is dimensionally stable and is supplied as a pre-blended dry powder designed for application between 2 - 20mm. It is protein-free which allows it to be used in biologically sensitive areas such as hospitals.

STOPGAP 300 is suitable for use over a wide range of subfloor types including sand/ cement screed, concrete, calcium sulphate (e.g. anhydrite), minimal adhesive residues, sound asphalt, granolithic, terrazzo, epoxy and polyurethane resins, ceramic and quarry tiles and STOPGAP waterproof surface membranes.

Technical Information:

  • Appearance: Lined paper sack
  • Consumption per mm thickness: 1.67 kg/m2
  • Working Time @ 20°C: 20 - 30 minutes
  • Walk on hardness time @ 20°C: 90 minutes
  • Coverage (approx.): A 25kg bag of STOPGAP 300 mixed with 5.5 litres of clean water will cover approximately 5.0m2 at a thickness of 3mm.
    Note: Coverage rates will depend on the condition and absorbency of the subfloor


Pour the mixed material onto the prepared subfloor and allow to flow and attain a smooth finish. Minimal work with a smoothing trowel is required. The use of a spiked roller will help eliminate entrapped air and smooth out flow lines to give a more uniform surface appearance.

The mixed material should be applied at a thickness between 2mm to 15mm, but can be taken down to feathered edge if required. For optimum smoothing and levelling characteristics, an overall thickness of at least 3mm should be maintained. 

STOPGAP 300 is self-smoothing, but should any imperfections remain they can be removed by rubbing with a carborundum stone when the underlayment will accept foot traffic - typically 90 minutes after application at 20°C. This time will be extended with reduced temperatures i.e. approximately 3 hours at 10°C.

For any areas under question please consult the F Ball Technical team.


Drying is dependent on the absorbency of the subfloor, ambient temperature and humidity. On absorbent surfaces, at a nominal 3mm thickness, the compound will be ready to receive resilient floorcoverings after 6 hours. For greater thicknesses and for application onto nonabsorbent surfaces, we would recommend that resilient floorcoverings are installed after 12 hours.


Suitable steel smoothing trowel, spiked roller, mixing bucket, electric drill and power whisk or suitable pumping equipment. Wash tools with water immediately after use.


This product must be stored under cover, in unopened bags clear of the ground in cool dry conditions, protected from frost and excessive draught. Dampness will reduce the shelf life and may cause the powder to set in the sack

Shelf Life:

6 months in unopened bags and stored under good conditions.

Delivery Information

We aim to dispatch all orders within 2 working day of receipt. Occasionally public holidays, weekends, weather events, or extremely busy periods may result in extended delivery times. In these circumstances, we will endeavour to communicate with you about the delay and resolve and resulting issues.

Please note that we do not make delivery date promises, however:

- Orders placed before 1pm on a weekday will be processed the same day.

- Orders placed after 1pm on a weekday will be processed the following morning. 

- Orders placed after 1pm on Thursday will be processed and dispatched the following day and out for delivery the following Monday (if Next Day Delivery is selected).

- Orders placed after 1pm on Fridays will be processed and dispatched on the following Monday.

For more information about our Shipping & Delivery services click HERE


UK Mainland Delivery Options:


Free Delivery: Applicable for orders of £125 excl. VAT and above
(Monday – Friday, excluding public holidays)


Collect From Store: 41 Markfield Road, London N15 4QA
(Monday – Friday, 9am–5pm excluding public holidays)


Standard Delivery: 3-5 Working Days
(Monday – Friday, excluding public holidays)


Express Delivery: Next Working Day
(Monday – Friday, excluding public holidays)

Out Of Zone Delivery Surcharges:

Isle of Wight

£12.50 per item (3-5 Working Days)

Isles of Scilly

£12.50 per item (3-5 Working Days)

Northern Ireland

£25.00 per item (3-5 Working Days)

Western Isles

£25.00 per item (3-5 Working Days)

Shetland Isles

£30.00 per item (3-5 Working Days)


£30.00 per item (3-5 Working Days)

Isle Of Man

£30.00 per item (3-5 Working Days)

Channel Islands

£30.00 per item

Republic of Ireland

Not Available


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