F Ball - Stopgap 850 Exterior (25kg) Exterior Floor Smoothing Compound

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F Ball - Stopgap 850 (25kg)
  • 10 items +    £42.22
  • 25 items +    £41.02
  • Available for Next Day Delivery
  • FREE Delivery when you spend over £100

F Ball - Stopgap 850 Exterior (25kg) Exterior Floor Smoothing Compound

STOPGAP 850 is a non structural exterior grade smoothing compound for use in light to medium duty applications to smooth and level rough or mechanically damaged concrete or sand / cement screeds. 

STOPGAP 850 is ideally suited for smoothing areas such as balconies, patios, garages and walkways and is unaffected by rain or frost when set and dried. It is also suitable for smoothing subfloors prior to the application of a suitable non-slip coating or external covering such as artificial grass. 

STOPGAP 850 is also suitable for internal application over damp, uneven concrete and sand/cement screeds, prior to application of STOPGAP Waterproof Surface Membranes and STOPGAP ISOLATOR MEMBRANE. 

STOPGAP 850 can be left as a stand-alone exterior wearing surface. To give a more natural surface finish and to reduce the potential for slip, if left uncovered, it is recommended that a scratch coat is applied to the surface and brush finished to a textured profile. 

STOPGAP 850 can also be pump applied up to 900m2 per day, dependent upon manpower, thickness applied and equipment used.

Technical Information:

  • Appearance: 25kg Lined paper sack
  • Working Time @ 20°C: 10-15 minutes
  • Walk on hardness time @ 20°C: 2 hours
  • Consumption per mm thickness: 1.72 kg/ m²
  • Application thickness: from 5-15mm



A 25kg bag of STOPGAP 850 mixed with 4.25 litres of clean water will cover approximately 3m2 at a thickness of 5mm. 
NoteCoverage rates for 5-15mm are based on 4.25 litres water addition and up to 50mm based on 4.0 litres water addition. These figures will vary according to the condition 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 5mm to 15mm. For best results, an overall thickness of at least 5mm should be maintained when used as an exterior resurfacing compound. 

STOPGAP 850 can also be applied to slight gradients. To ensure the consistency is suitable and reduce the flow properties, we recommend reducing the water content to 4.0 litres to produce a stiffer consistency. Further reductions can be made if required e.g. at increased thicknesses, but we would recommend no lower than 3.75 litres of water per 25kg unit. 

STOPGAP 850 is self-smoothing, but should any imperfections remain they can be removed by rubbing with a carborundum stone when the compound will accept foot traffic - typically 2 hours after application at 20°C. This time will be extended with reduced temperature i.e. approximately 4 hours at 10°C.

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

Scratch Coat:

To achieve a scratch coat, mix 25kg of STOPGAP 850 with 4.25 litres of water and apply to freshly set material. Pour the material onto the surface and spread thinly using a steel trowel across the surface to leave a textured appearance. Alternatively a broom finish can be used if required.


Drying is dependent on the absorbency of the subfloor, ambient temperature and humidity. Where a floorcovering is being bonded onto the subfloor, at a nominal 5mm thickness, STOPGAP 850 will be ready to receive most floorcoverings or coatings after 24 hours. 


The applied material should be protected from sun whilst applying and drying – if necessary, temporary shading / protection should be considered. Do not apply in excessively windy conditions as this can affect the surface drying and the finished appearance. Ensure the surface cannot be contaminated from loose debris – e.g. leaves, litter etc. as this can dry into the surface of the material. Do not apply in rain or when rain is forecast or in frosty conditions – if necessary, temporary protection should be installed. Protect from frost while the material is drying. New concrete should be allowed to cure for 28 days before the application of STOPGAP 850. This product is not suitable for application to tarmac or asphalt subfloors. 


Suitable steel smoothing trowel, spiked roller, mixing bucket, electric drill and power whisk. 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. When stored correctly, as above, and used within 6 months of the date shown on the packaging, the activity of the reducing agent added will be maintained and this product will contain, when mixed, no more than 0.0002% (2ppm) soluble chromium (VI) of the total dry weight of the cement.

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 £120 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