F. Ball Stopgap F77 is a professional, solvent-free, two-part epoxy resin system that cures to form a high-performance waterproof surface membrane. It impedes residual construction moisture and rising damp in suitable concrete and sand/cement screeds before smoothing compounds, adhesives and floor coverings are installed.
Applied as a single coat, F77 can be used at subfloor relative humidity readings of up to 98% RH. It cures from approximately three hours at 20°C, making it ideal for fast-track domestic and commercial flooring installations where waiting for the subfloor to dry naturally would cause unnecessary delays.
Stopgap F77 is supplied as a pre-measured resin and hardener kit and is available from WWFS in practical 7kg and 14kg sizes.
Always test and record the subfloor moisture level before choosing the application rate. Stopgap F77 must be applied to a clean, absorbent and slightly textured surface. Remove laitance, surface hardeners, adhesive contamination, oil, grease and anything else that could prevent adhesion. Power-floated concrete must be mechanically prepared.
The substrate should have a surface strength greater than 1.5N/mm². The cured membrane must form a continuous, glossy black coating without pinholes, weak areas or missed sections. Never exceed the specified coverage rate, as spreading the product too thinly may prevent it from providing the required moisture protection.
Stopgap F77 is a one-coat system at both application rates. Higher moisture readings require a heavier coat applied with the supplied 1.5mm × 5mm trowel, rather than two standard coats.
Immediately back-roll the applied epoxy with a pre-coated paint roller to flatten the ridges and create an even, continuous and pinhole-free membrane. Where a very absorbent surface leaves a subdued shine, or pinholes or weak areas remain, a second application will be required.
| Product Type | Solvent-free, two-part epoxy waterproof surface membrane |
|---|---|
| Available Sizes | 7kg and 14kg kits |
| Components | Pre-measured resin and hardener |
| Colour | Black |
| Maximum Moisture Reading | Up to 98% RH on suitable cementitious subfloors |
| Underfloor Heating | Up to 90% RH on correctly commissioned cementitious heated screeds at approximately 1.8m² per kg |
| Working Time | Approximately 30 minutes at 20°C once mixed and poured onto the floor |
| Curing Time | From approximately three hours at 20°C |
| Application | Specified notched trowel followed immediately by back-rolling |
| Suitable Substrates | Prepared, clean and absorbent concrete and sand/cement screeds |
| Minimum Substrate Strength | Greater than 1.5N/mm² |
| Indoor Use | Yes |
Use an appropriate calibrated hygrometer to establish and record the relative humidity of the subfloor. The reading determines the required application rate and coverage.
Remove laitance, surface treatments, weak material and contamination to produce a clean, absorbent and slightly textured surface. Power-floated concrete must be mechanically prepared. New concrete and sand/cement screeds should normally be left for at least seven days before preparation and application.
Rough, uneven or damaged cementitious subfloors must be repaired or pre-smoothed before applying F77. Suitable products can include Stopgap 1200 Pro or another compatible Stopgap product selected for the substrate and required depth.
Any smoothing compound installed beneath the membrane must be fully dry and sufficiently strong before F77 is applied. Take care to minimise pinholes in the pre-smoothed surface.
Add all of the hardener to the resin container. Mix using a suitable power whisk and low-speed drill for approximately two minutes, scrape the sides and base of the container, and then continue mixing for a further two to three minutes until a uniform colour and consistency are achieved.
Mix only in full packs. Do not split the kit. Incomplete or incorrectly proportioned mixing can leave soft, uncured areas and render the membrane ineffective.
Once mixed, pour the product onto the prepared floor immediately. Leaving mixed epoxy inside the container significantly reduces its working time.
For readings above 85% RH and up to 98% RH, or commissioned underfloor heating screeds up to 90% RH, spread the membrane using the supplied 1.5mm × 5mm trowel at approximately 1.8m² per kg.
For readings up to 85% RH, use a A2 notched trowel (Bona 200F / A2) at approximately 2.5m² per kg.
Immediately back-roll the applied F77 using a pre-coated paint roller. This flattens the trowel ridges and helps form an even, glossy, continuous and pinhole-free coating.
At approximately 20°C, F77 can cure in around three hours. Cooler temperatures will extend the curing time. Do not proceed until the entire surface is hard, fully cured and tack-free.
Once F77 has fully cured, apply Stopgap P141 Primer neat before installing most Stopgap smoothing compounds.
Typical system:
Prepared cementitious subfloor → Stopgap F77 → neat Stopgap P141 → compatible Stopgap smoothing compound → flooring adhesive → floor covering.
On installations without underfloor heating, Stopgap 1200 Pro can be applied directly to fully cured F77 within 24 hours without P141. Where underfloor heating is present, prime the fully cured F77 with neat P141 before applying the selected compatible smoothing compound.
F. Ball STYCCOBOND B95 wood flooring adhesive may be applied directly to fully cured Stopgap epoxy waterproof surface membranes within 24 hours under suitable conditions, provided the surface is smooth enough and the complete installation meets F. Ball's requirements.
Do not assume a Bona or another manufacturer's adhesive can be bonded directly to F77. Unless the exact combination has been approved by the adhesive manufacturer, use F77 followed by P141 and a compatible Stopgap smoothing compound before applying the selected adhesive.
The correct system depends on the substrate, moisture reading, floor covering, underfloor heating and whether the surface requires repair or levelling. Contact our flooring specialists before ordering if you are unsure which products are required.
Coverage, working and curing times are approximate and depend on temperature, substrate texture, porosity, application technique and site conditions. Never exceed the specified coverage rate. Product specifications and manufacturer recommendations can change, so always consult the latest technical information before use.