Asphalt “cutback” adhesive is an almost outdated product that was used for the last half century for installation of vinyl asbestos tile (va tile), vinyl composition tile (vct), and asphalt tile.
The term “cutback” refers to the asphalt bituminous resin in the adhesive, which was thinned with a solvent (generally naphtha). Olefin fiber is now used in formulating asphalt resin adhesives, instead of asbestos. Cutback adhesives made with asbestos were taken off the market in January 1983 due to asbestos regulations.
Fiber is included in the product to allow the asphalt adhesive to maintain the ridge left by the trowel. Otherwise, the adhesive would self-level. Mixing of the adhesive is important before use as the asbestos fibers would settle to the bottom; and olefin fibers would float.
Cutback also came in different working times, which was controlled by the combining of hard and soft asphalt bituminous resins. Cutback was kept active by the plasticizers in the tile. This is why the adhesive would transfer to the back of the tile, unlike the pressure sensitive adhesives used today. Over time, the cutback adhesive would dry and turn brittle.
When determining tile bond it is necessary to check the adhesive. The best way is to remove a tile and take a pocket knife and scrape the cutback. Active cutback will remain in an elastomeric state. Inactive cutback will be scaly and brittle.
When dealing with cutback, it is always necessary to know if it contains asbestos or not. Testing must be done by a laboratory as you cannot visually identify asbestos. To find a local testing lab check the Yellow Pages or Internet under “Analytical Laboratories.” If the adhesive is found to contain asbestos, it must be abated to local standards.
If there is no asbestos contained in the adhesive, there are three ways to handle the removal of cutback from a concrete slab: Adhesive removers, encapsulating the cutback residue with a membrane, or using a cementitous barrier coat.
Adhesive removers are widely used and can create a lot of problems if not used properly. Before using an adhesive remover consider the porosity of the concrete, absorption of the concrete, and temperature.
The length of time the remover sets on the concrete will determine the amount of absorption into the concrete and the depth of penetration. Before applying the adhesive remover, scrape up as much of the excess adhesive as possible. This can be done mechanically or by hand, depending on the size of the area. The less adhesive remover you use, the better.
One problem with using an adhesive remover is, if the penetration is too deep, the cleaning process will not neutralize the adhesive remover. Instead, the adhesive remover will resurface at a later time and attack the new adhesive. The key to successful removal is to get the adhesive removed as soon as possible with little or no penetration.
The porosity of the concrete will determine the time the remover should set on the slab’s surface. Once the adhesive remover is removed, the clean-up should be started immediately. The clean-up process should be a combination of hot water and a degreasing detergent. The solution should be applied to the slab, then the slab should be scrubbed, immediately wet vacuumed and rinsed with clean potable water, then thoroughly wet vacuumed to remove any water. The slab should be allowed to thoroughly dry to prevent any moisture from attacking the new adhesive.
The major concern: Has the adhesive remover been completely removed? It is difficult to make that determination. If there is any adhesive remover left in the concrete it is generally down in the slab and is not visible.
The second method is to use a membrane to encapsulate the cutback residue. This is done by removing the cutback adhesive to a thin residue. Use a power scraping device to achieve this. All puddles, trowel ridges and excess adhesive need to be removed -- leaving the surface of the concrete with a stained appearance.
Once the power scraping is complete the concrete’s surface can be coated with an encapsulant and allowed to dry. The encapsulants, which are available from adhesive manufacturers, will coat the thin residue of cutback left on the concrete surface. This coating will render the slab non-porous and require the installation of resilient flooring to be installed over the slab, as though the slab is non-porous.
The use of a cementitous barrier coat is the final option. It also requires the cutback adhesive to be removed down to a thin residue. This thin residue can then be coated with a thin layer of cementitous underlayment compound. Depending upon the material being used and the underlayment, the thickness can be anywhere from 1/16” to 1/8”.
The underlayment applied will usually require a primer and sometimes an additive mixed into the underlayment. Make sure to not overwater the barrier coat mix, as overwatering will cause it to fail with future traffic.
All three methods of removing cutback adhesive require a lot of attention to detail. Caution must be used when using an adhesive remover, as it has the highest failure rate. If you use that method, be sure there is no residual adhesive remover left in the concrete – otherwise it will surface later and attack the new adhesive.