Solvent-Based Sealer Produces ‘Spider Web’ Effect

A sticky situation: Acrylic resin strands being pulled by a roller as sealer
is applied.

Question:
While I was using a roller to apply a solvent-based acrylic sealer on an outside patio, the sealer came off the roller in long, thin, white strands. Now the sealed surface looks blotchy and uneven. What happened, and how do I avoid it.

Answer:
This is known as the “cotton candy” or “spider webbing” effect. It occurs when the solvent evaporates (flashes off) before the resin (an acrylic in this case) can form its film. This is more likely to happen when one or more of the following conditions exist during roller or spray application of a solvent-based acrylic sealer:• The concrete surface or air temperature is high, above 90 F. • The surface being sealed is exposed to warm, windy conditions.• The sealer is being overworked with the roller.

With any one-part acrylic sealer, the plastic resin needs to wet out (penetrate) the concrete surface and form a film as the solvent evaporates. If the solvent evaporates too fast, the sticky, soft resin is pulled into strands by the roller. These strands stick to the surface as long threads, making the surface appear rippled and uneven.

Temperature and wind are the real culprits behind this problem. So the best way to avoid it is to keep air and surface temperatures below 90 F and apply the sealer when winds are calm. Also avoid overworking the sealer with the roller, and always maintain a wet edge. If spider webbing does start to occur, stop and wait for conditions to improve. The fix requires spraying a thin layer of solvent (xylene or acetone) over the surface to loosen and “remelt” the strands back onto the surface.
February 06, 2006