Banishing Blisters in a Stampable Overlay
Question:
When I apply stampable overlays I often get blisters ranging in size from a dime to a half dollar. What causes these flaws, and how do I get rid of them after the surface has cured?
Answer:
When a dry cement-based mix of any kind is combined with water, it begins to react as it hydrates, giving off gases (CO2, H20, and others). Most concrete surfaces are porous enough during the finishing stages to allow for these gasses to work their way to the surface and escape directly into the atmosphere. Since stampable overlays are polymer-modified, off-gassing can be more of problem when compared to typical concrete. The polymer (plastic) creates a tighter surface when finished with a trowel. Finishing the surface too early or adding extra water or a finishing aid to help close up the surface can trap gas and create blisters. A second factor that can contribute to blister formation is failing to apply a primer to the substrate before overly application. Not only does the primer act as a glue to adhere the overlay to the surface, it also closes the pores in the substrate and prohibits gas transmission to the overlay.
To prevent blistering, wait a bit longer to finish the surface or cut back on the amount of surface moisture used to aid in finishing. Remember that stampable overlays are porous by nature. Trying to get a tight finish similar to what you can achieve with concrete is not feasible and can create problems, blisters being one of them. If you see blisters forming while finishing, use a sharp-pointed object to pierce the blister and then use a trowel to rework the material back into the surface. If you find blisters after the overlay has cured, try injecting the hollow areas with epoxy or remove the blister and fill the spot with the same overlay material, blending the edges to create a less noticeable patch.
1 Comments:
Great topic and post Chris...
This is a problem that is typical of guys new to the business. Generally, blistering is caused from one of three reasons in thin stamped overlayments.
1. The contractor does not saturate the substrate prior to the application of the bond coat that is installed right before the actual thin stamped material causing the material to dry at the bond point up instead of from the top down. This is so very critical as it is a near must for the material to dry from the top down to ensure proper adhesion and good impression without material lift.
2. The bond coat begins to dry before the stamped material is placed and smoothed. If this happens, the stamped material actually rewets the partially dry bond coat causing it to delaminate and resist adhesion to the intial skim coat. Unforunately there is no immediate quick fix here. If the bond coat begins to dry, wait for it to completely dry and apply another bond coat. Accellerating the process will only lead to improper adhesion and ultimately failure.
3. The contractor is waiting too long to emboss the material. Stamping overlaysments is nothing like stamping concrete except for the finished result. Stamping overlayments while the material is wet and before the bond point has begun to dry is key. If the contractor waits for the material to "set up" and get hard, the bond point may be in the drying stage and material may lift with the stamp.
Although there are some quick fixes and remedies for some issues, the bad news in all of this is that if blisters appear, you can bet that the level of permanent and proper adhesion is suspect throughout the entire application regardless how successful they are at "patching" the problem.
Kindest regards,
Ken Freestone
By Ken Freestone, at 2:04 PM
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