Stamp Overlay Failure
Stamp overlay failure
Question:
What caused this stamped overlay on a patio to fail?
Answer:
While this is quite a devastating situation, and will cost both time and money to repair, the cause is quite simple and direct. Lack of surface preparation causes 90% or more of overlay failures, and is without a doubt what caused this failure.
In most decorative overlay projects, surface preparation should cost more and take longer to perform then the actual overlay installation itself. Creating a profile (or degree of roughness) of at least #6 on the International Concrete Repair Institute (ICRI) surface preparation scale is mandatory for successful adhesion. The surface needs sufficient “bite” for the overlay to bond, otherwise delaminating failure can result. As can be seen in the picture, the surface under this overlay is smooth, with little to no profile.
Unfortunately, not much can be done to save this patio overlay. The remedy involves removal of the entire overlay, proper surface profiling using a mechanical scabbler or scarifier, and re-application of the overlay. To find out more about surface profile, contact the International Concrete Repair Institute.
1 Comments:
Chris,
I found your blog pages while looking for some of our advertisements on concreteproductsweb.com. Interesting questions and answers.
I wanted to elaborate on "Stamp Overlay Failure" question and answer topic...
I agree that most overlays fail because of improper substrate preparation but 1/4" thin stamping failure is typically something different. Let me first say that where typical thinner overlay applications fail because of a poorly prepared surface, 1/4" thin stamped overlays typically dont show failure from poor prep nearly as quickly as thinner finishes. This is primarily due to the fact that because of the added thickness, there is an increase in the coatings tensile strength. Not a lot, but enough to maintain structure longer. Of course there is also the added benefit of the coating bing 4 to 8 times heavier but that doesnt extend the failure by much.
On to the problem... When I worked with Chris Stewart with Bomanite/QC, in developing a 1/4" thin stamped overlay for them, I voiced three serious concerns: 1. The polymer content, sand size, shape and composition was not suitable for the application. 2. The addition of other ingredients such as micro-silica, silica fume and super plastisizer not only was required if the mix design and polymer composition was correct but it would actually harm the short and long term performance characteristics. 3. And probably the most critical was that the process of applied products leading up to the application of the actual 1/4" topping that was to be stamped that he wanted to recommened would almost certainly lead to product failure.
I was correct, as about 10,000 sq. ft was applied at a U.S. Embassy in Mexico and it was only a few days before they saw failure like what you have shown in the picture.
The problem was two fold really. First of all, the "premium acrylic" that Chris was suggesting for use as a primer was the wrong pH. I say wrong, because it was not compatible with the pH of the concrete and it was not compatible with the pH our hybrid polymer modifier in the mix. I tried to explain this to Chris but he didnt want to hear it. The second problem which is such a huge factor in most overlay companies thin stamped product failing is due to the drying process of modified mixes. If the 1/4" coating dries faster at the point of bond at the substrate than the top does, it ALWAYS leads to failure. This can be cured by:
1. Applying a neutral pH cementitious base coat to a surface damp / saturated substrate where the pH of the water in the capilaries of the concrete is neutralized to a pH of 7. This is easily done, but wont explain here. Prefered finish grain is about 70% 40/60 blend sieve.
2. Allow the first coat to dry. Not just dry to the touch but dry so masking tape will adhere to it. Now, using the same material as step one, apply the product to the surface, followed immediately with the neutral pH thin stamping material. IMMEDIATELY. The second application of base coat material must not dry at all.
If it does dry before the thin stamping material is applied or if the first base coat is not totally dry, the 1/4" matirial will rewet the coat undernear of it and lose adhesion even before the surface is stamped or textured.
Recap to help prevent thin stamped failure:
1. Saturate the substrate before intial base coat.
2. Make sure the pH of the base coat material is neutral (7).
3. Make the water in the capilaries of the concrete substrate if neutral (7). Note: You cannot chnage the pH of the concrete itself but you can change the pH of the water in the concrete to allow hybrid polymer flow into the capilaries.
3. Be sure to applied a second wet/primer coat of base coat to the surface before the application of 1/4" material.
4. Make sure the pH of the 1/4" material has a pH of 7 as well.
Of course there are other issues such as: will the material being used for the base coat re-emulsify? But that seems to be a sore and sticky subject amounst manufacturers these days so I wont go there...
I could go on and on with other issues and tips and tricks but I have got to get back to work.
Tell Jim I said hello.
By Ken Freestone, at 6:38 AM
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