Fix for Non-air entrained exterior concrete 1

[fredPE]

On a recent project, there was a mix-up on some exterior architectural concrete elements where air entrainment inadvertantly got left out of the concrete. What would be the mitigation for this (short of removal and replacement) . . . the concrete supplier is suggesting a penetrating sealer to be applied to prevent water from building up in the concrete. Is this sufficient, and how often will the sealer have to be reapplied? Will the sealer change the appearance of the concrete.

I realize that the contractor is getting away from pouring his air entrained mix and putting more work on the owner to maintain the concrete for the life of the structure, and we can handle that part of it with money if needed.

Also, I have heard somewhere (I think college) that air entrainment is only "technically" required on horizontal exterior surfaces, and I believe that this is relatively common belief, as the contractor and concrete supplier are both saying it as well. Reading ACI 318-08 and later, table 4.2.1 has different exposure categories now and requires air for vertical surfaces exposed to soil (which is what I have always done, but it seems that this is codified now - exterior footings, stemwalls, retaining walls all shall get a specific amount of air entrainment). So is am I the only one to here the urban legend about horizontal surfaces requiring air entrainment?

Finally, the structure is in a pretty moderate climate (west side of cascades in Washington State) . . . it gets below freezing during the winter on occasion, but it isn't like it is the midwest. Does the climate region ever come into play regarding the exposure categories?

 

[Ron]

fredPE...the purpose of air entrainment is to provide an interstitial "cushion" against expansion of freezing water near the surface. The requirements apply to both horizontal and vertical surfaces, keeping in mind that there is a greater likelihood of water penetration on horizontal surfaces than vertical surfaces.

You are correct in that a penetrating sealer will change the burden from the contractor who should have done it right to the owner who has to deal with the increased maintenance costs of resealing periodically.

The "life" of a clear sealer depends on the type chosen. If a silane or siloxane sealer is used, the first application will last a couple of years and subsequent applications only marginally longer. If you use a methacrylate sealer, it will last quite a bit longer, but will still have to be re-applied, usually in the 5 to 7 year range. This type of sealer is quite a bit more expensive than the chlorinated hydrocarbon sealers like Prime-A-Pell Plus (Series 662) or some other siloxane/silane. Other than that, it can be painted with an appropriate coating, but again, will require maintenance.

The following would be my preferences (in order).....
A. Methyl Methacrylate (MMA) – Sika Pronto 19 or approved equivalent
B. Polyester – Lasti‐Seal or approved equivalent
C. Siliconized penetrant – Frogskin or approved equivalent
D. Siloxane – Prime-A-Pell Plus or approved equivalent

If you elect to use a coating, my recommendation would be Dow AllGuard.

Good luck and make the contractor contribute long term to the increased maintenance costs!