Prepping and coating exposed aggregate with PAP

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Vince M

I did some searching in the forum but wasn't able to find this topic, if it is already somewhere. Lately, I've gotten calls to coat patios with exposed aggregate. We really only deal with PAPs and I was wondering how we should prep a surface like that? Also, how would you treat cracks? What are common pitfalls and challenges with coating surfaces like this? I'll include some pictures.



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Lindy A.'s picture
Lindy A.
Since exposed aggregate

Since exposed aggregate surfaces are not flat/level you can't use a floor grinder as you would be the norm. You could use a high pressure washer with a sand injector (wet/sand blast) to remove previous coatings/sealers. Followed by cleaning/scrubbing with biodegradable cleaner, rinsing throughly, then allowing to COMPLETELY dry (this will take longer than flat concrete surfaces since water collects in exposed down in it (as you know, polyaspartics will react with water resulting in tiny bubbles).

Outdoor concrete substrates rarely have moisture barriers placed beneath them as interior concrete floors do; therefore, they area more likey to have excess MVE (moisture vapor emission) issues exceeding 3 lb per 1000 feet which adversely effect their bond/longevity/performance.  You will need to make sure there is adequate drainage away from the slab so that water doesn't build up and encroach/wick underneath the slab then try to rise up through it in order to escape bringing about excess MVE in reference to impervious coatings such as polyaspartics.  I recommend testing the concrete with a moisture meter, which should not exceed 50 to 60%, with the probe type providing superior insight into what is occuring within the slab.  Calcium chloride test are difficult to adequately perform on non-flat ungulating exposed aggregate surfaces.

As for treatment of the cracks ... you notice i used the term "treatment" since I never state or alude to them being "repaired" (the word "repaired" has a permanent ring to it which is not the case if the conditions (stress, swelling soil, errosion, etc) which brought the cracks about presented itself again in days/weeks/months/or years down the road ... you can chase them out and fill with a flexible/non-biogradable  urethane grout (NP1 by Sonniborn in concrete gray color or one equal to it, pushing some aggregate down into it to sort of treat/camoflauge the filled in crack) or use a polyaspartic crack filler (such as Andrews Fast Fix) adding aggregate to it to blend in. 

Polyasparitc will sefl prime,, wet out/penetrate into the concrete, resist the elements of nature, has excellect chemcial resistance, and other highly sought after features/benefits as you know.  Personally I have staked my reputation of over 30 years on the polyaspartics of Flexmar Coatings (who is also one of our DCF sponsors) since Jack Bracco/President first being providing them to the industry in 2005.  Apparently you have a polyaspartic you have been using, but it you would like detailed info on Flexmar's drop me an line or give me a call.