Fundamentaly there are 2 categories that concrete sealers will fit into. Topical, where the majority of the sealer sits on top of the concrete. And penetrating where the sealer is designed to sink in.
Penetrating sealers are very successful at protecting very smooth concrete like polished concrete floors and bench tops etc. Their disadvantage is that they will be virtually undetectable on an exposed aggregate driveway. In our expeirience when it comes to exposed aggregate or coloured and broomed external concrete penetrating sealers only have limited potential to resist mould and no ability to protect the surface from wear.
We will usually use a zylene based topical sealer for exposed aggregate. However we will usually only recomend it if we think you will get a visual benefit or you will have a potential mould issue. Some exposed mixes really pop with a coat of sealer while others you can hardly tell. Coloured broom or sponge finished concrete is a bigger issue. We will try to avoid sealer if we can. We will generally recomend that the client chooses a colour much richer than they want and then let it fade ( which happens over days not months )
A topical sealer will definitely give you the semi gloss finish that so many of our clients like. However a very common issue with this type of sealer is deglazing, where the film of sealer on top goes milky and wears away prematurely. This is because that particular coat of sealer has not properly penetrated the surface. It has either been applied incorrectly or onto concrete that has not properly cured (dried). This can also occur when re-sealing concrete where the new coat of sealer does not properly bond with the existing sealer. There are a couple of pics attached.
Our general rule is only seal where necessary. We often quote against contractors who include sealing. Dont be fooled, this will usually be one coat of low solids sealer within days of pouring the concrete. I wish this process worked but it doesn’t. We wont seal within 6 weeks of pouring and then when we do it will usually involve a proper acid wash and 2 coats of extended wear sealer. There are situations where we will recommend sealing but only when we think there is a real benefit. Our aim is to provide a quality job that will last. You can rely on our authentic long term experience.