In order to pick the right sealer for any given application, you need to understand the options available, what makes them different, and how each of them works. Hopefully, this little treatise will help clarify some of the considerations worth, uh… considering. And bear in mind that for my purposes here, I am including not only “Concrete”, but any “Cement-Based” formulation (i.e.; concrete, mortar, hypertufa, etc.) as the potential recipient of these treatments.
But before we get into the whys & wherefores of the different products themselves, here’s a quick overview of what is generally available these days:
Sealer Formulation Options:
- Water-Based Film Forming Sealers block fluid penetration and contaminants by creating a barrier that is bonded to surface in much the same way paint is applied to wood. Generally available in…
- Low Gloss
- High Gloss
- “Wet Look” extreme High Gloss
- Solvent-Based Penetrating Sealers actually penetrate into the concrete surface to a depth of about 1 to 4 mils to increase water repellency and resist stains on otherwise absorbent concrete. Generally available in…
- “Natural Look” – (No visible effect whatsoever)
- Low Gloss
- High Gloss
First off…To Seal, or Not to Seal…yadda, yadda, yadda.
Let’s start with the most fundamental sealer question of all. Why bother?
Well, there are really only three basic reasons to apply sealer to a cement-based piece of work:
1.) To keep bad stuff out
2.) For appearances’ sake (To keep “pretty” in)
3.) To impart a gloss or sheen that intensifies any coloration in the surface material
Keeping Bad Stuff Out
It’s perfectly natural to think of a big ol’ chunk of concrete as “solid”. After all, it seems dense, is definitely heavy and certainly appears to be very solid. It’s also perfectly wrong. While you can easily see the differences in density and porosity between CONCRETE (cement + sand + gravel or rock + water),…MORTAR (cement + lots of sand + water), and HYPERTUFA (cement + sometimes sand + sometimes peat moss + sometimes perlite + sometimes vermiculite + sometimes whatever happens to be handy at the moment + water), in reality, at the microscopic level they are all like sponges. The real question is how sponge-like. Because the more open and porous the material, the more it will soak up stuff from the outside and the greater the need for protection.
Traditionally mixed concrete will have the highest density, mortar will be next and hypertufa will be the lowest. Any of these products can and will suck up everything around them. Out of the ground, out of the air and certainly out of any liquid that comes in contact with them. And a lot of the stuff they soak up is very bad for their health. Most of that bad stuff is carried in by water so let’s talk a bit about good old H2O and its relationship with cement-based mixes.
Even in its’ purest form, water can totally destroy any cement-based material. Probably the most common problem is the result of internal water freezing and expanding. The resulting pressure is capable of splitting apart even the toughest of materials. Additionally, if there are enough “wicking” materials present in the mix that expand in the presence of water (like many varieties of wood, for example), they too can create damaging pressures from within, even without exposure to freezing temperatures.
And if your mixture has been applied over a ferrous metal armature or framework, be aware that even “pure” water contains chemicals and ions that can kick-start the process of oxidation in that metal. Rust. And, unfortunately for you and your work, rust occupies four-times the volume that the metal does. Just picture an explosion taking place in extreme slow motion and you’ll get the idea.
And since very little water qualifies as “pure”, a real concern is what the water these formulations will be exposed to might contain. Minerals, salts, acids; there are a host of elements capable of producing a wide range of less than desirable consequences. (NOTE: while this concern definitely includes the water used to mix the formula in the first place, the issue of sealers deals only with what comes later.). All in all, there are many very good reasons to seal a piece of work executed in any cement-based medium.
Keeping Pretty In
If you are like most artists, you put a lot of energy into your work and want it to maintain the “look” you fretted over achieving. The right sealer can help you accomplish that mission. Additionally…it can also be used to create the look itself, as there are varying degrees of gloss finish available. As noted above, the finish options include everything from an utterly “natural” appearance (no visible effect on the surface)…all the way to an extremely high gloss that can only be described as a “wet, sticky look”. It’s your call. But understand that each finish option comes with its’ own set of maintenance and longevity considerations that are directly associated with the material type and how they form their bond with the surface. Some form a film on top of the surface like paint, while others penetrate into the material more like wood stains. Here are some of the principal considerations associated with these products and their bonding mechanisms.
Film Forming Sealers – Because they bond to the surface, they…
- Will wear, peel or flake off over time requiring reapplications for both appearance & protection
- Act as a “sacrificial” surface and do provide some measure of abrasion protection to the underlying material
- Only protect against fluid penetration as long as their surface is completely intact
- Can usually be applied on top of other finishing materials such as paint or stains
- Some are available with UV screening properties which can help when used over otherwise unstable coloring systems
Penetrating Sealers – Because they penetrate into the material, they…
- Cannot wear off the surface and only require maintenance if the surface itself is abraded or damaged or worn below the penetration level
- Do not provide protection against mechanical wear & abrasion of the cementitious surface material
- Do provide very long term protection against fluid penetration
- Are available in the full range of sheen (“Natural Look” to High Gloss)
- Can only be properly applied directly to the cementitious material to achieve penetration. Great over acid-etch stains, but do not use over paint, wax or any type of film forming material.
- Contrary to popular belief, appear to be as environmentally stable when cured as water-based sealers
Use of Sealers
While it is absolutely necessary to read and follow each different manufacturer’s instructions and safety precautions, here are a few general guidelines:
- Nearly all recommend/advise applying only to FULLY CURED material. That means at least 28 days.
- Always use an appropriate respirator per their instructions. Especially if you opt to spray it on.
- The surface needs to be clean, dry and free of dust
- When using a “Film-Forming” sealer, remember that it will remain tacky for a while and that dust, dirt or anything that comes in contact with it will stick to it just as it would wet paint.
Will it Hold Water
A lot of folks decide to seal a piece of work because they intend for it to actually hold water (bird baths, for example). If that’s the case, then you really need to read the instructions closely. Not all sealers are rated as totally “waterproof”, or may require multiple coats to achieve it. And, if you are thinking about using a “wood sealer” like Thompson’s, for example. I strongly recommend against it. They are simply not made for cement and not up to the task at hand.
While you may have noticed from some discussions on the forum that my personal preference tends to run towards the “Natural Look” penetrating sealers, they are by no means the only answer. That just happens to be what works best for me on most of the work I do. What’s best for you and your work depends entirely on how you choose to balance your needs and expectations against the different product options and considerations above. As you have hopefully determined by now, some choices are purely creative while others are technical in nature. Balance the right considerations and you will find a concrete sealer that will do just what you want it to.
Footnotes regarding environmental & “Pet-Safe” issues related to the use of concrete sealers:
While researching material for the sealer technical bulletin, I came to the following conclusions:
- There are environmental considerations, but since they are very much product/brand specific in nature, the only viable approach for anyone considering their use is to read & heed each manufacturer’s instructions.
- The only precautions I was able to note during this research were limited to the material in its liquid and uncured state. These generally involved issues related to breathing the vapors, ingesting the liquid and proper disposal of the containers.
- To date I have found no information available that indicates there is any degree of toxicity associated with the fully cured materials, whether water or solvent-based.*
*That’s not to say that either or both are proven to be 100% safe once cured. It only indicates that there appears to be no data to support anything to the contrary.
Personal Note:Many of these products have been used for years to seal and waterproof pond liners and swimming pool additions such as waterfall and slides, so if there were any major concerns, one would think they’d have been discovered and discussed by now.
Purchasing Note: Many specialty concrete suppliers sell smaller “sample” containers of most leading brand sealer products. The best bet is to do a little experimenting to see exactly what to expect from any given type/brand.