What is a sealer.
A sealer in very basic terms is resin solids held as a liquid by a solvent (this can be oil based or water based) which when the solvent evaporates returns to a liquid to create a hard non porous coating on the surface.
All sealers these days penetrate into the surface to one degree or another so don't get sucker in by claims the a sealer is "penetrating". Topical sealers or sealers that only sit on the surface are an old technology and as far as I know are not used anymore.
Sealers come in a range of finishes from invisible to high gloss and everything in between
There are a myriad of different resin out there on the market Acrylic, MMA, Urethanes, Epoxies, Fluoropolymers, Silicones, Siloxanes and so on, there are also different grades within each type (sometimes hundreds).
So to keep things simple I will be talking about the most commonly used, widely available sealers.
Different types of sealer.
There are, in general terms 2 different types of sealer, these are Water based or Oil based (most commonly referred to as Solvent based).
Water Based Sealers
There are many different types of water based sealer, like other sealers there are different qualities of resin that are used for making sealers these range from PVA to Acrylic/Urethane hybrids.
The main factor of Water based sealers it that in general the do not enhance the colour of the surface, essentially leaving the paving looking like it does when it is dry.
Modern day water based sealers are as good as solvent/oil based sealers in terms of longevity, so as long as you are buying a good quality sealer this shouldn't be a concern.
Water based sealer don't suffer the same with blooming (trapped moisture) as Oil based sealers so can be applied when the surface is damp (sealers should always ideally be applied when the surface is dry) but they do need to be applied in warmer temperatures (10 degrees +) than oil based (5 degrees +).
Solvent/Oil Based sealers
Solvent Based sealers have been around longer than their water based counterparts and many installers only use Solvent/Oil based sealers as they feel that they are superior to water based sealers but as I mentioned in the previous paragraph, modern day water based sealers can be just as good as oil based they just give a different finish.
Generally speaking Solvent/Oil based sealer will enhance the colour of the paving leaving if looking like it does when it is damp/wet.
There are several different types of resin that go into Solvent/Oil based sealer but the most common are Acrylic and Urethane (commonly referred to as Polyurethane, I will here on in refer to this resin as Urethane) It is a common misconception that Urethane sealers are the best sealers on the market, this however is not necessarily the case and I will discuss the pros and cons of each in future posts.
The main thing to remember when applying a Solvent/Oil based sealer is that the paving need to be 100% before applying it and the weather needs to be dry until the sealer has dried (2 hours + drying time varies depending on the sealer being used).
If the paving is damp or it rains on it before it is dry you can get a problem commonly referred to as blooming, when moisture is present as the sealer is drying it creates microscopic bubbles in the sealer which give a frosted/white appearance to the sealer, depending on what sealer has been used this is either easy to remove or impossible I will go into further detail in the pros and cons post.
Impregnators
Impregnating sealer has become something of a buzz word of late especially with the likes of architects and specifiers.
This type of coating is not technically a sealer due to the way that it protects the paving, an impregnator is usually water based (can also be solvent based but using less harsh solvents so is more eco friendly).
These coatings alter the surface of the paving to stop liquids from soaking into the paving but they offer little to no protection against wear either from foot or vehicle traffic and the weather, for this reason I tend to refer to these coatings as a stain guard for paving.
Most water based impregnators are breathable, the main issue with a breathable coating is that because it is breathable it will allow efflorescence to come to the surface which would be stopped by a traditional sealer, because of this you need to ensure that any efflorescence has been allowed to come to the surface and be removed before applying these coatings
Resin Percentages
This is the amount of resin solids in the sealer, sealers can range from 3-5% (cheap hardware shop sealers) to 25% (Adseal Super Plus) some are sold as high as 50% but these sealers require solvent to thin it down before you can use it.
Most sealers are in the 10-25% and most of the time this is reflected in the price, the lower solid sealers are cheap and usually sold on sites like eBay, most manufacturers of sealers (Adseal, PICS, Smartseal) tend to sell sealers with 15+%.
However the percentage of the resin isn't the be all and end all, the quality of the resin used is more important which is why I alway recommend staying clear of the cheapest sealer on eBay, Amazon etc as these tend to be low solids, low quality resin.
Price of sealer
You will see from a little bit of research that there is a very wide range of prices when it comes to sealer, these can range from £40 to £500+. Whilst price is a fair indication of quality don't think that you need to buy the most expensive sealer on the market, like I said I would avoid the cheap eBay, Amazon, B&Q sealers, for a good quality sealer you should be looking to spend £100-£200 for a 25 litre drum of sealer.
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