Every binder has its limitations. Tar and bitumen can be damaged by mineral oils and so cannot be used where such substances occur or if the floor may be used for different purposes in the future.

Clay floors were inadequate because of the risk of softening through moisture and because their compressive strength was inadequate. Therefore concrete was poured onto a filling of gravel, as thinly as possible at first to save cost. Astonishingly enough such floors usually remained intact because at first the loads were not so great. But during the course of time they became damaged with greater frequency as day-to-day industrial loads constantly increased. Also thin slabs tended to bulge more than thick slabs, so that now a layer thickness of 20 cm is standard in Germany. In the USA, however, slabs only 15 cm thick are still used so they too seem to be acceptable.

Since, at first, floor builders were not able to produce an adequately smooth surface finish, a mortar layer used to be applied an top of the concrete. This was known as an overlay. This wearing layer was excellent for smoothing because of the high water-cement ratio frequently used at first and the small grain size. However, it also had many disadvantages, from which renovation and repair firms are now profiting.

Chemical resistance
For many purposes this overlay - correctly placed - is fully adequate. The only problem with this hardened cement paste is the action of acids and sulphates. Acids dissolve away the smallest particles but the larger gravel grains only later. This produces the familiar "exposed aggregate concrete effect". Sulphates split the concrete owing to the volume increase connected with the formation of ettringit. Oxidation causes sulphates to be produced from sulphides and sulphites. Concrete must therefore be protected against these chemicals. To sum up: concrete is resilient but does not resist every chemical and nor every error in use.

Surface properties
Also until the late 1960s it was not appreciated just how important the aggregate grading curve, compaction, water-cement ratio and keeping the concrete or mortar moist are for the later serviceability of the floor. For this reason the mortar or concrete had many times the compressive and flexural tensile strength demanded by the relevant standard but these properties did not apply to the surface zone. The interior of the material was strong but the surface screed gave way and everybody was amazed that it became unusable after such a short time in spite of the required standard values being complied with.

Reaction polymers for upgrading and repair
Repair and renovation of premature wear and also protection against the above-mentioned chemicals is possible using reaction polymers. If correctly applied and used for the described purposes reaction polymers can have different compositions including methacrylates, epoxides, and polyurethanes.