Six
side Sealing of stone – Breaking myths of Debonding
For years the use of
sealers has been expressly for the protection of the stone or tile surface.
Most, if not all, adhesive companies warranty their adhesives only if the back
of the stone is free from any sealer as sealers are seen as “bond breakers”
adversely affecting the integrity of the adhesives ability to bond to the stone
or tile surface. However this situation has meant that many of the problems
created by water absorption through the back and the sides of stone have gone
unresolved. New and current technology now offers sealers that can successfully
be applied to the bonded surfaces of stone without becoming bond breakers. To
look at these and how they work I firstly want to investigate the problems and
issues relating to porous stone and specifically water absorption through the
sides and back.
Picture framing,
efflorescence, soluble mineral contamination (for example iron Sulphides such
as Pyrite) and prolonged water marking are some of the problems created when
water is absorbed by the back and sides of some types of stone. The mechanics
are as follows. When a stone is installed over a concrete substrate the
concrete can contain potential soluble contaminants such as salts and other
minerals. The underlying cement based screed or topping as well as the cement
based adhesive and grout also have the potential to hold some of these
contaminants. In most cases the contaminants will not react unless there is
water present. Water is both the catalyst as well as the transport mechanism.
The initial and most important source of water that triggers much of the
reaction originates from the hydrating adhesive or mortar bed that is even more
aggressive due to its high ph. With water the soluble minerals travel to the
surface by way of evaporation and capillary action working their way through
the stone and grout. In many cases the grout is more porous having higher water
absorption than the stone creating an easier exit for the evaporating soluble
minerals. This explains why in many cases the resulting stains are revealed as
picture framing or at least concentrated around the sides of the stone and
grout joint. Once on or near the surface the contaminants further react with
the increasing rate of oxygen and ambient air temperature to form various
compounds or simply evaporate or dissolve only partially leaving behind the
unwanted stain or compound.
A good example of
this mechanism at work is the soluble iron salts found in the granites and
marbles across various projects.
The water from the
thick mortar bed under the stone once absorbed into the stone body easily
reacted with the soluble salts to form highly visible iron blooms. In some
cases the iron salts would turn the complete stone a light shade of yellow. The
solution to this problem is simple – if the stone’s natural water absorption
could be reduced close to zero then the risk of iron contamination would be
similarly reduced. The best and most cost effective way to reduce the stones
water absorption is to seal the stone on all six sides.
We have all known for many years that the trick to
managing many of the water related problems of soluble mineral staining such as
the iron salts is to lower the stones natural water absorption by sealing it on
all six sides while still maintaining good vapor transmission. (The ability for
the sealer to breath is very important as any trapped water can create other
issues such as surface debonding by way of excessive moisture expansion.
However the formation of the contaminants is not only due to the presence of
water but also the quantity of water and rate of evaporation. If the amount of
water is reduced and the rate of evaporation high enough that the water does
not condense then the soluble minerals will also exhaust through the surface
rather than solidify ). The problem however is that most sealers either did a
poor job of repelling water in a high alkaline environment as that found at the
interface between stone and cement mortar, or reduced the bond strength of the
adhesive system. The latter is the reason why most adhesive manufacturers only
warranted their adhesives when applied to clean unsealed stone. This claim in
turn made clients reject any sealer solution to the problem as well as making
sealer manufacturers uninterested in developing specific sealer technology.
However as stone’s use increased globally so did the problems related to the
high water absorption and chemistry of certain stones. All of this at last led
to the development of sealers that could in fact both reduce a stone’s water
absorption as well as maintaining the adhesive’s bond.
RachTR has designed
the sealer specifically for application to the back and sides of stone called RachTR Back Seal. It is designed to hit
the main market requirements for such a product – low cost per m2 (or sq ft),
highly water repellent, good vapour transmission and of course not being a bond
breaker for the adhesive. However we realized that the best way to apply
sealers to the sides and back in a cost effective manner was to dip the entire
stone. However this presented a problem in that many clients wanted a low cost
sealer for the back and sides such as RachTR Back
Seal but wanted a premium product for the actual surface, which
would be exposed to long-term dirt and contamination. Therefore any specialized
back applied sealer had not only to be compatible with a premium sealer but
also needed to allow the premium sealer to penetrate it so the correct quantity
of premium sealer could be applied to the surface. RachTR Top
Seal is designed to satisfy both these conditions. The sub surface
sealers will penetrate right through the RachTR
Back Seal enabling the complete and correct quantity of premium
sealer to be applied guaranteeing the long term performance of the final
sealer.
Both of these sealers
are tested regarding shear bond to ensure they do not act as bond breakers.
The contemporary
existence of sealers that can be applied to the sides and back of a stone or
tile now help to manage and greatly reduce the risk of the long endured
problems created by moisture moving through the stone especially during
installation and the process of final cure. The argument by both clients and
adhesive manufacturers to not seal all sides due to the possibility of the
sealer being a bond breaker is no longer valid now the technology exits to do
so.
Using a suitable
sealer on all six sides is part of a total water management system that should
be implemented to fully control the uses around leaching of soluble minerals.
These include for example the use, where appropriate, of waterproof membranes,
epoxy remediation systems, proper falls, factory prepared adhesives and grouts
etc.
