Hi ropetow,
The phenomenon you are observing is known as "concrete outgassing".
CONCRETE REPAIR TERMINOLOGY
outgassing?the upward and outward emission of air or moisture vapor
from concrete or mortar.
http://www.icri.org/onlineresources/ConcreteRepairTerminology.pdf.
Outgassing:
"Outgassing in regards to moisture also surfaces in the form of
blisters in floor coatings, but unlike vapor emissions, outgassing is
a temporary condition usually occurring during installation.
Outgassing is caused when components of the coating, usually in
urethanes and methylmethacylates, are incompatible with moisture in
the concrete. The chemical reaction takes place and the moisture, now
in a gaseous form, rises to the top of the slab and becomes trapped
beneath or may even react with the new covering.
One way to lessen the effects of the chemical reaction is to install
the coating when the concrete is cooling and the water molecules are
less active. In the warm seasons, daytime temperatures rise rapidly,
and as the temperature of the concrete increases, the water molecules
become active and move rapidly.
Installers should avoid any attempt to install a coating when the
molecules of water are at their peak of activity (while the
temperature is still rising). The activity serves merely as a catalyst
to the outgassing."
http://www.itwresintech.com/pdf/library/waterwat.pdf
"Air will move in and out of concrete with changes in temperature and
barometric pressure. The conditions of air expanding (as temperature
increases) and releasing itself through the concrete pores is
considered ?outgassing?. When barrier coatings or polymeric flooring
systems (ie. DURALKOTE 240, DURAL 1004 or DURALTEX) are applied to
concrete which is ?outgassing? a blister can form at the pore
location. This will result in a defect/void in the film."
http://www.tamms.com/concrete_outgas_tip.html
A second benefit of primers in industrial flooring applications is to
reduce the effects of ?outgassing? which may cause pinhole defects in
the flooring. Such defects are caused when entrapped air from the
substrate migrates through the uncured coating (See TAMMS TIP ?Coating
Defect ? Concrete Outgassing). A suitable primer seals the surface
prior to the application of the topcoat thus reducing the amount of
air exhausting from the concrete surface."
http://www.tamms.com/Prime_or_not_tip.html
Bubbling
"...Outgassing occurs when the outdoor temperature rises and causes
the moisture in the concrete to rise or "outgas" out, therefore
causing bubbles to develop. A helpful hint to prevent this is to
install the floor coating either early in the morning or late in the
afternoon on hot days (above 80 degrees). Rapid and excessive air
movement during the installation and curing of the material is another
cause of bubbling. It is recommended to reduce the air flow during the
installation and not to use a fan to help with the curing process."
http://www.flectec.com/techsupport.htm
I hope this helps. If you have any questions, please post a
clarification request *before* closing/rating my answer and I'll be
happy to reply.
Thank you,
hummer
Google Search Terms Used:
concrete outgassing
blisters "concrete outgassing "
concrete waterproofing blisters |
