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What types of materials to use in building repairing? How do I check the quality of materials used? Should I use SBR or acrylic as a cement modifier? These and many more questions cross the minds of customers who intend to undertake building maintenance work. Following FAQs can help them solve some of them.
What are the products generally used in repairing buildings?
Various materials are used depending upon types of repairs.
For non-structural repairs, polymer-based crack fillers, mortar admixtures, waterproofing compounds, bonding agents, paint additives, water repellants, rust removers, shot-creting, guniting etc, are used at the discretion of the repair consultant keeping in view the future life of the building.
For structural repairs, specialised products and services are utilised. The products basically consists rust removers, repair compound based on styrene butadiene rubber, acrylic co-polymers, plasticisers, super fluid micro concretes, epoxy bonding agents, injection grouting systems, readymade polymer plasters as per the discretion of the repair consultant.
Which are the main products used in structural rehabilitation works?
Styrene butadiene rubber (SBR) and acrylic polymers (pure acrylic emulsions) are the main products which are used in a slurry form with cement as the anti-corrosive coating over the steel reinforcements. Mortars modified with these products form the protective corrosion inhibiting cover concrete. These mortars show strengths in excess of the parent concrete.
As a cement modifier, which one is superior SBR or the acrylic?
It is difficult to say but some structural repair consultants prefer SBR while some seem to prefer Acrylics. Consultants generally go by their past experience with these products. All over the world, SBR has been in use for a longer time in repairs and rehabilitation works. But SBR is not resistant to ultra violet rays. Since they are not used as exterior wall paint in this type of application, this demerit does not affect the repair system and is ignored. In case the right grade of SBR is not available it is preferable to go in for an acrylic systems, like wise if a right grade of acrylic is not available it is preferable to go in for an SBR system. Perhaps this is what influences a consultant from project to project.
How do I test the quality of the polymers?
The quality test for polymer consists of determination of the pH and the solid content of the product to compare and verify with the data given in the product literature. Any other physical findings such as cream formed on the surface of the product or settlements at the bottom indicate a bad quality product.
What types of adulterations are possible in these products?
These polymers are milky white liquids having specific gravity very close to 1. Hence if someone adds water in the ratio of 1:1 in these products common man can’t make out. Even a hydrometer test may show the specific gravity close to the specified one in the literature. Only analysis of solid contents will prove the dilution of the products. Hence it is necessary that the polymers are kept in the godown under lock and supplied to the contractor as per daily requirement. .
How can we be sure that the solid contents found in the lab, are those of the polymer only and not of an adulterant?
Yes fine lightweight powders could be dissolved in these polymers, which could show a higher solid content. The laboratory will not be in a position to say whether the solid contents are of the polymer or any other cheap filler. But the sedimentation when kept in a glass for 48 hours proves the adulteration of this nature.
Another method to find this out is to take small quantity of polymer in a test tube and add double the quantity of solvent recommended by the manufacturer into the test tube, shake well and keep it for some time. If the polymer is adulterated you will see three phases. The water settles at the bottom in the middle you will notice milky white polymer dissolved in the solvent and on top you will find the adulterated powder floating. Ethylene chloride generally dissolves most polymers.
How do the polymers compare with the epoxy and polyurethane system?
Epoxies and polyurethane are sufficiently strong and expensive products. Their mortars and coatings generally tend to be more rigid hence has a tendency to crack during movement/deflection, which the beams and roof slabs constantly face. Non-uniformity of coefficient of thermal expansion of concrete and these products also creates the possibility of creep or lateral movement at the repair interface. Moreover general grades of epoxy and polyurethane are not compatible with cement concrete system hence rarely used in structural rehabilitation works.
How do I proceed with the specifications?
M A Waheed, Director, Perma Construction Aids
Can we hire a contractor directly for such jobs?
Yes you can hire a contractor directly for such jobs. But you could never be sure of the specification and the quality of materials utilised. When we have a health problem it preferable to go to a doctor than to a medical shop for consultation.
M A Waheed is the Director of Perma Construction Aids Pvt Ltd
These guidelines are given by Perma Construction Aids Pvt Ltd, a leading manufacturer of construction chemicals for the guidance of general public in good faith and without any prejudice. Should anyone have any specific enquiry they can contact Perma through their authorised distributors, applicators, or Perma’s technical personnel directly. For details, contact at info@permaindia.com
