SUBSTRATE QUALITY / PRE-TREATMENT.
All surfaces must be clean, dry and free from dust, grease and other contaminants.
MIXING.
Mixing procedures for topping and screeds containing Cembond SBR are similar to those used to conventional compositions, with gauging water partly replaced by Cembond SBR. However, mixing time should be minimised to limit air entrainment. Mixing should be carried out in a forced action mixer. The usual procedure is to pre-mix sand and cement in the mixer, pour in the Cembond SBR, mix for 2 - 3 mins, then slowly add water to the required consistency.
NB. Over addition of water causes rapid thinning of latex modified mortars owing to the plasticising effect of the latex. The mix design depends upon thickness and intended use. However, typically mixes for a 12mm topping or screed are as follows:
Screed Topping
O.P.C - 1 1
Moist sand - 3.5 1.75
3mm Washed
Granite - 0 1.75
SBR - 0.2 0.2 (i.e. 10L / 50Kg of cement)
Water - As required. As required.
All parts are by volume of uncompacted material.
APPLICATION METHOD / TOOLS.
▪ PRIMING.
Application of a SBR primer coat is necessary to obtain maximum adhesion of the topping or screed.
▪ FLOORING APPLICATIONS
This concerns the use of Cembond SBR in screeds and toppings over background concrete. Adding Cembond SBR to a floor screed or topping gives the following advantages.
▪ A low water/cement ratio allows a minimum of delay when overcoating is required.
▪ Reduced permeability to liquids.
▪ Improved chemical, abrasion and impact resistance.
▪ Resistance to dusting.
▪ Thinner screeds, achieving reduction in weight and savings in materials.
▪ Excellent slip resistance.
▪ Cembond SBR has a long and successful track record of use in the construction industry.
SELECTION OF MATERIALS.
To obtain maximum performance from mixes modified with Cembond SBR it is important that attention is paid to the quality of the other materials used. Sand should be well washed and sharp. The grade of sand will depend upon the mix design. Cement Portland, High Alumina and sulphate resisting cements are compatible with SBR Bond. Portland cement should be fresh but cool. Cement containing air set lumps should not be used. Coarse aggregate e.g. Granite chippings. These should be dust free. Air entraining agents should not be used.
POT LIFE.
The mix has a pot life of approximately 30 minutes and batch size should be calculated accordingly. APPLICATION.
Step 1 - Apply topping or screed onto wet or tacky primer.
Step 2 - Compact and level with screed bar. Finish with steel float. It is essential that the topping or screed is finished as the work proceeds.
Step 3 - The topping or screed would be cured for 1 - 2 days using conventional techniques. Curing should be started quickly after application.
CLEANING OF TOOLS.
All tools should be cleaned immediately after use with water because hardened Cembond SBR modified toppings and screeds have excellent adhesion and are therefore difficult to remove. Once dried use solvents such as white spirit with a coarse wire brush. LIMITATIONS.
In common with other SBR products, Cembond SBR is not suitable for coloured exterior decorative renders which will not be subsequently overpainted. Its poor UV resistance may cause discolouration.
HEALTH & SAFETY, ECOLOGY.
MSDS available upon request.
