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The no-fines (voided concrete without sand) construction technique for buildings is not particularly suited to drilling of holes to provide adequate fixings.
The base coat of rendered walls generally has a good bond to the no-fines concrete. It may therefore be possible to fix light loads (signs, rain water goods) to the base coat. Fixings that are self-tapping or self-drilling without a plug may be suitable. Expandable fixings where a nylon plug is inserted into a hole and a pin driven or screwed into the plug can take slightly heavier loads. Other methods include flexible pins that are driven straight into the no-fines that deflect around the aggregate lodging in the void and expanding foam adhesives.
Accurate location of fixings may not be possible. The use of brackets or battens securely located into the no-fines may be necessary onto which objects can then be fixed with more precision.
Acknowledgement: The Concrete Society
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