W A Ferguson Building Research Establishment
The screw pull-out test has been developed to provide a simple and inexpensive method of assessing the quality of building mortar and units used in masonry. The tests reported have been carried out on a selection of mortars, ranging from a 1:3:12 cement: lime: sand mortar to 1:3 cement: sand mortar. The analysis of the data, using the f-test, has shown that the results for each brick and mortar combination were significantly different. They also suggest that the pull-out strength of the same mortar mix varied with the types of units used to make up the couplet. In addition, they show that 10 pull-out tests should be sufficient to provide an indication of the strength of mortar in any single test location. In general, whilst the results are not totally satisfactory, taken in conjunction with earlier work, they provide the basis for some optimism that the pull-out test will enable an assessment to be made of the in-situ strength of low strength (less than 10 N/mm2) masonry materials.