Have you had experience with pumping mortar into a stone wall for a repointing project? We had request to use the pump machine called the Putzmeister, a company known for large concrete projects. They want to pump the mortar into the voids and then finish the joint by hand. My inclination is not to allow its use for this task, but thought it would be good to hear your experiences and thoughts.
For the several repointing projects I have been on, we have never come up with a mortar formulation that that could be pumped, and would meet all of the performance and appearance requirements. The consistency of the appropriate mortar always seems to be far too thick and stiff to move through any kind of pump or injection system. Any additives to the mortar formula that would help it flow also seemed to have a downside on performance or appearance.
You have to ask why they want to pump the mortar? Probably, it is to increase the production rate or to decrease the overall cost of the repointing. There may be other ways to achieve these objectives, such as: reduce the amount of repointing needed by doing only spot repointing (may require a closer visual match to surrounding mortar); or, train the work crew in more effective hand-and-trowel methods and techniques (some tradespeople are not responsive enough to be trained, others are).
Of the few repointing projects I have seen that used mortar pumping, there have always been problems that did not exist on projects using hand-placement, such as: mortar slopping onto the face of the masonry units resulting in a poor appearance or requiring much more cleanup time and effort resulting in the loss of any savings of mortar application time; or, shortened service life due to mortar additives; or, shifting/jacking of the masonry units and unintended filling of internal wall voids that need to be left empty.
I have always found pumping to be problematic. While there may be solutions to the problems and pumping may work effectively on some projects, you may not be able to get involved with these sorts of technical or organizational issues. If you have to make a quick and simple “for or against” decision, I would suggest “against” because I have seen many more successful repointing projects with hand-placement, than with pumping.
No matter what placement method is used, repointing projects should always have control over the mortar recipe, a strong work-sampling or demonstration panel component, approvals of samples and supervision of work to assure all work matches the sample. If they can prove pumping works with effective work samples right on the building, and that the mortar will be long-lasting, they should have the opportunity to use it.
John Leeke is a preservation consultant who helps homeowners, contractors and architects understand and maintain their historic buildings. You can contact him at 26 Higgins St., Portland, Maine, 04103; or by E-mail: johnleeke@HistoricHomeWorks.com; or log onto his website at: www.HistoricHomeWorks.com
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