Masonry Mortar Question

October 11, 2009 8:07 AM

Masonry Mortar Question: I'm doing an artsy birdbath out of riverstone and for the top water-holding basin I need a mortar that adheres well to stone, lasts, endures shrinking/expanding well (as it will be in contact w/ H2O even in the winter), and of course holds water well (or can be be waterproofed).

Here's an img of the basin. I could just use mortar and waterproof it, but I'm a little afraid of shrinking/expanding = cracking. I thought of using Quikrete Water Stop Cement, but the work-time (after you HAND MIX it, with gloves on, into putty) is maybe three minutes and seems a bit of a pain. I could use masonry cement and it would be more expensive but probably work brilliantly, but it contains chemicals that are carcinogenic/can cause birth defects, so I resent that it's not environmentally friendly and would probably leech VOCs and other nastiness into the air and into the birds' water for quite some time.

Any suggestions? I'm leaning toward using regular mortar, waterproofing it, and then replacing the cracked bits every few years (if I'm still living here). Then I could also tint the mortar that curves from the retaining wall stones down to the basin bottom (not the mortar between and under the retaining stones, which can stay gray to match the mortar of the pedestal) so the mortar somewhat matches the stone.

posted by argybarple to home & garden (3 comments total)

There are admixtures that can be added to portland cement mortars to do anything. Grace sells water repellent mixtures and also admixtures to strengthen mortar. Here is one type.
posted by JJ86 at 8:14 AM on October 11, 2009

Thanks, JJ86. That's what I'm looking for, but my local brick-n-mortar (heh) hardware store for some reason only carries a latex additive that cannot be mixed with regular portland mortar. I need this today so I guess I'll be driving around to other stores.
posted by argybarple at 8:23 AM on October 11, 2009

Well, I picked up a cheap, small bottle of latex-type admix, and I can't say if it will be as waterproof as I like or resist cracking for years under freeze/thaw/freeze/thaw conditions, but otherwise it's beautiful stuff. The mortar was nicely workable and INCREDIBLY tacky, and the tackiness probably indicates I'm getting a great bond as well. I'll put a coat of sealer over the basin when it's done, and I think it'll be the best possible solution without heinous chemicals.

In other words, thanks -- I never mess with anything but cement, mortar and stone in the artistic stuff I do as a hobby, I learned the basics from A) my uncle who did this type of masonry including fireplaces and walls for a couple Frank Lloyd Wright-designed houses and B) from a series of books first published in 1934 (my edition was pub'd 1950), so obviously I'm clueless as to all the additives that are out there -- marking this resolved.
posted by argybarple at 4:16 PM on October 11, 2009