Surface Bonding Cement - Final Thoughts

I finally got through applying all the surface bonding cement; 37 bags, 50 lbs each, about $450 for those who are interested. Initial purchase was 35 bags (one whole pallet). Only having to buy two additional bags tells me my first estimate was pretty good.

Each bag of cement has a small chart that tells you how many square feet of surface area the bag will cover at different thicknesses. I used 1/8” cement thickness for my estimate (though I found out later in another document that 1/16” thick is plenty strong). I’m sure in some places mine is 1/8” thick, but thicker (and thinner) in others.

The variation in thickness I think is caused mostly by temperature and by how I mixed it. While I could’ve used the cement mixer to do a whole bag at a time, I didn’t want to have that much material wet at once. If something happened (and it always does) my material might set up on the mortar board; and at roughly $12.50 a bag, that hurts. So, at first I mixed it by hand with a trowel (really slow) and later in a bucket with an electric drill and one of those stirring paddles (much, much easier). If you use the drill and paddle, this stuff is thick, so get a good drill, or you will burn out a cheap one. Ask me how I know this.

It’s not obvious but the same amount of water and cement does not always yield the same mixture density. Outside temperature comes into play, but they don’t tell you that on the bag. And with each batch being slightly different in density, it affects the thickness of application too. One or two batches were absolutely soupy they were so thin. And, troweling on soupy mortar is impossible, you’ve never seen a bigger mess. When that happens, either add a little more cement, or just wait a little while and the stuff will start to set up and become a good mix all by itself.

As you apply the stuff, on a hot day, it starts setting up pretty quick, which makes it hard to trowel. That is solved easily by having a water misting bottle handy (like Windex or counter top cleaner comes in). They don’t tell you that on the bag either. Hit it with a couple of squirts and the mix becomes workable again.

Another tip I learned along the way was on a really hot day, to wet the wall down really well before starting application of cement. The bag instructions say wet the wall, but don’t soak it. No, on a hot day, soak it. Now, if you do soak it, for heavens sake don’t use too much water and end up with a soupy mix too.

Troweling that much cement on to the walls wasn’t hard once you get the hang of it, but it did take up a LOT of time and it also got awfully repetitious. But, it’s finished now; so on to building with wood.

I’ve seen a couple of jobs locally where a contractor applied this stuff to a foundation wall for waterproofing. After looking at his work and then my own work, I’m glad I did my own work. Yes, it took longer, a lot longer for me to do it myself, but getting this house built fast is not the main goal.