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geefreck 01-10-2011 02:50 PM

Surface Bonding cement as exterior siding
Hi. First time posting here, I'll probably be a regular visitor.

I have been slowly working on a plan to build my own home over the last few years. The idea is to build all concrete block construction with no wood framing involved. I plan on using surface bonding cement on the outside of the walls for structural reasons.

What I'm basically wondering (if anyone knows) is if there is any real problem with using surface bonding cement as the exterior siding. I get the impression that SBC should hold up well and (likely) offers a nice exterior appearance. I like the idea of not having to stucco, or bother with any other additional siding costs, which would keep things simple and save time.

Erring on the side of caution, any problems this may pose, anyone happens to know of?

Nolan Scheid 01-10-2011 06:36 PM

Surface bonding cement
Hello Geefreck,
I am new here as well but your post caught my attention enough to jump in. I have a passion for surface bonding cement as a building system for DIY builders.
It is a great system because of the simplicity, cost savings and durability.
I have a collection of SBC information:
It includes the original UDSA bonded block guide. Allot has improved since the guide was written. Now you can easily buy premixed SBC all around the country. I tend to go that route because it is all proportioned nicely and sticks well.
There are instructions on the bag. My one caution would be to follow the directions closely when it comes to the amount of water you add. Too much water can kill a good mix.
Depending on the final look you want. I would consider either a colored stucco top coat or an acrylic paint designed to go over stucco to help with the water resistance.

How soon will you be starting your home?

Best regards,

kenh 01-11-2011 06:58 PM

I have used SBC on the dry-stacked block walls of two projects - a green house and a pump house. Generally worked well for me. I had some trouble getting a cement dye to come out the right color. My next project with SBC is to seal the inside of my cement block cistern. I am trying to find out if I will need another sealant over the SBC.

geefreck 01-12-2011 05:30 PM

Thanks for the replies, the site looks informative.

My question is, does SBC work as the outermost exterior layer without any issues? Or are Extra treatments or layers required?

Earnie 01-12-2011 08:51 PM

ABC is way outside of my knowledge area but an interesting concept for use on a home.

How does it relate to what is used for constructing in-ground pools? The term escapes me but if it can stay waterproof underwater, it shoud work on rain.

concretemasonry 01-12-2011 09:11 PM

When it is applied thickly it works like a fiberglass reinforced parge coat or stucco that has more strength. The glass fibers also resist the small surface micro cracks.


Nolan Scheid 06-30-2011 12:49 PM

Surface bonding cement update
In the last few months, I have been receiving more calls about SBC and surface bonded bloc construction. A new trend has started to show. I think that some of the manufacturers of the bagged SBC may have leaned out their mix designs a little too much. This must be be an attempt to save money and be a price leader.

The result is some of the mixes are less sticky or 'rich' feeling. These are taking longer to mix to get each particle of sand coated.

I have started searching for producers of premium blends of surface bonding cement so I can make a side by side comparison.

I don't want to start pointing fingers on the forum. If you have a favorite blend that works great OR you have one that has stood out as not performing well, please send me an email.

Thank you,
Nolan Scheid

concretemasonry 06-30-2011 01:01 PM

The "new trend" may be welcome from the few people that still make the products. They have waiting for over 40 years to see a glimmer of acceptance.

Good for a specialized costly coating, but a real false economy when it comes to construction of a good wall with any structural integrity. Dry stacking of block is far more costly than anyone thinks and mortar will ALWAYS be necessary.


jacksdad 11-09-2011 11:39 AM

Just joined and found this thread while I was searching the forums. Like geefreck I want to build my own place, except I'm planning an earth sheltered home. I have reams of stuff about SB block construction, and I haven't read anything that suggests it can't be used as an exterior finish. Just don't work it too much as I understand that can bring the fibers to the surface.
What I've read all leans toward the system working properly when there is no gap between the blocks (no mortar). The fiberglass strands are typically about 1/2" long, and the addition of millions of them allows enough to line up across the joints to hold the blocks together. It's effectively a fiberglass skin that allows the blocks to resist side loads better than a mortared wall - about six times better - which makes it an ideal method for constructing earth bermed houses. Mortar would increase the gap and prevent the strands from bridging it as effectively, which would then weaken the wall laterally. I was always told that mortar isn't a glue, just a means to keep each course level, and the dry stacked part is key to this system's strength.
However, as mentioned earlier by concretemasonry, the lack of mortar does diminish the wall's vertical strength. The loads are not transferred evenly across a mortar joint - as in conventional construction - and consequently the rough surfaces of adjoining blocks put pressure on small individual high points which will give way if enough weight is applied. Not building too high is key.

concretemasonry 11-09-2011 03:11 PM

jacksdad -

You are little in error on your concepts of masonry design, performance and construction and may be looking at the wrong resources available.

Surface bonding is just a thin coating on a masonry surface that increases the flexural strength (if unreinforced), but has less vertical and and lateral shear strength (lateral and longitudinal). The reason it that SBC is just a coating and does not reduce the point contact that dramatically reduces the contact and compressive strength of the wall. - just look at the manufacturers wall test reports. The strength of the mortar in walls is not critical and the ASTM specifications recommend to use the lowest strength possible to carry the structural loads. The mortar is a part of a masonry wall and integrity to act as a structural unit.

If you talk to anyone the has built a home (especially earth sheltered or earth bermed). There no way you can't get away without using mortar or grout (odd horizontal dimensions required or setting the block on a slab) since there are always some variations on the bedding or contact surfaces.

Dry stacked block should be shimmed to make the wall truly plumb and vertical (read the instructions and guides), but the point contacts cause stress concentrations that drastically reduce the compressive strength. Mortar (even very low strength) eliminates the concentration and creates a stronger wall. People that have built homes with dry stack and SBC would use conventional masonry the next time, but may use it and a exterior surface coating since it works well for that purpose. Beause I have been aware of the SBC concept since 1970, there have some minor changes (and a few major early errors when cement ate up the wrong glass fibers), but it has been establish that it is adequate if used properly

For a basement, nothing beats a little reinforcement and partial (not fully grouted) grouting for a higher wall for strength. For an above ground low structure like a shed it can be doable and easy because the loads are minimal.

Just dig a little deeper on your research (not just the promoters) and talk to people that have done it.


jacksdad 11-09-2011 07:04 PM

Appreciate the input - I'll be the first to hold up my hands and admit I'm a noob that's still learning, and while I've personally never used this method of building I know of several homes built with SBC and (specifically) dry stacked blocks that have shown themselves well capable of taking the side loads that significant earth berming impose on them. And I have actually spoke to people that have built earth sheltered homes that wouldn't use anything but dry stacking and SBC next time. I'm sure you can do both SBC and mortar, but proponents of the dry stacked system seem dead against any mortar for the reasons I mentioned earlier. I'm aware that shims are often needed to correct variations in block dimensions, and I agree that bedding the first course is absolutely a necessary step. Not trying to pick a fight with someone that does this for a living - just quoting what others have found in their experience, principally Rob Roy who built his two story house, Earthwood, in New York in the early 80's. It's bermed up to 13 feet high on the north side with approximately 500 tons of earth and not a drop of mortar between the blocks and it's still standing without any problems. In fact, he uses it to the day as the base for his building school. I agree on the reinforcement issue and never said it was unnecessary, and I'm not by any means saying it's wise to rely on the SBC coating alone - Roy himself took the wise precaution of filling blocks every few feet with rebar and concrete for vertical reinforcement, and horizontal bond beams every few courses - something that I'll be doing as well, as I'm on the west coast and it can get a little shaky here. The rest of the blocks he filled with sand to provide extra thermal mass.
I actually agreed with you on vertical strength in my first post, but lateral strength is where the system is touted as outperforming bricks and mortar, and that's why I was saying it's ideally suited for earth berming. I've seen "six times stronger" quoted by several sources, and I can provide links if you need them.

concretemasonry 11-09-2011 08:18 PM

jacks dad -

The "six times" is referring to a comparison of a ungrouted, unrefinforced hollow masonry compared to a srface bonded wall, which is rare with lateral loads. In a basement, that type of construction will fail with a horizontal shear failure/crack one to three two courses above the floor, so the rest of the wall never sees the real load because of the failure. Touting is different from sound construction advice.

For a high wall, it must be engineered and any intersecting walls pick up the lateral loads. I have seem some 13' high unreinforced hollow masonry was performing and looking well, but I would never live in one because of soil conditions. I have seen far too many failures where advertising claims were use for construction.

Links claiming "6 times stronger" by several unknown sources are really meaningless and I have seen most of them since I am a Structural Engineer with many years of seeing the concept, but it CAN work for the right application, until there is a problem.

Just try to get a permit or ever have to undergo any inspection if an addition/modification is required. The cost of of updating and renovation is very costly if the original construction is discovered.

SBC can be used on a basement, it the height is limited and the application is controlled. Don't ever expect to use it in a partially reinforced 20 story load-bearing building with 6" block that is frequently built in many countries under the U.S. codes.


treese 11-30-2012 12:43 AM

Surface bond or stacked block is a good building a system but it sure is a whole lot of work.
Start with a good foundation. Walls crack with a weak foundation..
We ( the wife and I) stacked blocks and hand filled cores every 4 feet with concrete and rebar. The corners solid filled as well. Leveling the blocks is a pain. All blocks are not created equal. We leveled blocked with corrugated metal shims. Top was U block filled with concrete and extra rebar above doors and windows..Used j bolts embedded in concrete to mount the top plate that a standard truss and metal roof was attached to later
Be sure to remember conduit in blocks if you plan for electrical outlets on the wall. Drilling thru 8 inches of concrete header is a pain.
Now for the fun. We used fiber reenforced surface bond (quickcrete) to cover the blocks. Hand trowel bottom to top , hand mixed in wheelbarrow in our case. Takes a while to get the right consistency and weather does matter. Work in shade if you can.Hot sun sets it fast. Be sure and mist it constantly. Remember it's a chemical process.
We had a contractor with a crane lay the truss(32 feet span) ,plywood and metal roof.Use hurricane clips, gives strength and they are cheap for what they do. Our roof guy made us sign a waiver because he was unsure of this construction method.
It stood all winter with driving rain and I had no problem with the wall. We eventually covered the outside with 2 inches of eifs (synergy system). 4 inches would have been better . Hand applied plaster on top of surface bond for the inside wall. Painted with standard latex.
It moderates the temperature well due to mass located on inside Very sound proof (we have many a rescued dog in the backyard). Low utility bills.
We live in North Alabama tornado alley.. These walls will beat any wood house. If it had a concrete roof it would be a semi bomb shelter. It is a good house and we are proud of it..
I kept my house insurance guy involved all the way. Glad I did.

50 year old electronics tech with HS diploma. Not a member of the trade. Just a guy with ambition,the internet ,a few code and building books from amazon. It took years many weekends and vacations. With the exception of roof and finishing the slab we did it all, with some regret. .
Do your research, ask questions. Follow or exceed code if you can. This house cost me dearly in time, labor, grief and time spent with the children. Think seriously before you jump in to this kind of D I Y endeavor.

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