Stucco News

Question and answers on Stucco and Plastering-- August, 2011

Brown coat crumbling-mortar way too thin
Hey RT  read some of your stucco problem posts.  Please take a look at my brown coat photo's below..

I'd spoken + pointed out w contractor holes (voids) in the surface which crumble when stroked.. he said that was normal. (? true or BS?)

Both scratch & brown appeared to me to be less than 3/8" in many if not most places as indicated by thinness of walls at holes / voids.
 .. in some areas I pressed against the outside and it gave inwardly?  problem?

before starting spoke w contractor re:desire to double reinforce wire net around corners to ward off corner cracks -22 newly installed vinyl windows
.. He said it wasn't necessary. (is this true ?  all were left single layer wire.

Since surface of scratch coat & more than half of brown coat surface is sandy & a bit crumbly,
could this be due to an improper, i.e. too much sand in mixture?

He used 94lb Riverside Portland plasticized cement (Red brown wrapper delivered from Westwood Materials Lawndale, CA )

I'm unsure how many sacks he used for 2000 sq ft 222 yd job.
believe delivery was 1 pallet of 16ea 94 lb sacks, for each of scratch & brown coats + third dump truck of sand, each caot. I have photo's of each delivery. 

What quantities scratch + brown coats plasticized cement & sand are appropriate for 222 yd job?

I will contact Westwood Bldg Matls again Monday to find the delivered quantities requested by AMC the contractor
(Sales =no delivery stats access on Sat's, dispatch doesn't wk Sat's)
Sales agent said he thought 96 sacks correct for 222yd. which is only 1/3 of what I witnessed delivered (32 sacks total)
unless contractor chose thinner than 3/8" coats he stated or my 222yd estimate is mistaken
(2 story 5 bed 3 ba house w/ attached 2 car garage, 22 windows, 3 outside doors, 16x8 garage door, 2 thruwall A/C's, 5ea 17x24 house upper vents, 24ea 6x15 lower vents, 2ea 18x24 underhouse access, 1 fireplace chimney 10x10' lower 3' to above roof)

Westwood suggests Basex + fiber mesh to remediate cracks.

since it appears Basex dries rigid, I'd fear continued cracking and separatation.. your opinion?

My thoughts: use flexible polyeurethane caulk such as SchneeMorehead Future Flash III or a silicone rubber
pressure forced into cracks forming an expandable flex seal within the crack to either sice wall of crack then
overlayed with Basex
then mesh than another Basex finish coat, may be more effective   (your opinion?) 
note: perhaps scratch up surface after caulk so Basex gets best grip.


scratch & brown layers are most likely too flawed  so need demolished and reapplied (by another contractor?),
which present contractor is going to resist. (I've already paid him for 80% of job as he requested before I found the cracks)

No, crumbling is not normal. The surface should be so hard you can't shoot a bullet through it.

The cracking here is excessive, and the cracks are wide. What  happened:

Mortar was applied way to thin. The standard thickness for stucco is 3/4", NOT 3/8".
In California, they say 7/8" min.

I usually use 2-1/2 - 3 bags to a square, a square is 100 sq ft. We would normally use 55-70 bags for a job this size,
not 32. (I just finished a house, 3200 square feet, that used 80 bags for the scratch and brown.) I used eight weighed tons of sand, or
1 ton for ten bags.

 Here, all the lathing we do is over sheathing, usually plywood or OSB. In California style open frame construction,
one would use more mortar, as more mortar is squished behind the lath.

The crumbling is because the brown coat dried out before it  set up, as a result of being too thin.

Also, the mortar might have been retempered (mixing water in the mortar after it starts to set.).  If mortar is mixed in a mixer, clean water should be used, the mixer not allowed to run too long, as the longer you mix, the faster the mortar sets. Metal mortar boxes, wheelbarrows, etc. should be shaded in hot weather.

We rarely retemper mortar. The idea is to not .to mix mortar much faster than you can use it.

The wall SHOULD NOT move when you push on it.

I think the extra reinforcement overwindow corners does more harm than good, sometimes. It seems to restrict mortar from being forced in for a good key.

This is a half assed job, or less than half.

I do have a solution, without tearing everything off and not using the tape.

The tape causes humps in the wall, and prevents a good bond. I have seen
people use tape, and the mortar just peels off the tape.

Hopefully, you haven't put on the tape already.

My solution:

As long as all the mortar isn't way too crumbly, the loosest areas can be scraped off, and the walls recoated with my once secret formula.

As long as the walls haven't been painted,  you can coat the walls with two coats of mortar using an acrylic bonding admixture.

The first coat is your standard brown mix, maybe a little less sand, with my liquid mix of flex-con, half and half with  water. This spreads better if it is dry mixed first, then wet mixed with a drill. This base coat should be put on at least 1/4" thick, and the surface left rough, by using a float or a stiff brush.

The finish should be applyed using the same half and half mix. This stiffens up the wall and reduces cracks by adding flexibility to the mortar.

I have a 18 second video on our wet mix on my video page:

We did a job just like this  here:

Scroll down to bad stucco redone.

To this day,there is only one crack that you can see from the street, on the garage side.

I hope all this helps. Thanks for the good question.