Hi All. We have about 70 cracks in our shotcrete floor (I kid you not), from around 1' to 2' long. (We're owner-builder.) We did everything right: Watered the shotcrete 4+ times a day for 7 days. It also rained all day for 2 of the 7 days and the humidity was high 6 out of the 7 days. Like I said, we did everything right. Our shotcrete subs did not. As you can see from the pictures below (I only posted a few) some of the cracks are hairline and some are not. Approximately 20 of the cracks are about 1/16" wide (you can fit a coin in them) and are anywhere from 3/4" to 2 1/4" in deep. Some of the cracks appeared when the subs were still here on the day they did the shotcrete. I would say within 2 days or so all the cracks were visible. (Btw, our soil is granite and very stable and the shotcrete was 3500 psi.)
We told the owner of the shotcrete company (who was not on site the day of the shoot) about the cracks (how many there are and how deep/wide they are) and he said they were shrinkage cracks and no big deal. (We also sent him pictures, the same pictures as below, but he never commented on them.) We also contacted our pool engineer, Ron Lacher of Pool Engineering Inc. and, after looking at the pictures, he said there appeared to be 2 reasons for the cracks: Shrinkage due to using a more economical wet shotcrete mix that has a higher water content and spreading re-tempered waste (rebound) over the previously shot floor. He also went on to say that hopefully what's under the rebound isn't more rebound, but properly applied shotcrete. He suggested contacting some plasterers and then, based on what he said and what the plasterers said make a decision as to what to do and that it would not be unreasonable to ask the owner of the shotcrete company to remove the top layers of rebound and fix the cracks.
So first we contacted 2 plasterers, both with many, many years of experience in the business and this is what they said: The first plasterer (23+ years plastering) came out on Wednesday and said it was the worst shotcrete job he'd ever seen and that he'd never seen so many cracks before in shotcrete. In addition to the cracks, he said our entire pool floor is really uneven. The shallow end is higher by 2" on the right side vs. the left. In fact the entire right side of the pool floor is higher than the left. There's humping in the middle of the pool and the shotcrete subs had troweled in the rebound so the majority of the pool floor is smooth. The plasterer said he wouldn't be able to apply the plaster because the surface is too smooth. He was at a loss to offer any solutions other than to get the shotcrete subs back to somehow fix the problems. He went ahead and gave us an estimate for plastering, but said that it would be hard for him to give us a warranty on the plaster because the cracking is so excessive. The second plasterer came out the next day and said it was extremely shoddy work and was just amazed that anyone could do such a bad job and that he'd never seen so many cracks before. He said he could "brown coat" the entire pool shell (1/4" thick) to make the shell more water tight and give the plaster something to adhere to since the pool floor was too smooth. However, he was also concerned about the depth of the cracks so he would need to send out his shotcrete expert and see what could be done about those. That was Thursday.
Fast forward to today. The owner of the shotcrete company sent out a plasterer he recommends to his customers to look at our job. The first thing this plasterer said was that the job looked pretty bad. He said he wasn't sure what the subs did, but it looked as if they had created a "patch" over the majority of the pool floor. If you look at the pictures you'll see what he's talking about. The area of the floor that looks lighter (i.e. most of the pool floor) is the rebound (aka the "patch" he's talking about) and the small darker area that goes from the pool floor and up the side of the pool is the only area of the floor that was done correctly. This plasterer decided to "open up" the one crack in the floor that goes down 2 1/4" to see what it looked like underneath. Once it was opened up he filled it with water. He only filled it halfway with water and it took about 20 minutes before the water disappeared, which, to me, meant that the crack must go all the way through the shell. He then got out a hammer and tapped on either side of a lot of the cracks to test for hollowness and said the shell sounded solid. (I had already done this, as well as the other 2 plasterers, and it sounded solid.) His recommendation: No need to do anything. Just fill the cracks with plaster. He waffled on what to do about the pool bottom being 2 inches shorter on one side and the overall unevenness of the pool bottom. At first he said he couldn't use plaster to even it out because it would be too much plaster and it would crack and then he changed his mind and said he could do it.
It's hard for me to believe that a layer of plaster could solve all the problems with the shotcrete. It looks so bad, is it even salvageable? How do I find out if the sub-floor is any good? At this point, I'm more concerned with finding a proper and long-lasting solution, if it's possible, so if anyone has any advice for me in that respect that would be great. Also, who should do the repairing, the plasterer or another shotcrete guy? Thanks so much for your help. I really appreciate the support from the people on this forum.
(Btw, the shotcrete company came highly recommended and has been mentioned a number of times on TFP. Out of respect for the rules of this forum I have not mentioned the company name, but for anyone looking to do an OB in Southern California please PM me and I can let you know who it is. I don't want this to happen to anyone else.)
The lighter area on the pool floor is rebound? You can also get a general idea of some of the overall cracking from this picture: