Hello! If you stand under our balcony on our house, built in 1954, now during the snowmelt, you can see two things that make me a bit concerned. Firstly, there is a white fluff, salt deposits, and secondly, it is wet in certain areas underneath. On the balcony, there are tiles that are in fairly poor condition. I wonder if this is something I should be worried about in the long run? What does the white fluff mean? Is there a risk of the reinforcement rusting and frost damage? Should one lay something more waterproof with a slope on the top?
If the tile is in bad condition, it might be time to remove it? It retains moisture against the slab (i.e., the moisture that has seeped down between the joints).
If the house and the tile are from 1954, you probably don't have any moisture protection worth the name under the tile. If the slope is bad, it might even be that the moisture in the concrete slab can move towards the facade.
Yeah, that's probably something to fix for the summer. The question is, what kind of waterproofing should be used in such an exposed place?
Last summer, I patched over quite shallow exposed reinforcement that had become visible after some of the concrete came off on the underside, with concrete filler. I imagine that the deterioration will continue if the surface layer isn't sealed. Would it be okay to seal from above, or should additional measures be taken to preserve the balcony? It seems to be cast in two layers because there's a clear seam in the middle. Should the entire top layer perhaps be chipped away and recast?
Is it a cantilever balcony? No steel frame around the concrete slab? Do you live in a Brf? Is there a large number of balconies on the property?
Some general information about damages on balconies:
The condition of the top reinforcement is most important on a cantilever balcony. Possible corrosion of the top reinforcement on a cantilever balcony is serious. Damages on the undersides of a cantilever balcony are often initially of an aesthetic nature and possibly dangerous for pedestrians if concrete pieces fall off.
However, damages on balcony undersides and their bottom reinforcement are most common. This is because undersides are more exposed to carbonation, i.e., a pH decrease in the concrete occurs over the years. When the carbonation front has reached the reinforcement (usually takes decades and depends on concrete quality and moisture load), it can start to rust provided that moisture and oxygen are available. Initial rust often shows as hollow areas (can be identified with a hammer) and possible small spallings. However, the top sides are often, as in your case, more protected against carbonation. The moisture on balcony top sides helps inhibit/stop carbonation (CO2 intrusion), and the existing tiles and any additional casting/mortar also provide protection. However, there is still a risk of damage. It's often difficult to detect damage on balcony tops like yours without removing existing tiles, mortar, and any waterproofing layers. The difficulty in spotting damage with the naked eye makes it somewhat tricky.
In rare cases, someone might have the idea to de-ice (chlorides) the balconies, leading to reinforcement corrosion, which is often worse than corrosion caused by carbonation. Another rare case can be embedded chlorides from the construction period during winter casting.
Now to your question... What you see on the underside is likely lime efflorescence. In small amounts, lime efflorescence itself is relatively harmless. However, it's probably the case that the balcony slab lacks a waterproofing layer under the tiles and mortar, or the waterproofing has passed its technical lifespan.
What you can do is clear the balcony of tiles and mortar down to the construction concrete. Then hammer test the top side and look for any spallings and possible rusting top reinforcement.
If access is available to the underside, you can also hammer test it, usually difficult to reach. You should also take carbonation samples and measure the concrete cover. Possibly take some chloride samples to rule out chlorides in the concrete.
However, I recommend that you hire an expert in condition assessments of concrete structures.
Such repairs you mention are patch repairs and will come off sooner than done. I have inspected thousands of balconies and seen many such repairs that make it harder to detect damage. If there is rust-attacked reinforcement, the best action is to remove the loose concrete. If you are to do partial repairs as you talk about, the entire circumference of the reinforcement bar should be exposed until non-rusted reinforcement is found. The exposure should be at least 25-30 mm from the remaining concrete. Then the reinforcement should be blasted clean before repair with concrete. Generally, when balconies start to get damaged, a condition assessment should be done, resulting in a lifespan assessment and then, when it can no longer be delayed, jackhammer away all the concrete and keep the reinforcement if it is viable. Then blast and pour a whole new slab with possible supplementary reinforcement. This depends on finance, management strategy, and, of course, safety comes first.
I'm borrowing the thread a bit since I'm wondering if you have an idea of what such a balcony renovation usually costs (very roughly)? That is, what would it cost to chisel away damaged concrete, sandblast and improve reinforcement, and then cast new concrete?
The conditions are a "normal-sized" balcony on a 1 1/2 story house from the 50s. Are we talking about 20000? 50000? 100000? More?
Unfortunately, I'm not as confident about the financial aspects. But I can estimate somewhere between 50-100k SEK if it's a complete removal, blasting, and recasting. I haven't been involved in procuring any repairs, only suggesting measures, etc.
The alternative is to "snip" the entire slab and build a cantilever balcony, but that might not be as appealing on an older house.
Thank you for your informative response concrete expert! The balcony in question is on our villa, so fortunately, it's just this one that I need to think about. The balcony is about 2.5 meters up so it’s easy to examine closely from all angles. Additionally, it rests on two concrete pillars at the outer edge. Unfortunately, the corners of the pillars have also started to crumble, showing the reinforcement in some places. This summer, I'll have to remove the tiles and get someone who knows about concrete constructions to take a look.
Then you don't have a cantilever balcony. Does the balcony have steel beams forming a frame around the concrete slab, a so-called steel frame balcony? How is the balcony anchored to the facade? Is it part of the house's floor structure? In any case, the columns are support at one end of the slab. In this case, the bottom reinforcement also plays a significant role for the slab's load-bearing capacity, i.e., tensile forces at the bottom of the slab. Unlike a traditional cantilever balcony I mentioned earlier, where the top reinforcement is load-bearing and the bottom reinforcement is secondary from a load perspective. In your case, you seem to have different stress conditions in the slab.
It sounds like a good idea to bring in an expert knowledgeable in both statics and degradation and damage mechanisms. When it's only a balcony (with what sounds like relatively extensive damage), it might be an idea to let a contractor demolish and build an entirely new balcony. Meaning a total measure. For a balcony, consultant costs can become relatively high in comparison.
Can you send some pictures, an overview of the balcony, details of the damages, it would be interesting.
Hello! Thank you for your response. The balcony is level with the house's intermediate flooring, but I'm not sure about how the attachment looks.
I'm including a couple of pictures here. As mentioned earlier, I have "repaired" some damages with concrete filler, so the damages might be quite hard to assess. One column's corner had damage of maybe 40 cm, but after removing the loose concrete, the reinforcement in the corner was visible along almost the entire length of the column. The columns otherwise had similar small damages just in the corners but far from as extensive. The rest of the concrete in the column seemed solid.
One picture also shows damage in the right corner of the balcony (if you stand below and look up). There, concrete from the lower slab has fallen off, and the reinforcement is visible.
The slightly darker gray spots on the underside are my repairs in a couple of places. About 20x10 cm large.
Great, the pictures are interesting. You probably have a cast-in-place concrete slab in the house!?
The damage in the corner is ongoing rebar corrosion, obviously. It looks a bit like the concrete in the area may be frost-damaged (in cases of frost damage, the concrete takes on a "crumbly" character). Sometimes different damage mechanisms can work together. The damage on the underside that you have repaired is likely due to corrosion caused by carbonation (a very common cause of damage on balcony undersides). Damaged areas with rebar corrosion likely have small covering concrete layers, i.e., the distance from the concrete surface to the reinforcement. The distance can vary on different parts of the structure.
The columns and the area around the columns' connection to the balcony slab are obviously damaged and should be further investigated to assess the balcony's condition. As we discussed earlier, it's also important to examine the top of the slab. The damage seems to be relatively extensive, and don't wait too long before deciding on a course of action. Naturally, one must be on-site to conduct an investigation and take samples and perform measurements to make an accurate assessment.
What you could do yourself is to tap the entire underside and the columns (as this is where you can access the structural concrete) with a hammer. Any areas that sound hollow are loose concrete and likely have rebar corrosion behind them. You can mark all areas with chalk, i.e., outline all hollow areas. Then you can see the extent of the damage to the balcony and whether your repairs are holding. Next, you can measure all hollow areas for the columns and the underside of the slab and quantify the damaged areas. This way, you get a good understanding of the extent of the damage.
If you cast an entirely new balcony structure, it is likely designed for a lifespan of 50 years. Generally, I would say that higher demands are placed on a contractor who is to patch and repair a damaged concrete structure to ensure the result is good than to cast new slabs and columns.
What is the biggest danger with this type of balconies (which have damage similar to what has been described above)? Is it falling concrete or that the load-bearing capacity of the structure becomes so poor that the slab risks collapsing?
I have a similar balcony myself that extends from the concrete slab of the house (though without pillars). I have noticed minor damage similar to the thread creator's. Not as large, though.
If you want to contact a person with knowledge about this, who do you contact? Are there inspectors specialized in balconies?
I have discussed a bit with various craftsmen and even our inspector when we bought the house. But I feel that no one seems to have the interest/knowledge to be able to give any advice/action recommendations similar to those you have given in this thread.
The biggest risk generally is that the damage becomes so extensive that the load-bearing capacity cannot be guaranteed. Then, different damages in different locations have more or less significance for the load-bearing capacity.
In your case, eviljava, you have a cantilever balcony without pillars. The condition of the top reinforcement on the upper side of the balcony slab is primary for the balcony's load-bearing capacity. In your case, small damages on the underside are probably aesthetic at the moment. However, falling concrete is always a risk that can cause injury to people and property. Do you have any overlay/coating/tiles that prevent you from inspecting the top side?
Where in the country do you live? I'm thinking about suitable inspection companies. Many simply do not have the knowledge when it comes to the breakdown and damage of concrete structures. There are some companies that are specialized in concrete repairs.
The optimal is to get a condition assessment carried out with the necessary concrete testing. A condition assessment should include an assessment of the current status of the structure from both a load-bearing perspective and from a degradation perspective. Then, one should be able to get a lifespan assessment of the remaining lifespan and suggestions for actions with different alternatives. Thereafter, you have a good basis for either repairing locally, doing a full repair, or waiting and taking action later. If one is to repair, one has a good basis of expertise to hand over to a suitable contractor. You might possibly go directly to a knowledgeable contractor specialized in concrete repairs as it's only a balcony. Could perhaps request a site visit and hear their opinion to start with.
Looking more closely at picture no. 2, it seems like there is an overlay on the upper side or alternatively the slab has delaminated horizontally. I think I see a horizontal "crack," whether it's the layer between the balcony and the overlay or if the balcony has delaminated is harder to tell from the picture. What do you think, having seen the area up close?
Additional comment on picture 2: The reinforcement in the picture appears quite heavily corroded, and the concrete in the area likely does not have much interaction with the reinforcement. The damage looks serious, especially since it is in an area where force transfer and interaction with columns occur.
Another aspect regarding balconies is to check the status of the railing fastenings. If the edges of the slab are damaged, the railing fastenings may be poor if they are attached to the edge of the slab.
Now that I take a closer look at picture number 2, it looks like you have an overlay on the top or the slab has delaminated horizontally. I seem to see a horizontal "crack" whether it's the layer between the balcony and the overlay or if the balcony has delaminated, it's harder to tell from the picture. What do you think, having seen the area up close?
Thank you for your response Betongexperten! I'm not entirely sure if I understood you correctly. The concrete slab itself is approximately 30 cm thick, as a guess. Roughly right in the middle of this slab, all around it, there's a crack. The slab forms, as you say, two layers. I imagined that's how the slab is constructed, with an under- and upper layer, but maybe that's not the case. Is there a possibility that the balcony has actually split?
One thing I haven't noticed before, and only saw now, upon closer inspection of the balcony, is that it's bowing. Looking at the first picture and comparing how much of the concrete slab is visible at the pillars versus the middle of the balcony, you can see that the slab is barely visible under the railing at the pillars, while you can see a few centimeters of the slab if you look between the pillars.
If you look at the plans of the house as it was intended originally, there was supposed to be a fuel storage in a small area under the balcony, but then it was built only with pillars, without walls around it. A thought that struck me is that the balcony might therefore have been under-dimensioned.
I'll see if I can get a better picture of the delamination.
/Sam
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