# Forum Home Renovation Pools, Spa & Water Features  Bulge in the side of Fibreglass Pool Wall

## DaleBlack

Hi see images below   
The photos probably don't show it too well but there is a noticeable bulge in my pool around the removed slab you see, There is in addition to the bulge a hard little pronounced ridge on the bulge that you can distinctly feel with your feet, this is in the photo with the red arrow pointing. 
The bulge has been there for the 5 years I have owned the place, I haven't done the bucket level test yet but I believe I loose water a little bit too much then can be blamed on evaporation (no pool cover) 
I just removed the slab where you can see sand as it had subsided downwards, the end closest to the capping. 
I don't see anything obvious just the yellow sand. 
It seems that pressure outside the shell is stronger than the water inside. my reading indicates its hydrostatic pressure causing it, maybe Soil liquefaction is the answer where soil looses its structure  and becomes a liquid with almost density of concrete= external pressure  =2.5 times internal. All around the pool the concrete is a few cms to inches away from the fibreglass capping make the whole perimeter a default soakwell in winter. Or maybe the source of the water is a piping leak though this basic pool only has one jet and its on the other side at the other end. There is no solar heating pipes. 
I could seal up the gap for starters around the capping and concrete deck. 
I see here  Top 5 Fiberglass Pool Problems and Solutions 
they promote crushed blue stone,    

> The  one thing you CAN control is the backfill material, and based on our  experience, using gravel backfill is the only insurance against wall  bulges in any situation with any pool.   Clean crushed blue stone ¾" or  smaller is the gravel used in our installations because it has several  distinct advantages over sand or even round pea gravel.  First, its  properties do not change when it becomes saturated with water so it  performs the same wet or dry.  This makes it ideal for any situation and  especially in areas with a high water table or difficult soil  conditions.  Second, the point on point friction that occurs between the  pieces of gravel make it a very stable material on the sides of the  pool; much better than saturated sand that liquefies or pea gravel that  acts like little ball bearings.    Third, the gravel compacts upon  placement unlike sand which needs to be placed in lifts and compacted  with water.

  I assume this fill material is a good idea for a new pool but for repair? I could start digging down deep in that narrow gap but I am worried Ill cause some other issue. 
Any ideas?

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## r3nov8or

I'm having trouble working out the third photo. Is it under the pool or something?

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## r3nov8or

Certainly gravel or crusher dust is used these days to set a fibreglass pool. There would be 100-200mm of gravel under the pool and the same or crusher / stone dust all around the sides at a similar thickness. Water can then freely settle and can be pumped out of the standpipe; another 'recent' addition like hydrostatic valves since a fibreglass pool or two 'popped' up several inches when there was more pressure outside the pool than within it.

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## droog

It is very hard to see exactly what it is in the photo's attached.
Another possibility is fibreglass osmosis where you get water between the gel coat and the glass layers, with the pool full it could be hard to tell but when empty the blisters from osmosis have some give in them and will ooze water.

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## r3nov8or

Just a tip. Don't empty the pool!

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## DaleBlack

> I'm having trouble working out the third photo. Is it under the pool or something?

  its the underside of the capping

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## cyclic

I believe the raised bump/sharp section is most likely a crack letting water into what looks like brickies loam surrounding the pool.
Time to talk to people who install/repair these pools in your area.

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## DaleBlack

> I believe the raised bump/sharp section is most likely a crack letting water into what looks like brickies loam surrounding the pool.
> Time to talk to people who install/repair these pools in your area.

  Hi, thats what I was thinking. I have a guy coming friday. Interestingly he said if its just a bulge, one can brace the pool, pump the water out, then dig down the side of the bulge (which in my case is to the bottom of the pool). Then slowly add water, then refill with sand always keeping the water a few feet above the sand level, supposingly the bulge will flatten out. 
In my case, I have that pronounced ridge and a suspected leak, so that wouldnt be enough. 
I mentioned to him on the phone the gravel and he says some people do this as a base, when I mentioned it should be the sides as well he said newer shells are built tough enough it doesnt matter. As mine is a old shell, i think i might specify the gravel not sand. 
I will obtain a quote on the re surface as well, he mentions Fibretech Vinyl ester resins and the AQUAGAURD top coat system as the market leader is this true?

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## cyclic

> I will obtain a quote on the re surface as well, he mentions Fibretech Vinyl ester resins and the AQUAGAURD top coat system as the market leader is this true?

  I have done some fibreglassing over the years but I would have no idea as to what the best repair is for those pools, hence my suggestion for an experienced person.

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## PlatypusGardens

Tree root?

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