Cracks appearing in shell fiberglass

[soakin]

Hello all,

I have a hot tub that is approximately 20 years old. The season before last I noticed a couple black spots in footwell area. I thought these were stains from a leaf or something else. When I went to fill up the hot tub last season, I tried to clean the black spots and noticed it wasn't dirt or a stain but there was a very small crack in the fiberglass where the black was coming from. I contacted Spa Depot and asked them if they sold a product to fix this. They told me to buy Plast Aid and coat the cracks with this product. I did this and to my disappointment the black came through the Plast Aid within a few weeks. I have also noticed some bumps appearing in the fiberglass area of the footwell as well as widespread very small spider webbing.

I'm imagining the fiberglass cracked and water got in causing the black spots. If so, what is the best way to fix this? Also, do I need to do anything about the spiderwebbing or the bumps?

I have attached some pictures.

 

[Texas Splash]

20 years is a long time. I wonder if you're starting to see a delaminating of sorts that might come with age. Are there any equipment pars/plumbing under that area of the footwell that could account for the staining bleeding through? Do you add any unique products to the water other than stabilizer, chlorine, and acid?

 

[soakin]

I was wondering if 20 years is about the end of the life of a fiberglass hot tub. There is not any equipment or anything in the areas of the staining. The staining is in multiple areas and not just one area.

The only unique product I add to the water, other than routine maintenance products, is jet clean when I change the water.

 

[Texas Splash]

I would like to call in @RDspaguy for his thoughts as well.

 

[RDspaguy]

Not all fiberglass tubs are the same, and some are even patented. Since acrylic and fiberglass expand at different rates hairline cracks, bubbles, and even whole sections delaminating are common in older and cheaper tubs. Generally they do not leak as the damage is only in the acrylic, but can be very unsightly. As is their recommended repair, but it's cheap and easy.
I usually hire out acrylic repair if I'm going to bother with it. Someone who does that stuff all day every day can blend it perfectly for a few hundred $. Us spa techs slap some epoxy on it and call it a day. Hairline cracks can be filled with clearcoat or acrylic nail polish, but bubbles and delams are another story.
I have had good luck with bathtub refinishing products on bathtubs, but it would cost way too much to do a decent sized spa.

 

[soakin]

Not all fiberglass tubs are the same, and some are even patented. Since acrylic and fiberglass expand at different rates hairline cracks, bubbles, and even whole sections delaminating are common in older and cheaper tubs. Generally they do not leak as the damage is only in the acrylic, but can be very unsightly. As is their recommended repair, but it's cheap and easy.
I usually hire out acrylic repair if I'm going to bother with it. Someone who does that stuff all day every day can blend it perfectly for a few hundred $. Us spa techs slap some epoxy on it and call it a day. Hairline cracks can be filled with clearcoat or acrylic nail polish, but bubbles and delams are another story.
I have had good luck with bathtub refinishing products on bathtubs, but it would cost way too much to do a decent sized spa.

You mentioned generally they don't leak but can be very unsightly. If I didn't do anything to them do you think it would be ok and not spread or cause any other problems?

Do you think the plasti aid I put on is porous and that caused the black to come back through?

If spa techs just put epoxy on these cracks I could do that. Do you know what type of epoxy is used and if / what preparation is needed before applying the epoxy.

Thanks

 

[RDspaguy]

If I didn't do anything to them do you think it would be ok and not spread or cause any other problems?

The staining would continue to spread.

Do you think the plasti aid I put on is

Not familiar. I use epoxy or acrylic clearcoat.
Typically, staining is on surfaces, and in this case is likely chemicals reacting with the fiberglass or bonding layer. Acid should remove the stains, but will cause more reaction. Sealing it is crucial, which you will not do without significant surface prep, specifically sanding. So, how well did you prep your surface?
I have seen isolated instances where low-end manufacturers have put plywood, INSIDE of the fiberglass/acrylic for cheaper support. In these cases acrylic cracks led to the wood being exposed, swelling, staining, and cracking out large sections of acrylic. One was a recliner back and another the footwell. Both damaged initial repairs as wood deterioration continued.
Some manufacturers use a plastic material, not fiberglass, to back the acrylic, or use just the plastic without acrylic. These may lack the structural support of fiberglass so often have wooden/foam support structures beneath the shell. As this deteriorates (from leaks, poor drainage, poor support, age) it can create numerous cracks, both in the acrylic and the plastic as well. These might leak, and will thwart repairs that don't involve rebuilding the support.
Also, uneven or settling base surfaces can cause extensive damage of every type, including shell cracks.

Do you know what type of epoxy is used

I have used A/B pool putty (off-white), plumbers epoxy putty from home depot (light gray), JB Weld (dark gray), marine epoxy putty (color varies), and acrylic fingernail polish (dry thoroughly, multiple layers with clearcoat).
Prep is key. Sand thoroughly, grind out cracks into a V (dremel tool works magic). Let it cure completely before filling.
But again, if it's on a rotten frame or such it's just a band-aid.

 

[soakin]

The staining would continue to spread.


Not familiar. I use epoxy or acrylic clearcoat.
Typically, staining is on surfaces, and in this case is likely chemicals reacting with the fiberglass or bonding layer. Acid should remove the stains, but will cause more reaction. Sealing it is crucial, which you will not do without significant surface prep, specifically sanding. So, how well did you prep your surface?
I have seen isolated instances where low-end manufacturers have put plywood, INSIDE of the fiberglass/acrylic for cheaper support. In these cases acrylic cracks led to the wood being exposed, swelling, staining, and cracking out large sections of acrylic. One was a recliner back and another the footwell. Both damaged initial repairs as wood deterioration continued.
Some manufacturers use a plastic material, not fiberglass, to back the acrylic, or use just the plastic without acrylic. These may lack the structural support of fiberglass so often have wooden/foam support structures beneath the shell. As this deteriorates (from leaks, poor drainage, poor support, age) it can create numerous cracks, both in the acrylic and the plastic as well. These might leak, and will thwart repairs that don't involve rebuilding the support.
Also, uneven or settling base surfaces can cause extensive damage of every type, including shell cracks.


I have used A/B pool putty (off-white), plumbers epoxy putty from home depot (light gray), JB Weld (dark gray), marine epoxy putty (color varies), and acrylic fingernail polish (dry thoroughly, multiple layers with clearcoat).
Prep is key. Sand thoroughly, grind out cracks into a V (dremel tool works magic). Let it cure completely before filling.
But again, if it's on a rotten frame or such it's just a band-aid.

I appreciate the reply and information!

If I remember correctly, I just sanded the surrounding area with 100 grit sandpaper and cleaned with rubbing alcohol. After I saw the repair failed I thought the same thing you mentioned that I probably should have opened up the crack and filled it rather than just coating over it.

I think I am going to try the plumber's epoxy you mentioned since my tub shell is a grayish color. I plan on using a grinding wheel attachment on my Dremel to open up the cracks as you suggested.

I do have a few questions:

1.) Is there a specific brand of plumber's epoxy you like, trust, or have used with good success?
2.) Does the epoxy need to be top-coated with any type of sealant?
3.) What would you recommend for surface prep?
4.) How long would you allow the epoxy to cure before filling up the tub, 24 hours?



Thanks again

 

[RDspaguy]

1 no
2 no
3 sand it
4 follow package instructions

 

[soakin]

When I was grinding open the bad spots with the Dremel I noticed that the cracks seem to have originated from the very fine spider webbing cracking in the top coat, whatever this is called.

The very fine spider webbing is widespread. Can the surface be refinished, if so is it expensive, or has this hot tub seen it's days?

 

[RDspaguy]

I know quite a bit about a surprising number of things, but any acrylic repair beyond a simple patch is the job of an acrylic specialist, not me.

is it expensive

It would be expensive to redo the clearcoat on the entire spa if you did it yourself with spray cans from home depot, in my opinion. I guess it depends on your definition of expensive. It will be a big job, I can tell you. It might be time to shop for a tub, only you can decide. These type of cracks usually do not leak, so it's a question of looks. How much do you hate it? How much $ do you want to throw at it?

 

[soakin]

As far as this hot tub is concerned it's 20 years old and I don't really want to put much more time or money into it. That's good to hear these type of cracks don't typically leak. If I can get another year or two out of it I would be happy and then look into get a new tub.

As always, thanks for the reply and information!

 

[DangerBoy]

The Plast-aid product you used is only useful for bonding Acrylic, ABS or PVC. It doesn't work on any other plastics or materials. The liquid solution softens/ partially dissolves the acrylic and the powder that you push into the crack also gets softened/partially dissolved by the liquid. Then the liquid evaporates off and the softened acrylic fuses once again eliminating the crack. The advantage of the product over an adhesive is that the bonds that are formed are molecular where the actual acrylic molecules are actually bonded to one another like a contiguous uncracked material. This is a much stronger bond than a regular adhesive would create because those bonds would be the adhesive material just hanging on to the plastic substrate and not actually fusing with it on a molecular bond level.

I used Plast-aid on my tub which has an acrylic over ABS shell and it worked fantastic. The crack was in an area of the shell that flexes a little when you step onto the bench to get in and out of the tub so the crack was a fatigue type stress crack and there was a great risk of the crack propagating further. To prevent that from happening, I drilled two round holes at the ends of the crack. I know from my engineering classes that relieves the stresses at the ends of the crack and stops the crack from propagating further (same reason ships have round portholes on them and not square windows - stresses concentrate in the corners of square windows but on round portholes there are no corners for stresses to concentrate at). To give the Plast-aid more surface area to fuse with, I ground out the crack in a V shape with a Dremel tool. Because I wanted to make extra sure the repaired area would absolutely stand up to the stresses that are placed on it every time you get in and out of the tub, I pushed a little carbon fibre into the area being repaired before the Plast-aid set/hardened. The idea there was to give the repair more tensile strength across the formerly cracked area so hopefully the material in the repaired area would actually have more tensile strength than it used to and would therefore be more resistant to cracking again from the repeated stresses it's subjected to. It's been over three years now since I made the repair and it has held perfectly.

If the shell on your tub is acrylic or ABS, then Plast-aid is the correct product to use but if the cracks have emerged because of fatigued material that either is constantly under stress or periodically stressed and unstressed like an area that you step onto when you get in and out of the tub, then you need to drill small round holes at the ends of the cracks to stop them from propagating. I also recommend you V out the cracks with a dremmel to give the Plast-aid more area to fuse with.

If your tub shell truly is fibreglass, then don't use Plast-aid. I would still terminate the cracks with small round holes (they don't have to go all the way through the shell) and maybe also V out the crack but then I'd use fibre-glass resin and fibre-glass to fix the cracks.