Painting GRP Tanks.

[Biggy]

I have a couple of very 'tired' looking Celmar (PolyProp)Lined GRP (Fibre Glass) tanks, internally there is nothing wrong, but the outside has lots of staining from 'old' weeping joints, rust staining from rain/mild steel fittings etc.

I have been asked to give them a coat of paint!

So the question is can I paint GRP with a primer then a coat of gloss paint, or do I have to have a pigmented layer of resin applied?

Please advise.....

Biggy

 

[rnd2]

Ideally you should carefully prepare the surface by lightly sanding or rotary wire brushing so that any surface staining or remaining gloss is removed. The prepared surface must be completely dry before and during and after painting. After that a UV stabilised two part epoxy should be fine but there are many excellent paint preparations available. Always seek step by step advice from a reputable paint supplier and preferably more than one.

 

[unclesyd]

Do you have a weathered, chalky, or glass fibers being exposed surface on your tank?

There are some tanks also that have an additional coat of resin that contains a wax, do you know if you have this type tank?

how big is the tank?

 

[Biggy]

The tank has a slight chalkyness - is that a real word? It is now! - to the surface. There are no exposed fibres, the The tank is 7m High x 2.75m Dia.

The resin is Crysic 397 (Bader).

 

[corrosionman]

We recently did a very similar job to this - - we used Crystic 406 ( general purpose resin ) thickened with talc and plenty pigment. We then gave it the final Gloss coat of resin plus pigment . It looked ok. Surface prep was a scrubbing brush with clean water. We considered ordinary gloss paint but realised it was more expensive than we pay for resin system.
also in a chemical enviroment we thought resin would survive better. However any good two part epoxy paint would certainly be very long lasting. Cheers David W

 

[unclesyd]

Though I haven't worked with that particular resin it can probably be painted. The main problem is getting them cleaned/prepared for painting as stated.

I would use a light 3M type brush/wheel, I would not use a wire bush unless it was for a smaller job and having a skilled operator. After brushing rinse well and allow to dry. After it appears dry get on the East or South side and dust or spray a little chalk dust, we use dye penetrant developer on a small area. This will tell you if you have any holes or voids in the existing tank that could cause problems with the paint. Wash the chalk off. If the surface on close examination appears to have any holes are voids prior to the painting preparation, I would try this test on a small area.

There are some materials available to clean the clean and prepare the surface for painting. I think most of the paint/coatings manufacturer have one and there are quite few on the market, especially at the larger marine stores, inexpensive to try.

The rust spots can be cleaned with any proprietary H3PO4 primer cleaner @ 100% concentration. Spray on let stand a few minutes and rinse off on small area at a time. As they say, to be determined by the operator. Watch out about cleaning with solvents if there are any holes or voids in the resin, they will trap the solvent the same as water.

You have the possibility of either using a primer for Polyester or as mentioned a high build Epoxy primer. If you use an epoxy keep it at the min thickness due to the tanks flexing. No matter which type primer you use stay with their brand of topcoat. I would trend toward a Urethane topcoat intended for surface exposure. Again as stated, I would talk to reliable paint supplier or two for their opinions and recommendations.

I also would contact the Scottbader people for a general if not a specific recommendation, then a general one like: use Epoxy, use Polyester, or not use either.

http://www.scottbader.com

Here is one now two companies, in one Carboline and Hersite that we used a great deal.

http://www.carboline.com/Products.html

We also use a lot of International, Henkal, and Dupont coatings.

The paint supplier is usually the one that has the best technical service.

The most important step is getting the right preparation with minimum surface damage and a good application that starts with a good applicator.

 

[rnd2]

I do not encourage the use of sovents when attempting resurfacing grp because of the attendant risk of solvent entering voids and gassing off if the temperature increases.
Having said that if this tank merely needs an aesthetic spruce up then just about any paint will do as long as it is appropriate for the environment the tank is exposed to.