Subject: Contact form submission: Ray
Message : Hi
Have used builders bog on a renovation in gym pie Queensland Aus. After filling with the product on the exterior damaged areas of hardwood clapboard, ie joints nail heads etcetc,
The exterior was given 3 coats of water based self priming exterior grade paint, pascal sunscreen. The exterior came up well I was happy with the result.
Over the past few weeks the area has had some significant rainfall. The areas of the house that are most exposed to the weather have started to have the paint bubble. With moisture appearing between the paint membrane and the filler. The problem is confined to where the filler has been used nowhere else. The pascal paint techs think it may be a reaction of the filler to the paint as exterior moisture increases at exposed areas during a rain event. It is my understanding that the filler which was purchased from Bunnings can be primed with either water or oil based paints.
I would appreciate your techs looking into find a possible solution
Firstly may I say I am sorry to hear of your problem.
Builder’s Bog, once cured with the correct amount of hardener, is very inert. Nothing dissolves it and there are no active substances within it that can react with paint.
It will absorb and desorb moisture like timber, but the moisture has no effect on it. As a result, if the timber itself has access to ambient humidity it will expand and contract, and the inert Builders Bog will not move as much. So a nail head fill may seem to contract when in fact the timber has expanded around it, especially if pilot holes were not drilled for screws and the screw head is just crushed into the timber fibres to countersink it before filling.
None of this seems to relate to your problem though.
I have exterior handrails on my 100 year-old house, painted with a very dark green Dulux water-based paint and it has repeatedly blistered in various places. Some blisters are between the Dulux water-based primer and the top coat, some between the primer and the filler, some between the primer and older oil-based paint and some between the timber and the primer. The problem was that this dark green should have been factory-made from a prime grind of pigment powders and resins. But the shop actually tinted it in-store, and this introduced too much of the colour paste, which contains glycols, which spoilt the paint! Being a very dark colour it got very hot on handrails too, which caused the blistering. The glycols etc are in the “universal tinters” to convert the colour powders to a paste for blending in-store.
Can I ask what colour your Pascal paint is, and was it a shop tint?
The only other possibilities, and I am not suggesting they apply in your case, are under-cure due to too little hardener, or too much hardener leaving excess very reactive peroxide behind in the fill. Both will upset the paint, but the permissible range, as in the directions, is very large.
Thanks for responding. The paint color is a light color from a white base “Strauss White”, shop tinted specifically at a masters hardware store. The color was chosen as experience has shown a light color has less heat stress etc etc. The blistering occurs mainly on the south side of the house which is exposed to the predominate weather which usually comes from the southeast. The boards trim on this side get wet up to close to the eave overhang the rain hits these areas and it gets quite a soaking under certain conditions. The southern side of the house was the last to be patched sanded and painted. To this stage I had used 2 tins of builders bog and was comfortable working with the product I have also had plenty of experience dealing with similar products. I am sure that it was mixed and applied as per directions. Could an application of an oil based or acrylic primer (after sanding repatching etc) applied to the filler and then 2x coats of pascal acrylic stop recurrence. Which product would be best an acrylic or oil based primer. Is there any other solution?
Thanks for the reply. An oil-based primer would be safer, because some of the acrylic based primers are very thixotropic and can flash-dry in hot weather before penetrating the surface of the filler or, in fact, penetrating smooth timbers too. This just gives a top skin with no real grip on the substrate. Oil based paints are inherently more penetrating.
I never solved my dark green handrail blisters. None have popped in the last (third) rectification run, and Dulux walked away from it, leaving me with a 20 litre pail full of the same paint!
I got too busy to chase it.
No help to you, I know, but you have my sympathy. I spent a long time investigating this close-at-hand failure of paint over our product and over other paints and timber. I am an Industrial Chemist and we have a full laboratory at my company. I formulated Builder’s Bog many years ago. We are also polyester resin experts and supply thousands of tons per month to the fibreglass industry in NZ and the Islands, so we cannot afford to take failures lightly.
he cured surface of Builders bog is different from timbers (which all differ greatly too from one another). If you look under the microscope you will see millions of tiny craters in our filler, put there to allow the paint to get a good grip on the surface. The inside of these craters is borosilicate glass, believe it or not, from the half-sanded hollow bubbles we use in the filler. These glass hemispheres are both hydrophilic and oleophilic, so they are wetted by both types of paint. But water-based paints need a chance to penetrate and stick before flash-drying, so this could be the problem.
Contamination with oils, silicones, dust are other causes, of course. A wipe over with solvent is a good way to be sure you are free of these. Turps will not affect the timber or Builder’s Bog, but will remove any contaminants and dust.
I will give the oil based primer a shot. I’m fairly confident it shall stop recurrence. The first thing I did when I saw the problem was check some online forums re painting timber exteriors in Queensland most recommended using a undercoat sealer primer on all patching with two coats of finish coat over, I shall let you know how it goes. I’m painted out at the moment so may not get to it for a week or so.
Many thanks for your prompt response and potential solutions