Sanding sealer

[Øyvind Sørlie]

I am building a NH Tucano and it is time to covering the model.

The surface of all that Soft balsa makes me wonder ,if it would look more than a porkypine, unless i seal and sand it.

Never used sanding sealer before and need to be tought a lesson. I would prefer something without health hazard.

Any advice somewon.

[Erfolg]

There is little risk or health hazard with sanding sealer if used in a well ventilated area.

there is probably more of a hazard from dust from sanding the balsa, particularly if done in a unventilated confined space.

Advice do all this type of operation outside or in the garage with the doors open. Although I think the risk is very low for any hobbyist where ever your operations are undertaken.

The risks are possibly higher from doing your tax returns, from repetitive stress injury, from the writing.

Erfolg

[andy watson]

And even higher from not doing your tax returns!!

[Alistair Taylor]

Hi

You don't really need to seal the balsa surface for the Tucano (the 45" version I assume?), just sand it nice and smooth, make sure ALL the balsa dust has been removed from the surface, and cover with film. Sanding sealer is used to prepare a balsa surface for painting, by sealing the grain of the wood which would otherwise rise up when the paint was applied. Film doesn't do this, so no need for sealer.

 There are a couple of tricky bits on the Tucano where getting the covering down smoothly is not easy - the rear fuselage top surface in particular. A useful tool for doing this (in addition to iron/heat gun) would be a covering mit (or oven glove if you're a cheapskate) to smooth down the covering without leaving iron marks all over it. Mine ended up looking a right dog's breakfast, but this was entirely down to my poor covering techniques (and not using a mitt/glove). Sanding sealer would not have prevented it, and (IMHO) only adds unnecessary weight on what it supposed to be a lightweight airframe.

AlistairT

[Øyvind Sørlie]

Thanks Alistair.

I am either using Profilm or 100 micron Dokulam for covering .That fuselage top surface have been given me a slight headache. wold a soft cotton or fleece glove do the trick ?.

And to the two other guys, since i am living in a sivilised country there is no healt risk not to do the tax refund, but it is bloody expensive!!.

I am working in an industry with a high focus at healt issues , caused by dust and toxid fumes /gas. So i am always trying to use remedies without this issues. The sanding sealers i have seen advertised is full of the stuff you dont want to breed inn ,and it would probably been banned in proffessionally use.

I do have som other projects going on, so i am wondering if there is anyone that have som experience with waterbased or similar IF there are any.

Cheers

[Alistair Taylor]

Hi again

water-based polyurethane varnish is probably just as good. This can be made more like filler by adding talcum powder (so I'm told).

HTH

 AlistairT

[Øyvind Sørlie]

Hi again.

I am quite a fan of Poly-C, This is some sort of PVA solution,it is OK to sand as long it`s not getting warm.( Then it softens a bit).

Maybe an idea to try the Talcum with this.

[Myron Beaumont]

I've always used dope with talcum powder mixed in to whatever consistancy  you're happy with for the porosity of the wood

[Øyvind Sørlie]

Hi Myron.

 I can`t even remember when i last saw cellulose dope for sale in Norway, Its a bit difficult to have it sendt by post because  it`s to flameable and liguid.

I also think that the ARTF wave have struck us as well, so there isn`t any real good shops that supplies trad builders anymore. When you can find it it is expensive as H.....

I usally buys my stuff from UK stores with a good web service, and I have to say that they gives exellent service in all matters.

Cheers

[Erfolg]

I use water based varnish to attach glass cloth to balsa and blue foam, works well, is cheap and can be bought from any UK DIY store Wickes in my case).

I see no reason why talc could not be added as a filler, after all that is all sanding sealer is (a filler plus an adhesive). The varnish will both raise some grain and the filler will go into the grain etc. It can be cut back and the process repeated.

All as some one else has previously suggested.

Erfolg

[Øyvind Sørlie]

Time to scavage the kids closet, if i am not wrong there should be some leftover from the days they were only cute, and not so rude. Thanks for always good response and that you shearing your experience and knowledge.

[Bob Howard]

Firstly, I cannot see much need to use sanding sealer if you are using an iron-on finish. It could lead to bubbles of air trapped between the film and the sealed wood, which will expand in warm conditions. 

Sanding sealer is used in the furniture industry, and comprises a filler powder (usually shellac) suspended in a quick-drying clear cellulose lacquer (similar to clear dope).

The technique is to brush or spray the sealer on to the wood, allow to dry and rub down with fine abrasive paper. Several coats are needed, rubbing down between each coat.

The model will then need to be covered in tissue (some model shops still stock it). The usual technique is to cut the tissue oversize, spray it with water to allow it to expand, lay it on the surface and brush thinned dope through the tissue. Instead of dope, I have used Clearcoat, which is fuel resistant and does not shrink (which can pull sheet components out of shape).

Finally, more sanding sealer and rubbing down, and you are ready for a coat of paint.

If this all sounds like hard work, it is. That's why most people use film nowadays, but the finish is very durable, and will not bubble up in the sun on a hot day (if we ever get one).

As to sourcing the sanding sealer, I have tried a product made by Trimite Paints in Uxbridge - very good stuff, but they usually only sell it in 5 litre cans. It was very much better than the stuff sold in model shops, which I suspect uses talcum as a cheaper filler.

Screwfix sell their own sanding sealer in 500ml bottles (£4.99 inc. VAT - stock no. 13842-90). If you still wish to go down this route, give it a try & let us know how you get on.

One final tip. If you are using this method on a foam wing, it is possible for the thinners to damage the foam. On way to avoid this is to use finishing epoxy before the first coat of sealer. This will seal any cracks & fissures in the wood, and will also stop the sealer from soaking into the wood and adding weight.

[Former Member]

[This posting has been removed]

[Guest]

I think aircraft dope is stronger than model dope and you may need to add thinners - available from same source of dope.

 Erfolg,  I use water based polyurethane varnish to finish off fabric covering but it is only fuel proof against exhaust glow fuel providing you wash with soapy water at end of flying and do not let it soak in as the fuel dissolve the varnish.

 I have been to told that water based acrylic varnish is a better covering ( dont know about fuel proof properties ?? )

and that you get it at Wickes.  My Wickes had the poly stuff in ltre cans but they also had a water based varnish for floor painting in 2.5 litre sizes. can did not say what the base was.  Ant ideas - what one do you use ?? 

I assume as you are sticking covering to foam and balsa that you are not shrinking material ??

John

[Erfolg]

The stuff I am using, says it is

"Interior Varnish" the can i have is 750ml, apparently Alchol resistant, heat tesistant.  Touch dry within 1 hr. For some reason avoid contact with ferous metals.

Does not give many clues really.

The cost was about £7 I think.

I have just bought a 1lt can Baufix universal thineers, from Lidel, for £2. For thinning Nitro cellulose, polyester resin, resin paints, PUR paints, could be used to thin. I will be trying it to thin my HMG full strength Dope. 

Erfolg