Screw head filler.

I've just been asked to find out what the best filler is for use filling screw heads & countersunk holes in steel panels on timber framed coaches.
The filler bursting out seems to be an age old problem, even being visible on photos taken pre WW2.

Bob.

 

I would use a car body/polyester type filler. There are various brands like isopon P38, upol etc. You could read the reviews of them online before deciding.
Don't go to somewhere like Halfords as they will charge crazy prices for some small tub. Check online for the best best prices. Google shopping, Ebay, Amazon etc. Try also automotive places that sell car body paint, filler etc. Normally I use Screwfix or Toolstation for many such purchases as they have good prices, but as this is more 'automotive' then check online.

Back in the day pre WW2 they would probably have used Linseed putty but there are better alternatives available above now.

 

Whatever you use will pop eventually, though!

 

Thanks for the answers. We use standard car body filler at the moment, but we're wondering if there is anything better.

Bob.

 

One of the things to consider when using car body filler is that it is hygroscopic in that it can absorb moisture if left unpainted in damp conditions, which may contribute to the filler 'bursting'.

Taken from a US site and I'm not sure that all our fillers contain fibreglass. However, one product we do use - can't remember the name, carries a high proportion of fibreglass strands and can be used to bridge voids.

If you are having problems with steel on wooden frames then it may be that the moisture is entering the filler from behind. A possible solution could be to, after making the attachment, paint on a coat of Flexocryl which itself contains fibre strands, as a sort of 'filler undercoat'. This may then serve to isolate the subsequent filler from moisture ingress from the wood (side).

As to whether the attachment point would benefit from another coat of Flexocryl, after 'flatting' is probably debatable? However, it may be an approach worth considering.

 

Not my department but something I'm working on had screw holes filled with a filler with fibres in and joints between steel and timber with a product designed for use on car bumpers. Both seem to be working at the moment.

Sawdust.

 

I think there is basically two different products, for example the brand Isopon P38 which doesn't have fibres in it and the Isopon P40 which does. The P40 stuff is more for filling holes. In the case of filling in Screw heads I would stay you need it without the fibres. I think other brands may be the same.

I would use two pack wood filler for any screws into wood that you want to fill.

 

I'm not convinced that moisture is such a big issue with fillers. Steel sheets attached to wood will "work" as a result of the frame flexing with running and thermal expansion/contraction. Such movement is inevitably going to loosen the filler's grip on the panelling.

 

Also if the screw holding on the steel panel is not under enough tension when screwed in then when that side of the carriage is in direct sunlight there is a risk of the screw expanding slightly in length and pushing the filler off.

Sawdust.

 

Dumb suggestion time - ever thought of using decorators caulk?........

It'll flex with whatever its stuck to, so no danger of cracking unlike other fillers - I've done various vehicles with it & it & the result still looks good years down the line and when you have to repaint - just dig most of it out & replace & paint over.

Oh, and the stuff's as cheap as chips!

 

Does it get hard enough to rub down?

 

No, you 'smooth' it off with a soapy rag - think bathroom silicone - its a rubbery mass when it goes off fully - it will come in line with a flat surface & you wont know its there.

If in doubt - do a trial & see how you get on......

When you come to do a repaint, you'll know where it is when it burrs as the sandpaper goes over it - so as said, dig out re do & go from there.

 

No but I've know someone who has used polyurethane mastic before now.


Sawdust.

 

I use one of the Upol range - car body filler - to cover fixings. Haven't had any problems, but I'm dealing with low mileage wooden heritage carriages.