Garden Railway Forum

Have just build a pair of laser cut MDF coaches. A mate of mine who is a chippy mentioned using a sealer on them prior to painting.
What does everyone else think.
Any ideas?

Can't do any harm - MDF will absorb water so sealing it before painting can't hurt.

I'm building an IP Engineering tram loco with an mdf body. I didn't use a primer or sealer. I have tried to paint the body sides using two Humbrol Acrylic spray cans of crimson rubbing each coat with wet and dry to get the surface smooth but I still need to buy another tin. Its looking good but still needs another coat.
Silly thing is I have spray cans of white, grey and black primer which I used on the roof, wooden frame parts and the chassis, but thought a good first coat of acrylic spray paint would be enough to seal the mdf. The stuff is like blotting paper.
Use a primer or sealer, is my advice.

Dilute PVA glue will seal MDF nicely.

You should use a sealer otherwise you will be spending a fortune on paint. There are many MDF sealers available from hardware stores some dry clear some dry white. The sealer will also help the finish. Many of the fibres get flattened when sanding, this gives it the feeling of being smooth. The sealer will make these flattened fibres stand up, with a second sanding the fibres get sheared off, repeat this process once or twice and you will end up with a really good surface for rattle can spray or brush painting. Its important to check paint compatibility also. Important to pay special attention to the edges as this is where it really soaks in.

tegfan railway:101438 wrote:You should use a sealer otherwise you will be spending a fortune on paint. There are many MDF sealers available from hardware stores some dry clear some dry white. The sealer will also help the finish. Many of the fibres get flattened when sanding, this gives it the feeling of being smooth. The sealer will make these flattened fibres stand up, with a second sanding the fibres get sheared off, repeat this process once or twice and you will end up with a really good surface for rattle can spray or brush painting. Its important to check paint compatibility also. Important to pay special attention to the edges as this is where it really soaks in.

Exactly what I did with my HGLM coaches. I used a good spray over with a 50% mix of thick PVA and water, followed when dry with a coat of cheapo dark primer (£1.00 a can from the pound shop). Overnight dry, rub down carefully with fine paper, quick vac brush over to clear the dust and then two coats of Plasticoat spray. Then as usual a quick coat of either flat clear Plasticoat varnish or alternatively the orrible bright shiny finish. It ends up as a very hard finish indeed.

I have also experimented with a couple of sprayed coats of Reeves well water thinned acrylic allowed to dry out well and rubbed down between coats, then finishing with flat Plasticoat varnish overspray. The little HGLW locos have been finished this way and they are fine. Cheap medium to use which leaves out the primer. The thinned acrylic dries like a primer so it's cheap and very cheerful.

im a chippy too yes you should seal it a coat of primer undercoat ,or there is a paint called MSP multi surface paint will do it or a coat of watered down PVA or a coat of spray paint will do the trick iv used all these methods for boxing in mdf pipework in toilet's etc and thay all work fine .

Thanks for the advice folks.
Sealed it shall be.
If I use a mixture of 50/50 pva and water are there any types of paint to avoid?

I never had any problems with the paint if its been coated in pva it should be fine .people say mdf will absorb water it does but only if its really really wet all the time try getting a bit of mdf and put it in a bucket of water it will absorb it but it takes a long time

You can also (if your paint is water based) add some paint to the PVA:water mix so you start to get a base colour from the start, especially useful if the MDF has been laser cut and has darker areas from the laser heat.